[vsnet-grb-info 13610] GRB 130626A: Swift-XRT possible detection and UVOT upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14937
SUBJECT: GRB 130626A: Swift-XRT possible detection and UVOT upper limits
DATE:    13/06/27 13:31:45 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

K.L. Page (U. Leicester), S.R. Oates (UCL-MSSL) and M. De Pasquale
(UCL-MSSL) report on behalf of the Swift-XRT and UVOT teams:

We have analysed 9.5 ks of Swift-XRT Photon Counting mode data collected
for GRB 130626A, starting 111 s after the trigger (De Pasquale et al., GCN
Circ. 14931). Of these data, only 10s were collected promptly following
the trigger before Swift had to slew away because of a pointing
constraint.

Within the onboard BAT error circle, there is a possible source detected,
with a count rate (averaged between 111 s and 34.7 ks after the trigger)
of (2.0 +0.5/-0.4) x 10^-3 count s^-1. The position of this source is RA,
Dec = 273.14043, -9.50093, which is equivalent to:

RA (J2000):   18h 12m 33.70s
Dec (J2000): -09d 30' 03.3"

with an uncertainty of 5.5 arcsec (radius, 90% confidence). It is not
possible to determine whether this candidate source is fading at present;
a follow-up observation will be performed at a later date.

We do note, however, that there are other possible sources detected at a
similar level in the XRT field of view, although outside the BAT error
circle.

The Swift-UVOT began settled observations of the field of GRB 130626A
67 s after the BAT trigger (De Pasquale et al., GCN Circ. 14931).
In the initial UVOT exposures, no optical afterglow is found within
the BAT error circle or consistent with the candidate XRT position.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial
exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white (FC)          67          124          57          >20.5
white               67         5608          597         >22.0
v                 4384         5892          269         >19.8
b                 3768         5403          393         >21.1
u                 3563         5198          393         >20.7
w1                4794         4993          197         >20.1

The magnitudes in the table are not corrected for the heavy, but
uncertain, Galactic extinction due to the reddening of E(B-V) = 1.45 in
the direction of the burst (Schlegel et al. 1998).

This circular is an official product of the Swift-XRT and UVOT teams.