[vsnet-grb-info 23423] LIGO/Virgo S190828j: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25522
SUBJECT: LIGO/Virgo S190828j: Upper limits from Fermi-GBM Observations
DATE:    19/08/28 16:14:43 GMT
FROM:    Peter Veres at UAH  <veresp at gmail.com>

P. Veres (UAH) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group:

For S190828j and using the updated bayestar skymap (GCN 25504), Fermi-GBM
was observing 83% 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 S190828j (GCN 25497). 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 (in units of erg/s/cm^2):


Timescale  Soft     Normal   Hard
--------------------------------------
0.128 s:   5.5e-07  7.5e-07  1.7e-06
1.024 s:   1.8e-07  2.8e-07  6.8e-07
8.192 s:   7.1e-08  1.3e-07  2.5e-07

Assuming the median luminosity distance of 1800 Mpc (z=0.34) 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
------------------------------------
0.128 s:     3.4          4.1         16
1.024 s:     1.1          1.5         6.2
8.192 s:     0.44         0.71        2.3