Difference: GCNCIRCULAR20756 ( vs. 1)

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.

-- ThomasKupfer - 27 Feb 2017