TITLE: GCN CIRCULAR NUMBER: 25095 SUBJECT: LIGO/Virgo S190718y: Upper limits from Fermi-GBM Observations DATE: 19/07/19 00:24:34 GMT FROM: Bagrat Mailyan at UAH B. Mailyan (UAH), R. Hamburg (UAH) and A. Goldstein (USRA) report on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For the LIGO/Virgo detection of GW trigger S190718y (GCN 25087) and using the initial BAYESTAR skymap, Fermi-GBM was observing 24.0% of the localization probability at event time. There was no Fermi-GBM onboard trigger around the event time of S190718y. 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 = 15.0 and Dec = 11.4 with a radius of 67.3 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, weighted by GW localization probability, (in units of 10^-8 erg/s/cm^2): Timescale soft norm hard -------------------------------------- 0.128 s: 7.2 16. 47. 1.024 s: 3.6 7.2 18. 8.192 s: 1.1 2.0 5.4 Assuming the median luminosity distance of 227 Mpc (z=0.051) from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s): Timescale soft norm hard -------------------------------------- 0.128 s: 6.84 14.2 68.4 1.024 s: 3.42 6.37 26.2 8.192 s: 1.04 1.77 7.86