[vsnet-grb-info 5325] GRB 071028: Swift-XRT Team refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7014
SUBJECT: GRB 071028:  Swift-XRT Team refined analysis
DATE:    07/10/28 23:13:12 GMT
FROM:    Judith Racusin at PSU  <racusin at astro.psu.edu>

J. Racusin (PSU) reports on behalf of the Swift-XRT Team:

We have analysed the first 2 orbits of Swift-XRT data obtained for GRB
071028 (Racusin et al. GCN Circ. 7012), totaling 61 s of Windowed Timing
(WT) data and 2.9 ks of Photon Counting (PC) data.

Using 399 s of overlapping XRT Photon Counting mode and UVOT V-band data,
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 = 119.81936, 21.48482 which is equivalent to:

RA (J2000):  07 59 16.65
Dec (J2000): +21 29 05.4

with an uncertainty of 1.9 arcsec (radius, 90% confidence).  This is 6.5
arcsec from the previous XRT position (GCN Circ. 7012), and 51 arcsec from
the refined BAT position (Cummings et al., GCN Circ. 7013).

The bright X-ray light-curve can be fit by a broken power-law, with an
initial steep decay index of 3.3 +/- 0.4 followed by a flatter decay index
of 1.1 +/- 0.3 after a break at 475 +/- 150 seconds.

The WT data (124-182 seconds) can be modeled as an absorbed power-law,
with photon index of 1.9 +/- 0.2 and a total absorbing column of NH = (5.9
+/- 5.6)e20 cm^-2, consistent with the Galactic value of 5.1e20 cm^-2. The
0.3-10 keV observed (unabsorbed) flux during this time is 3.1e-10
(3.6e-10) erg cm^-2 s^-1.

Assuming the source continues to decay with the same decay index of 1.1,
we predict an XRT count rate of 5.5e-4 counts/s at T+24 hours, which
corresponds to an 0.3-10.0 keV observed flux of 2.3e-14 ergs cm^-2 s^-1.

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