TITLE: GCN CIRCULAR NUMBER: 24185 SUBJECT: LIGO/Virgo S190425z: Fermi GBM Observations DATE: 19/04/25 15:35:23 GMT FROM: Cori Fletcher at USRA/NASA C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For S190425z and using the initial BAYESTAR skymap, Fermi-GBM was observing 55.6% of the probability region at event time. There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo detection of GW trigger S190425z (GCN 24168). 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. Assuming a detectable relativistic jet, it likely originated from the 44% of the LVC localization behind the Earth for Fermi, located at RA=194.64, Dec=22.47 with a radius of 67.2 degrees. This region is also consistent with the highest probability density region of the BAYESTAR map. Otherwise, we set the following upper limits for the remaining 90% localization region not blocked by the Earth. 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 (in units of 10^-7 erg/s/cm^2): Timescale Soft Normal Hard ------------------------------------ 0.1 s: 4.2-117 8.8-84. 27.-93. 1.0 s: 1.3-35. 2.7-25. 7.8-28. 10 s: 0.4-11. 0.9-7.7 2.4-8.7 Assuming the mean luminosity distance of ~155 Mpc from the GW detection, we estimate intrinsic luminosity upper limits of (0.03-5.1)E49 erg/s for the soft template, (0.04-3.4e)E49 erg/s for the normal template, and (0.2-6.2)E49 erg/s for the hard template over the 1 keV-10 MeV energy range.