GRB 050223: a faint gamma-ray burst discovered by Swift

K. L. Page, E. Rol, A. J. Levan, B. Zhang, J. P. Osborne, P. T. O'Brien, A. P. Beardmore, D. N. Burrows, S. Campana, G. Chincharini, J. R. Cummings, G. Cusumano (+7 others)
2005 Monthly Notices of the Royal Astronomical Society: Letters  
GRB050223 was discovered by the Swift Gamma-Ray Burst Explorer on 23 February 2005 and was the first Gamma-Ray Burst to be observed by both Swift and XMM-Newton. At the time of writing (May 2005), it has one of the faintest GRB afterglows ever observed. The spacecraft could not slew immediately to the burst, so the first X-ray and optical observations occurred approximately 45 minutes after the trigger. Although no optical emission was found by any instrument, both Swift and XMM-Newton detected
more » ... XMM-Newton detected the fading X-ray afterglow. Combined data from both of these observatories show the afterglow to be fading monotonically as 0.99 +0.15/-0.12 over a time frame between 45 minutes to 27 hours post-burst. Spectral analysis, allowed largely by the higher through-put of XMM-Newton, implies a power-law with a slope of Gamma=1.75 +0.19/-0.18 and shows no evidence for absorption above the Galactic column of 7 x 10^20 cm^-2. From the X-ray decay and spectral slopes, a low electron power-law index of p = 1.3-1.9 is derived; the slopes also imply that a jet-break has not occured up to 27 hours after the burst. The faintness of GRB050223 may be due to a large jet opening or viewing angle or a high redshift.
doi:10.1111/j.1745-3933.2005.00086.x fatcat:s2muok2t7bcyflllymsnwaofha