GCN Circular 23121
Subject
Swift Trigger 852625: Swift/BAT/XRT/UVOT observations
Date
2018-08-10T17:52:21Z (7 years ago)
From
Valerio D'Elia at ASDC <valerio.delia@ssdc.asi.it>
V. D���Elia (SSDC), A. D���A�� (INAF-IASFPA), F. E. Marshall (NASA/GSFC), A. Y. Lien (GSFC/UMBC) and M. J. Moss (George Washington University)
report on behalf of the Swift team:
We analysed the full Swift dataset for the possible burst which triggered BAT (Trigger 852625, Moss et al., GCN Circ. 23115).
The BAT ground analysis uses data from T-60 to T+243 sec. The BAT image significance is only 4.9 sigma (15-350 keV). Also, the mask-weighted light curve does not show anything significant.
The XRT data consist of 2.64 ks and are entirely in PC mode. No new X-ray source is found inside the BAT error region, down to a limit of ~0.001 cts/s, corresponding to a 0.3-10 keV observed flux of ~4e-14 erg cm^-2 s^-1 (assuming a typical GRB spectrum) The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/possible_GRBs/00852625/index.php
The Swift/UVOT began settled observations 154 s after the BAT trigger. No optical afterglow consistent with the BAT position is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 154 304 147 >19.9
u_FC 312 562 246 >19.2
We thus conclude that this trigger was just a noise fluctuation.
This circular is an official product of the Swift team.