TITLE:   GCN CIRCULAR
NUMBER:  18709
SUBJECT: LIGO/Virgo G184098: Fermi-LAT search for high-energy gamma-ray counterpart
DATE:    15/12/17 22:43:56 GMT
FROM:    Nicola Omodei at Stanford U  <nicola.omodei@stanford.edu>

Nicola Omodei (Stanford), Julie McEnery (GSFC), and Giacomo Vianello 
(Stanford) report on behalf of the Fermi-LAT team:

We have searched Fermi-LAT data for possible high-energy gamma-ray 
emission in spatial/temporal coincidence with the LIGO/Virgo trigger 
G184098. We have mapped the LIGO/Virgo probability map into 8 different 
Region Of Interests (ROIs), each with a radius if 10 degrees centered on 
the following coordinates (J2000, degrees):

a) R.A., Dec. =  132.60,    5.60
b) R.A., Dec. =  144.00,   -6.00
c) R.A., Dec. =  146.00,  -60.00
d) R.A., Dec. =  131.00,  -66.00
e) R.A., Dec. =  115.00,  -68.00
f) R.A., Dec. =   98.00,  -69.00
g) R.A., Dec. =   78.00,  -67.00
h) R.A., Dec. =   63.00,  -60.00


None of the ROIs enters the LAT Field Of View (FOV) prior to 4200 
seconds after the trigger time (2015-09-14 09:50:45 UTC).
For every passage of each ROI inside the LAT FOV within -3/+1 day from 
the trigger, we searched for point-like excess gamma-ray emission 
integrated over the transit time (typically a few thousand seconds). A 
comparison of the distributions of the maximum Test Statistic (TS) 
within the ROIs before and after the trigger shows no significant excess.

The Fermi-LAT point of contact for this candidate is Nicola Omodei 
(nicola.omodei@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.