| 1. |
- Mach, Henryk, et al.
(författare)
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The single-particle and collective features in the nuclei just above Sn-132
- 2007
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Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 38:4, s. 1213-1218
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Tidskriftsartikel (refereegranskat)abstract
- The Advanced Time Delayed method has been used to measure the lifetimes of excited states in the exotic nuclei Sb-134, Sb-135 and Te-136 populated in the beta decay of Sn-134, Sn-135 and Sn-136, respectively. High purity Sn beams were extracted at the ISOLDE separator using a novel production technique utilizing the molecular SnS+ beams to isolate Sn from contaminating other fission products. Among the new results we have identified the 1/2(+) state in Sb-135 and its E2 transition to the lower-lying 5/2(+) state was found to be surprisingly collective. This measurement represents also one of the first applications of the LaBr3 scintillator to ultra fast timing.
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| 2. |
- 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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| 3. |
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| 4. |
- O'Sullivan, Shane P., et al.
(författare)
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The intergalactic magnetic field probed by a giant radio galaxy
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
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Forskningsöversikt (refereegranskat)abstract
- Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). Using data from the LOFAR Two Metre Sky Survey (LoTSS), we present the Faraday rotation measure (RM) and depolarisation properties of the giant radio galaxy J1235+5317, at a redshift of z = 0.34 and 3.38 Mpc in size. We find a mean RM difference between the lobes of 2.5 ±0.1 rad m -2 , in addition to small scale RM variations of ∼0.1 rad m -2 . From a catalogue of LSS filaments based on optical spectroscopic observations in the local universe, we find an excess of filaments intersecting the line of sight to only one of the lobes. Associating the entire RM difference to these LSS filaments leads to a gas density-weighted IGMF strength of ∼0.3 μG. However, direct comparison with cosmological simulations of the RM contribution from LSS filaments gives a low probability (∼5%) for an RM contribution as large as 2.5 rad m -2 , for the case of IGMF strengths of 10-50 nG. It is likely that variations in the RM from the Milky Way (on 11′ scales) contribute significantly to the mean RM difference, and a denser RM grid is required to better constrain this contribution. In general, this work demonstrates the potential of the LOFAR telescope to probe the weak signature of the IGMF. Future studies, with thousands of sources with high accuracy RMs from LoTSS, will enable more stringent constraints on the nature of the IGMF.
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| 5. |
- Chen, Ping, et al.
(författare)
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A 12.4-day periodicity in a close binary system after a supernova
- 2024
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 625:7994, s. 253-258
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Tidskriftsartikel (refereegranskat)abstract
- Neutron stars and stellar-mass black holes are the remnants of massive star explosions1. Most massive stars reside in close binary systems2, and the interplay between the companion star and the newly formed compact object has been theoretically explored3, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. Here we report a stripped-envelope supernova, SN 2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow Hα emission is detected in late-time spectra with concordant periodic velocity shifts, probably arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi-LAT γ-ray source is temporally and positionally consistent with SN 2022jli. The observed properties of SN 2022jli, including periodic undulations in the optical light curve, coherent Hα emission shifting and evidence for association with a γ-ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the γ-ray emission.
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| 6. |
- Hobbs, David, et al.
(författare)
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All-sky visible and near infrared space astrometry
- 2021
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 51:3, s. 783-843
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Tidskriftsartikel (refereegranskat)abstract
- The era of all-sky space astrometry began with the Hipparcos mission in 1989 and provided the first very accurate catalogue of apparent magnitudes, positions, parallaxes and proper motions of 120 000 bright stars at the milliarcsec (or milliarcsec per year) accuracy level. Hipparcos has now been superseded by the results of the Gaia mission. The second Gaia data release contained astrometric data for almost 1.7 billion sources with tens of microarcsec (or microarcsec per year) accuracy in a vast volume of the Milky Way and future data releases will further improve on this. Gaia has just completed its nominal 5-year mission (July 2019), but is expected to continue in operations for an extended period of an additional 5 years through to mid 2024. Its final catalogue to be released ∼ 2027, will provide astrometry for ∼ 2 billion sources, with astrometric precisions reaching 10 microarcsec. Why is accurate astrometry so important? The answer is that it provides fundamental data which underpin much of modern observational astronomy as will be detailed in this White Paper. All-sky visible and Near-InfraRed (NIR) astrometry with a wavelength cutoff in the K-band is not just focused on a single or small number of key science cases. Instead, it is extremely broad, answering key science questions in nearly every branch of astronomy while also providing a dense and accurate visible-NIR reference frame needed for future astronomy facilities.
