SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Tanvir N.) "

Sökning: WFRF:(Tanvir N.)

  • Resultat 1-50 av 54
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Veres, P., et al. (författare)
  • Observation of inverse Compton emission from a long gamma-ray burst
  • 2019
  • Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 575:7783, s. 459-
  • Tidskriftsartikel (refereegranskat)abstract
    • Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectron volt-to-mega electronvoltband, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission(1,2). Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands(1-6). The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock(7-9). Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C(10,11). Here we report multifrequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 x 10(-6) to 10(12) electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
  •  
2.
  • Amati, L., et al. (författare)
  • The THESEUS space mission concept : science case, design and expected performances
  • 2018
  • Ingår i: Advances in Space Research. - : ELSEVIER SCI LTD. - 0273-1177 .- 1879-1948. ; 62:1, s. 191-244
  • Tidskriftsartikel (refereegranskat)abstract
    • THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1 sr) with 0.5-1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift similar to 10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s/early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).
  •  
3.
  • Marconi, A., et al. (författare)
  • ANDES, the high resolution spectrograph for the ELT : science case, baseline design and path to construction
  • 2022
  • Ingår i: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IX. - : SPIE - International Society for Optical Engineering. - 9781510653504 - 9781510653498
  • Konferensbidrag (refereegranskat)abstract
    • The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of similar to 100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 mu m with the goal of extending it to 0.35-2.4 mu m with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coude room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.
  •  
4.
  • Abbafati, Cristiana, et al. (författare)
  • 2020
  • Tidskriftsartikel (refereegranskat)
  •  
5.
  • Tanvir, N. R., et al. (författare)
  • A γ-ray burst at a redshift of z~8.2
  • 2009
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 461, s. 1254-1257
  • Tidskriftsartikel (refereegranskat)abstract
    • Long-duration γ-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z>20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-α emitting galaxy. Here we report that GRB090423 lies at a redshift of z~8.2, implying that massive stars were being produced and dying as GRBs ~630Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.
  •  
6.
  • Cano, Z., et al. (författare)
  • A trio of gamma-ray burst supernovae : GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu
  • 2014
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 568
  • Tidskriftsartikel (refereegranskat)abstract
    • We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical spectroscopy at t-t(0) = 16.1 d, which covers rest-frame 3000-6250 angstrom. Based on Fell lambda 5169 and Sill lambda 6355, our spectrum indicates an unusually low expansion velocity of similar to 4000-6350 km s(-1), the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A/SN 2013fu, we used our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we took advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Meszros (2001, ApJ, 552, L35), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P = 12 ms and a magnetic field of B = 1.1 x 10(15) G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs.
  •  
7.
  • Greiner, J., et al. (författare)
  • GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
  • 2012
  • Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 34:2, s. 551-582
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the corresponding telescopes placed on a separate satellite. The Gamma-Ray Imaging, Polarimetry and Spectroscopy ("GRIPS") mission with its three instruments Gamma-Ray Monitor (GRM), X-Ray Monitor (XRM) and InfraRed Telescope (IRT) addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate γ-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.
  •  
8.
  • Ackley, K., et al. (författare)
  • Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv
  • 2020
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.
  •  
9.
  • Starling, R. L. C., et al. (författare)
  • Discovery of the nearby long, soft GRB 100316D with an associated supernova
  • 2011
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 411:4, s. 2792-2803
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the Swift discovery of the nearby long, soft gamma-ray burst GRB 100316D, and the subsequent unveiling of its low-redshift host galaxy and associated supernova. We derive the redshift of the event to be z = 0.0591 +/- 0.0001 and provide accurate astrometry for the gamma-ray burst (GRB) supernova (SN). We study the extremely unusual prompt emission with time-resolved gamma-ray to X-ray spectroscopy and find that the spectrum is best modelled with a thermal component in addition to a synchrotron emission component with a low peak energy. The X-ray light curve has a remarkably shallow decay out to at least 800 s. The host is a bright, blue galaxy with a highly disturbed morphology and we use Gemini-South, Very Large Telescope and Hubble Space Telescope observations to measure some of the basic host galaxy properties. We compare and contrast the X-ray emission and host galaxy of GRB 100316D to a subsample of GRB-SNe. GRB 100316D is unlike the majority of GRB-SNe in its X-ray evolution, but resembles rather GRB 060218, and we find that these two events have remarkably similar high energy prompt emission properties. Comparison of the host galaxies of GRB-SNe demonstrates, however, that there is a great diversity in the environments in which GRB-SNe can be found. GRB 100316D is an important addition to the currently sparse sample of spectroscopically confirmed GRB-SNe, from which a better understanding of long GRB progenitors and the GRB-SN connection can be gleaned.
  •  
10.
  • Castro-Tirado, A. J., et al. (författare)
  • GRB 030227 : The first multiwavelength afterglow of an INTEGRAL GRB
  • 2003
  • Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 411:1, s. 315-319
  • Tidskriftsartikel (refereegranskat)abstract
    • We present multiwavelength observations of a gamma-ray burst detected byINTEGRAL (GRB 030227) between 5.3 hours and ~ 1.7days after the event. Here we report the discovery of a dim opticalafterglow (OA) that would not have been detected by many previoussearches due to its faintess (R ~ 23). This OA was seen to declinefollowing a power law decay with index alpha R = -0.95 +/-0.16. The spectral index beta_ opt/NIR yielded -1.25 +/- 0.14. Thesevalues may be explained by a relativistic expansion of a fireball (withp = 2.0) in the cooling regime. We also find evidence for inverseCompton scattering in X-rays.Based on observations with INTEGRAL, an ESA project with instruments andscience data centre funded by ESA member states (especially the PIcountries: Denmark, France, Germany, Italy, Switzerland, Spain), CzechRepublic and Poland, and with the participation of Russia and the USA.Also partially based on observations collected by the Gamma-Ray BurstCollaboration at ESO (GRACE) at the European Southern Observatory, Chile(ESO Large Programme 165.H-0464).
  •  
11.
  • Evans, P. A., et al. (författare)
  • Swift and NuSTAR observations of GW170817 : Detection of a blue kilonova
  • 2017
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 358:6370, s. 1565-1569
  • Tidskriftsartikel (refereegranskat)abstract
    • With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (approximate to 0.03 solar masses) wind-driven outflow with moderate electron fraction (Y-e approximate to 0.27). Combined with the x-ray limits, we favor an observer viewing angle of approximate to 30 degrees away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a gamma-ray burst afterglow).
  •  
12.
  • Kann, D. A., et al. (författare)
  • THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS
  • 2010
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
  • Tidskriftsartikel (refereegranskat)abstract
    • We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
  •  
13.
  • Tanvir, N. R., et al. (författare)
  • The structure of star clusters in the outer halo of M31
  • 2012
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 422:1, s. 162-184
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a structural analysis of halo star clusters in M31 based on deep Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. The clusters in our sample span a range in galactocentric projected distance from 13 to 100 kpc and thus reside in rather remote environments. Ten of the clusters are classical globulars, whilst four are from the Huxor et al. population of extended, old clusters. For most clusters, contamination by M31 halo stars is slight, and so the profiles can be mapped reliably to large radial distances from their centres. We find that the extended clusters are well fit by analytic King profiles with similar to 20 parsec core radii and similar to 100 parsec photometric tidal radii, or by Sersic profiles of index similar to 1 (i.e. approximately exponential). Most of the classical globulars also have large photometric tidal radii in the range 50-100 parsec; however, the King profile is a less good fit in some cases, particularly at small radii. We find 60 per cent of the classical globular clusters exhibit cuspy cores which are reasonably well described by Sersic profiles of index similar to 2-6. Our analysis also reinforces the finding that luminous classical globulars, with half-light radii <10 parsec, are present out to radii of at least 100 kpc in M31, which is in contrast to the situation in the Milky Way where such clusters (other than the unusual object NGC 2419) are absent beyond 40 kpc.
  •  
14.
  • Ahmed, Tanvir, 1970, et al. (författare)
  • Enhanced immunogenicity of an oral inactivated cholera vaccine in infants in Bangladesh obtained by zinc supplementation and by temporary withholding breast-feeding.
