Carpet-2 limits on E>100 TeV gamma rays associated with the IceCube 201120A neutrino alert in the Cygnus Cocoon
ATel #14237; D. Dzhappuev, A. Kudzhaev, V. Petkov, S. Troitsky on behalf of the Carpet-2 group (INR RAS)
on 2 Dec 2020; 05:34 UT
Credential Certification: Yuri Y. Kovalev (yyk@asc.rssi.ru)
Subjects: VHE, UHE, Neutrinos, Transient
Referred to by ATel #: 14255
Despite considerable progress, the origin of astrophysical neutrinos with energies above 100 TeV remains uncertain. A part of them may come from Galactic sources; in this case accompanying gamma rays of similar energies can reach the Earth. Here we present the first ever constraints on the E>100 TeV gamma-ray emission associated with a neutrino alert from a possible Galactic source.
On MJD 59173.4, the IceCube Collaboration reported (GCN #28927) a 154-TeV neutrino from the direction RA=307.53 (+5.34, -5.59) deg, Dec=+40.77 (+4.97, -2.80) deg consistent with the Cygnus Cocoon. This star-forming region was discussed as a particle acceleration site (see Bykov at al. 2020) and a possible neutrino source (Yoast-Hull et al. 2017).
Carpet-2 is an air-shower array at Baksan Neutrino Observatory of the Institute for Nuclear Research of the Russian Academy of Sciences, capable of detecting cosmic gamma rays above 100 TeV (see Dzhappuev et al. 2020 for the description of neutrino-alert analyses and further references). The direction of the Cygnus Cocoon was 10 degrees out of the field of view of Carpet-2 at the time of the neutrino arrival, so we report the result of the search for gamma-ray candidate events over the time interval +/-12 hours around the time. No E>100 TeV photon candidates have been observed, which results in the upper limit on the fluence of <4.2 GeV/cm2 (95% CL), <3.3 GeV/cm2 (90% CL), assuming E-2 spectrum. Assuming the effective area for BRONZE IceCube alerts at Dec.>+30 deg. from IceCube (2019), the fluence in a single 154-TeV neutrino event would be ~3 GeV/cm2, close to our upper limit.
In addition, assuming a steady source in the neutrino arrival direction, we found no excess of E>100 TeV gamma-ray candidates above the background in 700 live days of Carpet-2 data taking in 2018-2020, which results in in the upper limit of <1.1*10-13 cm-2 s-1 (95% CL) on the integral E-2 flux of gamma rays above 100 TeV from this direction.
