GCN Circular 23382

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

On 2018/10/23 16:37:32.65 UTC IceCube detected a track-like, very-high-energy event with a high probability of being of astrophysical origin, at RA=270.18d and Dec=-8.57d (J2000) as reported in GCN circular 23375
Not found
 
 
.

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 2.6 sigma at RA=270.62d and Dec=-8.88d. We estimate the number of trials to be ~100. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 1.1e-12 (E/TeV)^-0.5 TeV cm^-2 s^-1.

*We searched using data corresponding to the month previous to the IceCube-181023A alert (2018-09-25 21:48 to 2018-10-25 00:41 UTC). Using the same spectral index and search window, the maximum significance is 1.6 sigma at RA=269.34d and Dec=-9.22d. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 3.9e-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-181023A in HAWC's field of view (2018/10/22 12:35:33 to 2018/10/24 00:55:13 UTC). Using the same spectral index and search window, the maximum significance is 2.1 sigma at RA=269.69d and Dec=-9.29d. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 4.0e-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.