Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 8031

GRB 080727B: Swift-XRT refined analysis
2008-07-27T17:16:40Z (16 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester) and S. Immler (CRESST/GSFC/UMD) report
on behalf of the Swift-XRT team:

We have analysed 1.6 ks of XRT data for GRB 080727B (Immler et al., GCN
Circ 8022). The data were taken in two snapshots; the first started 105
s after the trigger and contained 51 s of Windowed Timing mode data
followed by 500 s of Photon Counting (PC) mode data. The second snapshot
began at T0+11 ks, and contained 1.2 ks of data, all in PC mode.

The UVOT-enhanced XRT position has been given by Goad et al. (GCN Circ.

The light curve shows an initial steep decay with a power-law index of
2.47 (+1.38, -0.39), with a break to a shallower decay of 1.05 (+0.20,
-0.13). The break occurred at T0+267 (+89, -100) s.

A spectrum formed from all available PC mode data can be modelled by an
absorbed power law with a photon index on 1.61 (+0.43, -0.38). The best
fitting absorption column is 8.7 (+4.1, -2.9) x 10^21 cm^-2, in excess
of the Galactic value in the direction of the burst (3.6 x 10^21,
Kalberla et al. 2005). The counts to observed 0.3-10 keV flux
conversion factor deduced from this spectrum is 5.0 x 10^-11 erg cm^-2
s^-1 count^-1.

If the light curve continues to decay with a slope of 1.05, the count
rate at 24 hours post-trigger will be 1.8 x 10^-3, corresponding to an
observed (unabsorbed) flux of 9.0 x 10^-14 (4.2 x 10^-13) erg cm^-2

This circular is an official product of the Swift-XRT team.
Looking for U.S. government information and services? Visit