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GCN Circular 25122

Subject
LIGO/Virgo S190720a: Upper limits from Fermi-GBM Observations
Date
2019-07-20T12:31:57Z (5 years ago)
From
Joshua Wood at MSFC/Fermi-GBM <joshua.r.wood@nasa.gov>
J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group:

For the LIGO/Virgo detection of GW trigger S190720a (GCN 25115) and using the initial BAYESTAR skymap, Fermi-GBM was observing 73.2% of the localization probability at event time.

There was no Fermi-GBM onboard trigger around the event time of S190720a. 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.

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 (in units of 10^-8 erg/s/cm^2):

Timescale ��Soft �� Normal �� Hard
------------------------------------
0.128 s: �� 37. �� ��57. �� �� ��110.
1.024 s: �� 13. �� ��17. �� �� ��40.
8.192 s: �� 3.2 �� ��4.9 �� �� ��9.5 

Assuming the median luminosity distance of 1071 Mpc (z=0.215) 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: �� 78.6 �� 110. �� �� 352.
1.024 s: �� 27.6 �� 32.7 �� �� 128.
8.192 s: �� 6.80 �� 9.42 �� �� 30.4
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