GCN Circular 6852
Subject
GRB 070810B: further XRT analysis
Event
Date
2007-10-05T18:33:55Z (18 years ago)
From
Rhaana Starling at U of Leicester <rlcs1@star.le.ac.uk>
R. Starling, J.P. Osborne, K.L. Page (U. Leicester) and F.E. Marshall
(NASA/GSFC) report, on behalf of the Swift XRT team:
Previously, Swift XRT data for the short GRB 070810B (trigger=287409;
Marshall et al., GCN Circ. 6743) up to 13.8 ks after the BAT trigger
showed two possible sources within the BAT refined error circle, detected
at 2-sigma significance in 7.2 ks and termed S1 and S2 (Starling et al.,
GCN Circ. 6754).
We have analysed a further 12.6 ks of Swift XRT photon counting mode data
beginning 42 days and ending 54 days after the burst, in order to assess
the variability of the two possible afterglow candidates.
In this second epoch of data we detect one X-ray source at 4-sigma
significance within the refined BAT error circle (Sakamoto et al., GCN
Circ. 6753), corresponding to the source S2 described in GCN Circ. 6754.
Using Bayesian analysis we find that S2 has between 20 and 54 counts at
the 99% confidence level or 1.6e-3 to 4.3e-3 count/s, consistent with the
first epoch limits of 5.6e-4 to 3.6e-3 count/s. This suggests that S2 is
a persistent faint source, and not the afterglow of GRB 070810B.
The possible source S1 (GCN Circ. 6754), detected only at the 2-sigma
level in the intial epoch observations, is not detected in the second
epoch observations, providing an upper limit on the count rate of 6.7e-4
count/s at 99% confidence based on the background count rate. This is
above the 3-sigma lower limit on the source count rate at epoch 1 of
5.6e-4 count/s, hence we cannot determine whether or not this source has
faded.
This is an official product of the Swift XRT team.