TITLE: GCN CIRCULAR NUMBER: 25523 SUBJECT: LIGO/Virgo S190828l: Upper limits from Fermi-GBM Observations DATE: 19/08/28 16:15:56 GMT FROM: Peter Veres at UAH P. Veres (UAH) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For S190828l and using the initial bayestar skymap, Fermi-GBM was observing 29% 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 S190828l (GCN 25503). 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 templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV (in units of erg/s/cm^2): Timescale Soft Normal Hard ------------------------------------ 0.128 s: 1.8e-07 2.3e-07 5.0e-07 1.024 s: 6.4e-08 1.0e-07 2.1e-07 8.192 s: 2.7e-08 3.5e-08 7.7e-08 Assuming the median luminosity distance of 1609 Mpc (z=0.31) 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 Normal Hard ------------------------------------ 0.128 s: 8.9 10 37 1.024 s: 3.2 4.4 16 8.192 s: 1.3 1.5 5.7