| 1. |
- Bufano, Filomena, et al.
(författare)
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THE HIGHLY ENERGETIC EXPANSION OF SN 2010bh ASSOCIATED WITH GRB 100316D
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:1, s. 67-
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Tidskriftsartikel (refereegranskat)abstract
- We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed Type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Thanks to the detailed temporal coverage and the extended wavelength range (3000-24800 angstrom), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0 rest-frame days) and a fainter absolute peak luminosity (L-bol approximate to 3 x 10(42) erg s(-1)) than previously observed SN events associated with GRBs. Our estimate of the ejected Ni-56 mass is 0.12 +/- 0.02 M-circle dot. From the broad spectral features, we measure expansion velocities up to 47,000 km s(-1), higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda 5876 and He I 1.083 mu m, blueshifted by similar to 20,000-30,000 km s(-1) and similar to 28,000-38,000 km s(-1), respectively, may be present in the optical spectra. However, the lack of coverage of the He I 2.058 mu m line prevents us from confirming such identifications. The nebular spectrum, taken at similar to 186 days after the explosion, shows a broad but faint [O I] emission at 6340 angstrom. The light curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass (E-k approximate to 10(52) erg and M-ej approximate to 3 M-circle dot). The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB SNe.
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| 2. |
- Gall, Christa, et al.
(författare)
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Rapid formation of large dust grains in the luminous supernova 2010j1
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 511:7509, s. 326-
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Tidskriftsartikel (refereegranskat)abstract
- The origin of dust in galaxies is still a mystery(1-4). The majority of the refractory elements are produced in supernova explosions, but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1 to 0.5 solar masses of dust in nearby supernova remnants(5-7) suggests in situ dust formation, while other observations reveal very little dust in supernovae in the first few years after explosion(1,8,10). Observations of the spectral evolution of the bright SN 2010j1 have been interpreted as pre-existing dust(11), dust formationlz(12,13) or no dust at all(14). Here we report the rapid (40 to 240 days) formation of dust in its dense circumstellar medium. The wavelength-dependent extinction of this dust reveals the presence of very large (exceeding one micrometre) grains, which resist destruction(15). At later times (500 to 900 days), the near-infrared thermal emission shows an accelerated growth in dust mass, marking the transition of the dust source from the circumstellar medium to the ejecta. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media.
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| 3. |
- Leloudas, Giorgos, et al.
(författare)
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An asymmetric electron-scattering photosphere around optical tidal disruption events
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:10, s. 1193-1202
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Tidskriftsartikel (refereegranskat)abstract
- A star crossing the tidal radius of a supermassive black hole will be spectacularly ripped apart with an accompanying burst of radiation. A few tens of such tidal disruption events have now been identified in optical wavelengths, but the exact origin of the strong optical emission remains inconclusive. Here we report polarimetric observations of three tidal disruption events. The continuum polarization appears independent of wavelength, while emission lines are partially depolarized. These signatures are consistent with photons being scattered and polarized in an envelope of free electrons. An almost axisymmetric photosphere viewed from different angles is in broad agreement with the data, but there is also evidence for deviations from axial symmetry before the peak of the flare and significant time evolution at early times, compatible with the rapid formation of an accretion disk. By combining a super-Eddington accretion model with a radiative transfer code, we simulate the polarization degree as a function of disk mass and viewing angle and we show that the predicted levels are compatible with the observations for extended reprocessing envelopes of similar to 1,000 gravitational radii. Spectropolarimetry therefore constitutes a new observational test for tidal disruption event models, and opens an important new line of exploration in the study of tidal disruption events.
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| 4. |
- Leloudas, Giorgos, et al.
(författare)
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Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 837:1
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Tidskriftsartikel (refereegranskat)abstract
- We present imaging polarimetry of the superluminous supernova SN 2015bn, obtained over nine epochs between -20 and +46 days with the Nordic Optical Telescope. This was a nearby, slowly evolving Type I superluminous supernova that has been studied extensively and for which two epochs of spectropolarimetry are also available. Based on field stars, we determine the interstellar polarization in the Galaxy to be negligible. The polarization of SN. 2015bn shows a statistically significant increase during the last epochs, confirming previous findings. Our well-sampled imaging polarimetry series allows us to determine that this increase (from similar to 0.54% to greater than or similar to 1.10%) coincides in time with rapid changes that took place in the optical spectrum. We conclude that the supernova underwent a phase transition at around +20 days, when the photospheric emission shifted from an outer layer, dominated by natal C and O, to a more aspherical inner core, dominated by freshly nucleosynthesized material. This two-layered model might account for the characteristic appearance and properties of Type I superluminous supernovae.
