| 1. |
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| 2. |
- Veres, P., et al.
(författare)
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Observation of inverse Compton emission from a long gamma-ray burst
- 2019
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 575:7783, s. 459-
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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.
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| 3. |
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| 4. |
- Ackley, K., et al.
(författare)
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Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
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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.
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| 5. |
- Scolnic, D., et al.
(författare)
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How Many Kilonovae Can Be Found in Past, Present, and Future Survey Data Sets?
- 2018
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 852:1
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of a kilonova (KN) associated with the Advanced LIGO (aLIGO)/Virgo event GW170817 opens up new avenues of multi-messenger astrophysics. Here, using realistic simulations, we provide estimates of the number of KNe that could be found in data from past, present, and future surveys without a gravitational-wave trigger. For the simulation, we construct a spectral time-series model based on the DES-GW multi-band light curve from the single known KN event, and we use an average of BNS rates from past studies of 103Gpc(-3) yr(-1), consistent with the one event found so far. Examining past and current data sets from transient surveys, the number of KNe we expect to find for ASAS-SN, SDSS, PS1, SNLS, DES, and SMT is between 0 and 0.3. We predict the number of detections per future survey to be 8.3 from ATLAS, 10.6 from ZTF, 5.5/69 from LSST (the Deep Drilling/Wide Fast Deep), and 16.0 from WFIRST. The maximum redshift of KNe discovered for each survey is z = 0.8 for WFIRST, z = 0.25 for LSST, and z = 0.04 for ZTF and ATLAS. This maximum redshift for WFIRST is well beyond the sensitivity of aLIGO and some future GW missions. For the LSST survey, we also provide contamination estimates from Type Ia and core-collapse supernovae: after light curve and template-matching requirements, we estimate a background of just two events. More broadly, we stress that future transient surveys should consider how to optimize their search strategies to improve their detection efficiency and to consider similar analyses for GW follow-up programs.
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| 6. |
- Agudo, I., et al.
(författare)
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Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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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.
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| 7. |
- Gutierrez, C. P., et al.
(författare)
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DES16C3cje : A low-luminosity, long-lived supernova
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 496:1, s. 95-110
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Tidskriftsartikel (refereegranskat)abstract
- We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of less than or similar to 1500 km s(-1), and the light curve shows an initial peak that fades after 50 d before slowly rebrightening over a further 100 d to reach an absolute brightness of M-r similar to 15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of Co-56, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either (i) a low explosion energy (0.11 foe) and relatively large Ni-56 production of 0.075 M-circle dot from an similar to 15 M-circle dot red supergiant progenitor typical of other SNe II, or (ii) a relatively compact similar to 40 M-circle dot star, explosion energy of 1 foe, and 0.08 M-circle dot of Ni-56. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of similar to 0.5 x 10(-)(8) M-circle dot s(-1).
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| 8. |
- Nicholl, M., et al.
(författare)
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Slowly fading super-luminous supernovae that are not pair-instability explosions
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 502:7471, s. 346-
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Tidskriftsartikel (refereegranskat)abstract
- Super-luminous supernovae(1-4) that radiate more than 1044 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae(5,6). Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of Ni-56 are synthesized; this isotope decays to Fe-56 via Co-56, powering bright light curves(7,8). Such massive progenitors are expected to have formed from metal-poor gas in the early Universe(9). Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova(1,10). Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae(2,11,12), which are not powered by radio-activity. Modelling our observations with 10-16 solar masses of magnetar-energized(13,14) ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 x 10(-6) times that of the core-collapse rate.
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| 9. |
- Smartt, S. J., et al.
(författare)
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PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 579
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January - April and August - December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5(m) for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 angstrom between 3345-9995 angstrom. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 mu m and resolutions 23-33 angstrom) and imaging with broadband JHK(s) filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012-2013). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically similar to 15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHK(s) imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey.
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| 10. |
- Brennan, S. J., et al.
(författare)
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Photometric and spectroscopic evolution of the interacting transient AT 2016jbu(Gaia16cfr)
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5642-5665
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from a high-cadence, multiwavelength observation campaign of AT 2016jbu (aka Gaia16cfr), an interacting transient. This data set complements the current literature by adding higher cadence as well as extended coverage of the light-curve evolution and late-time spectroscopic evolution. Photometric coverage reveals that AT 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of MV ∼ −18.5 mag. This is similar to the transient SN 2009ip whose nature is still debated. Spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. AT 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (CSM). We see slowly evolving asymmetric hydrogen line profiles, with velocities of 500 km s−1 seen in narrow emission features from a slow-moving CSM, and up to 10 000 km s−1 seen in broad absorption from some high-velocity material. Late-time spectra (∼+1 yr) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from H, He I, and Ca II. Strong asymmetric emission features, a bumpy light curve, and continually evolving spectra suggest an inhibit nebular phase. We compare the evolution of H α among SN 2009ip-like transients and find possible evidence for orientation angle effects. The light-curve evolution of AT 2016jbu suggests similar, but not identical, circumstellar environments to other SN 2009ip-like transients.
