GCN Circular 23219
Israel Martinez (University of Maryland) and Ignacio Taboada (Georgia Tech) report on behalf of the HAWC collaboration (https://www.hawc-observatory.org/collaboration/): On 2018/09/08 19:59:31.84 UT IceCube detected a track-like, very-high-energy event with a high probability of being of astrophysical origin, at RA=144.58d and Dec=-2.13d J2000 as reported in GCN circular 23214. The event was not in the field of view of HAWC, so we analyze the data in three timescales: *We searched for a steady source in archival data from November 2014 to April 2018. Assuming a spectral index of -2.5 we searched in the reported 90% PSF containment circle.The maximum significance is 1.2 sigma at RA=143.9deg and Dec=-1.8deg. We estimate the number of trials to be ~40. We set an upper limit 95% CL on gamma rays for this period of: E^2 dN/dE = 6.4e-13 (E/TeV)^-0.5 TeV cm^-2 s^-1. *We searched using data corresponding to the month previous to the IceCube-180908A alert (MJD 58340.674-58370.815). Using the same spectral index and search window, the maximum significance is 1.0 sigma at RA=144.7deg and Dec=-2.8deg. We set an upper limit 95% CL on gamma rays for this period of: E^2 dN/dE = 2.9e-12 (E/TeV)^-0.5 TeV cm^-2 s^-1. *We also performed a study using data corresponding to the two nearest transits of IceCube-180908A in HAWC���s field of view (MJD 58369.59-58369.81 and 58370.59-58370.81). Using the same spectral index and search window, the maximum significance is 0.6 sigma at RA=145.0deg and Dec=-1.8deg. We set an upper limit 95% CL on gamma rays for this period of: E^2 dN/dE = 1.6e-11 (E/TeV)^-0.5 TeV cm^-2 s^-1. HAWC is a very-high-energy gamma-ray observatory located in Central Mexico at latitude 19 deg North. It operates 24 hours per day 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.