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GCN Circular 21616

LIGO/Virgo G298389 : Fermi-LAT search for a high-energy gamma-ray counterpart
2017-08-20T13:32:33Z (7 years ago)
Daniel Kocevski at NASA/MSFC <>
D. Kocevski (NASA/GSFC), S. Buson (NASA/GSFC), N. Omodei (Stanford), and G. Vianello (Stanford) report on behalf of the Fermi-LAT team: 

We 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 G298389. At the time of the trigger (T0 = 2017-08-19 15:50:47.999, 524850652.999 MET), the Fermi gamma-ray space telescope was within the South Atlantic Anomaly (SAA).  During SAA passages the LAT does not collect data due to the high charged particle background in this region. The LAT resumed data taking upon exiting the SAA at roughly T0 + 460s,  At that time 26% of the LIGO/Virgo probability map was in the LAT field of view, and we reached 100% cumulative coverage within 9779 s after the trigger. 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/Virgo map in the time window from T0 to T0 + 10 ks, and no significant new sources are found. Similarly, the Automated Science Processing search, which looks for variation in flux from known sources and for new transients on a variety of time scales (Chiang 2012), did not detect any new transient consistent within the 90% contour of the G298389 map, during a six-hour interval from T0-3hr to T0+3hr.

The Fermi-LAT point of contact for this event is Daniel Kocevski ( 

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.
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