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.

This paper presents the results of applying the matrices of silicon photomultipliers (SiPMs) as multichannel photodetectors for the scintillation detectors based on a liquid scintillator. We consider the possibility of using the SiPM matrices with an appropriate optical collector to obtain an image of the luminous tracks of charged particles passing through a scintillator. Such a method allows one to obtain an image of an event inside the scintillator volume, the analysis of which makes it possible to separate different classes of events. It is expected that the proposed particle detection technique may be useful in the creation of new large detectors for neutrino astrophysics and geophysics. The detector is an acrylic sphere with a diameter of 500 mm, filled in with a liquid scintillator. The scintillator is viewed through an optical collector based on two Fresnel lenses with two matrices of 64 SiPMs. The paper describes the data collection system and the detector design, we also demonstrate a three-dimensional image of a recorded event.

В статье дается краткий обзор детекторов, которые способны регистрировать нейтринную вспышку от сверхновой (СН). Представлен статус эксперимента по регистрации нейтринных вспышек на Баксанском подземном сцинтилля- ционном телескопе ИЯИ РАН. Обсуждается возможная связь нейтрино от СН с экспериментами по поиску легкой темной материи (с массой частиц ≤ МэВ). The article gives a brief overview of the detectors that are capable of registering a neutrino burst from a supernova (SN). The status of the experiment on registration of neutrino bursts at the Baksan underground scintillation telescope of the INR RAS is presented. A possible connection between SN neutrinos and experiments on the search for light dark matter (with a particle mass of ≤ MeV) is discussed

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.

Baksan underground scintillation telescope (BUST) operates under the program of neutrino burst search since the middle of 1980. We report the current status of the experiment and the results associated with analysis of background events and facility operation stability. We demonstrate the BUST potentialities in detecting neutrino bursts from close supernovae. Over the period from 30.06.1980 to 30.06.2021, the observation time is 35.5 years. During this time, not a single candidate for a neutrino burst has been registered. This leads to an upper bound of the mean frequency of gravitational collapses of stars in our Galaxy of 0.065 year–1 at the 90% confidence level.

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.

At present in the Institude for Nuclear Research of RAS has been working on the creation of a large-volume scintillation detector at the Baksan Neutrino Observatory (BNO) to register natural low-energy neutrino fluxes, including from astrophysical sources. One of the prototypes of such a detector being developed at the BNO is an acrylic sphere with the diameter of 500~mm filled with a liquid scintillator. Matrices of silicon photomultipliers (SiPM) as photosensors are used to measure the total light output from the interaction of particles in a scintillator and to obtain images of such events. This approach makes it possible to separate useful events from background ones and thereby to lower the background when monitoring Supernova explosions in our Galaxy. The paper describes the prototype of a large-volume detector and presents the measurement results.

The results of searching for neutrino events from the blazar PKS 0735+17 at the Baksan Underground Scintillation Telescope (BUST) are presented. A neutrino from the PKS 0735+17 region was detected at BUST on December 4, 2021, during a strong outburst of this object, coinciding with an observed Fermi LAT gamma-ray outburst. The BUST neutrino event preceded the detections of high-energy neutrino events from the PKS 0735+17 region by IceCube, Baikal-GVD, and KM3NeT.

Using data of the Baksan Underground Scintillation Telescope we have searched for muon neutrinos and antineutrinos with energies above 1 GeV coinciding with the gravitational wave (GW) event GW170817 that was recorded on August 17, 2017, by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo observatories. This is the first detection of the new type of events occurring as a result of a merger of two neutron stars in a binary system. A short gamma-ray burst (GRB) GRB170817A accompanying this event is evidence of particle acceleration in the source whose precise position was determined by detection of the subsequent optical signal. No neutrino signals were found with the Baksan Underground Scintillation Telescope in the interval ±500 s around the moment of the gravitational wave event GW170817, as well as during the next 14 days. The upper limits on integral fluxes of muon neutrino and antineutrino from the source are derived.

The LIGO/Virgo collaborations have reported the results of their searches for gravitational-waves from the first half of their third observing run. 39 events were combined into the second Gravitational-Wave Transient Catalog (GWTC-2), reaching the total number of 50. In addition to these, two neutron star - black hole merger events were also confirmed. The search for neutrino counterparts of LIGO/Virgo gravitational-wave events was performed on the Baksan Underground Scintillation Telescope. The processing algorithm and the results of the counterpart search are described.

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.

В последние годы в ИЯИ РАН ведутся работы по созданию в Баксанской нейтринной обсерватории (БНО) сцинтилляционного детектора большого объема. Детектор будет являться частью мировой сети нейтринных детекторов. Один из разрабатываемых в БНО прототипов такого детектора представляет собой акриловую сферу диаметром 500 мм, заполненную жидким сцинтиллятором. В качестве фотоприемников используются матрицы кремниевых фотоэлектронных умножителей (КФЭУ). Такие фотоприемники уже много лет используются в различных физических экспериментах. В нашем случае, в отличие от других экспериментов, матрицы КФЭУ применяются не только для измерения общего световыхода от взаимодействия частиц в сцинтилляторе, но и для получения изображений таких событий. Данный подход позволит отделять полезные (нейтринные) события от фоновых и в том числе проводить мониторинг взрывов Сверхновых в нашей Галактике. Характеристики оптического коллектора прототипа детектора определяются акриловой сферой и линзами Френеля диаметром 300 мм и фокусным расстоянием 120 мм. В качестве фотоприемников выбраны матрицы КФЭУ фирмы SensL (ARRAYJ-60035-64P-PCB). Проведены измерения просматриваемого матрицами объема с помощью закрепленного на рычаге светодиода. Описана система сбора данных MDU3-GI64X2 (фирмы AiT Instruments). В каждом цикле измерений производится калибровка каналов. Приведен зарядовый спектр в детекторе – суммарный сигнал, измеренный 64 КФЭУ матрицы. Представлено изображение трека мюона. В настоящее время отрабатывается методика проведения измерений и анализа полученных данных, а также ведется подготовка к работе со следующим прототипом детектора, который представляет собой акриловую сферу диаметром 1 м.

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.

The core collapse of a massive star in the Milky Way will produce a neutrino burst, which will be detected by the Baksan Underground Scintillation Telescope (BUST). The stable and enough low background at the BUST is a clear asset for searching for neutrino bursts. Now two parts of the facility (with the total mass of 242 tons) are used as independent coinciding detectors. Such approach allows us to increase dependability detection of the neutrino signal and the radius of sensitivity of the BUST. The facility has the potential to see a supernova in the Galaxy independently from other detectors. No burst candidate for the core collapse has been detected during the observation period of June 30, 1980, to June 30, 2019. The actual observation time is 33.477 years. This is the longest observation time of our Galaxy with neutrinos at the same facility. An upper bound on the mean frequency of gravitational collapses in the Galaxy is 6.88 per century (at 90% C.L.).