  • 2009
  • Ingår i: Vaccine. - : Elsevier BV. - 0264-410X. ; 27:9, s. 1433-9
  • Tidskriftsartikel (refereegranskat)abstract
    • The killed oral cholera vaccine Dukoral is recommended for adults and only children over 2 years of age, although cholera is seen frequently in younger children and there is an urgent need for a vaccine for them. Since decreased immunogenicity of oral vaccines in children in developing countries is a critical problem, we tested interventions to enhance responses to Dukoral. We evaluated the effect on the immune responses by temporarily withholding breast-feeding or by giving zinc supplementation. Two doses of Dukoral consisting of killed cholera vibrios and cholera B subunit were given to 6-18 months old Bangladeshi children (n=340) and safety and immunogenicity studied. Our results showed that two doses of the vaccine were safe and induced antibacterial (vibriocidal) antibody responses in 57% and antitoxin responses in 85% of the children. Immune responses were comparable after intake of one and two doses. Temporary withholding breast-feeding for 3 h before immunization or supplementation with 20 mg of zinc per day for 42 days resulted in increased magnitude of vibriocidal antibodies (77% and 79% responders, respectively). Administration of vaccines without buffer or in water did not result in reduction of vibriocidal responses. This study demonstrates that the vaccine is safe and immunogenic in children under 2 years of age and that simple interventions can enhance immune responses in young children.
  •  
15.
  • Ferguson, A M N, et al. (författare)
  • The stellar populations of the M31 halo substructure
  • 2005
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 622:2, s. 109-112
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first results from our survey of stellar substructure in the outskirts of M31 using the Advanced Camera for Surveys on board the Hubble Space Telescope. We discuss the stellar populations associated with five prominent stellar overdensities discovered during the course of our panoramic ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera; a sixth pointing targets a region of "clean" halo. The color-magnitude diagrams, which contain between approximate to 10,000 and 90,000 stars and reach 4 mag below the horizontal branch, reveal clear variations in morphology between most fields, indicating that the age and/or metallicity mix of stars is not constant at large radius. This directly confirms the existence of large-scale population inhomogeneities within the halo of M31 and lends further support to the notion that M31 has formed, at least in part, through satellite accretions. We find a striking similarity between the populations of the giant stellar stream and those of another overdensity, the NE shelf, which lies northeast of the galaxy center. If these overdensities are associated with the same population, then the difference in their red clump magnitudes implies that the NE shelf lies in front of the stream by several tens of kiloparsecs, in good agreement with recent orbit calculations for the stream progenitor.
  •  
16.
  • Fynbo, J. P. U., et al. (författare)
  • Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows : Biases in the Swift Sample and Characterization of the Absorbers
  • 2009
  • Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 185:2, s. 526-573
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Lyα covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., γ-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher γ-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope βOX < 0.5, is 14% in group (1), 38% in group (2), and >39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the most dusty sight lines. This should be taken into account when determining, e.g., the redshift or metallicity distribution of GRBs and when using GRBs as a probe of star formation. Finally, we characterize GRB absorption systems as a class and compare them to QSO absorption systems, in particular the damped Lyα absorbers (DLAs). On average GRB absorbers are characterized by significantly stronger EWs for H I as well as for both low and high ionization metal lines than what is seen in intervening QSO absorbers. However, the distribution of line strengths is very broad and several GRB absorbers have lines with EWs well within the range spanned by QSO-DLAs. Based on the 33 z > 2 bursts in the sample, we place a 95% confidence upper limit of 7.5% on the mean escape fraction of ionizing photons from star-forming galaxies. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs 275.D-5022 (PI: Chincarini), 075.D-0270 (PI: Fynbo), 077.D-0661 (PI: Vreeswijk), 077.D-0805 (PI: Tagliaferri), 177.A-0591 (PI: Hjorth), 078.D-0416 (PI: Vreeswijk), 079.D-0429 (PI: Vreeswijk), 080.D-0526 (PI: Vreeswijk), 081.A-0135 (PI: Greiner), 281.D-5002 (PI: Della Valle), and 081.A-0856 (PI: Vreeswijk). Also based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Some of the data obtained herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck foundation.
  •  
17.
  • Hartoog, O. E., et al. (författare)
  • VLT/X-Shooter spectroscopy of the afterglow of the Swift GRB 130606A Chemical abundances and reionisation at z similar to 6
  • 2015
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 580
  • Tidskriftsartikel (refereegranskat)abstract
    • Context: The reionisation of the Universe is a process that is thought to have ended around z similar to 6, as inferred from spectroscopy of distant bright background sources, such as quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy of a GRB afterglow provides insight in its host galaxy, which is often too dim and distant to study otherwise.Aims: For the Swift GRB 130606A at z = 5.913 we have obtained a high S/N spectrum covering the full optical and near-IR wavelength region at intermediate spectral resolution with VLT/X-Shooter. We aim to measure the degree of ionisation of the intergalactic medium (IGM) between z = 5.02-5.84 and to study the chemical abundance pattern and dust content of its host galaxy.Methods: We estimated the UV continuum of the GRB afterglow using a power-law extrapolation, then measured the flux decrement due to absorption at Ly alpha,beta, and gamma wavelength regions. Furthermore, we fitted the shape of the red damping wing of Lya. The hydrogen and metal absorption lines formed in the host galaxy were fitted with Voigt profiles to obtain column densities. We investigated whether ionisation corrections needed to be applied.Results: Our measurements of the Ly alpha-forest optical depth are consistent with previous measurements of QSOs, but have a much smaller uncertainty. The analysis of the red damping wing yields a neutral fraction x(HI) < 0.05 (3 sigma). We obtain column density measurements of H, Al, Si, and Fe; for C, O, S and Ni we obtain limits. The ionisation due to the GRB is estimated to be negligible (corrections < 0.03 dex), but larger corrections may apply due to the pre-existing radiation field (up to 0.4 dex based on sub-DLA studies). Assuming that [Si/Fe] = +0.79 +/- 0.13 is due to dust depletion, the dust-to-metal ratio is similar to the Galactic value.Conclusions: Our measurements confirm that the Universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z > 5.6. GRBs are useful probes of the ionisation state of the IGM in the early Universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions. The high [Si/Fe] in the host can be due to dust depletion, a-element enhancement, or a combination of both. The very high value of [Al/Fe] = 2.40 +/- 0.78 might be due to a proton capture process and is probably connected to the stellar population history. We estimate the host metallicity to be -1.7 < [M/H] < -0.9 (2%-13% of solar).
  •  
18.
  • Hawlader, M. D. H., et al. (författare)
  • Quality of life of COVID-19 recovered patients : a 1-year follow-up study from Bangladesh
  • 2023
  • Ingår i: Infectious Diseases of Poverty. - : Springer Nature. - 2095-5162. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: The COVID-19 pandemic posed a danger to global public health because of the unprecedented physical, mental, social, and environmental impact affecting quality of life (QoL). The study aimed to find the changes in QoL among COVID-19 recovered individuals and explore the determinants of change more than 1 year after recovery in low-resource settings. Methods: COVID-19 patients from all eight divisions of Bangladesh who were confirmed positive by reverse transcription-polymerase chain reaction from June 2020 to November 2020 and who subsequently recovered were followed up twice, once immediately after recovery and again 1 year after the first follow-up. The follow-up study was conducted from November 2021 to January 2022 among 2438 individuals using the World Health Organization Quality of Life Brief Version (WHOQOL-BREF). After excluding 48 deaths, 95 were rejected to participate, 618 were inaccessible, and there were 45 cases of incomplete data. Descriptive statistics, paired-sample analyses, generalized estimating equation (GEE) analysis, and multivariable logistic regression analyses were performed to test the mean difference in participants’ QoL scores between the two interviews. Results: Most participants (n = 1710, 70.1%) were male, and one-fourth (24.4%) were older than 46. The average physical domain score decreased significantly from baseline to follow-up, and the average scores in psychological, social, and environmental domains increased significantly at follow-up (P < 0.05). By the GEE equation approach, after adjusting for other factors, we found that older age groups (P < 0.001), being female (P < 0.001), having hospital admission during COVID-19 illness (P < 0.001), and having three or more chronic diseases (P < 0.001), were significantly associated with lower physical and psychological QoL scores. Higher age and female sex [adjusted odd ratio (aOR) = 1.3, 95% confidence interval (CI) 1.0–1.6] were associated with reduced social domain scores on multivariable logistic regression analysis. Urban or semi-urban people were 49% less likely (aOR = 0.5, 95% CI 0.4–0.7) and 32% less likely (aOR = 0.7, 95% CI 0.5–0.9) to have a reduced QoL score in the psychological domain and the social domain respectively, than rural people. Higher-income people were more likely to experience a decrease in QoL scores in physical, psychological, social, and environmental domains. Married people were 1.8 times more likely (aOR = 1.8, 95% CI 1.3–2.4) to have a decreased social QoL score. In the second interview, people admitted to hospitals during their COVID-19 infection showed a 1.3 times higher chance (aOR = 1.3, 95% CI 1.1–1.6) of a decreased environmental QoL score. Almost 13% of participants developed one or more chronic diseases between the first and second interviews. Moreover, 7.9% suffered from reinfection by COVID-19 during this 1-year time. Conclusions: The present study found that the QoL of COVID-19 recovered people improved 1 year after recovery, particularly in psychological, social, and environmental domains. However, age, sex, the severity of COVID-19, smoking habits, and comorbidities were significantly negatively associated with QoL. Events of reinfection and the emergence of chronic disease were independent determinants of the decline in QoL scores in psychological, social, and physical domains, respectively. Strong policies to prevent and minimize smoking must be implemented in Bangladesh, and we must monitor and manage chronic diseases in people who have recovered from COVID-19. Graphical Abstract: [Figure not available: see fulltext.] 
