[vsnet-grb-info 5691] GRB080229: Swift XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7346
SUBJECT: GRB080229: Swift XRT refined analysis
DATE:    08/03/01 12:39:34 GMT
FROM:    Jirong Mao at INAF-OAB  <jirong.mao at brera.inaf.it>

GRB080229: Swift XRT refined analysis

J.Mao, (INAF-OAB), A. Moretti (INAF-OAB), J. Canizzo (NASA/UMBC), C. 
Guidorzi
(Univ. Bicocca & INAF-OAB), A, Beardmore (U Leicester)
P. Evans (U Leicester) report on behalf of the Swift-XRT team:

We have analysed the first 2 orbits of Swift-XRT data obtained for
BAT GRB 080229 (trigger #304379, Cannizzo, et al., GCN Circ. 7335).

The data consist of 149 s in Windowed Timing (WT) mode, starting 90 s
after the BAT trigger and 8.34 ks in Photon Counting (PC) mode.
The astrometrically corrected X-ray position is given  in Beardomre et 
al. GCN 7324.

The XRT light-curve shows a flare peaking few seconds after the beginning
of the observation (103+/-2 s). The descending part of the flare can be 
fit by a power law with
a slope of alpha1=4.45+/-0.09 up to a break at t1=192.4+/- 2.5 s, which is
followed by a flat decay with a slope of alpha2=0.18+/-0.01.
A second break is present at 2700+/-1000 s with alpha3=0.8+/-0.5

The spectrum formed from all the WT data can be modeled with a
power-law of photon index Gamma = 2.88 ± 0.09, with an absorbing
column of NH = (3.1 ± 0.2)e21 cm^-2 (in excess with respect to the
Galactic value of 8.97e20 cm^-2). The spectrum formed from the PC data
can be modeled with a power-law of photon index Gamma = 1.99 ±
0.07, with an absorbing column of NH = (3.1 ± 0.2)e21 cm^-2, which
is in agreement with the WT one.

If the light-curve continues to decay with a slope of 0.8, the
afterglow at 24 hour will be still bright with an expected count
rate of 0.3 count s^-1. This corresponds to an observed (unabsorbed) flux
of 1.41E-11(2.2e-11) erg cm-2 s-1.

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