TITLE: GCN CIRCULAR NUMBER: 25841 SUBJECT: LIGO/Virgo S190924h: Upper limits from Fermi-GBM Observations DATE: 19/09/24 12:05:42 GMT FROM: Eric Burns at GSFC E. Burns (NASA/GSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group For S190924h and using the initial 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 S190924h (GCN 25829). 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 set upper limits on impulsive gamma-ray emission for the LVC localization region. 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 Normal Hard ------------------------------------ 0.128 s: 5.9 8.9 15. 1.024 s: 1.6 3.0 5.4 8.192 s: 0.3 0.6 1.1 Assuming the median luminosity distance of 514 Mpc 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: 2.7 3.8 11. 1.024 s: 0.7 1.3 3.8 8.192 s: 0.1 0.3 1.1