  •  
19.
  • Micah, Angela E., et al. (författare)
  • Tracking development assistance for health and for COVID-19 : a review of development assistance, government, out-of-pocket, and other private spending on health for 204 countries and territories, 1990-2050
  • 2021
  • Ingår i: The Lancet. - : Elsevier. - 0140-6736 .- 1474-547X. ; 398:10308, s. 1317-1343
  • Forskningsöversikt (refereegranskat)abstract
    • Background The rapid spread of COVID-19 renewed the focus on how health systems across the globe are financed, especially during public health emergencies. Development assistance is an important source of health financing in many low-income countries, yet little is known about how much of this funding was disbursed for COVID-19. We aimed to put development assistance for health for COVID-19 in the context of broader trends in global health financing, and to estimate total health spending from 1995 to 2050 and development assistance for COVID-19 in 2020. Methods We estimated domestic health spending and development assistance for health to generate total health-sector spending estimates for 204 countries and territories. We leveraged data from the WHO Global Health Expenditure Database to produce estimates of domestic health spending. To generate estimates for development assistance for health, we relied on project-level disbursement data from the major international development agencies' online databases and annual financial statements and reports for information on income sources. To adjust our estimates for 2020 to include disbursements related to COVID-19, we extracted project data on commitments and disbursements from a broader set of databases (because not all of the data sources used to estimate the historical series extend to 2020), including the UN Office of Humanitarian Assistance Financial Tracking Service and the International Aid Transparency Initiative. We reported all the historic and future spending estimates in inflation-adjusted 2020 US$, 2020 US$ per capita, purchasing-power parity-adjusted US$ per capita, and as a proportion of gross domestic product. We used various models to generate future health spending to 2050. Findings In 2019, health spending globally reached $8. 8 trillion (95% uncertainty interval [UI] 8.7-8.8) or $1132 (1119-1143) per person. Spending on health varied within and across income groups and geographical regions. Of this total, $40.4 billion (0.5%, 95% UI 0.5-0.5) was development assistance for health provided to low-income and middle-income countries, which made up 24.6% (UI 24.0-25.1) of total spending in low-income countries. We estimate that $54.8 billion in development assistance for health was disbursed in 2020. Of this, $13.7 billion was targeted toward the COVID-19 health response. $12.3 billion was newly committed and $1.4 billion was repurposed from existing health projects. $3.1 billion (22.4%) of the funds focused on country-level coordination and $2.4 billion (17.9%) was for supply chain and logistics. Only $714.4 million (7.7%) of COVID-19 development assistance for health went to Latin America, despite this region reporting 34.3% of total recorded COVID-19 deaths in low-income or middle-income countries in 2020. Spending on health is expected to rise to $1519 (1448-1591) per person in 2050, although spending across countries is expected to remain varied. Interpretation Global health spending is expected to continue to grow, but remain unequally distributed between countries. We estimate that development organisations substantially increased the amount of development assistance for health provided in 2020. Continued efforts are needed to raise sufficient resources to mitigate the pandemic for the most vulnerable, and to help curtail the pandemic for all. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.
  •  
20.
  • Rossi, A., et al. (författare)
  • A blast from the infant Universe : The very high-z GRB210905A
  • 2022
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 665
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a detailed follow-up of the very energetic GRB 210905A at a high redshift of z = 6.312 and its luminous X-ray and optical afterglow. Following the detection by Swift and Konus-Wind, we obtained a photometric and spectroscopic follow-up in the optical and near-infrared (NIR), covering both the prompt and afterglow emission from a few minutes up to 20 Ms after burst. With an isotropic gamma-ray energy release of Eiso = 1.27−0.19+0.20 × 1054 erg, GRB 210905A lies in the top ∼7% of gamma-ray bursts (GRBs) in the Konus-Wind catalogue in terms of energy released. Its afterglow is among the most luminous ever observed, and, in particular, it is one of the most luminous in the optical at t ≳ 0.5 d in the rest frame. The afterglow starts with a shallow evolution that can be explained by energy injection, and it is followed by a steeper decay, while the spectral energy distribution is in agreement with slow cooling in a constant-density environment within the standard fireball theory. A jet break at ∼46.2 ± 16.3 d (6.3 ± 2.2 d rest-frame) has been observed in the X-ray light curve; however, it is hidden in the H band due to a constant contribution from the host galaxy and potentially from a foreground intervening galaxy. In particular, the host galaxy is only the fourth GRB host at z > 6 known to date. By assuming a number density n = 1 cm−3 and an efficiency η = 0.2, we derived a half-opening angle of 8.4 ° ±1.0°, which is the highest ever measured for a z ≳ 6 burst, but within the range covered by closer events. The resulting collimation-corrected gamma-ray energy release of ≃1 × 1052 erg is also among the highest ever measured. The moderately large half-opening angle argues against recent claims of an inverse dependence of the half-opening angle on the redshift. The total jet energy is likely too large to be sustained by a standard magnetar, and it suggests that the central engine of this burst was a newly formed black hole. Despite the outstanding energetics and luminosity of both GRB 210905A and its afterglow, we demonstrate that they are consistent within 2σ with those of less distant bursts, indicating that the powering mechanisms and progenitors do not evolve significantly with redshift.
  •  
21.
  • Agudo, I., et al. (författare)
  • Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
  • 2023
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (∼150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transienta's tightly constrained age, its relatively faint peak magnitude (Mi ∼ -16.7 mag), and the r-band decline rate of ∼1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only ∼0.1 M·, with 56Ni comprising ∼20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
  •  
22.
  • Cano, Z., et al. (författare)
  • GRB 161219B/SN 2016jca : A low-redshift gamma-ray burst supernova powered by radioactive heating
  • 2017
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605
  • Tidskriftsartikel (refereegranskat)abstract
    • Since the first discovery of a broad-lined type Ic supernova (SN) with a long-duration gamma-ray burst (GRB) in 1998, fewer than fifty GRB-supernovae (SNe) have been discovered. The intermediate-luminosity Swift GRB 161219B and its associated supernova SN 2016jca, which occurred at a redshift of z = 0.1475, represents only the seventh GRB-SN to have been discovered within 1 Gpc, and hence provides an excellent opportunity to investigate the observational and physical properties of these very elusive and rare type of SN. As such, we present optical to near-infrared photometry and optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three months since its discovery. GRB 161219B exploded in the disk of an edge-on spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB 161219B itself is an outlier in the E-p,E-i - E-gamma,E-iso plane, while SN 2016jca had a rest-frame, peak absolute V-band magnitude of M-V = -19.0 +/- 0.1, which it reached after 12.3 +/- 0.7 rest-frame days. We find that the bolometric properties of SN 2016jca are inconsistent with being powered solely by a magnetar central engine, and demonstrate that it was likely powered exclusively by energy deposited by the radioactive decay of nickel and cobalt into their daughter products, which were nucleosynthesised when its progenitor underwent core collapse. We find that 0.22 +/- 0.08 M-circle dot of nickel is required to reproduce the peak luminosity of SN 2016jca, and we constrain an ejecta mass of 5.8 +/- 0.3 M-circle dot and a kinetic energy of 5.1 +/- 0.8 x 10(52) erg. Finally, we report on a chromatic, pre-maximum bump in the g-band light curve, and discuss its possible origin.
