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GCN Circular 26315

LIGO/Virgo S191129u: No counterpart candidates in Fermi-LAT observations
2019-11-30T08:56:10Z (5 years ago)
Magnus Axelsson at Stockholm U. <>
M. Crnogorcevic (Univ. of Maryland & NASA/GSFC), E. Bissaldi (Politecnico & INFN Bari), M. Axelsson (KTH & Stockholm Univ.), and F. Longo (University and INFN, Trieste), report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on Nov 29, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S191129u (GCN 26303).

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.

The Fermi Gamma-ray Space Telescope was passing through the South Atlantic Anomaly (SAA) at the time of the trigger (T0 = 2019-11-29 13:40:29.197 UTC). During SAA passages both the LAT and the Gamma-ray Burst Monitor (GBM) do not collect data due to the high charged particle background in this region. The LAT resumed taking data upon exiting the SAA at roughly T0 + 150 s. At that time the instantaneous coverage was ~25% of the LIGO probability map, and reached 100% cumulative coverage after ~6.2 ks.

We performed a search for a transient counterpart within the observed region of the 90% contour of LIGO map in a fixed time window from T0 to T0 + 10 ks. 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, and no additional excesses were found.

Energy flux upper bounds for the fixed time interval between 100 MeV and 1 GeV for this search vary between 5.4e-11 and 2.0e-07 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Milena Crnogorcevic (<>).

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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