[vsnet-grb-info 22013] LIGO/Virgo S190412m: Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24112
SUBJECT: LIGO/Virgo S190412m: Fermi-GBM Observations
DATE:    19/04/12 18:52:52 GMT
FROM:    Adam Goldstein at Fermi-GBM, USRA  <adam.michael.goldstein at gmail.com>

A. Goldstein (USRA) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group

For S190412m, and using the initial BAYESTAR skymap, Fermi-GBM was
observing 99.8% of the localization probability region at event time.

There was no Fermi-GBM onboard trigger around the event time of the
LIGO/Virgo detection of a GW trigger (GCN 24098). 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 considering
the 90% credible region of the GW localization. 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:     4.7-5.7  9.1-10   25-27
1.0 s:     1.5-1.8  2.8-3.2  7.4-7.9
10  s:     0.5-0.6  0.9-1.0  2.3-2.4

Assuming the mean luminosity distance of 812 Mpc from the GW detection, we
estimate intrinsic luminosity upper limits of (0.6-6.9)E49 erg/s for the
soft template, (1.0-11)E49 erg/s for the normal template, and (4.2-50)E49
erg/s for the hard template over the 1 keV-10 MeV energy range.