  •  
23.
  • Chapman, R., et al. (författare)
  • Soft Gamma Repeaters and Short Gamma Ray Bursts: Making Magnetars from WD -- WD Mergers
  • 2007
  • Ingår i: ASP Conference Proceedings. ; 372, s. 415-415
  • Konferensbidrag (refereegranskat)abstract
    • Recent progress on the nature of short duration Gamma Ray Bursts (GRBs) has shown that a fraction of them originate in the local universe. These systems may well be the result of giant flares from Soft Gamma Repeaters (SGRs) believed to be magnetars (neutron stars with extremely large magnetic fields ≥1014G). If these magnetars are formed via the core collapse of massive stars, then it would be expected that the bursts should originate from predominantly young stellar populations. However, correlating the positions of BATSE short bursts with structure in the local universe reveals a correlation with all galaxy types, including those with little or no ongoing star formation. This is a natural outcome if, in addition to magnetars forming via the core collapse of massive stars, they also form via accretion induced collapse following the merger of two white dwarfs (WDs), one of which is magnetic. We investigate this possibility and find that the rate of magnetar production via WD--WD mergers in the Milky Way is comparable to the rate of production via core collapse. However, while the rate of magnetar production by core collapse is proportional to the star formation rate, the rate of production via WD--WD mergers (which have long lifetimes) is proportional to the stellar mass density, which is concentrated in early-type systems. Therefore magnetars produced via WD--WD mergers may produce SGR giant flares which can be identified with early-type galaxies. We also comment on the possibility that this mechanism could produce a fraction of the observed short duration GRB population at low redshift.
  •  
24.
  •  
25.
  • Daniel, Ed, et al. (författare)
  • IceBear : an intuitive and versatile web application for research-data tracking from crystallization experiment to PDB deposition
  • 2021
  • Ingår i: Acta Crystallographica Section D. - : International Union of Crystallography (IUCr). - 2059-7983. ; 77:2, s. 151-163
  • Tidskriftsartikel (refereegranskat)abstract
    • The web-based IceBear software is a versatile tool to monitor the results of crystallization experiments and is designed to facilitate supervisor and student communications. It also records and tracks all relevant information from crystallization setup to PDB deposition in protein crystallography projects. Fully automated data collection is now possible at several synchrotrons, which means that the number of samples tested at the synchrotron is currently increasing rapidly. Therefore, the protein crystallography research communities at the University of Oulu, Weizmann Institute of Science and Diamond Light Source have joined forces to automate the uploading of sample metadata to the synchrotron. In IceBear, each crystal selected for data collection is given a unique sample name and a crystal page is generated. Subsequently, the metadata required for data collection are uploaded directly to the ISPyB synchrotron database by a shipment module, and for each sample a link to the relevant ISPyB page is stored. IceBear allows notes to be made for each sample during cryocooling treatment and during data collection, as well as in later steps of the structure determination. Protocols are also available to aid the recycling of pins, pucks and dewars when the dewar returns from the synchrotron. The IceBear database is organized around projects, and project members can easily access the crystallization and diffraction metadata for each sample, as well as any additional information that has been provided via the notes. The crystal page for each sample connects the crystallization, diffraction and structural information by providing links to the IceBear drop-viewer page and to the ISPyB data-collection page, as well as to the structure deposited in the Protein Data Bank.
  •  
26.
  • D'Elia, V., et al. (författare)
  • VLT/X-shooter spectroscopy of the GRB 090926A afterglow
  • 2010
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 523, s. 36-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: The aim of this paper is to study the environment and intervening absorbers of the gamma-ray burst GRB 090926A through analyzing optical spectra of its afterglow. Methods: We analyzed medium-resolution spectroscopic observations (R = 10 000, corresponding to 30 km s-1, S/N = 15-30 and wavelength range 3000-25 000) of the optical afterglow of GRB 090926A, taken with X-shooter at the VLT ~22 h after the GRB trigger. Results: The spectrum shows that the ISM in the GRB host galaxy at z = 2.1071 is rich in absorption features, with two components contributing to the line profiles. In addition to the ground state lines, we detect C ii, O i, Si ii, Fe ii, and Ni ii-excited absorption features, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The distance of component I is found to be 2.40 ± 0.15 kpc, while component II is located far away from the GRB, possibly at ~5 kpc. These values are compatible with those found for other GRBs. The hydrogen column density associated to GRB 090926A is log NH/cm -2 = 21.60 ± 0.07, and the metallicity of the host galaxy is in the range [X/H] = -2.5 to -1.9 with respect to the solar values, i.e., among the lowest values ever observed for a GRB host galaxy. A comparison with galactic chemical evolution models has suggested that the host of GRB090926A is likely to be a dwarf-irregular galaxy. No emission lines were detected, but a Hα flux in emission of 9 × 10-18 erg s-1 cm-2 (i.e., a star-formation rate of 2 M_ȯ yr-1), which is typical of many GRB hosts, would have been detected in our spectra, and thus emission lines are well within the reach of X-shooter. We put an upper limit to the H molecular fraction of the host galaxy ISM, which is f < 7 × 10-7. The continuum has been fitted assuming a power-law spectrum, with a spectral index of β = 0.89-0.02+0.02. The best fit does essentially not require any intrinsic extinction because EB-V < 0.01 mag adopting a SMC extinction curve. Finally, the line of sight of GRB 090926A presents four weak intervening absorption systems in the redshift range 1.24 < z < 1.95. Based on observations collected at the European Southern Observatory, ESO, the VLT/Kueyen telescope, Paranal, Chile, during the science verification phase, proposal code: 060-9427(A).
  •  
27.
  • Eyles, R. A. J., et al. (författare)
  • An unusual transient following the short GRB 071227
  • 2019
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 489:1, s. 13-27
  • Tidskriftsartikel (refereegranskat)abstract
    • We present X-ray and optical observations of the short duration gamma-ray burst GRB 071227 and its host at z= 0.381, obtained using Swift, Gemini South, and theVery Large Telescope. We identify a short-lived and moderately bright optical transient, with flux significantly in excess of that expected from a simple extrapolation of the X-ray spectrum at 0.2-0.3 d after burst. We fit the SED with afterglow models allowing for high extinction and thermal emission models that approximate a kilonova to assess the excess' origins. While some kilonova contribution is plausible, it is not favoured due to the low temperature and high luminosity required, implying superluminal expansion and a large ejectamass of similar to 0.1 M-circle dot. We find, instead, that the transient is broadly consistent with power-law spectra with additional dust extinction of E(B - V) similar to 0.4 mag, although a possibly thermal excess remains in the z band. We investigate the host, a spiral galaxy with an edge-on orientation, resolving its spectrum along its major axis to construct the galaxy rotation curve and analyse the star formation and chemical properties. The integrated host emission shows evidence for high extinction, consistent with the afterglow findings. The metallicity and extinction are consistent with previous studies of this host and indicate the galaxy is a typical, but dusty, late-type SGRB host.
  •  
28.
  • Faria, Daniel, et al. (författare)
  • Probing the nature of the G1 clump stellar overdensity in the outskirts of M31
  • 2007
  • Ingår i: The Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 133:4, s. 1275-1286
  • Tidskriftsartikel (refereegranskat)abstract
    • We present deep Hubble Space Telescope ACS observations of the G1 clump, a distinct stellar overdensity lying at similar to 30 kpc along the southwestern major axis of M31, close to the G1 globular cluster ( from the work of Ferguson and coworkers). Our well-populated color-magnitude diagram reaches similar to 7 mag below the red giant branch tip with 90% completeness, and allows the detection of various morphological features that can be used to derive detailed constraints on the age and metallicity of the constituent stellar population. We find that the color-magnitude diagram is best described spread in metallicity is constrained to be P = 0.5 dex. The star formation rate in this region has declined over time, with the bulk of the stellar mass having formed > 6 Gyr ago. Nonetheless, a nonnegligible mass fraction (approximate to 10%) of the population has formed in the last 2 Gyr. We discuss the nature of the G1 clump in light of these new stellar population constraints and argue that the combination of stellar content and physical size make it unlikely that the structure is the remnant of an accreted dwarf galaxy. Instead, the strong similarity between the stellar content of the G1 clump and that of the M31 outer disk suggests that the substructure is a fragment of the outer disk, perhaps torn off from the main body during a past accretion/merger event; this interpretation is consistent with extant kinematical data. If this interpretation is correct, our analysis of the stellar content provides further evidence that the outskirts of large disk galaxies have been in place for a significant time.
