GCN Circular 34095
Subject
LIGO/Virgo/KAGRA S230627c: Upper limits from Fermi-GBM Observations
Date
2023-06-27T19:14:07Z (3 years ago)
From
Sarah Dalessi at UAH <sd0104@uah.edu>
S. Dalessi (UAH) reports on behalf of the Fermi-GBM Team:
For S230627c (GCN 34086 and GCN 34087) and using the updated Bilby skymap, Fermi-GBM was observing 99.8% 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 S230627c . 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 [1,2,3], the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.
For Fermi, part of the LVK localization region is behind the Earth, located at an RA=84.8, Dec=-18.5 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: 1.9 3.3 5.4
1.024 s: 0.7 0.9 1.5
8.192 s: 0.2 0.3 0.5
Assuming the median luminosity distance of 291.0 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: 0.047 0.066 0.215
1.024s: 0.015 0.019 0.060
8.192s: 0.004 0.006 0.018
[1] Blackburn et al. 2015, ApJS 217, 8
[2] Goldstein et al. arXiv:1612.02395
[3] Goldstein et al. arXiv:1903.12597