GCN Circular 21810

LIGO/Virgo G298389: Fermi GBM Flux Upper Limits

R. Hamburg (UAH) and C. Wilson-Hodge (NASA/MSFC) report on behalf of
the GBM-LIGO
Group:
L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E.
Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N.
Christensen (Carleton College), V. Connaughton (USRA), A. Goldstein (USRA),
C. M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy
(LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH),
J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GA Tech), L. Singer
(NASA/GSFC), J. Veitch (Birmingham), P. Veres (UAH)

At the time of the LIGO/VIRGO candidate G298389, Fermi was passing through
the South Atlantic Anomaly, and the GBM detectors were disabled. We set the
following flux upper limits for the visible sky map within the 90% credible
region.

Using the Earth Occultation technique (Wilson-Hodge et al. 2012, ApJS, 201,
33) to estimate the amount of persistent emission during a 48-hour period
centered on the LIGO trigger time, we place the following range of 3-sigma
day-averaged flux upper limits based on observed sources over the entire
90% credible region of the LIGO sky map:

   Energy   min  max  median
    -----------------------------------
  12-27 keV:  0.09 0.22 0.14  Crab
  27-50 keV:  0.15 0.37 0.23  Crab
 50-100 keV:  0.22 0.55 0.33  Crab
100-300 keV:  0.39 1.02 0.60  Crab
300-500 keV:  2.69 7.59 4.20  Crab

These limits are based on the minimum requirement that each source in the
Earth Occultation catalog was Earth-occulted at least 6 times in each of
the 24 hour periods preceding and following the LIGO trigger and that the
occultations were well separated from nearby bright sources.