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| 7. |
- Holland, Stephen T., et al.
(författare)
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GRB 090417B and its host galaxy : a step toward an understanding of optically dark gamma-ray bursts
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 717:1, s. 223-234
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Tidskriftsartikel (refereegranskat)abstract
- GRB 090417B was an unusually long burst with a T-90 duration of at least 2130 s and a multi-peaked light curve at energies of 15-150 keV. It was optically dark and has been associated with a bright star-forming galaxy at a redshift of 0.345 that is broadly similar to the Milky Way. This is one of the few cases where a host galaxy has been clearly identified for a dark gamma-ray burst (GRB) and thus an ideal candidate for studying the origin of dark bursts. We find that the dark nature of GRB 090417B cannot be explained by high redshift, incomplete observations, or unusual physics in the production of the afterglow. Assuming the standard relativistic fireball model for the afterglow we find that the optical flux is at least 2.5 mag fainter than predicted by the X-ray flux. The Swift/XRT X-ray data are consistent with the afterglow being obscured by a dense, localized sheet of dust approximately 30-80 pc from the burst along the line of sight. Our results suggest that this dust sheet imparts an extinction of A(V) greater than or similar to 12 mag, which is sufficient to explain the missing optical flux. GRB 090417B is an example of a GRBs that is dark due to the localized dust structure in its host galaxy.
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| 8. |
- Konstantopoulou, Christina, et al.
(författare)
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Dust depletion of metals from local to distant galaxies : II. Cosmic dust-to-metal ratio and dust composition
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 681
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of cosmic dust content and the cycle between metals and dust in the interstellar medium (ISM) play a fundamental role in galaxy evolution. The chemical enrichment of the Universe can be traced through the evolution of the dust-to-metal ratio (DTM) and the dust-to-gas ratio (DTG) with metallicity. The physical processes through which dust is created and eventually destroyed remain to be elucidated. We use a novel method to determine mass estimates of the DTM, DTG, and dust composition in terms of the fraction of dust mass contributed by element X ( fMX ) based on our previous measurements of the depletion of metals in different environments (the Milky Way, the Magellanic Clouds, and damped Lyman-α absorbers (DLAs) towards quasars (QSOs) and towards gamma-ray bursts (GRBs)), which were calculated from the relative abundances of metals in the ISM through absorption-line spectroscopy column densities observed mainly from VLT/UVES and X-shooter, and HST/STIS. We also derive the dust extinction from the estimated dust depletion (AV,depl) for GRB-DLAs, the Magellanic Clouds, and the Milky Way, and compare it with the AV estimated from extinction (AV,ext). We find that the DTM and DTG ratios increase with metallicity and with the dust tracer [Zn/Fe]. This suggests that grain growth in the ISM is the dominant process of dust production, at least in the metallicity range (-2 ≤ [M/H]tot . 0.5) and redshift range (0.6 < z < 6.3) that we are studying. The increasing trend in the DTM and DTG with metallicity is in good agreement with a dust production and evolution hydrodynamical model. Our data suggest that the stellar dust yield is much lower (about 1%) than the metal yield and thus that the overall amount of dust in the warm neutral medium that is produced by stars is much lower than previously estimated. The global neutral gas metallicity is decreasing over cosmic time and is traced similarly by quasar-DLAs and GRB-DLAs. We find that, overall, AV,depl is lower than AV,ext for the Milky Way and in a few lines of sight for the Magellanic Clouds, a discrepancy that is likely related to the presence of carbonaceous dust associated with dense clumps of cold neutral gas. For the other environments studied here, we find good agreement overall between the AV,ext and AV,depl.We show that the main elements ( fMX > 1%) that contribute to the dust composition, by mass, are O, Fe, Si, Mg, C, S, Ni, and Al for all the environments, with Si, Mg, and C being equivalent contributors. There are nevertheless variations in the dust composition depending on the overall amount of dust. The abundances measured at low dust regimes in quasar- and GRB-DLAs suggest the presence of pyroxene and metallic iron in dust. These results give important information on the dust and metal content of galaxies across cosmic times, from the Milky Way up to z = 6.3.
