TITLE:   GCN CIRCULAR
NUMBER:  7463
SUBJECT: GRB 080319A: Swift-XRT Team Refined Analysis
DATE:    08/03/19 22:07:29 GMT
FROM:    Claudio Pagani at PSU/Swift-XRT  <pagani@astro.psu.edu>

C. Pagani and J. L. Racusin (PSU) report on behalf of the Swift-XRT team:

The Swift-XRT started observing GRB 080319A (trigger=306754, Pagani et al. GCN
7426) at 05:54:59.4 UT, 557.4s after the trigger. The Swift slew to the burst
was delayed because of an Earth constraint and XRT observations were
interrupted by the Swift trigger on GRB 080319B. The current observations
consist of Photon Counting mode data from T+560s to T+1632s and from T+35ks to
T+37ks.

The best XRT position is the UVOT-enhanced position from Beardmore et al. (GCN
7448), consistent with the optical afterglow position reported by Cenko (GCN
7429).

The 0.3-10 keV X-ray light curve starts at a count rate of ~1 counts/s and shows
a decline with a decay slope of 0.94 +/- 0.05.

The spectrum of the PC data from T+560s to T+1632s can be well fit by an
absorbed powerlaw with photon index 2.1 +/- 0.3 and column density of (1.0 +/-
0.7)e21 cm^-2, in excess of the Galactic column density of 1.45e20 cm^-2 in
this direction. The average observed 0.3-10keV flux is 1.6e-11 erg cm^-2 s^-1,
which corresponds to an unabsorbed flux of 2.1e-11 erg cm^-2 s^-1.  The counts
to observed flux conversion factor at the time of this spectrum is 3.7e-11 erg
cm^-2 count^-1.

If the underlying powerlaw decay continues as is, we predict an XRT count rate
of 0.008 counts/s at T+24hr, which corresponds to an observed 0.3-10keV flux of
2.9e-13 erg cm^-2 s^-1.

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