[vsnet-grb-info 22544] LIGO/Virgo S190521r: Coverage and upper limits from Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24643
SUBJECT: LIGO/Virgo S190521r: Coverage and upper limits from Fermi-LAT observations
DATE:    19/05/21 18:17:12 GMT
FROM:    Elisabetta Bissaldi at INFN,Bari  <elisabetta.bissaldi at ba.infn.it>

E. Bissaldi (Politecnico & INFN Bari), M. Axelsson (KTH & Stockholm Univ.),
and D. Tak (Univ. of Maryland),
report on behalf of the Fermi-LAT Collaboration:


We have searched data collected by the Fermi Large Area Telescope (LAT)
on May 21, 2019, for possible high-energy (E > 100 MeV)
gamma-ray emission in spatial/temporal coincidence with
the LIGO/Virgo trigger S190521r (GCN 24632).

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 a time, and "cumulative coverage" as the integral of the
instantaneous coverage over time.
Fermi-LAT had instantaneous coverage of ~50% of the LIGO probability
at the time of the trigger (T0 = 2019-05-21 07:43:59.463 UTC),
and reached 100% cumulative coverage after ~4.3 ks.

We performed a search for a transient counterpart within
the observed region of the 90% contour of the LIGO map
in a fixed time window from T0 to T0+10 ks.
No significant 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
3.0e-10 and 6.4e-09 [erg/cm^2/s].


The Fermi-LAT point of contact for this event is Donggeun Tak
(takdg123 at umd.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.