[vsnet-grb-info 6037] GRB080503 XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7674
SUBJECT: GRB080503 XRT refined analysis
DATE:    08/05/03 22:52:44 GMT
FROM:    Jirong Mao at INAF-OAB  <jirong.mao at brera.inaf.it>

GRB 080503: Swift-XRT refined analysis


C. Guidorzi & J. Mao (INAF-OAB) report on behalf of the Swift-XRT team:

The Swift-XRT began observing GRB 080503 (trigger=310785, Mao et
al., GCN Circ. 7665) in Window Timing mode, 81 s after the BAT
trigger. The enhanced XRT position was given in Goad et al.
(GCN Circ. 7669).

The light curve from 81 s to 13.2 ks can be modelled with
the combination of an exponential with
a power law taking over at late time, with the following
best-fitting parameters: e-folding time= (72 ± 4) s, power-law
index alpha= 2.2 (-1.1, +0.6). The chisq/dof=202/151 is due to
short-term variability superposed to the model.

The WT mode spectrum spanning from 81 to 282 s can be fit by a
power-law model, with a photon index of 1.27 ± 0.03 and column
density consistent with the average Galactic column density in
this direction of 5.6e20 cm^-2.
The PC mode spectrum, starting from 282 s and totalling 6.3 ks
of exposure, is fit with a power law with a photon index of 2.45+/-0.25
and no evidence for any additional column density with respect
to the Galactic one.
The corresponding observed (unabsorbed) 0.3-10 keV flux is 2.9e-12
(3.9e-12) erg cm^-2 s^-1.

If the burst continues to decay at the same rate, we predict an
XRT count rate of 1.7e-6 count/s at T+24 hours, which corresponds
to an observed 0.3-10 keV flux of approximately 4e-17 erg cm^-2 s^-1.

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