  •  
29.
  • Izzo, L., et al. (författare)
  • Signatures of a jet cocoon in early spectra of a supernova associated with a γ-ray burst
  • 2019
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 565:7739, s. 324-
  • Tidskriftsartikel (refereegranskat)abstract
    • Long gamma-ray bursts are associated with energetic, broad-lined, stripped-envelope supernovae(1,2) and as such mark the death of massive stars. The scarcity of such events nearby and the brightness of the gamma-ray burst afterglow, which dominates the emission in the first few days after the burst, have so far prevented the study of the very early evolution of supernovae associated with gamma-ray bursts(3). In hydrogen-stripped supernovae that are not associated with gamma-ray bursts, an excess of high-velocity (roughly 30,000 kilometres per second) material has been interpreted as a signature of a choked jet, which did not emerge from the progenitor star and instead deposited all of its energy in a thermal cocoon(4). Here we report multi-epoch spectroscopic observations of the supernova SN 2017iuk, which is associated with the gamma-ray burst GRB 171205A. Our spectra display features at extremely high expansion velocities (around 115,000 kilometres per second) within the first day after the burst(5,6). Using spectral synthesis models developed for SN 2017iuk, we show that these features are characterized by chemical abundances that differ from those observed in the ejecta of SN 2017iuk at later times. We further show that the high-velocity features originate from the mildly relativistic hot cocoon that is generated by an ultra-relativistic jet within the gamma-ray burst expanding and decelerating into the medium that surrounds the progenitor star(7,8). This cocoon rapidly becomes transparent(9) and is outshone by the supernova emission, which starts to dominate the emission three days after the burst.
  •  
30.
  • Jakobsson, P, et al. (författare)
  • A mean redshift of 2.8 for Swift gamma-ray bursts
  • 2006
  • Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 447:3, s. 897-903
  • Tidskriftsartikel (refereegranskat)abstract
    • The exceptionally high luminosities of gamma-ray bursts (GRBs), gradually emerging as extremely useful probes of star formation, make them promising tools for exploration of the high-redshift Universe. Here we present a carefully selected sample of Swift GRBs, intended to estimate in an unbiased way the GRB mean redshift (z(mean)), constraints on the fraction of high-redshift bursts and an upper limit on the fraction of heavily obscured afterglows. We find that z(mean) = 2.8 and that at least 7% of GRBs originate at z > 5. In addition, consistent with pre-Swift observations, at most 20% of afterglows can be heavily obscured. The redshift distribution of the sample is qualitatively consistent with models where the GRB rate is proportional to the star formation rate in the Universe. We also report optical, near-infrared and X-ray observations of the afterglow of GRB 050814, which was seen to exhibit very red optical colours. By modelling its spectral energy distribution we find that z = 5.3 +/- 0.3. The high mean redshift of GRBs and their wide redshift range clearly demonstrates their suitability as efficient probes of galaxies and the intergalactic medium over a significant fraction of the history of the Universe.
  •  
31.
  • Kattge, Jens, et al. (författare)
  • TRY plant trait database - enhanced coverage and open access
  • 2020
  • Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 26:1, s. 119-188
  • Tidskriftsartikel (refereegranskat)abstract
    • Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.
  •  
32.
  • Lamb, G. P., et al. (författare)
  • Short GRB 160821B : A Reverse Shock, a Refreshed Shock, and a Well-sampled Kilonova
  • 2019
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 883:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We report our identification of the optical afterglow and host galaxy of the short-duration gamma-ray burst sGRB 160821B. The spectroscopic redshift of the host is z = 0.162, making it one of the lowest redshift short-duration gamma-ray bursts (sGRBs) identified by Swift. Our intensive follow-up campaign using a range of ground-based facilities as well as Hubble Space Telescope, XMM-Newton, and Swift, shows evidence for a late-time excess of optical and near-infrared emission in addition to a complex afterglow. The afterglow light curve at X-ray frequencies reveals a narrow jet, theta(j) similar to 1.9(-0.03)(+0.10) deg, that is refreshed at >1 day post-burst by a slower outflow with significantly more energy than the initial outflow that produced the main GRB. Observations of the 5 GHz radio afterglow shows a reverse shock into a mildly magnetized shell. The optical and near-infrared excess is fainter than AT2017gfo associated with GW170817, and is well explained by a kilonova with dynamic ejecta mass M-dyn = (1.0 +/- 0.6) x 10(-3) M-circle dot and a secular (post-merger) ejecta mass with M-pm = (1.0 +/- 0.6) x 10(-2) M-circle dot, consistent with a binary neutron star merger resulting in a short-lived massive neutron star. This optical and near-infrared data set provides the best-sampled kilonova light curve without a gravitational wave trigger to date.
  •  
33.
  • Levan, A. J., et al. (författare)
  • The Environment of the Binary Neutron Star Merger GW170817
  • 2017
  • Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 848:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present Hubble Space Telescope (HST) and Chandra imaging, combined with Very Large Telescope MUSE integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star merger detected via gravitational-wave emission by LIGO and Virgo, GW170817. The host galaxy, NGC 4993, is an S0 galaxy at z - 0.009783. There is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. This suggests that NGC 4993 has undergone a relatively recent (less than or similar to 1 Gyr) dry merger. This merger may provide the fuel for a weak active nucleus seen in Chandra imaging. At the location of the counterpart, HST imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. The population in the vicinity is predominantly old with less than or similar to 1% of any light arising from a population with ages <500 Myr. Both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius (r(e) similar to 3 kpc), providing an r(e)-normalized offset that is closer than similar to 90% of short GRBs. For the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. We do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy.
  •  
34.
  • Lyman, J. D., et al. (författare)
  • Hubble Space Telescope observations of the host galaxies and environments of calcium-rich supernovae
  • 2016
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 458:2, s. 1768-1777
  • Tidskriftsartikel (refereegranskat)abstract
    • Calcium-rich supernovae (SNe) represent a significant challenge for our understanding of the fates of stellar systems. They are less luminous than other SN types and they evolve more rapidly to reveal nebular spectra dominated by strong calcium lines with weak or absent signatures of other intermediate-and iron-group elements, which are seen in other SNe. Strikingly, their explosion sites also mark them out as distinct from other SN types. Their galactocentric offset distribution is strongly skewed to very large offsets (~1/3 are offset >20 kpc), meaning they do not trace the stellar light of their hosts. Many of the suggestions to explain this extreme offset distribution have invoked the necessity for unusual formation sites such as globular clusters or dwarf satellite galaxies, which are therefore difficult to detect. Building on previous work attempting to detect host systems of nearby Ca-rich SNe, we here present Hubble Space Telescope imaging of five members of the class three exhibiting large offsets and two coincident with the disc of their hosts. We find no underlying sources at the explosion sites of any of our sample. Combining with previous work, the lack of a host system now appears to be a ubiquitous feature amongst Ca-rich SNe. In this case the offset distribution is most readily explained as a signature of high-velocity progenitor systems that have travelled significant distances before exploding.
  •  
35.
