[vsnet-grb-info 22917] LIGO/Virgo S190706ai: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25016
SUBJECT: LIGO/Virgo S190706ai: Upper limits from Fermi-GBM Observations
DATE:    19/07/07 12:12:45 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007 at 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