HAWC-210507A

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.

Alexis Coleiro (APC/Univ de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration. 

Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported HAWC-210507A alert (event 1010067_1345 <https://gcn.gsfc.nasa.gov/notices_amon_hawc/1010067_1345.amon>). 

No up-going muon neutrino candidate events were detected within the error box of the HAWC event during a +/- 1h time-window centered on the HAWC event time (T0), and over which the potential source remained visible all time in the up-going field of view of ANTARES. At T0, the elevation of the alert was -24 degrees below the horizon for ANTARES. 

This leads to a preliminary 90% confidence level upper limit on the muon-neutrino radiant fluence from a point source of about 15 GeV.cm^-2 over the energy range 4 TeV ��� 4 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and about 37 GeV.cm^-2 (0.7 - 380 TeV) for an E^-2.5 spectrum. A search over an extended time window of +/-1 day has also yielded no detection (45% visibility). 

ANTARES <http://antares.in2p3.fr/> is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky.