GCN Circular 8701
Subject
GRB 081221: Swift-XRT Refined Analysis
Event
Date
2008-12-22T14:26:07Z (17 years ago)
From
Michael Stroh at PSU/Swift <stroh@astroh.org>
M.C. Stroh and E. A. Hoversten (PSU) report on behalf of the Swift-XRT
team:
We have analyzed the first seven orbits of XRT data from GRB 081221
(Hoversten et al., GCN 8687) beginning 73s after the trigger. The
Swift-XRT data consists of 803s in Windowed Timing (WT) mode and 5.9ks
in Photon Counting (PC) mode. The enhanced XRT position for this burst
was reported by Evans et al. (GCN Circ. 8690).
The X-ray light curve begins with count rates near 10^3 cts/s and has
an early flare reaching 1130 cts/s at T+103s. Following the flare, the
light curve can be modeled with a double broken power-law with initial
decay rate of 5.48 +/- 0.08, initial break time at T+207s, second
decay rate of 0.68 +/- 0.20, second break time at T+896s, and a final
decay rate of 1.35 +/- 0.04. If the light curve follows the same
decline, we predict count rates at T+24hr and T+48hr to be 1.6e-2 and
6.4e-3 respectively.
The time-averaged WT spectrum can be fit with an absorbed power law
with photon index Gamma = 1.994 (+/-0.014) and nH of 3.24 (+/- 0.05)
e21 cm^-2 which is in excess of the Galactic value of 2.03e20 cm^-2
(Kalberla et al. 2005). The absorbed (unabsorbed) 0.3-10.0 keV flux is
2.44 (3.86) e-9 ergs/cm^2/s.
The time-averaged PC spectrum can be fit with an absorbed power law
with photon index Gamma = 2.37 (+/-0.15) and nH of 3.5 (+/-0.5) e21
cm^-2. The absorbed (unabsorbed) 0.3-10.0 keV flux is 1.04 (2.17) e-11
ergs/cm^2/s.
This circular is an official product of the Swift-XRT team.