[vsnet-grb-info 7120] GRB 081221: Swift-XRT Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8701
SUBJECT: GRB 081221: Swift-XRT Refined Analysis
DATE:    08/12/22 14:26:07 GMT
FROM:    Michael Stroh at PSU/Swift  <stroh at 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.