GCN Circular 4374
Subject
GRB 051221: Swift XRT refined analysis
Event
Date
2005-12-21T18:46:53Z (20 years ago)
From
Milvia Capalbi at ISAC/ASDC <capalbi@asdc.asi.it>
M. Capalbi, M. Perri (ASDC), D.N. Burrows, D. Grupe (PSU), P. Boyd
(GSFC-UMBC), W. Voges (MPE) report on behalf of the Swift XRT team:
We have analyzed the first six orbits of the Swift XRT data of GRB
051221 (Parsons et al., GCN 4363).
Data in Windowed Timing (WT) mode started at 01:52:48 UT, 92 seconds
after the BAT trigger, then the XRT switched to Photon Counting mode.
The light curve shows an initial fading behavior up to 2.5 ks with a
decay index of -1.3 � 0.7. At later times, an indication of a
re-brightening is present.
A preliminary spectral fit (simple absorbed power-law) to the WT data in
the 0.5-10. 0 keV band yields a photon index of 2.0+/-0.4 and a column
density value consistent with the Galactic one (6.7E20 cm-2; Dickey &
Lockman 1990).
Extrapolating the initial decay, the unabsorbed 0.5-10.0 keV flux at 24
hours after the burst is estimated to be ~5E-14 erg cm^-2 s^-1.