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GCN Circular 3301

GRB 050421: early Swift XRT analysis results
2005-04-21T10:59:17Z (19 years ago)
David Burrows at PSU/Swift <>
O. Godet, M. Goad, K. Page, J. Osborne (U. Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC) report on behalf of the Swift XRT team:

We have analyzed the Swift XRT data from the first orbit observation of GRB
050421. The refined coordinates are:

RA(J2000) = 20h 29m 01.75s
Dec(J2000) = +73d 39' 17.4"

This position is 40 arcseconds from the BAT position given in GCN 3296
(Barbier et al 2005). We estimate a total uncertainty of 5 arcseconds radius
(90% containment).  We note that this refined position is 8.1 arcseconds 
from the XRT position reported in GCN 3296.  Optical observers should 
re-check their images for sources in the new error circle.

Our 0.2-10 keV light curve covers the interval 116-591 sec after the BAT
trigger. It is well-fit with a broken powerlaw with initial slope of 0.9
+1.1/-1.6 breaking to a steeper slope of 3.3 +0.6/-0.3 after 147 +/-10 sec.
All errors are 90% confidence. A single power law decline is not a good
fit to the data.

A preliminary spectral fit to the WT mode data gives a power law photon index
of 1.23 +0.37/-0.34 (error at 90% confidence level) in the 0.3-10 keV band,
assuming Galactic absorption (1.44 E21 cm^-2) and a possible excess in the
absorption of 6 +4/-3 E21 cm^-2.  The unabsorbed 0.3-10 keV flux is 8.5E-10
erg cm^-2 s^-1 in the interval 116-171 sec after the BAT trigger.
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