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| 11. |
- Brennan, S. J., et al.
(författare)
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Progenitor, environment, and modelling of the interacting transient AT 2016jbu (Gaia16cfr)
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5666-5685
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Tidskriftsartikel (refereegranskat)abstract
- We present the bolometric light curve, identification and analysis of the progenitor candidate, and preliminary modelling of AT 2016jbu (Gaia16cfr). We find a progenitor consistent with a ∼ 22–25 M⊙ yellow hypergiant surrounded by a dusty circumstellar shell, in agreement with what has been previously reported. We see evidence for significant photometric variability in the progenitor, as well as strong Hα emission consistent with pre-existing circumstellar material. The age of the environment, as well as the resolved stellar population surrounding AT 2016jbu, supports a progenitor age of >10 Myr, consistent with a progenitor mass of ∼22 M⊙. A joint analysis of the velocity evolution of AT 2016jbu and the photospheric radius inferred from the bolometric light curve shows the transient is consistent with two successive outbursts/explosions. The first outburst ejected material with velocity ∼650 km s−1, while the second, more energetic event ejected material at ∼4500 km s−1. Whether the latter is the core collapse of the progenitor remains uncertain. We place a limit on the ejected 56Ni mass of <0.016 M⊙. Using the Binary Population And Spectral Synthesis (BPASS) code, we explore a wide range of possible progenitor systems and find that the majority of these are in binaries, some of which are undergoing mass transfer or common-envelope evolution immediately prior to explosion. Finally, we use the SuperNova Explosion Code (SNEC) to demonstrate that the low-energy explosions within some of these binary systems, together with sufficient circumstellar material, can reproduce the overall morphology of the light curve of AT 2016jbu.
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| 12. |
- Cannizzaro, G., et al.
(författare)
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Accretion disc cooling and narrow absorption lines in the tidal disruption event AT2019dsg
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 504:1, s. 792-815
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a large multiwavelength follow-up campaign of the tidal disruption event (TDE) AT 2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive black hole of mass (5.4±3.2)×106M⊙ and careful analysis finds no evidence for the presence of an active galactic nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV, and optical. The X-ray emission becomes undetected after ∼100 d, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 d. Optical emission line signatures of the TDE are present up to ∼200 d after the light-curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 d, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy’s stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e. seen from the poles).
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| 13. |
- Kankare, E., et al.
(författare)
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Core-collapse supernova subtypes in luminous infrared galaxies
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 649
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Tidskriftsartikel (refereegranskat)abstract
- The fraction of core-collapse supernovae (CCSNe) occurring in the central regions of galaxies is not well constrained at present. This is partly because large-scale transient surveys operate at optical wavelengths, making it challenging to detect transient sources that occur in regions susceptible to high extinction factors. Here we present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG) NGC 3256. The first, SN 2018ec, was discovered using the ESO HAWK-I /GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of AV = 2:1+0:3 0:1 mag. The second, AT 2018cux, was discovered during the course of follow-up observations of SN 2018ec, and is consistent with a subluminous Type IIP classification with an AV = 2:1 +/- 0:4 mag of host extinction. A third CCSN, PSN J10275082 4354034 in NGC 3256, was previously reported in 2014, and we recovered the source in late-time archival Hubble Space Telescope imaging. Based on template light curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of AV = 0:3+0:4 0:3 mag. We also extend our study with follow-up data of the recent Type IIb SN 2019lqo and Type Ib SN 2020fkb that occurred in the LIRG system Arp 299 with host extinctions of AV = 2:1 +0:1 0 :3 and AV = 0:4 +0:1 0 :2 mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, that there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb /Ib /Ic /Ibn) and 15 H-rich (Type II /IIn) CCSNe have di fferent underlying progenitor age distributions, with the H-poor progenitors being younger at 3 sigma significance. However, we note that the currently available sample sizes of CCSNe and host LIRGs are small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages.
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| 14. |
- Fiore, A., et al.
