GCN Circular 20797

Adam Goldstein (USRA) and Colleen Wilson-Hodge (NASA/MSFC) report on behalf
of the GBM-LIGO Group:
Lindy Blackburn (CfA), Michael S. Briggs (UAH), Jacob Broida (Carleton
College), Eric Burns (UAH), Jordan Camp (NASA/GSFC), Tito Dal Canton
(NASA/GSFC), Nelson Christensen (Carleton College), Valerie Connaughton
(USRA), 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)

Fermi GBM observed 69% of the bayestar sky map at the time of the LIGO
trigger, and we set the following flux upper limits for the entire visible
sky map (excluded region is a circle with radius of 68 degrees centered on
RA, Dec = 326.9, -22.8).

Using a hard Band function with (Epeak, alpha, beta) = (500 keV, -0.5,
-2.5), we set a 3 sigma, 1-second-averaged flux upper limit for any
transient within 30 s of the LIGO trigger time in the 10-1000 keV band
ranging from 4.6e-7 to 6.0e-7 erg/s-cm^2.  Using an exponentially cutoff
power law parametrized with (Epeak, index) = (566 keV, -0.42), which
represents the average GBM-triggered short GRB, the upper limit ranges from
5.0e-7 to 6.4e-7 erg/s-cm^2.

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
LIGO sky map:

Energy       min  max  median
--------------------------------
 12- 27 keV: 0.08 0.45 0.12 Crab
 27- 50 keV: 0.14 0.66 0.20 Crab
 50-100 keV: 0.17 0.80 0.24 Crab
100-300 keV: 0.34 1.67 0.49 Crab
300-500 keV: 1.85 10.2 2.55 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.