TITLE: GCN CIRCULAR NUMBER: 39461 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations DATE: 25/02/24 19:45:19 GMT FROM: Lorenzo Scotton at UAH lscottongcn@outlook.com
L. Scotton (UAH) reports on behalf of the Fermi-GBM Team:
For S250223dk and the Swift/BAT-GUANO ID 762004910 (The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration along with the Swift/BAT-GUANO team, GCN 39443) and using the combined skymap combined-ext.multiorder.fits,3, 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/KAGRA (LVK) detection of GW trigger S250223dk, neither for the Swift/BAT-GUANO trigger ID 762004910. 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 joint localization region is behind the Earth for Fermi, located at RA=267.1, Dec=-5.5 with a radius of 68.0 degrees. We therefore set upper limits on impulsive gamma-ray emission for the joint 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 the joint LVK-Swift/BAT localization probability (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard ------------------------------------ 0.128 s: 2.00 2.90 6.40 1.024 s: 0.69 0.95 1.90 8.192 s: 0.23 0.32 0.63
Assuming the median luminosity distance of 6033 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^50 erg/s):
Timescale Soft Normal Hard ------------------------------------ 0.128s: 14.15 16.94 64.06 1.024s: 4.88 5.55 19.02 8.192s: 1.63 1.87 6.31
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