[AAVSO-HEN] Possible GRB 081211B - Swift-XRT analysis

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
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TITLE:   GCN CIRCULAR
NUMBER:  8666
SUBJECT: Possible GRB 081211B - Swift-XRT analysis
DATE:    08/12/13 09:19:47 GMT
FROM:    Kim Page at U.of Leicester  <kpa at star.le.ac.uk>

K.L. Page, P.A. Evans (U. Leicester) and S.T. Holland (CRESST/USRA/GSFC) 
report on behalf of the Swift-XRT team:

Swift-XRT performed a Target of Opportunity observation of the possible 
BAT Slew Survey (BATSS) burst GRB 081211B (Copete et al., GCN Circ. 8661), 
starting 81.6 ks after the slew in which it was detected, and found a 
single, uncatalogued X-ray source within the BATSS error circle.

Using 1878 s of XRT Photon Counting mode data and 4 UVOT images, we find 
an astrometrically corrected X-ray position (using the XRT-UVOT alignment 
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 
168.2646, 53.8300 which is equivalent to:

RA (J2000):  11 13 3.49
Dec (J2000): +53 49 48.1

with an uncertainty of 2.0 arcsec (radius, 90% confidence).

During the initial observation (81.6-92 ks), the mean X-ray count rate was 
0.035 +/- 0.005 count s^-1. A second observation (126-133 ks) showed a 
count rate of 0.018 +/- 0.006. The source, therefore, appears to have 
faded, with a power-law index, alpha = 1.4 +0.8/-0.9. However, we cannot 
rule out a constant source at this time, so cannot categorically confirm 
this is an X-ray afterglow.

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