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GCN Circular 24185

Subject
LIGO/Virgo S190425z: Fermi GBM Observations
Date
2019-04-25T15:35:23Z (5 years ago)
From
Cori Fletcher at USRA/NASA <corinne.l.fletcher@nasa.gov>
C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group:

For S190425z and using the initial BAYESTAR skymap, Fermi-GBM was
observing 55.6% of the probability region at event time.

There was no Fermi-GBM onboard trigger around the event time of
the LIGO/Virgo detection of GW trigger S190425z (GCN 24168).
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.

Assuming a detectable relativistic jet, it likely originated from the
44% of the LVC localization behind the Earth for Fermi, located at
RA=194.64, Dec=22.47 with a radius of 67.2 degrees. This region is
also consistent with the highest probability density region of the
BAYESTAR map. Otherwise, we set the following upper limits for the
remaining 90% localization region not blocked by the Earth. Using
the representative soft, normal, and hard GRB-like spectral templates
described in arXiv:1612.02395, we set the following 3 sigma flux
upper limits over 10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale  Soft     Normal   Hard
------------------------------------
0.1 s:     4.2-117  8.8-84.  27.-93.
1.0 s:     1.3-35.  2.7-25.  7.8-28.
10  s:     0.4-11.  0.9-7.7  2.4-8.7

Assuming the mean luminosity distance of ~155 Mpc from the GW
detection, we estimate intrinsic luminosity upper limits of
(0.03-5.1)E49 erg/s for the soft template, (0.04-3.4e)E49 erg/s
for the normal template, and (0.2-6.2)E49 erg/s for the hard template
over the 1 keV-10 MeV energy range.
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