TITLE: GCN CIRCULAR NUMBER: 24248 SUBJECT: LIGO/Virgo S190426c: Fermi GBM Observations DATE: 19/04/26 20:50:31 GMT FROM: Adam Goldstein at Fermi-GBM, USRA C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For S190426c, and using the updated BAYESTAR skymap, Fermi-GBM was observing 100% 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 S190426c (GCN 24237). 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 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: 3.9-7.0 8.3-12. 26.-30. 1.0 s: 1.2-2.2 2.6-3.7 7.7-8.8 10 s: 0.4-0.7 0.8-1.1 2.4-2.7 Assuming the mean luminosity distance of ~375 Mpc from the GW detection, we estimate intrinsic luminosity upper limits of (0.09-1.6)E49 erg/s for the soft template, (0.2-2.6)E49 erg/s for the normal template, and (0.9-10.6)E49 erg/s for the hard template over the 1 keV-10 MeV energy range.