GCN Circular 22010
Subject
BAT trigger 778435 is not a GRB.
Date
2017-10-13T16:03:27Z (7 years ago)
From
Boris Sbarufatti at PSU <bxs60@psu.edu>
B. Sbarufatti (PSU), A. Y. Lien (GSFC/UMBC) and S. R. Oates (Uni. of Warwick) report on behalf of the Swift team:
We report on further analysis of BAT trigger 778435/possible GRB 171013A (Sbarufatti et al., GCN Circ. 22007).
The BAT ground analysis using the data set from T-240 to T+962 s shows nothing significant in the mask-weighted light curve. Also, the BAT image significance in 15-350 keV is only 4.3 sigma.
The XRT ground analysis on 6.5 ks of data observed between T+107 s to T+21.6 ks. No X-ray source was detected inside the BAT error circle, down to a 3 sigma upper limit of 5.4e-3 cts s^-1, corresponding to a 0.3-10 keV observed flux of 2.7e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).
The Swift/UVOT began settled observations of the field of GRB 171013A 110 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) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 110 260 147 >20.2
u_FC 322 572 246 >19.1
white 110 621 167 >20.1
v 652 672 19 >17.0
b 577 597 19 >18.0
u 322 572 246 >19.2
m2 677 696 19 >17.2
w2 628 647 19 >17.5
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.97 in the direction of the burst (Schlegel et al. 1998).
We therefore conclude that BAT trigger 778435 was caused by a noise fluctuation.
This circular is an official product of the Swift Team