[vsnet-grb-info 24353] LIGO/Virgo S191215w: No counterpart candidates in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26452
SUBJECT: LIGO/Virgo S191215w: No counterpart candidates in Fermi-LAT observations  
DATE:    19/12/16 16:07:54 GMT
FROM:    Nicola Omodei at Stanford U.  <nicola.omodei at slac.stanford.edu>

N. Omodei (Stanford Univ.), M. Arimoto (Kanazawa Univ.), M. Axelsson (KTH & Stockholm Univ.),  F. Longo (University and INFNN, Trieste), D. Kocevski (NASA/MSFC), and M. Crnogorcevic (Univ. of Maryland & NASA/GSFC)

report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on December 15th, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S191215w (GCN 26441). 

We define "instantaneous coverage" as the integral over the region of the LIGO/Virgo 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. 

Fermi-LAT had an instantaneous coverage of ~56% of the LIGO probability at the time of the trigger (T0 = 2019-12-15 22:30:52 UTC), and reached 100% cumulative coverage after ~2.5 ks. 

We performed a search for a transient counterpart within the observed region of the 90% contour of LIGO/Virgo 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 3E-10 and 4E-9 [erg/cm^2/s].  

The Fermi-LAT point of contact for this event is  N. Omodei (nicola.omodei at stanford.edu).

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.