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GCN Circular 4433

Subject
GRB 060105: XRT refined analysis
Date
2006-01-05T18:51:52Z (18 years ago)
From
Olivier Godet at U.of Leicester <og19@star.le.ac.uk>
O. Godet, K. Page, A. Bearmore, J. Osborne (U. Leicester), D. N. Burrows
(PSU), D. Grupe (PSU), H. Ziaeepour (UCL-MSSL), P. Boyd (GSFC-UMBC), L.
Angelini (GSFC-JHU) report on behalf of the Swift XRT team:

We analyzed the first 5 orbits of XRT data from GRB 060105.  A 10.2ks
photon counting (PC) mode image provides a refined XRT position:

RA(J2000) = 19h 50m 00.6s
Dec(J2000) = +46d 20' 58.3''

with an uncertainty of 3.2 arcsecs (90% containment). This position is
4.5 arcsecs away from the on-board XRT position quoted in Ziaeepour et
al. (GCN 4429) and includes the latest XRT boresight correction. This
position is 83 arcseconds from the BAT position (Ziaeepour et al., GCN
4429).

The X-ray light curve can be fit with a double broken power-law with an
initial decay slope of alpha1 = -1.16+/-0.14, a break at t1-T = 196 +
23/-29s, and a shallower post-break slope of alpha2 = -0.80+/-0.02,
followed by another break at t2-T = 3306+/-200s and a steeper decay
slope of alpha3 = -2.30+/-0.08.

An absorbed power-law fit of the WT data (first orbit) from T+187s to
T+1287s gave a photon index of 2.06+/-0.03 and an excess absorption
value of (2.4+/-0.2)e21 cm**-2. The error bars are given at a 90%
confidence level. The Galactic hydrogen column density in the direction
of the burst is 1.8e21 cm**-2. The spectrum of the PC data (4 orbits)
can be fit by an absorbed power-law with Gamma=2.17+/-0.16 and excess
absorption of (2.8+/-0.8)e21 cm**-2.

If the burst continues decaying at the current rate (alpha3) we estimate
an XRT count rate of 0.0029 counts/s at T + 24hr, which corresponds to
an observed 0.5-10.keV flux of 6.26e-13 ergs cm**-2 s**-1 and an
unabsorbed flux of 9.82e-13 ergs cm**-2 s**-1.
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