GRB 050505: a high-redshift burst discovered by Swift

Autor: J. A. Kennea, Olivier Godet, Randall Smith, V. La Parola, Michael R. Goad, J. E. Hill, P. Romano, Bing Zhang, Neil Gehrels, David N. Burrows, D. B. Malesani, M. Perri, J. P. Osborne, Robert Chapman, Evert Rol, Cheryl Hurkett, Andrew P. Beardmore, Andrew J. Levan, Nial R. Tanvir, P. T. O'Brien, K. L. Page
Rok vydání: 2006
Předmět:
Zdroj: Monthly Notices of the Royal Astronomical Society. 368:1101-1109
ISSN: 1365-2966
0035-8711
Popis: We report the discovery and subsequent multi-wavelength afterglow behaviour of the high redshift (z = 4.27) Gamma Ray Burst GRB 050505. This burst is the third most distant burst, measured by spectroscopic redshift, discovered after GRB 000131 (z = 4.50) and GRB 050904 (z = 6.29). GRB 050505 is a long GRB with a multipeaked gamma-ray light curve, with a duration of T_90 = 63+/-2 s and an inferred isotropic release in gamma-rays of ~4.44 x 10^53 ergs in the 1-10^4 keV rest frame energy range. The Swift X-Ray Telescope followed the afterglow for 14 days, detecting two breaks in the light curve at 7.4(+/-1.5) ks and 58.0 (+9.9/-15.4) ks after the burst trigger. The power law decay slopes before, between and after these breaks were 0.25 (+0.16/-0.17), 1.17 (+0.08/-0.09) and 1.97 (+0.27/-0.28) respectively. The light curve can also be fit with a `smoothly broken' power law model with a break observed at ~ T+18.5 ks, with decay slopes of ~0.4 and ~1.8 before and after the break respectively. The X-ray afterglow shows no spectral variation over the course of the Swift observations, being well fit with a single power law of photon index ~1.90. This behaviour is expected for the cessation of continued energisation of the ISM shock followed by a break caused by a jet, either uniform or structured. Neither break is consistent with a cooling break. The spectral energy distribution indeed shows the cooling frequency to be below the X-ray but above optical frequencies. The optical -- X-ray spectrum also shows that there is significant X-ray absorption in excess of that due to our Galaxy but very little optical/UV extinction, with E(B-V) ~0.10 for a SMC-like extinction curve.
9 pages, 6 figures. Accepted by MNRAS
Databáze: OpenAIRE
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