(författare)
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Close, bright, and boxy : the superluminous SN 2018hti
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 512:3, s. 4484-4502
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Tidskriftsartikel (refereegranskat)abstract
- SN 2018hti was a very nearby (z = 0.0614) superluminous supernova with an exceedingly bright absolute magnitude of −21.7 mag in r band at maximum. The densely sampled pre-maximum light curves of SN 2018hti show a slow luminosity evolution and constrain the rise time to ∼50 rest-frame d. We fitted synthetic light curves to the photometry to infer the physical parameters of the explosion of SN 2018hti for both the magnetar and the CSM-interaction scenarios. We conclude that one of two mechanisms could be powering the luminosity of SN 2018hti; interaction with ∼10 M⊙ of circumstellar material or a magnetar with a magnetic field of Bp∼ 1.3 × 1013 G, and initial period of Pspin∼ 1.8 ms. From the nebular spectrum modelling we infer that SN 2018hti likely results from the explosion of a ∼40M⊙∼40M⊙ progenitor star.
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| 15. |
- Leloudas, G., et al.
(författare)
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The superluminous transient ASASSN-15lh as a tidal disruption event from a Kerr black hole
- 2016
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:1
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Tidskriftsartikel (refereegranskat)abstract
- When a star passes within the tidal radius of a supermassive black hole, it will be torn apart1. For a star with the mass of the Sun (M-circle dot) and a non-spinning black hole with a mass <10(8)M(circle dot), the tidal radius lies outside the black hole event horizon2 and the disruption results in a luminous flare(3-6). Here we report observations over a period of ten months of a transient, hitherto interpreted(7) as a superluminous supernova(8). Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution(6), the presence of highly ionized CNO gas in the line of sight(9) and our improved localization of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely(10,11). While the supermassive black hole has a mass >10(8)M(circle dot)(12,13), a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly(14). The rapid spin and high black hole mass can explain the high luminosity of this event.
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| 16. |
- Levan, Andrew J., et al.
(författare)
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A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:8, s. 976-985
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Tidskriftsartikel (refereegranskat)abstract
- The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.
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| 17. |
- McBrien, Owen R., et al.
(författare)
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SN2018kzr : A Rapidly Declining Transient from the Destruction of a White Dwarf
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 885:1
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Tidskriftsartikel (refereegranskat)abstract
- We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of M-r & xfffd;=& xfffd;?17.98, a peak bolometric luminosity of ?1.4 & xfffd;& x5e0;10(43) erg s(?1), and a rapid decline rate of 0.48 & xfffd;& xfffd;0.03 mag day(?1) in the r band. The bolometric luminosity evolves too quickly to be explained by pure Ni-56 heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of M-ej & xfffd;=& xfffd;0.10 & xfffd;& xfffd;0.05 M. Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering?the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf?neutron star merger with energy from disk wind shocks.
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| 18. |
- Melandri, A., et al.
(författare)
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GRB171010A/SN 2017htp : a GRB-SN at z=0.33
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 490:4, s. 5366-5374
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Tidskriftsartikel (refereegranskat)abstract
- The number of supernovae known to be connected with long-duration gamma-ray bursts (GRBs) is increasing and the link between these events is no longer exclusively found at low redshift (z less than or similar to 0.3) but is well established also at larger distances. We present a new case of such a liaison at z = 0.33 between GRB171010A and SN 2017htp. It is the second closest GRB with an associated supernova of only three events detected by Fermi-LAT. The supernova is one of the few higher redshift cases where spectroscopic observations were possible and shows spectral similarities with the well-studied SN 1998bw, having produced a similar Ni mass (M-Ni = 0.33 +/- 0.02 M-circle dot) with slightly lower ejected mass (M-ej = 4.1 +/- 0.7 M-circle dot) and kinetic energy (E-K = 8.1 +/- 2.5 x 10(51) erg). The host-galaxy is bigger in size than typical GRB host galaxies, but the analysis of the region hosting the GRB revealed spectral properties typically observed in GRB hosts and showed that the progenitor of this event was located in a very bright H II region of its face-on host galaxy, at a projected distance of similar to 10 kpc from its galactic centre. The star-formation rate (SFRGRB similar to 0.2 M-circle dot yr(-1)) and metallicity (12 + log(O/H) similar to 8.15 +/- 0.10) of the GRB star-forming region are consistent with those of the host galaxies of previously studied GRB-SN systems.
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| 19. |
- Nicholl, M., et al.
