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GCN Circular 9825

GRB 090817: Confirmation of the X-ray afterglow
2009-08-18T08:52:01Z (15 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester), C. Guidorzi (U Ferrara) and W.H. Baumgartner
(GSFC/UMBC) report on behalf of the Swift-XRT team:

Swift conducted a second observation of GRB 090817 (Beckmann et al. GCN
Circ. 9815), collecting 3.9 ks of Photon Counting (PC) mode XRT data in
the interval T0+50 ks to T0+58 ks. The source reported by Evans et al.
(GCN Circ. 9819) has faded to a level of ~0.015 ct s^-1. A power-law fit
to the light curve yields a temporal decay index of alpha=0.9+/-0.2

Inspecting the USNO-B1 catalogue within 3.5' of the GRB we find 216
objects with R2<20.0. The probability of finding a USNO-B1 source within
a 2" radius circle in this field is thus 2%. The strength of the
potential association between the XRT and USNO-B1 sources noted in GCN
Circ. 9819 is therefore fairly weak.

We therefore suggest that the XRT source is the afterglow of GRB 090817.

The results of the XRT-team automatic analysis are available at

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