GCN Circular 26828
Hugo Ayala (PSU) reports on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration): On 2020/01/17 11:08:29 UTC, the IceCube collaboration reported a track-like very-high-energy event that has a high probability of being an astrophysical neutrino, IceCube-200109A. Location is at RA: 116.24 (+0.71/-1.24 90% PSF containment) J2000 Dec: 29.14 (+0.9/-0.78 deg 90% PSF containment) J2000 https://gcn.gsfc.nasa.gov/gcn3/26802.gcn3 (GCN circular 26802). 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 November 2019. We searched inside the IceCube error region from the circular. The highest significance, 1.97 sigma (0.23 post-trials), is at RA 116.02 deg, Dec 29.78 deg (+-1.8 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 = 2.32e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1 Search for a transient source. Since the IceCube event falls inside the HAWC field of view, we report on the result for the current transit of the IceCube position. Data acquisition started on Data Start: 2020/01/16 09:26:45 UTC and ended 2020/01/18 09:41:14 UTC. The most significant location, with 2.74 sigma (1.63 post-trials), is at RA 116.85 deg, Dec 29.40 deg (+-1.78 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit at the position of maximum significance of: E^2 dN/dE = 8.11e-12 (E/1TeV)^-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.