TITLE: GCN CIRCULAR NUMBER: 25936 SUBJECT: IceCube-191001A: HAWC follow-up DATE: 19/10/03 13:58:22 GMT FROM: Hugo Ayala at Pennsylvania State University Hugo Ayala reports on behalf of the HAWC collaboration ( http://www.hawc-observatory.org/collaboration/): On 2019/10/01 at 20:09:18.17 UTC, the IceCube collaboration detected a track-like event with a high probability of being of astrophysical origin named IceCube-1901001A. The revised position is RA= 314.08 deg and Dec= 12.94 deg, J2000 (GCN circular 25913). We have performed a search in our archival data for a steady source as well as a transient source. We assume a power-law spectrum with a spectral index of -2.3. We use this spectrum for both analyses. * Search for a steady source: Archival data from November 2014 to May 2018 is used. We searched inside the uncertainty region reported by IceCube in the circular (8.82 deg x 2.97 deg). The highest significance found is 4.03 sigmas, at RA= 313.46 deg, Dec= 14.48 deg (J2000). Note that there are at least 133 trials in this search, so the post-trials significance is consistent with a non-detection. We set a 95% CL time-integrated upper limit on the gamma-ray flux of E^2 dN/dE = 2.3e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1. *Search for a transient source: Since the event was not in our field of view at the time reported on the GCN we report the combined result for the transit before and after the time of the IceCube event. We obtain the following results: Data acquisition started on 2019/09/30 05:46:52 UTC and ended 2019/10/02 06:03:29 UTC. The most significant location, with a pre-trials value of 2.55 sigma, is at RA= 313.84 deg, Dec= 12.71 deg (J2000). We set a time-integrated 95% CL upper limit on the gamma-ray flux at the position of maximum signficance of: E^2 dN/dE = 3.51e-13 (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.