[vsnet-grb-info 21121] IceCube-180908A: HAWC follow-up

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23219
SUBJECT: IceCube-180908A: HAWC follow-up
DATE:    18/09/11 00:51:53 GMT
FROM:    Israel Martinez at HAWC  <imc at umd.edu>

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

On 2018/09/08 19:59:31.84 UT IceCube detected a track-like,
very-high-energy event with a high probability of being of
astrophysical origin, at RA=144.58d and Dec=-2.13d J2000
as reported in GCN circular 23214.

The event was not in the field of view of HAWC, so we
analyze the data in three timescales:

*We searched for a steady source in archival data from November
2014 to April 2018.  Assuming a spectral index of -2.5 we
searched in the reported 90% PSF containment circle.The maximum
significance is 1.2 sigma at RA=143.9deg and Dec=-1.8deg. We
estimate the number of trials to be ~40. We set an upper limit
95% CL on gamma rays for this period of:

E^2 dN/dE = 6.4e-13 (E/TeV)^-0.5 TeV cm^-2 s^-1.

*We searched using data corresponding to the month previous
to the IceCube-180908A alert (MJD 58340.674-58370.815). Using
the same spectral index and search window, the maximum significance
is 1.0 sigma at RA=144.7deg and Dec=-2.8deg. We set an upper limit
95% CL on gamma rays for this period of:

E^2 dN/dE = 2.9e-12 (E/TeV)^-0.5 TeV cm^-2 s^-1.

*We also performed a study using data corresponding to the two
nearest transits of IceCube-180908A in HAWC’s field of view
(MJD 58369.59-58369.81 and 58370.59-58370.81). Using the same
spectral index and search window, the maximum significance is
0.6 sigma at RA=145.0deg and Dec=-1.8deg. We set an upper limit
95% CL on gamma rays for this period of:

E^2 dN/dE = 1.6e-11 (E/TeV)^-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 24 hours
per day 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.