[vsnet-grb-info 23788] LIGO/Virgo S190930t: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25887
SUBJECT: LIGO/Virgo S190930t: Upper limits from Fermi-GBM Observations
DATE:    19/09/30 20:01:02 GMT
FROM:    Joshua Wood at MSFC/Fermi-GBM  <joshua.r.wood at nasa.gov>

J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190930t and using the initial bayestar.fits.gz skymap, Fermi-GBM was observing 58.5% of the localization probability at event time.

There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo detection of GW trigger S190930t (GCN 25876). 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.

We therefore set upper limits on impulsive gamma-ray emission. 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:   2.8      4.1      8.8
1.024 s:   0.8      1.2      2.6
8.192 s:   0.3      0.4      0.8

Assuming the median luminosity distance of 108 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s):

Timescale  Soft     Normal   Hard
------------------------------------
0.128 s:   5.93     8.13     28.7
1.024 s:   1.61     2.38     8.47
8.192 s:   0.64     0.83     2.57