GCN Circular 12334
Subject
GRB 110825A: Further Swift/XRT Observations
Event
Date
2011-09-12T20:59:08Z (14 years ago)
From
Binbin Zhang at PSU <buz12@psu.edu>
B.-B. Zhang (PSU), D. Grupe (PSU), D. N. Burrows (PSU), J. Gelbord (PSU)
and S. D. Barthelmy (GSFC) report on behalf of the Swift-XRT team:
We report further observations of the possible X-ray counterpart
(Zhang & Grupe, GCN 12308) of the IPN-detected burst GRB 110825A
(Hurley etal., GCN 12307). The Swift/XRT found a relatively bright
X-ray source located at
RA (J2000): 02 59 11.63
Dec(J2000): +15 25 38.4.
We performed follow-up XRT observations of this field at T0+1 day,
T0+5 days,T0+12 days and T0+16 days (where T0 = 2011 Aug 25 at
02:26:48.0 UT ), in order to determine whether or not the X-ray source
had faded. The observed count rates in the 0.3-10 keV band are as follows :
T-T0 Count Rate
(8.7+/-0.6)x10^3 s 0.0129+/-0.0025 count/s
(4.8+/-0.2)x10^5 s 0.0045+/-0.0011 count/s
(1.1+/-0.01)x10^6 s 0.0065+/-0.0025 count/s
(1.4+/-0.07)x10^6 s 0.0083+/-0.0018 count/s
We find that this source is now at a count rate consistent with
that of our first observation on T0+1 day at the 1.5 sigma level.
The chance probability for the source being steady is about 0.015,
indicating that it is variable, but it is not decaying as expected for
a GRB. We conclude that this source is not the afterglow of GRB 110825A.
Thus, no afterglow was detected by XRT for this burst.
We note that the variability of this X-ray counterpart in the last two weeks
suggests that it may be a background AGN.
The updated results of the XRT-team automatic analysis are available
at <http://www.swift.ac.uk/xrt_products/00020183>.