GCN Circular 10691

D. Grupe (PSU) reports on behalf of the Swift-XRT team:

We have analyzed 14.2 ks of XRT data for GRB 100425A (Grupe et al.
GCN Circ. 10673
Not found
 
 
), from 85 s to 81 ks after the BAT trigger. The
data consist of 106s in Windowed Timing mode (WT) and 14.1 ks
in  Photon Counting (PC) mode. The current XRT light curve can be
fit by a broken power law model with an initial decay slope of
5.3+/-0.3 with a beak at 330+/-20 s followed by a shallow decay
slope of 0.55+/- 0.05. The last data point at 77 ks after the
burst suggests a break at about 60ks. However, this is based on
one data point. Therefore, a prediction on the future behavior of
the  X-ray afterglow can not be given at this point.


A spectrum formed from the WT mode data can be fitted with an
absorbed power-law with a photon spectral index of 4.00 (+/-0.15).
The best-fitting absorption column density is
1.49 (+0.18, -0.17) x 10^22 cm^-2, at a redshift of 1.755
(Goldini et al. GCN Circ 10684), in addition to the Galactic value
of 8.6 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum
has a photon index of 2.30+/-0.13 and a best-fitting
absorption column density consistent with the Galactic value.
Based on this spectrum, the counts to observed (unabsorbed)
0.3-10 keV flux conversion  factor deduced from this spectrum is
3.77 x 10^-11 (5.17 x 10^-11) erg cm^-2 count^-1.

Swift will continue observing the X-ray afterglow of GRB 100425A
over the next few days.


The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00420398.

This circular is an official product of the Swift-XRT team.