[vsnet-grb-info 23600] LIGO/Virgo S190910d: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25699
SUBJECT: LIGO/Virgo S190910d: Upper limits from Fermi-GBM Observations
DATE:    19/09/10 06:18:11 GMT
FROM:    Cori Fletcher at USRA  <cfletcher at usra.edu>

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group

For S190910d and using the initial bayestar skymap, Fermi-GBM was observing 91.6% 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 S190910d (GCN 25695). 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=194.6, Dec=-9.9 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     norm     hard
--------------------------------------
0.128 s:   3.3      6.5      12
1.024 s:   1.0      1.8      4.6
8.192 s:   0.4      0.67     1.3

Assuming the median luminosity distance of 606 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:    22       40      122
1.024 s:    6.7      11      47
8.192 s:    2.7      4.1     13