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GCN Circular 8875

GRB 090201: Swift-XRT refined analysis
2009-02-02T11:12:04Z (15 years ago)
Andy Beardmore at U Leicester <>
A.P. Beardmore, K.L. Page (U. Leicester), S.R. Oates (UCL-MSSL) report on
behalf of the Swift-XRT team.

The Swift-XRT started observing the BAT GRB 090201 (trigger #341749,
Oates et al., GCN circ. 8865) at 18:47:33 UT, 3.65ks after the trigger.
The UVOT-enhanced X-ray position has been reported in Beardmore et al.
(GCN Circ. 8872).

Using 14.5ks of photon counting mode data taken from T+3.65ks to T+39.2ks
after the trigger, we find the X-ray light curve can be described by a
broken powerlaw, with initial decay slope of 0.64 +0.17 -0.15, break time
of 7.2 +2.1 -1.5 ks and final decay slope of 1.45 +/- 0.11.

The spectrum spanning the same interval can be fit by an absorbed
powerlaw, with a photon index of 2.20 +/- 0.10 and column density of
4.78 +/- 0.42 x 10^21 cm^-2, compared with the Galactic column of 4.9
x 10^20 cm^-2 in the direction of the burst. The observed (unabsorbed)
0.3-10 keV flux is (1.00 +/- 0.06) x 10^-11 [(2.02+/-0.12) x 10^-11]
erg cm^-2 s^-1.

Assuming the decay continues at the same rate, we  predict a count rate
of 0.017 count/s 1 day after the trigger, which corresponds to an observed
0.3-10 keV flux of 7.4e-13 erg cm^-2 s^-1.

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