[vsnet-grb-info 2537] GRB 051221: Swift XRT refined analysis
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Thu Dec 22 03:49:07 JST 2005
TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4374
SUBJECT: GRB 051221: Swift XRT refined analysis
DATE: 05/12/21 18:46:53 GMT
FROM: Milvia Capalbi at ISAC/ASDC <capalbi at 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.
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