HAWC gamma ray data prior to IceCube-170922A
ATel #10802; Israel Martinez, Ignacio Taboada, Michelle Hui and Robert Lauer for the HAWC collaboration
on 30 Sep 2017; 02:10 UT
Credential Certification: Ignacio Taboada (firstname.lastname@example.org)
IceCube has reported a very-high-energy neutrino candidate, IceCube-170922A, on 2017/09/22 20:54:30.43 UT and located at RA=77.43d and Dec=5.72d, J2000 (Kopper, Blaufuss et al., GCN circular 21916). At the neutrino candidate time, this location was not in HAWC's field of view. So we examined this location's transits just prior and just after the neutrino candidate time. Limits on these 2 transits as well as all HAWC time integrated data available have been presented (Martinez, Taboada, et al. GCN circular 21924).
Fermi reported an increase in gamma ray activity from TXS 0506+056 from September 15 to September 27. TXS 0506+056 is a blazar within the candidate's uncertainty region (Tanaka, et al. ATel 10791 ). We have now also examined the time period that most closely matches Fermi's observation (from 2017-09-15 09:04:47 UT to 2017-09-19 14:41:33 UT and from 2017-09-21 08:41:11 UT to 2017-09-27 14:10:06 UT). The one transit gap in data collection is due to HAWC's power outage following Mexico's earthquake on September 19. We find no evidence for gamma ray emission during this 12 day time period. We have placed a limit on the spectrum at 1 TeV:
3.84e-13 TeV^-1 cm^-2 s^-1 (index=-2, 95% C.L.)
Null observations in the VHE band have also been reported by HESS on two consecutive nights (de Naurois, et al. ATel 10787) starting on 23 September 2017 at 01:05 UTC and starting 24 September 2017 at 03:10 UTC. We will continue to monitor this source.
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.