TITLE: GCN CIRCULAR NUMBER: 24146 SUBJECT: LIGO/Virgo S190421ar: Fermi-GBM Observations DATE: 19/04/22 19:19:06 GMT FROM: Peter Veres at UAH P. Veres (UAH), C. M. Hui (NASA/MSFC) and A. Goldstein (USRA) report on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: "At the time of the S190421ar GW trigger (2019-04-21 21:38:56.41 UT), based on the initial BAYESTAR skymap, Fermi-GBM was observing 78.6% of the localization probability region. There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo detection (GCN 24141). 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 for the +/-30 s interval around merger time, and also identified no counterpart candidates. We therefore set upper limits on impulsive gamma-ray emission considering the 90% credible region of the GW localization. Using the representative soft, normal, and hard GRB-like spectral 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: 4.3-6.6 8.5-11 26-29 1.0 s: 1.3-2.1 2.7-3.5 7.7-8.6 10 s: 0.4-0.6 0.8-1.1 2.4-2.6 Assuming the mean luminosity distance of ~2300 Mpc (z=0.42) from the GW detection, we estimate intrinsic luminosity upper limits of (4.1-67)E49 erg/s for the soft template, (7.1-98)E49 erg/s for the normal template, and (3.6-44)E50 erg/s for the hard template over the 1 keV-10 MeV energy range."