Swift observations of the X-ray-bright GRB 050315

This paper discusses Swift observations of the mu-ray burst GRB 050315 (z 1: 949) from 80 s to 10 days after the onset of the burst. The X-ray light curve displayed a steep early decay (t(-5)) for similar to 200 s and several breaks. However, both the prompt hard X-ray/gamma-ray emission ( observed by the BAT) and the first similar to 300 s of X-ray emission ( observed by the XRT) can be explained by exponential decays, with similar decay constants. Extrapolating the BAT light curve into the XRT band suggests that the rapidly decaying, early X- ray emission was simply a continuation of the fading prompt emission; this strong similarity between the prompt gamma-ray and early X- ray emission may be related to the simple temporal and spectral character of this X- ray-rich GRB. The prompt ( BAT) spectrum was steep down to similar to 15 keV and appeared to continue through the XRT bandpass, implying a low peak energy, inconsistent with the Amati relation. Following the initial steep decline, the X- ray afterglow did not fade for similar to 1.2 x 10(4) s, after which time it decayed with a temporal index of alpha approximate to 0.7, followed by a second break at similar to 2.5 x 10(5) s to a slope of alpha similar to 2. The apparent "plateau'' in the X- ray light curve, after the early rapid decay, makes this one of the most extreme examples of the steep-flat-steep X- ray light curves revealed by Swift. If the second afterglow break is identified with a jet break, then the jet opening angle was theta(0) similar to 5 degrees, implying E gamma greater than or similar to 10(50) ergs.