[vsnet-grb-info 6460] GRB 080805: Swift-XRT Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8072
SUBJECT: GRB 080805: Swift-XRT Refined Analysis
DATE:    08/08/06 03:27:50 GMT
FROM:    Claudio Pagani at PSU/Swift-XRT  <pagani at astro.psu.edu>

C. Pagani, J. Racusin and D. Grupe (PSU) report on behalf of the Swift-XRT team:

We have analysed the first four orbits of Swift-XRT data for GRB 080805 (Pagani
et al., GCN 8059) beginning at T0+71 s until T0+23.1 ks.

Using 728 s of XRT Photon Counting mode data and 2 UVOT images, we find an
astrometrically corrected X-ray position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 314.22312,
-62.44479 which is equivalent to:

RA (J2000):  20 56 53.55
Dec (J2000): -62 26 41.2

with an uncertainty of 2.6 arcsec (radius, 90% confidence).

The XRT lightcurve shows an initial flare and a steep decay followed by a
shallower phase. The decaying lightcurve can be fit with a broken power-law
with an initial decay index of 3.5+/-0.3, a break at approximately T0+500
seconds and a later decay index of 0.9+/-0.3.

The spectrum of the Windowed Timing mode data from the first orbit can be fit by
an absorbed power-law with a photon index of 1.3+/-0.1 and absorption consistent
with the Galactic value along the line of sight (3.5e20 cm^-2, Kalberla et al.
2005).  The average observed (unabsorbed) flux of the WT mode data is 1.7e-9
(1.9e-10) ergs cm^-2 s^-1.

Assuming the X-ray emission continues to decline at the same rate, we predict a
0.3-10.0 keV XRT count rate of 0.003 counts/s at T+24hr, which corresponds to
an observed flux of 1.5e-13 ergs cm^-2 s^-1.

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