  • Lyman, J. D., et al. (författare)
  • The optical afterglow of the short gamma-ray burst associated with GW170817
  • 2018
  • Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 2:9, s. 751-754
  • Tidskriftsartikel (refereegranskat)abstract
    • The binary neutron star merger GW170817 was the first multi-messenger event observed in both gravitational and electromagnetic waves(1,2). The electromagnetic signal began approximately two seconds post-merger with a weak, short burst of gamma rays(3), which was followed over the next hours and days by the ultraviolet, optical and near-infrared emission from a radioactively powered kilonova(4-11). Later, non-thermal rising X-ray and radio emission was observed(12,13). The low luminosity of the gamma rays and the rising non-thermal flux from the source at late times could indicate that we are outside the opening angle of the beamed relativistic jet. Alternatively, the emission could be arising from a cocoon of material formed from the interaction between a jet and the merger ejecta(13-15). Here we present late-time optical detections and deep near-infrared limits on the emission from GW170817 at 110 days post-merger. Our new observations are at odds with expectations of late-time emission from kilonova models, being too bright and blue(16,17). Instead, the emission arises from the interaction between the relativistic ejecta of GW170817 and the interstellar medium. We show that this emission matches the expectations of a Gaussian-structured relativistic jet, which would have launched a high-luminosity, short gamma-ray burst to an aligned observer. However, other jet structure or cocoon models can also match current data-the future evolution of the afterglow will directly distinguish the origin of the emission.
  •  
36.
  • Lyman, J. D., et al. (författare)
  • The progenitors of calcium-rich transients are not formed in situ
  • 2014
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 444:3, s. 2157-2166
  • Tidskriftsartikel (refereegranskat)abstract
    • We present deep Very Large Telescope and Hubble Space Telescope observations of the nearest examples of Ca-rich 'gap' transients - rapidly evolving transient events, with a luminosity intermediate between novae and supernovae. These sources are frequently found at large galactocentric offsets, and their progenitors remain mysterious. Our observations find no convincing underlying quiescent sources coincident with the locations of these transients, allowing us to rule out a number of potential progenitor systems. The presence of surviving massive-star binary companions (or other cluster members) is ruled out, providing an independent rejection of a massive star origin for these events. Dwarf satellite galaxies are disfavoured unless one invokes as yet unknown conditions that would be extremely favourable for their production in the lowest mass systems. Our limits also probe the majority of the globular cluster luminosity function, ruling out the presence of an underlying globular cluster population at high significance, and thus the possibility that they are created via dynamical interactions in dense globular cluster cores. Given the lack of underlying systems, previous progenitor suggestions have difficulty reproducing the remote locations of these transients, even when considering solely halo-borne progenitors. Our preferred scenario is that Ca-rich transients are high-velocity, kicked systems, exploding at large distances from their natal site. Coupled with a long-lived progenitor system post-kick, this naturally explains the lack of association these transients have with their host stellar light, and the extreme host-offsets exhibited. Neutron star-white dwarf mergers may be a promising progenitor system in this scenario.
  •  
37.
  • Malesani, D., et al. (författare)
  • Early Spectroscopic Identification of SN 2008D
  • 2009
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 692:2, s. L84-L87
  • Tidskriftsartikel (refereegranskat)abstract
    • SN 2008D was discovered while following up an unusually bright X-ray transient (XT) in the nearby spiral galaxy NGC 2770. We present early optical spectra ( obtained 1.75 days after the XT) which allowed the first identification of the object as a supernova ( SN) at redshift z = 0.007. These spectra were acquired during the initial declining phase of the light curve, likely produced in the stellar envelope cooling after shock breakout, and rarely observed. They exhibit a rather flat spectral energy distribution with broad undulations, and a strong, W-shaped feature with minima at 3980 and 4190 angstrom ( rest frame). We also present extensive spectroscopy and photometry of the SN during the subsequent photospheric phase. Unlike SNe associated with gamma-ray bursts, SN 2008D displayed prominent He features and is therefore of Type Ib.
  •  
38.
  •  
39.
  • Michalowski, M. J., et al. (författare)
  • Massive stars formed in atomic hydrogen reservoirs : H i observations of gamma-ray burst host galaxies
  • 2015
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 582
  • Tidskriftsartikel (refereegranskat)abstract
    • Long gamma-ray bursts (GRBs), among the most energetic events in the Universe, are explosions of massive and short-lived stars, so they pinpoint locations of recent star formation. However, several GRB host galaxies have recently been found to be deficient in molecular gas (H-2), believed to be the fuel of star formation. Moreover, optical spectroscopy of GRB afterglows implies that the molecular phase constitutes only a small fraction of the gas along the GRB line of sight. Here we report the first ever 21 cm line observations of GRB host galaxies, using the Australia Telescope Compact Array, implying high levels of atomic hydrogen (HI), which suggests that the connection between atomic gas and star formation is stronger than previously thought. In this case, it is possible that star formation is directly fuelled by atomic gas (or that the HI- to- H-2 conversion is very efficient, which rapidly exhaust molecular gas), as has been theoretically shown to be possible. This can happen in low-metallicity gas near the onset of star formation because cooling of gas (necessary for star formation) is faster than the HI- to- H-2 conversion. Indeed, large atomic gas reservoirs, together with low molecular gas masses, stellar, and dust masses are consistent with GRB hosts being preferentially galaxies which have very recently started a star formation episode after accreting metal-poor gas from the intergalactic medium. This provides a natural route for forming GRBs in low-metallicity environments. The gas inflow scenario is also consistent with the existence of the companion HI object with no optical counterpart similar to 19 kpc from the GRB 060505 host, and with the fact that the HI centroids of the GRB 980425 and 060505 hosts do not coincide with optical centres of these galaxies, but are located close to the GRB positions.
  •  
40.
  • Michalowski, M. J., et al. (författare)
  • Spatially-resolved dust properties of the GRB 980425 host galaxy
  • 2014
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 562, s. A70-
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma-ray bursts (GRBs) have been proposed as a tool for studying star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way special compared with other star-forming galaxies. Here we present spatially resolved maps of dust emission of the host galaxy of the closest known GRB 980425 at z = 0.0085 using our new high-resolution observations from Herschel, Atacama Pathfinder Experiment (APEX), Atacama Large Millimeter Array (ALMA) and Australia Telescope Compact Array (ATCA). We modelled the spectral energy distributions of the host and of the star-forming region displaying the Wolf-Rayet signatures in the spectrum (WR region), located 800 pc from the GRB position. The host is characterised by low dust content and a high fraction of UV-visible star formation, similar to other dwarf galaxies. These galaxies are abundant in the local universe, so it is not surprising to find a GRB in one of them, assuming the correspondence between the GRB rate and star formation. The WR region contributes substantially to the host emission at the far-infrared, millimetre, and radio wavelengths and we propose that this is a consequence of its high gas density. If dense environments are also found close to the positions of other GRBs, then the ISM density should also be considered, along with metallicity, an important factor influencing whether a given stellar population can produce a GRB.
  •  
41.
  • Michalowski, M. J., et al. (författare)
  • THE OPTICALLY UNBIASED GRB HOST (TOUGH) SURVEY. VI. RADIO OBSERVATIONS AT z less than or similar to 1 AND CONSISTENCY WITH TYPICAL STAR-FORMING GALAXIES
  • 2012
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 755:2, s. 85-
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of this paper is to determine the level of obscured star formation activity and dust attenuation in a sample of gamma-ray burst (GRB) hosts, and to test the hypothesis that GRB hosts have properties consistent with those of the general star-forming galaxy populations. We present a radio continuum survey of all z < 1 GRB hosts in The Optically Unbiased GRB Host (TOUGH) sample supplemented with radio data for all (mostly pre-Swift) GRB-SN hosts discovered before 2006 October. We present new radio data for 22 objects and have obtained a detection for three of them (GRB 980425, 021211, 031203; none in the TOUGH sample), increasing the number of radio-detected GRB hosts from two to five. The star formation rate (SFR) for the GRB 021211 host of similar to 825 M-circle dot yr(-1), the highest ever reported for a GRB host, places it in the category of ultraluminous infrared galaxies. We found that at least similar to 63% of GRB hosts have SFR < 100 M-circle dot yr(-1) and at most similar to 8% can have SFR > 500 M-circle dot yr(-1). For the undetected hosts the mean radio flux (<35 mu Jy 3 sigma) corresponds to an average SFR < 15 M-circle dot yr(-1). Moreover, greater than or similar to 88% of the z less than or similar to 1 GRB hosts have ultraviolet dust attenuation A(UV) < 6.7 mag (visual attenuation A(V) < 3 mag). Hence, we did not find evidence for large dust obscuration in a majority of GRB hosts. Finally, we found that the distributions of SFRs and A(UV) of GRB hosts are consistent with those of Lyman break galaxies, H alpha emitters at similar redshifts, and of galaxies from cosmological simulations. The similarity of the GRB population with other star-forming galaxies is consistent with the hypothesis that GRBs, a least at z less than or similar to 1, trace a large fraction of all star formation, and are therefore less biased indicators than once thought.
