[vsnet-grb-info 1977] GRB050815: XRT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3816
SUBJECT: GRB050815: XRT refined analysis
DATE:    05/08/16 02:29:08 GMT
FROM:    David Morris at PSU/Swift-XRT  <morris at astro.psu.edu>

D. C. Morris, D. N. Burrows, J. A. Kennea, J. L. Racusin (PSU), and N. 
Gehrels (GSFC) report on behalf of the Swift XRT team:

We have analysed the first three orbits of data for GRB050815 (GCN 3811, 
Fox et al., 2005).  Using xrtcentoid, the refined position is:

RA(J2000) = 19h 34m 23.2s
Dec(J2000) = +09d 08' 49.6"

with an uncertainty of 8 arcsec. This is 5.6 arcsec from the original 
XRT position (GCN 3812, Morris et al., 2005).

The XRT began taking data at 17:26:28UT, 69 seconds after the BAT 
trigger. The XRT collected data for only 123s during the first orbit 
before the source was occulted. The data show a faint source in the 
first orbit and suggest an initially shallow decay index of ~-0.2 
followed by a break occuring somewhere between 192s and 3000s to a 
steeper decay index of ~-2.1.

The spectrum is well fit (reduced chi-sq of 1.03 for 9 dof) by a power 
law with neutral hydrogen consistent with the galactic column density of 
2.7e21:

gamma=1.4 + / - 0.2
NH=2.1e21 + / - 7e20

Fixing the NH to the galactic column density also returns a good fit 
(reduced chi-sq of 1.00 for 10 dof):

gamma=1.5 + / - 0.1

The count rate at 10000s after the trigger is ~0.015 cts/s which 
converts to an unabsorbed flux of 9e-13 ergs cm^-2 s^-1 from 0.2-10keV.