TITLE: GCN CIRCULAR NUMBER: 24641 SUBJECT: LIGO/Virgo S190521g : Upper limits from Fermi-GBM observations DATE: 19/05/21 17:44:12 GMT FROM: Suraj Poolakkil at UAH S. Poolakkil (UAH) and A. Goldstein (USRA) report on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For S190521g, and using the updated LALInference skymap, Fermi-GBM was observing 70.9% 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 S190521g (GCN 24621). 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 = 172.7 and Dec = -25.4 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 spectral templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by the remaining visible GW localization probability (in units of erg/s/cm^2): Timescale soft norm hard -------------------------------------- 0.128 s: 7.6e-07 9.7e-07 1.8e-06 1.024 s: 2.6e-07 3.4e-07 5.2e-07 8.192 s: 6.7e-08 1.1e-07 1.9e-07 Assuming the median luminosity distance of ~3931 Mpc from the GW detection, we estimate intrinsic luminosity upper limits of (1.9-22.5)E50 erg/s for the soft template, (2.7-24.5)E50 erg/s for the normal template, and (8.1-77.3)E50 erg/s for the hard template over the 1 keV-10 MeV energy range.