[vsnet-grb-info 24817] LIGO/Virgo S200128d: Upper limits from Fermi-GBM Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26916
SUBJECT: LIGO/Virgo S200128d: Upper limits from Fermi-GBM Observations
DATE:    20/01/28 14:21:50 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 S200128d and using the bayestar.fits.gz,1 skymap, Fermi-GBM was observing
48.7% 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 S200128d (GCN 26906). 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=266.6, Dec=-24.9 with a radius of 67.5 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:    2.5    3.2      8.3
1.024 s:    0.8    1.3      2.7
8.192 s:    0.2    0.4      1.0

Assuming the median luminosity distance of 4031 Mpc from the GW detection,
we estimate the following intrinsic luminosity upper limits over the 1
keV-10 MeV energy range (in units of 10^50 erg/s):

Timescale   Soft   Normal   Hard
------------------------------------
0.128s:     7.8    8.5      37.
1.024s:     2.4    3.4      12.
8.192s:     0.7    1.0      4.5