  •  
42.
  • Palmer, Katie, et al. (författare)
  • Prevalence of dementia and factors associated with dementia in rural Bangladesh : data from a cross-sectional, population-based study
  • 2014
  • Ingår i: International psychogeriatrics. - : International Psychogeriatric Association. - 1041-6102 .- 1741-203X. ; 26:11, s. 1905-1915
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: There are currently no published reports of dementia prevalence or factors associated with dementia occurrence in Bangladesh. The aims are to report the prevalence of definite and questionable dementia in rural Bangladesh, and examine factors potentially associated with dementia occurrence, including sociodemographic, clinical, social, and nutritional factors. Methods: We used data from a population-based, cross-sectional study from Matlab, in rural Bangladesh, on 471 persons aged 60+ years. Participants underwent a clinical examination including diagnosis of somatic disorders, and a structured interview including questions about sociodemographic and social factors. Nutritional status was measured with the Mini Nutritional Assessment, and blood tests were conducted to assess a range of nutritional and clinical aspects. Age-and sex-specific dementia prevalence was calculated. Crude and adjusted logistic regression was used to examine associations between dementia and clinical, social, and nutritional factors. Dementia was diagnosed using a two-step procedure by physicians according to DSM-IV criteria. Results: The prevalence of questionable dementia was 11.5% and definite dementia was 3.6%. Dementia prevalence increased with increasing years of age (adjusted OR: 1.04; 95% CI = 1.002-1.1) and decreased with more years of education (adjusted OR: 0.8; 95% CI = 0.6-0.99). Being malnourished increased the odds of dementia almost six-fold (adjusted OR: 5.9; 95% CI = 1.3-26.3), while frequent participation in social activities was associated with a decreased odds (adjusted OR: 0.5; 95% CI = 0.2-0.9). Conclusions: The prevalence of dementia in rural Bangladesh is similar to other countries in the South Asia region, but lower than reports from other world regions. Malnutrition is strongly associated with dementia occurrence, and is a relevant area for future research within low-income countries.
  •  
43.
  • Postigo, A. de Ugarte, et al. (författare)
  • Spectroscopy of the short-hard GRB 130603B The host galaxy and environment of a compact object merger
  • 2014
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 563, s. A62-
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational waves. The detection of a kilonova-like signature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger. Aims. Our knowledge on SGRB has been, until now, mostly based on the absence of supernova signatures and the analysis of the host galaxies to which they cannot always be securely associated. Further progress has been significantly hampered by the faintness and rapid fading of their optical counterparts (afterglows), which has so far precluded spectroscopy of such events. Afterglow spectroscopy is the key tool to firmly determine the distance at which the burst was produced, crucial to understand its physics, and study its local environment. Methods. Here we present the first spectra of a prototypical SGRB afterglow in which both absorption and emission features are clearly detected. Together with multi-wavelength photometry we study the host and environment of GRB 130603B. Results. From these spectra we determine the redshift of the burst to be z = 0.3565 +/- 0.0002, measure rich dynamics both in absorption and emission, and a substantial line of sight extinction of A(V) = 0.86 +/- 0.15 mag. The GRB was located at the edge of a disrupted arm of a moderately star forming galaxy with near-solar metallicity. Unlike for most long GRBs (LGRBs), N-HX/A(V) is consistent with the Galactic ratio, indicating that the explosion site differs from those found in LGRBs. Conclusions. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the compact object binary.
  •  
44.
  • Rahman, F., et al. (författare)
  • Insomnia and job stressors among healthcare workers who served COVID-19 patients in Bangladesh
  • 2023
  • Ingår i: BMC Health Services Research. - 1472-6963. ; 23:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: The global outbreak of COVID-19 has created unprecedented havoc among health care workers, resulting in significant psychological strains like insomnia. This study aimed to analyze insomnia prevalence and job stressors among Bangladeshi health care workers in COVID-19 units. Methodology: We conducted this cross-sectional study to assess insomnia severity from January to March 2021 among 454 health care workers working in multiple hospitals in Dhaka city with active COVID-dedicated units. We selected 25 hospitals conveniently. We used a structured questionnaire for face-to-face interviews containing sociodemographic variables and job stressors. The severity of insomnia was measured by the Insomnia Severity Scale (ISS). The scale has seven items to evaluate the rate of insomnia, which was categorized as the absence of Insomnia (0–7); sub-threshold Insomnia (8–14); moderate clinical Insomnia (15–21); and severe clinical Insomnia (22–28). To identify clinical insomnia, a cut-off value of 15 was decided primarily. A cut-off score of 15 was initially proposed for identifying clinical insomnia. We performed a chi-square test and adjusted logistic regression to explore the association of different independent variables with clinically significant insomnia using the software SPSS version 25.0. Results: 61.5% of our study participants were females. 44.9% were doctors, 33.9% were nurses, and 21.1% were other health care workers. Insomnia was more dominant among doctors and nurses (16.2% and 13.6%, respectively) than others (4.2%). We found clinically significant insomnia was associated with several job stressors (p < 0.05). In binary logistic regression, having sick leave (OR = 0.248, 95% CI = 0.116, 0.532) and being entitled to risk allowance (OR = 0.367, 95% CI = 0.124.1.081) showed lower odds of developing Insomnia. Previously diagnosed with COVID-19-positive health care workers had an OR of 2.596 (95% CI = 1.248, 5.399), pointing at negative experiences influencing insomnia. In addition, we observed that any training on risk and hazard increased the chances of suffering from Insomnia (OR = 1.923, 95% CI = 0.934, 3.958). Conclusion: It is evident from the findings that the volatile existence and ambiguity of COVID-19 have induced significant adverse psychological effects and subsequently directed our HCWs toward disturbed sleep and insomnia. The study recommends the imperativeness to formulate and implement collaborative interventions to help HCWs cope with this crisis and mitigate the mental stresses they experience during the pandemic. 
  •  
45.
  • Schady, P., et al. (författare)
  • Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z =2-4 using JWST
  • 2024
  • Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:3, s. 2807-2831
  • Tidskriftsartikel (refereegranskat)abstract
    • Much of what is known of the chemical composition of the universe is based on emission line spectra from star-forming galaxies. Emission-based inferences are, nevertheless, model-dependent and they are dominated by light from luminous star-forming regions. An alternative and sensitive probe of the metallicity of galaxies is through absorption lines imprinted on the luminous afterglow spectra of long gamma ray bursts (GRBs) from neutral material within their host galaxy. We present results from a JWST/NIRSpec programme to investigate for the first time the relation between the metallicity of neutral gas probed in absorption by GRB afterglows and the metallicity of the star-forming regions for the same host galaxy sample. Using an initial sample of eight GRB host galaxies at z = 2.1–4.7, we find a tight relation between absorption and emission line metallicities when using the recently proposed ?^ metallicity diagnostic (±0.2 dex). This agreement implies a relatively chemically homogeneous multiphase interstellar medium and indicates that absorption and emission line probes can be directly compared. However, the relation is less clear when using other diagnostics, such as R23 and R3. We also find possible evidence of an elevated N/O ratio in the host galaxy of GRB 090323 at z = 4.7, consistent with what has been seen in other z > 4 galaxies. Ultimate confirmation of an enhanced N/O ratio and of the relation between absorption and emission line metallicities will require a more direct determination of the emission line metallicity via the detection of temperature-sensitive auroral lines in our GRB host galaxy sample.
  •  
46.
  •  
47.
