GCN Circular 24248
Subject
LIGO/Virgo S190426c: Fermi GBM Observations
Date
2019-04-26T20:50:31Z (6 years ago)
From
Adam Goldstein at Fermi-GBM, USRA <adam.michael.goldstein@gmail.com>
C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group:
For S190426c, and using the updated BAYESTAR skymap, Fermi-GBM was
observing 100% of the localization probability at event time.
There was no Fermi-GBM onboard trigger around the event time of the
LIGO/Virgo detection of GW trigger S190426c (GCN 24237). An automated,
blind search for short gamma-ray bursts below the onboard triggering
threshold in Fermi-GBM also identified no counterpart candidates. The GBM
targeted search, the most sensitive, coherent search for GRB-like signals,
was run from +/-30 s around merger time, and also identified no counterpart
candidates.
We therefore set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like spectral templates described
in arXiv:1612.02395, we set the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard
------------------------------------
0.1 s: 3.9-7.0 8.3-12. 26.-30.
1.0 s: 1.2-2.2 2.6-3.7 7.7-8.8
10 s: 0.4-0.7 0.8-1.1 2.4-2.7
Assuming the mean luminosity distance of ~375 Mpc from the GW detection, we
estimate intrinsic luminosity upper limits of (0.09-1.6)E49 erg/s for the
soft template, (0.2-2.6)E49 erg/s
for the normal template, and (0.9-10.6)E49 erg/s for the hard template over
the 1 keV-10 MeV energy range.