The brightest cosmic gamma-ray burst (GRB) ever detected, GRB 221009A, was accompanied by photons of very high energies. These gamma rays may be used to test both the astrophysical models of the burst and our understanding of long-distance propagation of energetic photons, including potential new-physics effects. Here we present the observation of a photonlike air shower with the estimated primary energy of 300 & thorn;43-38 TeV, coincident (with the chance probability of '9 x 10-3) with the GRB in its arrival direction and time. Making use of the upgraded Carpet-3 muon detector and new machine learning analysis, we estimate the probability that the primary was hadronic as '3 x 10-4. This is the highest-energy event possibly associated with any GRB.

—Over the last several years, an increase in the amplitude of a seasonal pressure wave and the concentration of heavy radionuclides in the near-surface layer of the atmosphere has been observed in the area of the Baksan Neutrino Observatory of Institute for Nuclear Research in the North Caucasus. This trend is being investigated along with accompanying anomalies in readings recorded by detectors in the fall and winter of 2017, and the winter and spring of 2021. Hypotheses regarding possible causes of these anomalies are considered.

Isotropic diffuse gamma-ray flux in the PeV energy band is an important tool for multimessenger tests of models of the origin of high-energy astrophysical neutrinos and for new-physics searches. So far, this flux has not yet been observed. Carpet-2 is an air-shower experiment capable of detecting astrophysical gamma rays with energies above 0.1 PeV. Here we report the upper limits on the isotropic gamma-ray flux from Carpet-2 data obtained in 1999–2011 and 2018–2022. These results, obtained with the new statistical method based on the shape of the muon-number distribution, summarize Carpet-2 observations as the upgraded installation, Carpet-3, starts its operation.

In the present work we report on the observation of an excess of gamma-ray candidate events in temporal and spatial coincidence with the IceCube high-energy neutrino alert consistent with the origin in the Cygnus Cocoon region. The observations have been performed with Carpet-2, a surface air-shower detector equipped with a large-area muon detector at the Baksan Neutrino Observatory in the Northern Caucasus. As well as we report about the current state of the Carpet-3 facility, which includes a muon detector with an increased area and an expanded surface array. The main aim of the Carpet-3 facility is the registration of cosmic gamma-rays with energy larger than 100 TeV. Moreover, it gives a possibility to carry out research on the composition of primary cosmic rays around the knee. It is planned that the Carpet-3 EAS array will be operation by the end of 2021.

The Carpet-3 array at the Baksan Neutrino Observatory is designed to detect extensive air showers generated by primary cosmic rays of more than 100 TeV in energy. The main aim is to search for cosmic extrahigh-energy gamma rays. In this work, we describe the current state of the facility and the results from searching for extrahigh-energy photons from regions of the localization of candidates for gravitational-wave events detected by LIGO/Virgo during the third observational period.

A glow in the night sky is registered at 43° north latitude during global magnetospheric disturbances. The glow is preceded by seismic activity generating an underground negative charge over the Earth’s surface with a positive current of 20–25 nA/m 2 .

The Carpet-3 experiment for investigation of gamma radiation with energy above 100 TeV is currently being prepared at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Science. At present the plastic scintillation counters with a total continuous area of 410 m $${}^{2}$$ are installed in the muon detector (MD) underground tunnel, and they are totally equipped with electronics. The counters’ gains and thresholds have been adjusted. Fifteen modules of shower detectors are placed on the surface of the MD absorber. Ten of them contain 9 standard plastic counters with an area of 1 m $${}^{2}$$ each. Also 24 modules without counters are arranged on the territory of the array. These modules will accomplish a surface part of the Carpet-3 array. The preliminary estimates show that the new array will have the best sensitivity to the flux of primary gamma rays with energy in region 100 TeV $$-$$ 1 PeV. The increased area of the surface part of the array gives a possibility to increase the area of location of the shower axis, thereby increasing the statistics of detected events and decreasing the energy threshold for primary cosmic radiation. The Carpet-3 experiment will start data taking at the end of 2021.

Используя метод диагностики электрического состояния грозовой атмосферы по вариациям вторичных частиц космических лучей, регистрируемых установкой «Ковёр» БНО ИЯИ РАН, обнаружено явление взаимного влияния магнитосферной бури и грозовой активности. Установлено, что во время магнитосферных суббурь малой мощности, на предварительной стадии и в начале фазы развития, возможно проникновение магнитосферно — ионосферных возмущений на средние широты (∼40° с.ш.) над грозовыми очагами. Этот эффект проявляется в виде диффузного свечения типа «полярное сияние» яркостью ∼3 ·10-4 кд·м-² и локальных возмущений электрического поля с характерной разностью потенциалов в тропосфере ±100 МВ. Зарегистрировано локальное магнитное возмущение (∼1 нТл), соответствующее возникновению локального вертикального тока в атмосфере, максимум которого совпал с началом взрывной фазы зарождения суббури. Using the method of diagnosing the electrical state of a thunderstorm atmosphere by variations of the secondary particles of cosmic rays recorded by the Carpet air shower array of the Baksan Neutrino Observatory (North Caucasus), the phenomenon of the mutual influence of a magnetic storm and thunderstorm activity was discovered. It has been established that during magnetic substorms of low power, at the preliminary stage and at the beginning of the development phase, penetration of magnetospheric–ionospheric disturbances at mid latitudes (∼400 N) above lightning centers is possible. This effect manifests itself in the form of a diffuse glow of the aurora type with a brightness of ∼3 ·10-4 cd·m-² and local disturbances of the electric field with a characteristic potential difference in the troposphere of order of ±100 MV. A local magnetic disturbance (∼ 1 nT) was recorded, corresponding to the appearance of a local vertical current in the atmosphere, whose maximum coincided with the beginning of the expansion phase of substorm nucleation.

Во время магнитосферной бури 22.06.2015, сопровождаемой Форбуш – понижением, отдельные установки, регистрирующие космические лучи на уровне земли, зафиксировали положительное возмущение интенсивности частиц в период 19:00 –22:00 UT. В работе приводится регистрация указанного всплеска на территории Кавказских гор установкой «Ковёр» БНО ИЯИ РАН. Приводится экспериментальное свидетельство медленного спуска в этот период большого отрицательного заряда с ионосферы на землю.

Во время магнитосферной бури 22.06.2015, сопровождаемой Форбуш – понижением, отдельные установки, регистрирующие космические лучи на уровне земли, зафиксировали положительное возмущение интенсивности частиц в период 19:00 –22:00 UT. В работе приводится регистрация указанного всплеска на территории Кавказских гор установкой «Ковёр» БНО ИЯИ РАН. Приводится экспериментальное свидетельство медленного спуска в этот период большого отрицательного заряда с ионосферы на землю. During a magnetic storm on June 22, 2015, was accompanied by a Forbush decrease, some detectors of cosmic rays on the ground level recorded a positive disturbance of the particle intensity in the period 19:00 – 22:00 UT. This paper presents the data of detecting this burst in the North Caucasus region by the Carpet air shower array of the Baksan Neutrino Observatory. Experimental evidence in favor of a slow transfer in this period of a large negative charge from the ionosphere to the ground is presented.

Используя метод диагностики электрического состояния грозовой атмосферы по вариациям вторичных частиц космических лучей, регистрируемых установкой «Ковёр» БНО ИЯИ РАН, обнаружено явление взаимного влияния магнитосферной бури и грозовой активности. Установлено, что во время магнитосферных суббурь малой мощности, на предварительной стадии и в начале фазы развития, возможно проникновение магнитосферно — ионосферных возмущений на средние широты (∼40° с.ш.) над грозовыми очагами. Этот эффект проявляется в виде диффузного свечения типа «полярное сияние» яркостью ∼3 ·10-4 кд·м-² и локальных возмущений электрического поля с характерной разностью потенциалов в тропосфере ±100 МВ. Зарегистрировано локальное магнитное возмущение (∼1 нТл), соответствующее возникновению локального вертикального тока в атмосфере, максимум которого совпал с началом взрывной фазы зарождения суббури.

The Baksan Neutrino Observatory setups are currently performing search for neutrino and ultra-high-energy gamma-ray counterparts of the events on the Gamma-ray Coordinates Network. The Gamma-ray Coordinates Network is a system for distributing alerts from gamma-ray bursts, transients. Muon neutrinos and antineutrinos with energies above 1 GeV are registered with the Baksan Underground Scintillation Telescope. Ultra-high-energy gamma rays are registered with the ‘‘Carpet-2’’ setup. Registration of events and analysis of alerts occurs in near-real time. Alerts from Swift BAT, Fermi-GBM, Fermi-LAT, INTEGRAL, IceCube, HAWC are used. This work presents the description of the alert processing program and preliminary results.

The Carpet-3 air shower array is being built at the Baksan Neutrino Observatory, which is located near Mount Elbrus (North Caucasus) at an altitude of 1700 m above sea level. The main aim of the experiment is gamma-ray astronomy in the energy range above 100 TeV to search for diffuse gamma radiation and sources and to study the generation mechanisms of this radiation. The paper provides an overview of the current state of the experiment, as well as its prospects.

The mechanisms of origin of ultrahigh-energy gamma radiation are poorly studied. One way to find out is to search for temporal and directional coincidences of high-energy galactic neutrinos with photons of similar energies. The results of such a search could provide indications of the hadronic origin of this radiation. In this paper, we report on the search for photons with energies above 300 TeV in coincidence with high–energy neutrinos. The searches of ultrahigh–energy gammas were carried out at the Carpet–2 EAS array, using three years of data taking.

Galactic sites of acceleration of cosmic rays to energies of order 10 15 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In 2020 November, the IceCube neutrino observatory reported an ∼150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1 σ (post-trial) excess of atmospheric air showers from the same direction, observed by the Carpet–2 experiment and consistent with a few months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma-rays in a Galactic source.

We report on the search of astrophysical gamma rays with energies in the 100 TeV to several PeV range arriving in directional and temporal coincidence with public alerts from HAWC (TeV gamma rays) and IceCube (neutrinos above ∼ 100TeV). The observations have been performed with the Carpet-2 air-shower detector at the Baksan Neutrino Observatory, working in the “photon-friendly” mode since 2018. Photon candidate showers are selected by their low muon content. No significant excess of the photon candidates have been observed, and upper limits on gamma-ray fluences associated with the alerts are obtained. For events with good viewing conditions, the Carpet-2 effective area for photons is of the order of the IceCube effective area for neutrinos of the same energy, so the constraints start to probe the production of neutrinos in fast flares of Galactic sources.