TITLE:   GCN CIRCULAR
NUMBER:  42655
SUBJECT: LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations
DATE:    25/11/12 21:37:57 GMT
FROM:    Angus Jameson <abj0023@uah.edu>

S. Bala (USRA) & A. Jameson (UAH) reports on behalf of the Fermi-GBM Team:

For S251112cm (GCN 42650) and using the initial/updated bayestar/Bilby skymap, Fermi-GBM was observing 68.6% of the localization probability at event time.

There was a Fermi-GBM onboard trigger 784653403/251112637, around two mins before the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW S251112cm, due to local particles (GCN 42652). 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 LVK localization region is behind the Earth for Fermi, located at an RA=4.4, Dec=25.2 with a radius of 68 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW 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 (Please put these in the appropriate units for 10^-7 erg/s/cm^2)
------------------------------------
0.128 s: 4.1 6.1 7.7
1.024 s: 2.0 2.7 3.4
8.192 s: 1.0 1.4 1.3

Assuming the median luminosity distance of 96 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s):

Timescale  Soft    Normal   Hard
------------------------------------
0.128s: 6.9 9.6 19.8
1.024s: 3.3 4.2 8.7
8.192s: 1.7 2.2 3.3