TITLE:   GCN CIRCULAR
NUMBER:  9952
SUBJECT: GRB 090927: Swift XRT refined analysis 
DATE:    09/09/27 15:13:01 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <grupe@astro.psu.edu>

D. Grupe and  L. Vetere (PSU) report on behalf of the Swift-XRT team:

Due to an observing constraint, the Swift XRT started observing the
field of GRB 090927 Grupe et al., GCN Circ. 9945) delayed at 10:43:03
UT, 2147s after the BAT trigger.

XRT found a faint, fading, uncatalogued X-ray source at
RA (J2000): 22h 55m 53.50s
Dec (J2000): -70d 58' 49.2"

with an uncertainty of 2.0 arcsec (radius, 90% confidence) as given
in Evens et al. (GCN Circular 9950).  This location is 24.8" from
the BAT on-board calculated location (Grupe et al., GCN Circular
9945), inside the BAT error circle, and 0.5" from the UVOT position
given in Gronwall & Grupe (GCN Circular 9946).

Based on the Photon Counting mode (pc) mode data of the first orbit
with an exposure time of 1421s we extracted a spectrum which can be
fitted with a single absorbed power law model with Gamma =
1.64+/-0.49 and an absorption column density consistent with the
Galactic value of 2.92 x 10^20 cm^-2 (Kalberla et al. 2005).

The light curve can be modelled with a single power-law decay with
an index of alpha=1.76+2.05/-0.96. If the afterglow continues to
decay with this slope the predicted count rate 24 hours after
the trigger is 2.5e-4 counts s^-1 or 1.3e-14 ergs s^-1 cm^-2.

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