GCN Circular 9952
Subject
GRB 090927: Swift XRT refined analysis
Date
2009-09-27T15:13:01Z (15 years ago)
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.