{
  "subject": "LIGO/Virgo/KAGRA S230518h: Upper limits from Fermi-GBM Observations",
  "eventId": "LIGO/Virgo/KAGRA S230518h",
  "createdOn": 1684442197502,
  "bibcode": "2023GCN.33818....1D",
  "submitter": "Sarah Dalessi at UAH <sd0104@uah.edu>",
  "circularId": 33818,
  "body": "S. Dalessi (UAH) and C. Fletcher (USRA) report on behalf of the\nFermi-GBM Team and the GBM-LIGO/Virgo/KAGRA group\n\nFor S230518h and using the updated Bilby skymap (GCN 33816), Fermi-GBM\nwas observing 48.9% of the localization probability at event time.\n\nThere was no Fermi-GBM onboard trigger around the event time of the\nLIGO/Virgo/KAGRA (LVK) detection of GW trigger S230518h (GCN 33813).\nAn automated, blind search for short gamma-ray bursts below the\nonboard triggering threshold in Fermi-GBM also identified no\ncounterpart candidates. The GBM targeted search, the most sensitive,\ncoherent search for GRB-like signals, was run from +/-30 s around\nmerger time, and also identified no counterpart candidates.\n\nPart of the LVK localization region is behind the Earth for Fermi,\nlocated at an RA=32.3, Dec=-3.6 with a radius of 67.6 degrees. We\ntherefore set upper limits on impulsive gamma-ray emission for the LVK\nConsortia localization region visible to Fermi at merger time. Using\nthe representative soft, normal, and hard GRB-like templates described\nin arXiv:1612.02395, we set the following 3 sigma flux upper limits\nover 10-1000 keV, weighted by GW localization probability (in units of\n10^-7 erg/s/cm^2):\n\nTimescale  Soft   Normal   Hard\n------------------------------------\n0.128 s:     1.4   2.7     6.1\n1.024 s:     0.4   0.8     2.0\n8.192 s:     0.1   0.3     0.8\n\nAssuming the median luminosity distance of  277.9  Mpc from the GW\ndetection, we estimate the following intrinsic luminosity upper limits\nover the 1 keV-10 MeV energy range (in units of 10^50 erg/s):\n\nTimescale  Soft     Normal   Hard\n------------------------------------\n0.128s: 0.020      0.035     0.132\n1.024s: 0.006      0.010     0.043\n8.192s: 0.002      0.004     0.018\n"
}