Examinando por Autor "Afonso, P.M.J."

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    Identifying the host galaxy of the short GRB 100628A
    (EDP Sciences, 2015-11) Nicuesa Guelbenzu, A.; Klose, S.; Palazzi, E.; Greiner, J.; Michałowski, M.J.; Kann, D.A.; Hunt, L.K.; Malesani, D.; Rossi, A.; Savaglio, S.; Schulze, S.; Xu, D.; Afonso, P.M.J.; Elliott, J.; Ferrero, P.; Filgas, R.; Hartmann, D.H.; Krühler, T.; Knust, F.; Masetti, N.; Olivares, E. F.; Rau, A.; Schady, P.; Schmidl, S.; Tanga, M.; Updike, A.C.; Varela, K.
    We report on the results of a comprehensive observing campaign to reveal the host galaxy of the short GRB 100628A. This burst was followed by a faint X-ray afterglow but no optical counterpart was discovered. However, inside the X-ray error circle a potential host galaxy at a redshift of z = 0.102 was soon reported in the literature. If this system is the host, then GRB 100628A was the cosmologically most nearby unambiguous short burst with a measured redshift so far. We used the multi-colour imager GROND at the ESO/La Silla MPG 2.2 m telescope, ESO/VLT spectroscopy, and deep Australia Telescope Compact Array (ATCA) radio-continuum observations together with publicly available Gemini imaging data to study the putative host and the galaxies in the field of GRB 100628A. We confirm that inside the X-ray error circle the most probable host-galaxy candidate is the morphologically disturbed, interacting galaxy system at z = 0.102. The interacting galaxies are connected by a several kpc long tidal stream, which our VLT/FORS2 spectroscopy reveals strong emission lines of [O ii], [O iii], Hα and Hβ, characteristic for the class of extreme emission-line galaxies and indicative of ongoing star formation. The latter leaves open the possibility that the GRB progenitor was a member of a young stellar population. However, we indentify a second host-galaxy candidate slightly outside the X-ray error circle. It is a radio-bright, luminous elliptical galaxy at a redshift z = 0.311. With a K-band luminosity of 2 × 1011L this galaxy resembles the probable giant elliptical host of the first well-localized short burst, GRB 050509B. If this is the host, then the progenitor of GRB 100628A was a member of an old stellar population. © ESO, 2015.
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    Multiwavelength analysis of three supernovae associated with gamma-ray bursts observed by GROND
    (EDP Sciences, 2015-05) Olivares, E.F.; Greiner, J.; Schady, P.; Klose, S.; Krühler, T.; Rau, A.; Savaglio, S.; Kann, D.A.; Pignata, G.; Elliott, J.; Rossi, A.; Nardini, M.; Afonso, P.M.J.; Filgas, R.; Nicuesa Guelbenzu, A.; Schmidl, S.; Sudilovsky, V.
    Context. After the discovery of the first connection between γ-ray bursts (GRBs) and supernovae (SNe) almost two decades ago, tens of SN-like rebrightenings have been discovered and about seven solid associations have been spectroscopically confirmed to date. Aims. We determine the luminosity, evolution, and origin of three SN rebrightenings in GRB afterglow light curves at z ∼ 0.5 along with accurate determinations of the host-galaxy extinction. We estimate physical parameters of the SN explosions, such as synthesised 56Ni mass, ejecta mass, and kinetic energy. Methods. We employ GROND optical/NIR data and Swift X-ray/UV data to estimate the host-galaxy extinction by modelling the afterglow spectral energy distribution, to determine the SN luminosity and evolution, and to construct quasi-bolometric light curves. The latter are corrected for the contribution of the NIR-bands using data available in the literature and black-body fits. We employ Arnett's analytic approach to obtain the physical parameters of the explosion. Results. The SNe 2008hw, 2009nz, and 2010ma observed by GROND exhibit 0.80, 1.15, and 1.78 times the optical (r′-band) luminosity of SN 1998bw, respectively. While SN 2009nz exhibits an evolution similar to SN 1998bw, SNe 2008hw and 2010ma show earlier peak times. The quasi-bolometric light curves (340-2200 nm) confirm the large luminosity of SN 2010ma (1.4 × 10 43 erg s-1), while SNe 2008hw and 2009nz reached a peak luminosity closer to that of SN 1998bw. The modelling indicates in 56 Ni masses of around 0.4-0.5 MO. Conclusions. By means of a very comprehensive data set, we found that the luminosity and the 56Ni mass of SNe 2008hw, 2009nz, and 2010ma resembles those of other known GRB-associated SNe. These findings strengthens previous claims of GRB-SNe being brighter than stripped-envelope SNe unaccompanied by GRBs. © ESO, 2015.
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    The optical/NIR afterglow of GRB 111209A: Complex yet not unprecedented
    (EDP Sciences, 2018-09) Kann, D.A.; Schady, P.; Olivares, E.F.; Klose, S.; Rossi, A.; Perley, D.A.; Zhang, B.; Krühler, T.; Greiner, J.; Nicuesa Guelbenzu, A.; Elliott, J.; Knust, F.; Cano, Z.; Filgas, R.; Pian, E.; Mazzali, P.; Fynbo, J.P.U.; Leloudas, G.; Afonso, P.M.J.; Delvaux, C.; Graham, J.F.; Rau, A.; Schmidl, S.; Schulze, S.; Tanga, M.; Updike, A.C.; Varela, K.
    Context. Afterglows of gamma-ray bursts (GRBs) are simple in the most basic model, but can show many complex features. The ultra-long duration GRB 111209A, one of the longest GRBs ever detected, also has the best-monitored afterglow in this rare class of GRBs. Aims. We want to address the question whether GRB 111209A was a special event beyond its extreme duration alone, and whether it is a classical GRB or another kind of high-energy transient. The afterglow may yield significant clues. Methods. We present afterglow photometry obtained in seven bands with the GROND imager as well as in further seven bands with the Ultraviolet/Optical Telescope (UVOT) on-board the Neil Gehrels Swift Observatory. The light curve is analysed by multi-band modelling and joint fitting with power-laws and broken power-laws, and we use the contemporaneous GROND data to study the evolution of the spectral energy distribution. We compare the optical afterglow to a large ensemble we have analysed in earlier works, and especially to that of another ultra-long event, GRB 130925A. We furthermore undertake a photometric study of the host galaxy. Results. We find a strong, chromatic rebrightening event at 0.8 days after the GRB, during which the spectral slope becomes redder. After this, the light curve decays achromatically, with evidence for a break at about 9 days after the trigger. The afterglow luminosity is found to not be exceptional. We find that a double-jet model is able to explain the chromatic rebrightening. The afterglow features have been detected in other events and are not unique. Conclusions. The duration aside, the GRB prompt emission and afterglow parameters of GRB 111209A are in agreement with the known distributions for these parameters. While the central engine of this event may differ from that of classical GRBs, there are multiple lines of evidence pointing to GRB 111209A resulting from the core-collapse of a massive star with a stripped envelope. © 2018 ESO.