GCN Circular 26937

M. Axelsson (KTH & Stockholm Univ.), F. Longo (University and INFN,  
Trieste), M. Kovacevic (INFN Perugia), E. Bissaldi (Politecnico & INFN  
Bari), D. Kocevski (NASA/MSFC), N. Omodei (Stanford Univ.) and M.  
Arimoto (Kanazawa University) report on behalf of the Fermi-LAT  
Collaboration:

We have searched data collected by the Fermi Large Area Telescope  
(LAT) on January 29, 2020, for possible high-energy (E > 100 MeV)  
gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo  
trigger S200129m (GCN 26926
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 ).

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. At the time of the trigger (T0 =  
2020-01-29 06:54:58.435 UTC), no part of the LIGO probability map was  
observable by Fermi-LAT. The region entered the LAT field of view  
around T0 + 3 ks, and 100% cumulative coverage was reached after ~8.8  
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 +  
3 ks to T0 + 10 ks. No significant new sources were 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 2.9e-10 and 7.1e-10 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Makoto Arimoto  
(arimoto@se.kanazawa-u.ac.jp)

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.