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GCN Circular 25714

Subject
LIGO/Virgo S190910h: Upper limits from Fermi-GBM Observations
Date
2019-09-10T12:40:57Z (5 years ago)
From
Cori Fletcher at USRA <cfletcher@usra.edu>
C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190910h and using the initial bayestar skymap, Fermi-GBM was observing 59.9% 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 S190910h (GCN 25707). 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=357.1, Dec=16.0 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     norm     hard
--------------------------------------
0.128 s:   3.3      5.7      12
1.024 s:   0.99     1.5      3.2
8.192 s:   0.32     0.53     0.93

Assuming the median luminosity distance of 242 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^48 erg/s):
Timescale  Soft     Normal   Hard
------------------------------------
0.128 s:    3.5      5.7      19.7
1.024 s:    1.1      1.5      5.2
8.192 s:    0.34     0.53     1.5
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