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| 9. |
- Michalowski, M. J., et al.
(författare)
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The second-closest gamma-ray burst: Sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including very long baseline interferometry observations with a positional error of 0.2 mas. The afterglow position is coincident with the disc of a galaxy ESO 58049 at z = 0.01326 (∼1″ from its centre), which makes GRB 111005A the second-closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously less luminous than those of cosmological GRBs. The radio flux was approximately constant and then experienced an unusually rapid decay a month after the GRB explosion. Similarly to only two other GRBs, we did not find the associated supernovae (SNe), despite deep near- and mid-infrared observations 1-9 days after the GRB explosion, reaching ∼20 times fainter than other SNe associated with GRBs. Moreover, we measured a twice-solar metallicity for the GRB location. The low y-ray and radio luminosities, rapid decay, lack of a SN, and super-solar metallicity suggest that GRB 111005A represents a rare class of GRB that is different from typical core-collapse events. We modelled the spectral energy distribution of the GRB 111005A host finding that it is a moderately star-forming dwarf galaxy, similar to the host of GRB 980425. The existence of two local GRBs in such galaxies is still consistent with the hypothesis that the GRB rate is proportional to the cosmic star formation rate (SFR) density, but suggests that the GRB rate is biased towards low SFRs. Using the far-infrared detection of ESO 580-49, we conclude that the hosts of both GRBs 111005A and 980425 exhibit lower dust content than what would be expected from their stellar masses and optical colors.
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| 10. |
- Thöne, Christina C., et al.
(författare)
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NGC 2770 : A Supernova Ib Factory?
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 698:2, s. 1307-1320
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Tidskriftsartikel (refereegranskat)abstract
- NGC 2770 has been the host of three supernovae (SNe) of Type Ib during the last ten years, SN 1999eh, SN 2007uy, and SN 2008D. SN 2008D attracted special attention due to the serendipitous discovery of an associated X-ray transient. In this paper, we study the properties of NGC 2770 and specifically the three SN sites to investigate whether this galaxy is in any way peculiar to cause a high frequency of SNe Ib. We model the global spectral energy distribution of the galaxy from broadband data and derive a star formation and SN rate comparable to the values of the Milky Way. We further study the galaxy using longslit spectroscopy covering the major axis and the three SN sites. From the spectroscopic study we find subsolar metallicities for the SN sites, a high extinction and a moderate star formation rate. In a high-resolution spectrum, we also detect diffuse interstellar bands in the line of sight toward SN 2008D. A comparison of NGC 2770 to the global properties of a galaxy sample with high SN occurrence (>= 3 SN in the last 100 years) suggests that NGC 2770 is not particularly destined to produce such an enhancement of observed SNe. Its properties are also very different from gamma-ray burst host galaxies. Statistical considerations on SN Ib detection rates give a probability of ~1.5% to find a galaxy with three Ib SNe detected in ten years. The high number of rare Ib SNe in this galaxy is therefore likely to be a coincidence rather than special properties of the galaxy itself. NGC 2770 has a small irregular companion, NGC 2770B, which is highly star-forming, has a very low mass and one of the lowest metallicities detected in the nearby universe as derived from longslit spectroscopy. In the most metal poor part, we even detect Wolf-Rayet (WR) features, which is at odds with most current models of WR stars which require high metallicities. Based on observations with the Nordic Optical Telescope, ESO proposal 080.D-0526, the GALEX and NED databases.
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