TITLE: GCN CIRCULAR NUMBER: 29958 SUBJECT: Alert from the HAWC Burst Monitor HAWC-210507A DATE: 21/05/07 15:56:02 GMT FROM: Hugo Ayala at Pennsylvania State University The HAWC Collaboration (http://www.hawc-observatory.org/collaboration/) reports: On May 07, 2021, at 10:38:22 UT, HAWC detected a burst signal from its Burst Monitoring named HAWC-210507A. This monitor system looks for excesses above the expected background in time windows of 0.2, 1, 10 and 100 seconds. This event was found in the 10-second time window starting at the reported trigger time. The position of the alert is RA (J200): 257.24 deg Dec (J2000): 8.08 deg Location uncertainty (68% containment): 0.4 deg (statistical only). The monitor system found that this alert has a false alarm rate of 3.76 alert(s) per year. We encourage follow-up observations of the HAWC alert region. We however note that it is consistent with background expectation based on the observation time. The initial automated alert is recorded here: https://gcn.gsfc.nasa.gov/notices_amon_hawc/1010067_1345.amon 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.