Pis’ma v ZhETF, vol. 109, iss. 4, pp. 223 - 223

February 25

Carpet-2 search for PeV gamma rays associated with IceCube

high-energy neutrino events

D. D. Dzhappuev⁺, I. M. Dzaparova^+∗, E. A. Gorbacheva⁺, I. S. Karpikov⁺, M. M. Khadzhiev⁺, N. F. Klimenko⁺,

A. U. Kudzhaev⁺, A. N. Kurenya⁺, A. S. Lidvansky⁺, O. I. Mikhailova⁺, V. B. Petkov^+∗, K. V. Ptitsyna⁺,

V. S. Romanenko⁺, G. I. Rubtsov⁺, S. V. Troitsky⁺¹⁾, A. F. Yanin⁺, Ya. V. Zhezher⁺

⁺Institute for Nuclear Research of the Russian Academy of Sciences, 117312 Moscow, Russia

^∗Institute of Astronomy, Russian Academy of Sciences, 119017 Moscow, Russia

Submitted 6 December 2018

Resubmitted 6 December 2018

Accepted 14

December 2018

DOI: 10.1134/S0370274X19040039

Carpet-2 is an air-shower array at Baksan Valley,

Galactic sources arrive to the observer without a signif-

Russia, equipped with a large-area (175 m²) muon de-

icant attenuation, while those from beyond the Galaxy

tector, which makes it possible to separate primary pho-

lose their energy in the pair-production processes; their

tons from hadrons. We report the first results of the

energy is transferred to the band observed by Fermi LAT

search for primary photons with energies E_γ > 1 PeV,

through electromagnetic cascades.

directionally associated with IceCube high-energy neu-

We performed a search for photon-like events from

trino events, in the data obtained in 3080 days of Carpet-

the directions coincident with the arrival directions of

2 live time.

IceCube events. We did not find any statistically sig-

The origin of high-energy (E ≳ 100 TeV) astrophys-

nificant excess of such events over the isitropic back-

ical neutrinos detected in recent years by the IceCube

ground. For 34 published IceCube events in the field of

experiment remains one of the most intriguing problems

view of the installation and having the uncertainty in

in modern astroparticle physics. The arrival directions

the arrival direction not worse than 3^◦, the stacked flux

of these neutrinos do not demonstrate any significant ex-

of photons with energies E_γ ≥ 1 PeV from these direc-

cess towards the Galactic disk, as it would happen for

tions is bounded from above by 1.06 × 10^-14 cm^-2 s^-1

most models of Galactic sources, while serious tensions

at the confidence level of 95 % (assuming the steady

with Fermi-LAT observations of the diffuse gamma-ray

flux). In addition, the neutrino event of December 10,

flux are present for extragalactic source models.

2016, happened in the field of view of the operating

In most astrophysical scenarios, energetic neutrinos

installation, which allowed to constrain the fluence of

are produced in decays of charged pions and are ac-

the hypothetical burst event in E_γ ≥ 1 PeV photons by

companied by gamma rays of the same energy from de-

< 5.4 × 10^-5 PeV/cm² (95 % CL).

cays of neutral pions. Energetic gamma rays produce

The Carpet-3 installation with a 410 m² muon detec-

electron-positron pairs when propagating through the

tor and additional surface stations, to be commissioned

background radiation. The mean free path of gamma

in 2019, will have a much better gamma-ray sensitivity

rays with energies E_γ ∼ (0.1-10) PeV, similar to those

and a lower energy threshold, ∼ 100 TeV.

of IceCube neutrinos, is of order of the size of a galaxy,

and therefore they become an important diagnostic tool

Full text of the paper is published in JETP Letters

for the origin of neutrinos: accompanying photons from

journal. DOI: 10.1134/S0021364019040015

¹⁾e-mail: st@ms2.inr.ac.ru

Письма в ЖЭТФ том 109 вып. 3 - 4

2019

223