GCN Circular 34805

Hugo Ayala (PSU) reports on behalf of the HAWC
collaboration (http://www.hawc-observatory.org/collaboration):

On 2023/10/04 14:39:41.18 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-231004A. Location is at
RA: 143.79 (+1.10/-1.01 deg  90% PSF containment) J2000
Dec: 25.04 (+1.03/-1.21 deg 90% PSF containment) J2000
(GCN circular 34791
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 ,34792
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 ).

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 October 2021. We searched
inside the reported IceCube error region.
The most significant location, with p-value 2.19e-03 (5.13e-02
post-trials),
is at RA 144.67 deg, Dec +24.91 deg (±0.42 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 = 1.11e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1

Search for a transient source.
Since the IceCube event fall inside the HAWC field of view,
we report on the result for the transit of the IceCube
position.

Data acquisition started on 2023/10/04 06:13:44 UTC and ended
2023/10/04 18:28:44 UTC.
The most significant location, with p-value 3.14e-02  (0.53 post-trials),
is at RA 143.17 deg, Dec +24.79 deg (±0.26 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 1.67e-11 (E/TeV)^-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.