  • Schulze, S., et al. (författare)
  • GRB 120422A/SN 2012bz : Bridging the gap between low- and high-luminosity gamma-ray bursts
  • 2014
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with luminosities that are substantially lower (L-iso less than or similar to 10(48.5) erg s(-1)) than the average of more distant ones (L-iso greater than or similar to 10(49.5) erg s(-1)). It has been suggested that the properties of several low-luminosity (low-L) GRBs are due to shock break-out, as opposed to the emission from ultrarelativistic jets. This has led to much debate about how the populations are connected. Aims. The burst at redshift z = 0.283 from 2012 April 22 is one of the very few examples of intermediate-L GRBs with a gamma-ray luminosity of L-iso similar to 10(49.6-49.9) erg s(-1) that have been detected up to now. With the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low-and high-L GRBs and the GRB-SN connection. Methods. We carried out a spectroscopy campaign using medium-and low-resolution spectrographs with 6-10-m class telescopes, which covered a time span of 37.3 days, and a multi-wavelength imaging campaign, which ranged from radio to X-ray energies over a duration of similar to 270 days. Furthermore, we used a tuneable filter that is centred at H alpha to map star-formation in the host and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and fitted the spectral energy distribution to extract the properties of the host galaxy. Results. Modelling the light curve and spectral energy distribution from the radio to the X-rays revealed that the blast wave expanded with an initial Lorentz factor of Gamma(0) similar to 50, which is a low value in comparison to high-L GRBs, and that the afterglow had an exceptionally low peak luminosity density of less than or similar to 2 x 10(30) erg s(-1) Hz(-1) in the sub-mm. Because of the weak afterglow component, we were able to recover the signature of a shock break-out in an event that was not a genuine low-L GRB for the first time. At 1.4 hr after the burst, the stellar envelope had a blackbody temperature of k(B)T similar to 16 eV and a radius of similar to 7 x 10(13) cm (both in the observer frame). The accompanying SN 2012bz reached a peak luminosity of M-V = -19.7 mag, which is 0.3 mag more luminous than SN 1998bw. The synthesised nickel mass of 0.58 M-circle dot, ejecta mass of 5.87 M-circle dot, and kinetic energy of 4.10x10(52) erg were among the highest for GRB-SNe, which makes it the most luminous spectroscopically confirmed SN to date. Nebular emission lines at the GRB location were visible, which extend from the galaxy nucleus to the explosion site. The host and the explosion site had close-to-solar metallicity. The burst occurred in an isolated star-forming region with an SFR that is 1/10 of that in the galaxy's nucleus. Conclusions. While the prompt gamma-ray emission points to a high-L GRB, the weak afterglow and the low Gamma(0) were very atypical for such a burst. Moreover, the detection of the shock break-out signature is a new quality for high-L GRBs. So far, shock break-outs were exclusively detected for low-L GRBs, while GRB 120422A had an intermediate L-iso of similar to 10(49.6-49.9) erg s(-1). Therefore, we conclude that GRB 120422A was a transition object between low-and high-L GRBs, which supports the failed-jet model that connects low-L GRBs that are driven by shock break-outs and high-L GRBs that are powered by ultra-relativistic jets.
  •  
48.
  • Selsing, J., et al. (författare)
  • The X-shooter GRB afterglow legacy sample (XS-GRB)
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 623
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we present spectra of all gamma-ray burst (GRB) afterglows that have been promptly observed with the X-shooter spectrograph until 31/03/2017. In total, we have obtained spectroscopic observations of 103 individual GRBs observed within 48 hours of the GRB trigger. Redshifts have been measured for 97 per cent of these, covering a redshift range from 0.059 to 7.84. Based on a set of observational selection criteria that minimise biases with regards to intrinsic properties of the GRBs, the follow-up effort has been focused on producing a homogeneously selected sample of 93 afterglow spectra for GRBs discovered by the Swift satellite. We here provide a public release of all the reduced spectra, including continuum estimates and telluric absorption corrections. For completeness, we also provide reductions for the 18 late-time observations of the underlying host galaxies. We provide an assessment of the degree of completeness with respect to the parent GRB population, in terms of the X-ray properties of the bursts in the sample and find that the sample presented here is representative of the full Swift sample. We have constrained the fraction of dark bursts to be <28 per cent and confirm previous results that higher optical darkness is correlated with increased X-ray absorption. For the 42 bursts for which it is possible, we have provided a measurement of the neutral hydrogen column density, increasing the total number of published HI column density measurements by similar to 33 per cent. This dataset provides a unique resource to study the ISM across cosmic time, from the local progenitor surroundings to the intervening Universe.
  •  
49.
  • Sparre, M., et al. (författare)
  • SPECTROSCOPIC EVIDENCE FOR SN 2010ma ASSOCIATED WITH GRB 101219B
  • 2011
  • Ingår i: The Astrophysical Journal Letters. - 2041-8205. ; 735:1, s. L24-
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the spectroscopic detection of supernova SN 2010ma associated with the long gamma-ray burst GRB 101219B. We observed the optical counterpart of the GRB on three nights with the X-shooter spectrograph at the Very Large Telescope. From weak absorption lines, we measure a redshift of z = 0.55. The first-epoch UV-near-infrared afterglow spectrum, taken 11.6 hr after the burst, is well fit by a power law consistent with the slope of the X-ray spectrum. The second-and third-epoch spectra (obtained 16.4 and 36.7 days after the burst), however, display clear bumps closely resembling those of the broad-lined type-Ic SN 1998bw if placed at z = 0.55. Apart from demonstrating that spectroscopic SN signatures can be observed for GRBs at these large distances, our discovery makes a step forward in establishing a general connection between GRBs and SNe. In fact, unlike most previous unambiguous GRB-associated SNe, GRB 101219B has a large gamma-ray energy (E(iso) = 4.2x10(51) erg), a bright afterglow, and obeys the Amati relation, thus being fully consistent with the cosmological population of GRBs.
  •  
50.
  • Sparre, M., et al. (författare)
  • THE METALLICITY AND DUST CONTENT OF A REDSHIFT 5 GAMMA-RAY BURST HOST GALAXY
  • 2014
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 785:2, s. 150-
  • Tidskriftsartikel (refereegranskat)abstract
    • Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A, from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Ly alpha absorber with a very large neutral hydrogen column density of log N (H I)/cm(-2) = 22.30 +/- 0.06 and a metallicity of [S/H] = -1.70 +/- 0.10. It is the highest-redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z = 5.0 system as the GRB host galaxy and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A(V) = 0.11 +/- 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-50 av 54
Typ av publikation
tidskriftsartikel (47)
konferensbidrag (3)
rapport (2)
forskningsöversikt (2)
Typ av innehåll
refereegranskat (53)
övrigt vetenskapligt/konstnärligt (1)
Författare/redaktör
Tanvir, N. R. (39)
Hjorth, J. (30)
Levan, A. J. (29)
Fynbo, J. P. U. (27)
Wiersema, K. (27)
Malesani, D. (23)
visa fler...
Jakobsson, P (23)
D'Elia, V (21)
Covino, S. (20)
de Ugarte Postigo, A ... (19)
Sollerman, Jesper (18)
Milvang-Jensen, B. (17)
Schulze, S. (16)
Pian, E. (15)
Watson, D. (15)
Xu, D. (14)
Tagliaferri, G. (14)
Vergani, S. D. (14)
Kann, D. A. (13)
Greiner, J. (13)
Piranomonte, S. (13)
Palazzi, E. (13)
D'Avanzo, P. (12)
Rossi, A. (11)
Cano, Z. (11)
Klose, S. (11)
Melandri, A. (11)
Starling, R. L. C. (11)
Gorosabel, J. (11)
Kaper, L. (11)
Wijers, R. A. M. J. (10)
Goldoni, P. (10)
Castro-Tirado, A. J. (10)
Izzo, L. (10)
Perley, D. A. (10)
Sánchez-Ramírez, R. (10)
Schady, P. (9)
Fruchter, A. S. (9)
Watson, D. J. (9)
Campana, S. (8)
Flores, H. (8)
De Pasquale, M. (8)
Heintz, K. E. (8)
Lyman, J. D. (8)
Thöne, C. C. (8)
Evans, P. A. (7)
van der Horst, A. J. (7)
O'Brien, P. T. (7)
Rosswog, Stephan (7)
De Cia, A. (7)
visa färre...
Lärosäte
Stockholms universitet (34)
Lunds universitet (9)
Uppsala universitet (6)
Kungliga Tekniska Högskolan (5)
Mittuniversitetet (3)
Karolinska Institutet (3)
visa fler...
Göteborgs universitet (2)
Jönköping University (1)
Chalmers tekniska högskola (1)
Karlstads universitet (1)
Högskolan Dalarna (1)
Sveriges Lantbruksuniversitet (1)
visa färre...
Språk
Engelska (54)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (44)
Medicin och hälsovetenskap (7)
Samhällsvetenskap (1)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy