[vsnet-grb-info 22625] Subject: LIGO/Virgo S190602aq: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24724
SUBJECT: Subject: LIGO/Virgo S190602aq: Upper limits from Fermi-GBM Observations
DATE:    19/06/03 00:35:20 GMT
FROM:    Colleen A. Wilson at NASA/MSFC/NSSTC  <colleen.wilson at nasa.gov>

C.A. Wilson-Hodge and C. M. Hui (NASA/MSFC) report on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190602aq and using the initial bayestar.fits skymap, Fermi-GBM was observing 67.3% 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 S190602aq (GCN 24717). 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 = 148.4 and Dec = -10.9 with a radius of 67.5 degrees.
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^-7 erg/s/cm^2):

Timescale  Soft     Normal   Hard
------------------------------------
0.1 s:           4.3       7.5         17.0 
1.0 s:           1.1       3.4          8.2
10  s:           0.27      0.63         1.7 

Assuming the median luminosity distance of 797 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^49 erg/s):
Timescale  Soft     Normal   Hard
------------------------------------
0.1 s:     5.0          8.0         30.0    
1.0 s:     1.3          3.6         14.5    
10  s:     0.3          0.7          3.0