GCN Circular 20756
Subject
LIGO/Virgo G275404: Fermi-LAT search for a high-energy gamma-ray counterpart
Date
2017-02-26T18:56:25Z (8 years ago)
From
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
D. Kocevski (NASA/MSFC), N. Omodei (Stanford), G. Vianello (Stanford), J. L. Racusin (NASA/GSFC),
S. Buson (NASA/GSFC) report on behalf of the Fermi-LAT team:
We have searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy
(E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger
G275404.
Fermi-LAT had an instantaneous coverage of ~10% at the time of the trigger (T0 = 2017-02-25
18:30:21.374 UTC), and reached 100% cumulative coverage within ~8 ks. We define "instantaneous
coverage" as the integral over the region of the LIGO probability map that is within the LAT field of
view at a given time, and "cumulative coverage" as the integral of the instantaneous coverage over
time.
We performed a search for a transient counterpart within the 90% contour of the LIGO map in the
time window from T0 to T0 + 10 ks, and no significant new sources are found.
We also performed a search which adapted the time interval of the analysis to the exposure of each
region of the sky. No significant candidate counterpart was found.
The position of the AGILE candidate counterpart (Tavani et al., GCN 20754) was outside of the LAT
field of view at the time of the LIGO event until T0+3.5 ks. Searching over an interval from T0+3.5 to
T0+6.7 ks, we do not find any significant excess at the AGILE position, placing an upper limit in the
100 MeV - 100 GeV band of 3e-10 erg/cm2/s.
Using LAT Low Energy (LLE) data (Pelassa et al 2010), we perform a counting analysis at energies
>30 MeV. LLE is a loose event selection allowing for larger incident angles and lower energies with
respect the standard LAT likelihood analysis. We searched for excesses coincident with the AGILE
candidate at the time of the LIGO trigger, and found no significant excess.
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to
greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in
the U.S. and many scientific institutions across France, Italy, Japan and Sweden.