GCN Circular 20365

E. Burns (UAH) reports on behalf of the GBM-LIGO Group:
Lindy Blackburn (CfA), Michael S. Briggs (UAH), Jacob Broida (Carleton
College), Jordan Camp (NASA/GSFC), Tito Dal Canton (NASA/GSFC), Nelson
Christensen (Carleton College), Valerie Connaughton (USRA), Adam Goldstein
(NASA/MSFC), Rachel Hamburg (UAH), C. Michelle Hui (NASA/MSFC), Pete Jenke
(UAH), Dan Kocevski (NASA/MSFC), Nicolas Leroy (LAL), Tyson Littenberg
(NASA/MSFC), Julie McEnery (NASA/GSFC), Rob Preece (UAH), Judith Racusin
(NASA/GSFC), Peter Shawhan (UMD), Karelle Siellez (GA Tech), Leo Singer
(NASA/GSFC), John Veitch (Birmingham), Peter Veres (UAH), Colleen
Wilson-Hodge (NASA/MSFC)

GBM was observing 82.4% of the initial LIGO BAYESTAR probability map for
G268556 at event time, with a large part of the southern high probability
region occulted by the Earth (specifically, locations within ~67 degrees of
(RA=297.7, Dec=-25.3)). The closest on-board trigger time was more than 12
hours earlier and was due to high particle activity on entry to the SAA.
The untargeted ground-based SGRB search of GBM data between ten and eleven
UTC (Briggs et al., in prep) found no candidates around G268556.

The targeted search of the GBM data ([1], [2]) also did not find a
significant gamma-ray signal. This search processes time scales of 0.265 to
8.192 s within 30 s of the LIGO event. The most significant candidate was
found on the longest timescale with the soft spectral template,
corresponding to a false alarm rate of ~0.003 Hz. The 8.192 s window of
this candidate begins 5.4 s before the T0 of G268556. The location
identified by the search is consistent with the high probability region of
the LIGO annulus, with the GBM localization peaking around (130, 10); the
targeted search location is marginally consistent with a galactic origin.
However, the signal appears in detectors observing different regions of the
sky. Further investigation rules out a solar origin. There is longer term
structure for tens of seconds in the low energy channels of GBM.

Both prompt and longer term upper limits will be sent in a forthcoming
circular.


[1] L. Blackburn et al. 2015, ApjS 217, 8
[2] A. Goldstein et al. arXiv:1612.02395
Not found