TITLE:   GCN CIRCULAR
NUMBER:  19743
SUBJECT: HAWC follow up of IceCube 160731
DATE:    16/07/31 14:24:27 GMT
FROM:    Ignacio Taboada at Georgia Inst of Tech  <itaboada@gatech.edu>

I. Taboada (Georgia Tech) reports on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration/):

On July 31, 2016, 1:55:04 UTC, the IceCube collaboration reported a track-like very-high-energy event that has a high probability of being an astrophysical neutrino, IceCube-160731, at RA 215.1090 and Dec -0.4581 (J2000). In HAWC’s sky, the neutrino was at zenith 31.55 deg and setting. We have searched to a steady source as well as a transient source.

* Search for a steady source in archival data from November 2014 to February 2016. Assuming a spectral index of -2.7 we searched in a 1.5 degree circle around IceCube’s reported location. The highest significance, 3.57 sigma, was at RA= 216.43 deg, Dec= 0.15 deg (J2000). Note that there are at least 100 trials in this search, so post-trials significance is lower. We set a time-integrated limit 95% CL upper limit on gamma rays of:

E^2 dN/dE = 2.56e-12 (E/TeV)^-0.7 TeV.cm^-2.s^-1

* We have also searched for transient sources. We have studied the transit of the location (start 2016/07/30 21:28:57 UTC / stop 2016/07/31 02:59:15 UTC). The most significant location, within 1.5 degrees is 1.12 sigma (RA = 214.67 deg, Dec= 1.04 deg, J2000).

HAWC is a very-high-energy gamma-ray observatory operating in Central Mexico at latitude 19 deg. north. Operating day and night with over 95% duty cycle, HAWC has an instantaneous field of view of 2 sr and surveys 2/3 of the sky every day. It is sensitive to gamma rays from 300 GeV to 100 TeV.