TITLE: GCN CIRCULAR NUMBER: 25411 SUBJECT: IceCube-190819A - HAWC follow-up DATE: 19/08/20 16:20:00 GMT FROM: Antonio Galvan at Inst.de Astronomia,UNAM Antonio Galvan (IA-UNAM), Israel Martinez-Castellanos (UMD) report on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration/): On August 19, 2019 at 17:34:24.24, the IceCube collaboration reported a track-like very-high-energy event that has a high probability of being an astrophysical neutrino, IceCube-190819A, at RA = 148.80 deg and Dec = 1.38 deg, J2000 (GCN circular 25402). In HAWC's sky, the neutrino was at zenith of 23.00 deg and setting. We have searched for a steady source as well as a transient source. * Search for a steady source in archival data from November 2014 to May 2018. Assuming a spectral index of -2.3 we searched in a 9.29 degree square around IceCube's reported location. The highest significance, 2.68 sigma, was at RA = 148.36 deg, Dec = 1.60 deg (J2000). Note that there are at least 46 trials in this search, so the post-trials significance is 0.96. We set a time-integrated upper limit 95% CL on gamma rays of: E^2 dN/dE = 3.20643e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1. * Search for a transient source. We integrated from 19:00 UTC to 21:22 UTC. Due to maintaince, we did not collect data during the period 15:42 UTC to 19:00 UTC,during which the IceCube location would had been otherwise observable by HAWC. For this observed period,the most significant location, within the 9.29 degree square,is 2.29 sigma (RA = 148.37 deg, Dec = 1.70 deg, J2000) with a post-trials significance of 0.027. We set a time-integrated upper limit 95% CL on gamma rays of: E^2 dN/dE = 2.3535e-11 (E/TeV)^-0.3 TeV cm^-2 s^-1. 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.