TITLE: GCN CIRCULAR NUMBER: 25196 SUBJECT: LIGO/Virgo S190728q: Upper limits from Fermi-GBM Observations DATE: 19/07/28 13:09:00 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For the LIGO/Virgo detection of GW trigger S190728q (GCN 25187) and using the triple-detector BAYESTAR skymap, Fermi-GBM was observing 84.1% of the localization probability at event time. Approximately 15 min before the S190728q event, GBM triggered onboard to the short gamma-ray burst GRB 190728A (GCN 25181). However based on the large temporal offset and the difference in localization, this trigger is not considered a likely counterpart. 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 = 129.9 and Dec = -11.1 with a radius of 67.5 degrees. We therefore set upper limits on impulsive gamma-ray emission for the LVC localization region visible to Fermi at merger time. 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^-7 erg/s/cm^2): Timescale soft norm hard -------------------------------------- 0.128 s: 5.3 6.0 15.0 1.024 s: 2.0 2.7 4.2 8.192 s: 0.6 0.8 1.1 Assuming the median luminosity distance of 795 Mpc (z=0.165) from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^49 erg/s): Timescale soft norm hard -------------------------------------- 0.128 s: 6.2 6.4 27.0 1.024 s: 2.3 2.9 7.6 8.192 s: 0.7 8.6 2.0