GCN Circular 8261
Subject
GRB 080916C: Swift XRT refined analysis
Date
2008-09-17T15:24:55Z (16 years ago)
From
Matteo Perri at ISAC/ASDC <perri@asdc.asi.it>
M. Perri, B. Preger, G. Stratta (ASDC) report on behalf of the
Swift XRT team:
The Swift XRT started observing the field of the FERMI GRB 080916C
(Goldstein et al., GCN Circ. 8245) at 2008-09-16 17:11:28 UT, about
17 hours after the trigger.
We confirm that the X-ray source reported by Kennea (GCN Circ. 8253) is
the afterglow of the GRB.
Using 2614 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 to the USNO-B1 catalogue): RA, Dec = 119.84684,
-56.63801 which is equivalent to:
RA (J2000): 07 59 23.24
Dec (J2000): -56 38 16.8
with an uncertainty of 1.9 arcsec (90% confidence). This position is
consistent with the XRT position reported by Evans et al. (GCN Circ. 8255)
using less data.
The X-ray light curve from T+61 ks to T+102 ks can be fit with a single
power-law model with a decay index of 1.7 (-0.7) (+1.0).
A 7.6 ks exposure X-ray spectrum from T+61 ks to T+102 ks can be well
fit by an absorbed power-law model with a photon index of 2.1 (+0.9 -0.7)
and a column density of 3.7 (+3.3) (-2.1) x 10^21 cm^-2. We note that
the Galactic column density value in the direction of the burst is
1.5 x 10^21 cm^-2.
The observed 0.3-10.0 keV flux is 8.6 x 10-13 erg cm^-2 s^-1 which
corresponds to an unabsorbed flux of 1.5 x 10^-12 erg cm^-2 s^-1.
Providing the source continues to decay at the same rate, we predict an
observed flux of about 3 x 10^-13 erg cm^-2 s^-1 at T+2 days.
This circular is an official product of the Swift-XRT team.