(författare)
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An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:1, s. 482-504
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Tidskriftsartikel (refereegranskat)abstract
- At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass approximate to 10(6) M-circle dot, disrupting a star of approximate to 1 M-circle dot. By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L proportional to t(2), consistent with a photosphere expanding at constant velocity (greater than or similar to 2000 km s(-1)), and a line-forming region producing initially blueshifted H and He II profiles with v = 3000-10 000 km s(-1). The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission - the first time this connection has been observed in a TDE. The light-curve rise begins 29 +/- 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N III) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at approximate to 10(41) erg s(-1). Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models.
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| 20. |
- Nicholl, M., et al.
(författare)
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On the diversity of superluminous supernovae : ejected mass as the dominant factor
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:4, s. 3869-3893
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Tidskriftsartikel (refereegranskat)abstract
- We assemble a sample of 24 hydrogen-poor superluminous supernovae (SLSNe). Parameterizing the light-curve shape through rise and decline time-scales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion time-scale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 mag brighter and have light curves three times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming. = 0.1 cm(2) g(-1), we estimate a mean (median) SLSN ejecta mass of 10 M-circle dot (6 M-circle dot), with a range of 3-30 M-circle dot. Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.
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| 21. |
- Nicholl, M., et al.
(författare)
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Superluminous supernovae from PESSTO
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 444:3, s. 2096-2113
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Tidskriftsartikel (refereegranskat)abstract
- We present optical spectra and light curves for three hydrogen-poor superluminous supernovae followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). Time series spectroscopy from a fewdays aftermaximum light to 100 d later shows them to be fairly typical of this class, with spectra dominated by Ca II, MgII, FeII, and Si II, which evolve slowly over most of the post-peak photospheric phase. We determine bolometric light curves and apply simple fitting tools, based on the diffusion of energy input by magnetar spin-down, Ni-56 decay, and collision of the ejecta with an opaque circumstellar shell. We investigate how the heterogeneous light curves of our sample (combined with others from the literature) can help to constrain the possible mechanisms behind these events. We have followed these events to beyond 100-200 d after peak, to disentangle host galaxy light from fading supernova flux and to differentiate between the models, which predict diverse behaviour at this phase. Models powered by radioactivity require unrealistic parameters to reproduce the observed light curves, as found by previous studies. Both magnetar heating and circumstellar interaction still appear to be viable candidates. A large diversity is emerging in observed tail-phase luminosities, with magnetar models failing in some cases to predict the rapid drop in flux. This would suggest either that magnetars are not responsible, or that the X-ray flux from the magnetar wind is not fully trapped. The light curve of one object shows a distinct rebrightening at around 100 d after maximum light. We argue that this could result either from multiple shells of circumstellar material, or from a magnetar ionization front breaking out of the ejecta.
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| 22. |
- Polshaw, J., et al.
(författare)
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LSQ13fn : A type II-Plateau supernova with a possibly low metallicity progenitor that breaks the standardised candle relation
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 588
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Tidskriftsartikel (refereegranskat)abstract
- We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a type II supernova with several hitherto-unseen properties. Although it initially showed strong symmetric spectral emission features attributable to He II, N III, and C III, reminiscent of some interacting SNe, it transitioned into an object that would fall more naturally under a type II-Plateau (IIP) classification. However, its spectral evolution revealed several unusual properties: metal lines appeared later than expected, were weak, and some species were conspicuous by their absence. Furthermore, the line velocities were found to be lower than expected given the plateau brightness, breaking the SN IIP standardised candle method for distance estimates. We found that, in combination with a short phase of early-time ejecta-circumstellar material interaction, metal-poor ejecta, and a large progenitor radius could reasonably account for the observed behaviour. Comparisons with synthetic model spectra of SNe IIP of a given progenitor mass would imply a progenitor star metallicity as low as 0.1 Z(circle dot). LSQ13fn highlights the diversity of SNe II and the many competing physical e ff ects that come into play towards the final stages of massive star evolution immediately preceding core-collapse.
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| 23. |
- Prentice, S. J., et al.
(författare)
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Transitional events in the spectrophotometric regime between stripped envelope and superluminous supernovae
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 508:3, s. 4342-4358
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Tidskriftsartikel (refereegranskat)abstract
- The division between stripped-envelope supernovae (SE-SNe) and superluminous supernovae (SLSNe) is not well-defined in either photometric or spectroscopic space. While a sharp luminosity threshold has been suggested, there remains an increasing number of transitional objects that reach this threshold without the spectroscopic signatures common to SLSNe. In this work, we present data and analysis on four SNe transitional between SE-SNe and SLSNe; the He-poor SNe 2019dwa and 2019cri, and the He-rich SNe 2019hge and 2019unb. Each object displays long-lived and variable photometric evolution with luminosities around the SLSN threshold of Mr < −19.8 mag. Spectroscopically however, these objects are similar to SE-SNe, with line velocities lower than either SE-SNe and SLSNe, and thus represent an interesting case of rare transitional events.
