[vsnet-grb-info 22047] LIGO/Virgo S190421ar: Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24146
SUBJECT: LIGO/Virgo S190421ar: Fermi-GBM Observations
DATE:    19/04/22 19:19:06 GMT
FROM:    Peter Veres at UAH  <veresp at gmail.com>

P. Veres (UAH), C. M. Hui (NASA/MSFC) and A. Goldstein (USRA) report on
behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group:


"At the time of the S190421ar GW trigger (2019-04-21 21:38:56.41 UT), based
on the initial BAYESTAR skymap, Fermi-GBM was observing 78.6% of the
localization probability region.

There was no Fermi-GBM onboard trigger around the event time of the
LIGO/Virgo detection (GCN 24141). 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 for the +/-30 s
interval 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:     4.3-6.6  8.5-11   26-29
1.0 s:     1.3-2.1  2.7-3.5  7.7-8.6
10  s:     0.4-0.6  0.8-1.1  2.4-2.6

Assuming the mean luminosity distance of ~2300 Mpc (z=0.42) from the GW
detection, we estimate intrinsic luminosity upper limits of (4.1-67)E49
erg/s for the soft template, (7.1-98)E49 erg/s for the normal template, and
(3.6-44)E50 erg/s for the hard template over the 1 keV-10 MeV energy range."