[vsnet-grb-info 23724] LIGO/Virgo S190923y: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25823
SUBJECT: LIGO/Virgo S190923y: Upper limits from Fermi-GBM Observations
DATE:    19/09/23 19:16:28 GMT
FROM:    Bagrat Mailyan at UAH  <bm0054 at uah.edu>

B. Mailyan (UAH) and J. Wood (NASA) report on behalf of the Fermi-GBM Team
and the GBM-LIGO/Virgo group

For S190923y and using the initial bayestar skymap, Fermi-GBM was observing
42.3% 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 S190923y (GCN 25814).
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 for the LVC
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     norm     hard
--------------------------------------
0.128 s:     2.2       4.1       8.8
1.024 s:     0.74     1.3       2.4
8.192 s:     0.26     0.4       0.79

Assuming the median luminosity distance of 438 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:      9.4         16.2     57.4
1.024s:      3.2          5.1      15.6
8.192s:      1.1         1.6       5.2