The Swift gamma-ray burst GRB 050422

A. P. Beardmore, K. L. Page, P. T. O'Brien, J. P. Osborne, S. Kobayashi, B. Zhang, D. N. Burrows, M. Capalbi, M. R. Goad, O. Godet, J. E. Hill, V. La Parola, F. Marshall, A. A. Wells

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We describe observations of GRB 050422, a Swift-discovered gamma-ray burst. The prompt gamma-ray emission had a T90 duration of 59 s and was multipeaked, with the main peak occurring at T + 53 s. Swift was able to follow the X-ray afterglow within 100 s of the burst trigger. The X-ray light curve, which shows a steep early decline, can be described by a broken power law with an initial decay slope of α1 ∼ 5.0, a break time t b ∼ 270 s and a post-break decay slope of α2 ∼ 0.9, when the zero time of the X-ray emission is taken to be the burst trigger time. However, if the zero time is shifted to coincide with the onset of main peak in the gamma-ray light curve then the initial decay slope is shallower with α1 3.2. The initial gamma-ray spectrum can be modelled by a power law with a spectral index of βB = 0.50 ± 0.19. However, the early time X-ray spectrum is significantly steeper than this and requires a spectral index of βX = 2.33 -0.55+0.58. In comparison with other Swift bursts, GRB 050422 was unusually X-ray faint, had a soft X-ray spectrum, and had an unusually steep early X-ray decline. Even so, its behaviour can be accommodated by standard models. The combined BAT/XRT light curve indicates that the initial, steeply declining, X-ray emission is related to the tail of the prompt gamma-ray emission. The shallower decay seen after the break is consistent with the standard afterglow model.

Original languageEnglish (US)
Pages (from-to)1473-1478
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Feb 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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