TITLE: GCN CIRCULAR NUMBER: 33892 SUBJECT: LIGO/Virgo/KAGRA S230529ay: Upper limits from Fermi-GBM Observations DATE: 23/05/30 01:55:30 GMT FROM: Stephen Lesage at Fermi-GBM Team sjl0014@uah.edu
S. Lesage (UAH) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo/KAGRA group
For S230529ay (GCN 33889 and GCN 33891) and using the Bilby skymap, Fermi-GBM was observing 60.7% 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 S230529ay. 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 LVK localization region is behind the Earth for Fermi, located at an RA=31.5, Dec=23.9 with a radius of 67.6 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW 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 GW localization probability (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard ------------------------------------ 0.128 s: 1.2 1.9 3.5 1.024 s: 0.5 0.7 1.2 8.192 s: 0.2 0.2 0.4
Assuming the median luminosity distance of 200.6 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: 0.009 0.013 0.039 1.024s: 0.003 0.005 0.013 8.192s: 0.001 0.002 0.005