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GCN Circular 24385

LIGO/Virgo S190503bf: Fermi-GBM Observations
2019-05-04T03:11:32Z (5 years ago)
C. Michelle Hui at MSFC/Fermi-GBM <>
C.M. Hui and C. A. Wilson-Hodge (NASA/MSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190503bf and using the initial BAYESTAR skymap, Fermi-GBM was observing 62% 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 S190503bf (GCN 24377). 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=73.8, Dec=21.9 with a radius of 67.2 degrees.  We therefore set upper limits on impulsive gamma-ray emission considering the 90% credible region of the GW localization not blocked by the Earth. 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:     4.1-4.6  8.6-9.5  27.-28.

1.0 s:     1.2-1.4  2.7-2.9  7.9-8.3

10  s:     0.3-0.4  0.8-0.9  2.5-2.6

Assuming the median luminosity distance of ~421 Mpc from the GW detection, we estimate intrinsic luminosity upper limits of (0.1-1.5) E49 erg/s for the soft template, (0.2-2.8)E49 erg/s for the normal template, and (1.2-14.)E49 erg/s for the hard template over the 1 keV-10 MeV energy range.
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