[vsnet-grb-info 25108] LIGO/Virgo S200225q: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27209
SUBJECT: LIGO/Virgo S200225q: Upper limits from Fermi-GBM Observations
DATE:    20/02/25 16:45:33 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 S200225q and using the latest BAYESTAR skymap, Fermi-GBM was observing
88.6% 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 S200225q (GCN Circ. 27193). 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=224.3, Dec=24.7 with a radius of 67.2 degrees. We therefore set upper
limits on impulsive gamma-ray emission for the LVC localization region
visible to Fermi at merger time. 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
---------------------------------
0.128 s:   10.      13.      23.
1.024 s:   3.7      3.8      6.6
8.192 s:   0.9      1.0      2.0

Assuming the median luminosity distance of 1234 Mpc from the GW detection,
we estimate the following intrinsic luminosity upper limits over the 1
keV-10 MeV energy range (in units of 10^50 erg/s):

Timescale  Soft     Normal   Hard
------------------------------------
0.128s:    2.8      3.3      9.8
1.024s:    1.0      1.0      2.8
8.192s:    0.2      0.2      0.8