GCN Circular 28480
Alberto Carrami��ana (INAOE) and Hugo Ayala (PSU) report on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration): On 2020/09/21 19:07:13 UTC, the IceCube collaboration reported a track-like very-high-energy event that has a moderate probability of being an astrophysical neutrino, IceCube-200921A. Location is at RA: 195.29 (+2.35/-1.73 deg 90% PSF containment) J2000 Dec: 26.24 (+1.51/-1.77 deg 90% PSF containment) J2000 (GCN circular 28468). We performed two types of analyses for the follow-up. The first is for a steady source in archival data and the second is a search for a transient source. We assume a power-law spectrum with an index of -2.3 for both analyses. - Search for a steady source in archival data: The archival data spans from November 2014 to May 2018. We searched inside the reported IceCube error region. The most significant location, with p-value 2.51e-04 (2.85e-02 post-trials), is at RA 193.67 deg, Dec +25.86 deg (��0.10 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit on gamma rays at the maximum position of: E^2 dN/dE = 3.03e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1 - Search for a transient source: The event was in our field of view at the time reported. Data acquisition started on 2020/09/21 16:13:38 UTC and ended 2020/09/21 22:39:47 UTC. The most significant location, with p-value 2.02e-04 (2.30e-02 post-trials), is at RA 197.67 deg, Dec +25.82 deg (��0.17 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit at the position of maximum significance of: E^2 dN/dE = 1.63e-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.