GCN Circular 21924

Israel Martinez (University of Maryland) and
Ignacio Taboada (Georgia Tech)
report on behalf of the HAWC collaboration
(https://www.hawc-observatory.org/collaboration/):

On 2017/09/22 20:54:30.43 UTC IceCube detected a track-like,
very-high-energy event with a high probability of being of astrophysical
origin, at RA=77.43d and Dec=5.72d J2000. The up-to-date values were
reported in GCN circular 21916
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 .

Two analyses were performed:

* Search for a steady source.
This analysis was performed on archival data from November 2014 to
June 2017. Assuming a spectral index of -2.5 we searched in a 1.3deg
circle around the IceCube reported location.The maximum significance is
3.5 sigma at RA=76.29deg and Dec=5.04deg. We estimate the number of trials
to be ~130. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 5.62e-15 (E/7TeV)^-0.5 TeV cm^-2 s^-1.

* Search for a transient source.
The event location was not in HAWC's FOV at the time of detection, so
this analysis was performed using data corresponding to the two nearest
transits (MJD 58018.35-59018.60 and 58019.35-59019.60). Using the same
spectral index and search window, the maximum significance is 2.4 sigma at
RA=76.45deg and Dec=5.58deg. We set an upper limit 95% CL on gamma rays
for this period of:

E^2 dN/dE = 2.26e-13 (E/7TeV)^-0.5 TeV cm^-2 s^-1.

HAWC is a very-high-energy gamma-ray observatory located in
Central Mexico at latitude 19 deg North. It operates 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.