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| 24. |
- Pursiainen, M., et al.
(författare)
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SN 2018bsz : A Type I superluminous supernova with aspherical circumstellar material
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- We present a spectroscopic analysis of the most nearby Type I superluminous supernova (SLSN-I), SN 2018bsz. The photometric evolution of SN 2018bsz has several surprising features, including an unusual pre-peak plateau and evidence for rapid formation of dust ≳200 d post-peak. We show here that the spectroscopic and polarimetric properties of SN 2018bsz are also unique. While its spectroscopic evolution closely resembles SLSNe-I, with early O II absorption and C II P Cygni profiles followed by Ca, Mg, Fe, and other O features, a multi-component Hα profile appearing at ∼30 d post-maximum is the most atypical. The Hα is at first characterised by two emission components, one at ∼+3000 km s−1 and a second at ∼ − 7500 km s−1, with a third, near-zero-velocity component appearing after a delay. The blue and central components can be described by Gaussian profiles of intermediate width (FWHM ∼ 2000–6000 km s−1), but the red component is significantly broader (FWHM ≳ 10 000 km s−1) and Lorentzian. The blue Hα component evolves towards a lower-velocity offset before abruptly fading at ∼ + 100 d post-maximum brightness, concurrently with a light curve break. Multi-component profiles are observed in other hydrogen lines, including Paβ, and in lines of Ca II and He I. Spectropolarimetry obtained before (10.2 d) and after (38.4 d) the appearance of the H lines shows a large shift on the Stokes Q – U plane consistent with SN 2018bsz undergoing radical changes in its projected geometry. Assuming the supernova is almost unpolarised at 10.2 d, the continuum polarisation at 38.4 d reaches P ∼ 1.8%, implying an aspherical configuration. We propose that the observed evolution of SN 2018bsz can be explained by highly aspherical, possibly disk-like, circumstellar material (CSM) with several emitting regions. After the supernova explosion, the CSM is quickly overtaken by the ejecta, but as the photosphere starts to recede, the different CSM regions re-emerge, producing the peculiar line profiles. Based on the first appearance of Hα, we can constrain the distance of the CSM to be less than ∼6.5 × 1015 cm (430 AU), or even lower (≲87 AU) if the pre-peak plateau is related to an eruption that created the CSM. The presence of CSM has been inferred previously for other SLSNe-I, both directly and indirectly. However, it is not clear whether the rare properties of SN 2018bsz can be generalised for SLSNe-I, for example in the context of pulsational pair instability, or whether they are the result of an uncommon evolutionary path, possibly involving a binary companion.
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| 25. |
- Reynolds, T. M., et al.
(författare)
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SN 2016gsd : an unusually luminous and linear Type II supernova with high velocities
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 493:2, s. 1761-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of the unusually luminous Type II supernova (SN) 2016gsd. With a peak absolute magnitude of V = -19.95 +/- 0.08, this object is one of the brightest Type II SNe, and lies in the gap of magnitudes between the majority of Type II SNe and the superluminous SNe. Its light curve shows little evidence of the expected drop from the optically thick phase to the radioactively powered tail. The velocities derived from the absorption in( )H alpha are also unusually high with the blue edge tracing the fastest moving gas initially at 20 000 km s(-1), and then declining approximately linearly to 15000 km s(-1) over similar to 100 d. The dwarf host galaxy of the SN indicates a low-metallicity progenitor which may also contribute to the weakness of the metal lines in its spectra. We examine SN 2016gsd with reference to similarly luminous, linear Type II SNe such as SNe 1979C and 1998S, and discuss the interpretation of its observational characteristics. We compare the observations with a model produced by the JEKYLL code and find that a massive star with a depleted and inflated hydrogen envelope struggles to reproduce the high luminosity and extreme linearity of SN 2016gsd. Instead, we suggest that the influence of interaction between the SN ejecta and circumstellar material can explain the majority of the observed properties of the SN. The high velocities and strong H alpha absorption present throughout the evolution of the SN may imply a circumstellar medium configured in an asymmetric geometry.
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