GRB 081007 AND GRB 090424: THE SURROUNDING MEDIUM, OUTFLOWS, AND SUPERNOVAE
- INAF-Osservatorio Astronomico di Brera, via Emilio Bianchi 46, I-23807 Merate (Italy)
- INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16, I-80131 Napoli (Italy)
- Instituto de Astrofisica de Canarias (IAC), E-38200 La Laguna, Tenerife (Spain)
- Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark)
- Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa (Italy)
- INAF-IASF Milano, via E. Bassini 15, I-20133 Milano (Italy)
- Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)
- Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Reykjavik (Iceland)
- Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, E-18008 Granada (Spain)
- Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana (Slovenia)
- Department of Physics, University of Ferrara, via Saragat 1, I-44122 Ferrara (Italy)
We discuss the results of the analysis of multi-wavelength data for the afterglows of GRB 081007 and GRB 090424, two bursts detected by Swift. One of them, GRB 081007, also shows a spectroscopically confirmed supernova, SN 2008hw, which resembles SN 1998bw in its absorption features, while the maximum magnitude may be fainter, up to 0.7 mag, than observed in SN 1998bw. Bright optical flashes have been detected in both events, which allows us to derive solid constraints on the circumburst-matter density profile. This is particularly interesting in the case of GRB 081007, whose afterglow is found to be propagating into a constant-density medium, yielding yet another example of a gamma-ray burst (GRB) clearly associated with a massive-star progenitor which did not sculpt the surroundings with its stellar wind. There is no supernova component detected in the afterglow of GRB 090424, likely due to the brightness of the host galaxy, comparable to the Milky Way. We show that the afterglow data are consistent with the presence of both forward- and reverse-shock emission powered by relativistic outflows expanding into the interstellar medium. The absence of optical peaks due to the forward shock strongly suggests that the reverse-shock regions should be mildly magnetized. The initial Lorentz factor of outflow of GRB 081007 is estimated to be {Gamma} {approx} 200, while for GRB 090424 a lower limit of {Gamma} > 170 is derived. We also discuss the prompt emission of GRB 081007, which consists of just a single pulse. We argue that neither the external forward-shock model nor the shock-breakout model can account for the prompt emission data and suggest that the single-pulse-like prompt emission may be due to magnetic energy dissipation of a Poynting-flux-dominated outflow or to a dissipative photosphere.
- OSTI ID:
- 22133891
- Journal Information:
- Astrophysical Journal, Vol. 774, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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