GRB 050505: A high-redshift burst discovered by Swift

C. P. Hurkett, J. P. Osborne, K. L. Page, E. Rol, M. R. Goad, P. T. O'Brien, A. Beardmore, O. Godet, D. N. Burrows, N. R. Tanvir, A. Levan, B. Zhang, D. Malesani, J. E. Hill, J. A. Kennea, R. Chapman, V. La Parola, M. Perri, P. Romano, R. SmithN. Gehrels

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20 Scopus citations

Abstract

We report the discovery and subsequent multiwavelength 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 γ-ray light curve, with a duration of T 90 = 63 ± 2 s and an inferred isotropic release in γ-rays of ∼ 4.44 × 10 53 erg in the 1-10 4 keV rest-frame energy range. The Swift X-Ray Telescope followed the afterglow for 14 d, detecting two breaks in the light curve at 7.4 -1.5 +1.5 and 58.0 -15.4 +9.9 ks after the burst trigger. The power-law decay slopes before, between and after these breaks were 0.25 -0.17 +0.16, 1-17 -0.09 +0.08 and 1.97 -0.28 +0.27, respectively. The light curve can also be fitted 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 fitted with a single power law of photon index ∼1.90. This behaviour is expected for the cessation of the continued energization of the interstellar medium 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 the 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-ultraviolet extinction, with E(B -V) ≈ 0.10 for a Small Magellanic Cloud like extinction curve.

Original languageEnglish (US)
Pages (from-to)1101-1109
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume368
Issue number3
DOIs
StatePublished - May 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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