GCN Circular 25016
Subject
LIGO/Virgo S190706ai: Upper limits from Fermi-GBM Observations
Event
Date
2019-07-07T12:12:45Z (7 years ago)
From
Rachel Hamburg at UAH <rkh0007@uah.edu>
R. Hamburg (UAH) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group:
For the LIGO/Virgo detection of GW trigger S190706ai (GCN 24998) and using
the initial BAYESTAR skymap, Fermi-GBM was observing 62.0% of the
localization probability at
event time.
There was no Fermi-GBM onboard trigger around the event time of S190706ai.
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.
Part of the LVC localization region is behind the Earth for Fermi, located
at RA = 170.4
and Dec = -20.2 with a radius of 67.5 degrees. We therefore set upper
limits on
impulsive gamma-ray emission. Using the representative soft, normal, and
hard GRB-like templates described in arXiv:1612.02395, we set the following
3 sigma flux upper limits
over 10-1000 keV, weighted by GW localization probability, (in units of
10^-7
erg/s/cm^2):
Timescale Soft Normal Hard
--------------------------------------
0.1 s: 5.7 7.5 13.
1.0 s: 1.5 2.2 3.9
10. s: 0.5 0.5 0.9
Assuming the median luminosity distance of 5725 Mpc (z=0.881) from the GW
detection,
we estimate the following intrinsic luminosity upper limits over the 1
keV-10 MeV energy
range (in units of 10^51 erg/s):
Timescale Soft Normal Hard
------------------------------------
0.1 s: 3.6 4.0 11.7
1.0 s: 1.0 1.2 3.5
10 s: 0.3 0.3 0.8