GCN Circular 26708
On 2020-01-08 at 09:30:14 UTC, the AMON Fermi-LAT+ANTARES stream detected a coincident event with a false alarm rate of 2.39 per year. Location of the coincidence is at RA: 43.48 J2000 Dec: -18.06 J2000 with an uncertainty of 0.832 deg (90% containment) https://gcn.gsfc.nasa.gov/gcn3/26674.gcn3 (GCN circular 26674). 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 reported error region from the circular. The highest significance, 1.76 sigma (0.17 post-trials), is at RA 44.52 deg, Dec -18.52 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 = 9.24e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1 Search for a transient source. Since the coincident alert fall outside the HAWC field of view, we report on the result for the transit before and after the event. Data acquisition started on Data Start: 2020/01/07 03:54:26 UTC and ended 2020/01/09 04:01:36 UTC. The most significant location, with 1.60 sigma (-0.26 post-trials), is at RA 44.03 deg, Dec -18.41 deg (+- 1.80 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit at the position of maximum significance of: E^2 dN/dE = 2.38e-11 (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.