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GCN Circular 34319

Subject

LIGO/Virgo/KAGRA S230802aq: Upper limits from Fermi-GBM Observations

Date

2023-08-02T20:57:42Z (9 months ago)

From

Joshua Wood at NASA/MSFC <joshua.r.wood@nasa.gov>

Via

Web form

J. Wood (NASA/MSFC) and J. Mangan (CNRS/IJCLab) report on behalf of the Fermi-GBM Team:

For S230802aq (GCN 34314Not found
 
 
) and using the initial bayestar skymap, Fermi-GBM was observing 59.4% 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 S230802aq. 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=335.9, Dec=25.3 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:1612.02395Not found
 
 
, 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       2.1       4.6
1.024 s:     0.3       0.6       1.3
8.192 s:     0.1       0.1       0.2

Assuming the a posteriori mean luminosity distance of 444 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^48 erg/s):

Timescale  Soft    Normal   Hard 
------------------------------------
0.128s:       4.3       7.0       25.
1.024s:       1.0       2.1       7.1
8.192s:       0.3       0.4       1.3