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| 5. |
- 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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| 6. |
- Roy, Rupak, et al.
(författare)
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SN 2007uy-metamorphosis of an aspheric Type Ib explosion
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 434:3, s. 2032-2050
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Tidskriftsartikel (refereegranskat)abstract
- The supernovae (SNe) of Type Ibc are rare and the detailed characteristics of these explosions have been studied only for a few events. Unlike Type II SNe, the progenitors of Type Ibc have never been detected in pre-explosion images. So, to understand the nature of their progenitors and the characteristics of the explosions, investigation of proximate events is necessary. Here we present the results of multiwavelength observations of Type Ib SN 2007uy in the nearby (similar to 29.5 Mpc) galaxy NGC 2770. Analysis of the photometric observations revealed this explosion as an energetic event with peak absolute R-band magnitude -18.5 +/- 0.16, which is about 1 mag brighter than the mean value (-17.6 +/- 0.6) derived for well observed Type Ibc events. The SN is highly extinguished, E(B - V) = 0.63 +/- 0.15 mag, mainly due to foreground material present in the host galaxy. From optical light curve modelling we determine that about 0.3 M-circle dot radioactive Ni-56 is produced and roughly 4.4 M-circle dot material is ejected during this explosion with liberated energy similar to 15 x 10(51) erg, indicating the event to be an energetic one. Through optical spectroscopy, we have noticed a clear aspheric evolution of several line-forming regions, but no dependency of asymmetry is seen on the distribution of Ni-56 inside the ejecta. The SN shock interaction with the circumstellar material is clearly noticeable in radio follow-up, presenting a synchrotron self-absorption dominated light curve with a contribution of free-free absorption during the early phases. Assuming a Wolf-Rayet (WR) star, with wind velocity greater than or similar to 10(3) km s(- 1), as a progenitor, we derive a lower limit to the mass-loss rate inferred from the radio data as M 2.4 10(-5) M-circle dot yr(-1), which is consistent with the results obtained for other Type Ibc SNe bright at radio frequencies.
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| 7. |
- Watson, Darach, et al.
(författare)
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HELIUM IN NATAL H II REGIONS : THE ORIGIN OF THE X-RAY ABSORPTION IN GAMMA-RAY BURST AFTERGLOWS
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 768:1, s. 23-
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Tidskriftsartikel (refereegranskat)abstract
- Soft X-ray absorption in excess of Galactic is observed in the afterglows of most gamma-ray bursts (GRBs), but the correct solution to its origin has not been arrived at after more than a decade of work, preventing its use as a powerful diagnostic tool. We resolve this long-standing problem and find that absorption by He in the GRB's host H II region is responsible for most of the absorption. We show that the X-ray absorbing column density (N-HX) is correlated with both the neutral gas column density and with the optical afterg(l)ow's dust extinction (A(V)). This correlation explains the connection between dark bursts and bursts with high N-HX values. From these correlations, we exclude an origin of the X-ray absorption which is not related to the host galaxy, i.e., the intergalactic medium or intervening absorbers are not responsible. We find that the correlation with the dust column has a strong redshift evolution, whereas the correlation with the neutral gas does not. From this, we conclude that the column density of the X-ray absorption is correlated with the total gas column density in the host galaxy rather than the metal column density, in spite of the fact that X-ray absorption is typically dominated by metals. The strong redshift evolution of N-HX/A(V) is thus a reflection of the cosmic metallicity evolution of star-forming galaxies and we find it to be consistent with measurements of the redshift evolution of metallicities for GRB host galaxies. We conclude that the absorption of X-rays in GRB afterglows is caused by He in the H II region hosting the GRB. While dust is destroyed and metals are stripped of all of their electrons by the GRB to great distances, the abundance of He saturates the He-ionizing UV continuum much closer to the GRB, allowing it to remain in the neutral or singly-ionized state. Helium X-ray absorption explains the correlation with total gas, the lack of strong evolution with redshift, as well as the absence of dust, metal or hydrogen absorption features in the optical-UV spectra.
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