[vsnet-grb-info 26609] Alert from the HAWC Burst Monitor HAWC-201019A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28709
SUBJECT: Alert from the HAWC Burst Monitor HAWC-201019A
DATE:    20/10/21 00:08:10 GMT
FROM:    Hugo Ayala at Pennsylvania State University  <hgayala at psu.edu>

The HAWC Collaboration  (http://www.hawc-observatory.org/collaboration/)
reports:
On 2020-10-19, at 21:43:42 UT, HAWC detected a burst signal
from its Burst Monitoring named HAWC-201019A. 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 100-second time window starting
at the reported trigger time.
The position of the alert is
RA (J200): 203.148 deg
Dec (J2000): 29.717 deg
Location uncertainty (68% containment): 0.6 deg (statistical only).

The monitor system found that this alert has a false alarm rate of 2.37
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/gcn/notices_amon_hawc/1009678_72.amon
We note that a quick search on the FAVA monitoring
(https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/), an old
alert, FAVA_223_2, is 0.29 deg away from HAWC-201019A, which
occurred on 2012-11-05 15:43:35.
See:
https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/LightCurve.php?ra=203.148&dec=29.717

The source 4FGL J1330.7+2933 is located 0.43 deg away from HAWC-201019A
and is also positionally consistent with the FAVA event.

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.