[vsnet-grb-info 24347] LIGO/Virgo S191215w: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26446
SUBJECT: LIGO/Virgo S191215w: Upper limits from Fermi-GBM Observations
DATE:    19/12/16 02:29:31 GMT
FROM:    Cori Fletcher at USRA  <cfletcher at usra.edu>

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S191215w and using the initial BAYESTAR skymap, Fermi-GBM was observing 49.2% 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 S191215w (GCN Circ. 26441). 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=322.6, Dec=18.9 with a radius of 67.1 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:      2.6        3.5         9.1
1.024 s:      1.1        1.5         3.0
8.192 s:      0.15      0.29       0.76

Assuming the median luminosity distance of 2215.5 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:       2.4       2.8          12.0
1.024s:       1.0       1.2          4.1
8.192s:       0.14      0.24       1.0