[vsnet-grb-info 4987] GRB 070802: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6702
SUBJECT: GRB 070802: Swift-XRT refined analysis
DATE:    07/08/02 19:48:18 GMT
FROM:    Vanessa Mangano at INAF-IASFPA  <vanessa at ifc.inaf.it>

V. Mangano, B. Sbarufatti, V. La Parola, E. Troja (INAF-IASF PA),
P. Evans (U. Leicester) and S. Immler (GSFC)
report on behalf of the Swift-XRT team:

We have analysed the first three orbits of Swift-XRT data obtained for
GRB 070802 (Barthelmy et al, GCN Circ. 6692), which include 3.4 ks of
Photon Counting (PC) data.

Using 599 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 = 36.89899, -55.52733 which is equivalent to:

RA (J2000):  02 27 35.76
Dec (J2000): -55 31 38.4

with an uncertainty of 2.1 arcsec (radius, 90% confidence).
This is 4.9 arcsec from the initial XRT position (Evans and Mangano,
GCN Circ. 6697) and 38 arcsec from the BAT ground-calculated position
(Cummings et al, GCN Circ. 6699). It is also 0.7 arcsec from the
optical position of Malesani et al. (GCN Circ. 6696) and 1.4 arcsec
from the I band position of Berger and Murphy (GCN Circ. 6695).

The XRT light-curve decays with slope -2.0+/-0.2 up to about T+500 s,
then flattens to slope -0.25+/-0.08. We do not see a further break up
to T+17 ks.

The spectrum can be fit with an absorbed power law with
a photon index of 1.9+/-0.3 and a column density consistent
with the Galactic value (2.9e20 cm^-2).
The absorbed (unabsorbed) 0.3-10.0keV flux for the spectrum is
(3.9+/-0.8)e-12 ((4.6+/-0.8)e-12) ergs cm^-2 s^-1.

If the decay continues with a slope of ~ 0.2, the count rate at 24
hours is predicted to be 3e-2 count s^-1. Using the spectral fit
described above, this corresponds to an observed flux of about
1.4e-12 ergs cm^-2 s^-1.

This circular is an official product of the XRT team.