[vsnet-grb-info 1993] GRB050819: refined XRT analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3832
SUBJECT: GRB050819: refined XRT analysis
DATE:    05/08/20 08:53:47 GMT
FROM:    Kim Page at U.of Leicester,Swift SDC  <kpa at star.le.ac.uk>

K.L. Page (U. Leicester), J.A. Kennea, D.N. Burrows (PSU), M. Ajello
(MPE), M. Trippico (GSFC-SSAI) report on behalf of the Swift/XRT team:

We have analysed the XRT data for GRB050819 (BAT Trigger 151131), between
146 and 3.7e4 seconds after the trigger. As previously reported by Kennea
et al in GCN 3827, there is an uncatalogued, fading X-ray source in the
field of view. The refined coordinates for this burst are

RA(J2000):  23:55:01.37
Dec(J2000): 24:51:31.28

with an uncertainty of 8 arcseconds radius (90% containment). This is 5.7
arcseconds from the XRT position given in GCN 3827 and 75 arcseconds from
the initial BAT position reported in GCN 3826.

XRT observations began in Windowed Timing mode 146 seconds after the
trigger, switching down to Photon Counting mode 58 seconds later. The
light-curve shows a steep initial decline with a decay index of alpha =
3.7 +/- 0.3, breaking to a very flat slope of < 0.28 at around 850
seconds.

The spectrum of the early afterglow shows no evidence for excess NH above
the Galactic value (4.6e20 cm^-2), and can be well fitted by a power-law
with Gamma = 2.2 +/- 0.2. Between 146 and 203 seconds, the unabsorbed
0.3-10 keV flux was 1.62e-10 erg cm^-2 s^-1.

If the light-curve continues without a further break, the predicted
count-rate at 24 hours will be 0.009 counts s^-1, corresponding to 0.3-10
keV flux of 3.2e-13 erg cm^-2 s^-1 (unabsorbed).