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GCN Circular 4895

GRB060319: Swift XRT refined analysis
2006-03-19T10:40:25Z (18 years ago)
Andy Beardmore at U Leicester <>
A.P. Beardmore, K.L. Page (U Leicester), J.A. Kennea, D.N. Burrows (PSU)
and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift/XRT team:

We have analysed the first two orbits of Swift XRT data on the BAT GRB
060319 (Ziaeepour, et al., GCN 4885; Sakamato et al., GCN 4891). The
XRT began observing in Photon Counting mode at 00:58:04UT on
2006-03-19, 173 s after the BAT trigger. With an exposure time of 4.5ks,
the refined XRT position is

RA(J2000)  =  11h 45m 33.8s
Dec(J2000) = +60d 00' 39.0"

with an uncertainty of 3.6" (90% containment). This is 2' away from
the centre of the refined BAT position quoted in GCN 4891 (Sakamoto et
al.), and 1.7" away from the initial XRT position quoted in GCN 4886
(Kennea et al.).

The 0.3-10 keV X-ray light curve initially rises from 0.5 count/s at
T+173s to a maximum of 2 count/s at T+265s, then shows a power-law
decline with a decay index of 1.02+/-0.05.

The X-ray spectrum covering the time period from T+173s to T+7.3ks is
well fit by an absorbed power-law with a photon index of 2.10+/-0.15
and column density of (4.6+/-0.6)e21 cm**-2. We note the Galactic column
density in the direction of the source is 1.37e20 cm**-2.  The observed
(unabsorbed) 0.3-10 keV flux for this spectrum is 1.2e-11 (2.2e-11)

Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 0.005 count/s at T+24hr, which
corresponds to an observed 0.3-10 keV flux of 2.7e-13 erg/cm**2/s.
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