[vsnet-grb-info 23511] LIGO/Virgo S190901ap: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25610
SUBJECT: LIGO/Virgo S190901ap: Upper limits from Fermi-GBM Observations
DATE:    19/09/02 05:11:21 GMT
FROM:    C. Michelle Hui at MSFC/Fermi-GBM  <c.m.hui at nasa.gov>

C. M. Hui (NASA/MSFC) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190901ap and using the initial bayestar skymap, Fermi-GBM was observing 61% 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 S190901ap (GCN 25606). 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 LVC localization region is behind the Earth for Fermi, located at RA=112.4, Dec=-9.7 with a radius of 67.2 degrees.  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     Normal   Hard
------------------------------------
0.128 s:     3.0     5.0     9.9
1.024 s:     0.9     1.5     3.5
8.192 s:     0.4     0.5     0.9

Assuming the median luminosity distance of 242 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
------------------------------------
0.128 s:     3.2          5.0        16.2
1.024 s:     1.0          1.5         5.7
8.192 s:     0.4          0.5         1.5