Search

Carpet-2 is an air-shower array at Baksan Valley, Russia, equipped with a large-area (175 m^2) muon detector, which makes it possible to separate primary photons from hadrons. We report the first results of the search for primary photons with energies E_\gamma>1 PeV, directionally associated with IceCube high-energy neutrino events, in the data obtained in 3080 days of Carpet-2 live time., Comment: 6 pages, 2 figures. V2: minor copy-editing changes. Accepted by JETP Letters

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 November 2020, 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-sigma (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., 7 pages, 3 figures, AASTeX. V2: minor changes; Appendix with more analysis details added. Version accepted by Astrophys. J. Letters. V3: title corrected (text unchanged), matches the published version

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 Carpet air shower array of the Baksan Neutrino Observatory is in operation for a long time, and it was modernized more than once. A short review of important results obtained with this array is given, as well as future prospects, since at the moment the new project called Carpet-3 is in progress, using the old array as its basis. The purpose of the new project is to substantially increase the muon detector area (quite soon up to 400 m2 and later up to 600 m2). This improvement will allow one to reach a very good sensitivity to diffuse cosmic photons by selecting muon-poor showers. The energy range where the new experiment will be competitive with other experiments of gamma-ray astronomy is near and below 100 TeV.

The recently published result of GRAPES-3 (a strong thunderstorm muon intensity change) and conclusions made on its basis by this collaboration are discussed and compared with the Baksan observations of muon variations during thunderstorms performed much earlier. It is demonstrated that generally both experiments are quite consistent as far as characteristic patterns of events are concerned, as well as conclusions about direct connection between amplitude of muon intensity disturbance and electric field strength in the atmosphere. However, the GRAPES-3 conclusion about gigavolt potentials associated with their event is doubtful and seems to contradict the fundamental limits on electric fields that can exist in the atmosphere.

Recently two collaborations (Tibet ASγ and HAWC) almost simultaneously reported about their measurements of ultra-high-energy (> 100 TeV) gamma rays from the Crab Nebula. The Baksan air shower array (BASA) recorded a burst from this very source as long ago as more than 20 years. At the moment the new experiment on gamma ray astronomy (Carpet-3 project) started at Baksan, and it is appropriate to recall old results of BASA to be compared with the new results, already published and expected.

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 ~100 TeV). 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., 4 pages paper + 5 pages Supplemental Material. V2: references added, version accepted by JETP Letters

Early results of the search for E_\gamma>1 PeV cosmic photons from point sources with the data of Carpet-2, an air-shower array equipped with a 175 m^2 muon detector, are presented. They include 95% CL upper limits on PeV photon fluxes from stacked directions of high-energy IceCube neutrino events and from four predefined sources, Crab, Cyg X-3, Mrk 421 and Mrk 501. An insignificant excess of events from Mrk 421 will be further monitored. Prospects of the use of the upgraded installation, Carpet-3 (410 m^2 muon detector), scheduled to start data taking in 2019, for searches of E_\gamma>100 TeV photons, are briefly discussed., Comment: 5 pages, 2 figures, webofc style. Presented at the VLVNT-2018 workshop, Dubna, October 2-4, 2018. V2: minor copy-editing changes

An experiment for measuring the flux of gamma rays of cosmic origin with energy above 100 TeV (the Carpet-3 experiment) is currently being prepared at the Baksan Neutrino Observatory. The experimental setup suggests substantial increase of the areas of both muon detector and surface air shower array. We present some results of calculations of selection efficiency of air showers from primary gamma rays for different configurations of the array. It is demonstrated that by increasing the muon detector area up to 615 m$^2$ (the maximum possible value) one can reach with the Carpet-3 the world-best sensitivity to 100 TeV gamma rays. The preliminary values of upper limits on the flux of cosmic diffuse gamma rays with energy higher than 930 TeV are also presented, derived from experimental data of the Carpet-2 shower array for a net exposure time of 9.2 years.

An experiment for measuring the flux of cosmic gamma rays with energy above 100 TeV is currently being prepared at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences. At present the plastic scintillation counters with a total continuous area of 410 m2 are installed in the muon detector (MD) underground tunnels, and they are totally equipped with electronics. Six modules of shower detectors have been already placed on the surface of the MD absorber. In each of them 9 standard plastic scintillation counters are placed with an area of 1 m2 each. These modules are components of the ground surface part of Carpet-3 shower array. The data acquisition system for this array is almost ready. Expected flux limits for cosmic diffuse gamma rays of galactic origin in this work is close to existing experimental limits in the range lower than about 5 PeV, and with improved sensitivity of Carpet-3 one can hope to detect this flux or at least to obtain the best upper limit.

Characteristics of the flares of gamma rays detected from the Crab Nebula by the AGILE and Fermi-LAT satellite instruments are compared with those of a gamma ray burst recorded by several air shower arrays on February 23, 1989 and with one recent observation made by the ARGO-YBJ array. It is demonstrated that though pulsar-periodicity and energy spectra of emissions at 100 MeV (satellite gamma ray telescopes) and 100 TeV (EAS arrays) are different, their time structures seem to be similar. Moreover, maybe the difference between “flares” and “waves” recently found in the Crab Nebula emission by the AGILE team also exists at ultra-high energies.

Strong variations of the intensity of secondary cosmic rays during thunderstorms are found to be accompanied in some cases by very clear pulsations of the geomagnetic field. The experiment is carried out in the Baksan Valley, North Caucasus, the Carpet air shower array being used as a particle detector. Magnetic field measurements are made with high-precision magnetometers located deep underground in the tunnel of the Baksan Neutrino Observatory, several kilometers apart from the air shower array., 8 pages, 2 figures

The present-day status of the problem of searching for primary cosmic gamma rays at energies above 100 TeV is discussed, as well as a proposal for a new experiment in this field. It is shown that an increase of the area of the muon detector of the Carpet-2 air shower array up to 410 square meters, to be realized in 2016, will make this array quite competitive with past and existing experiments, especially at modest energies. Some preliminary results of measurements made with smaller area of the muon detector are presented together with estimates of expected results to be obtained with the coming large-area muon detector., 7 pages. To appear in Proceedings of The International Workshop on Quark Phase Transition in Compact Objects and Multimessenger Astroronomy: Neutrino Signals, Supernovae and Gamma-Ray Bursts (Nizhny Arkhyz - Terskol, October 7-14, 2015)

We present the data on correlations of the intensity of the soft component of cosmic rays with the local electric field of the near-earth atmosphere during thunderstorm periods at the Baksan Valley (North Caucasus, 1700 m a.s.l.). The large-area array for studying the extensive air showers of cosmic rays is used as a particle detector. An electric field meter of the ‘electric mill’ type (rain-protected) is mounted on the roof of the building in the center of this array. The data were obtained in the summer seasons of 2000–2002. We observe strong enhancements of the soft component intensity before some lightning strokes. At the same time, the analysis of the regression curve ‘intensity versus field’ discovers a bump at the field sign that is opposite to the field sign corresponding to acceleration of electrons. It is interpreted as a signature of runaway electrons from the region of the strong field (with opposite sign) overhead.

A review of the present-day situation in the experimental studies of variations of cosmic rays during thunderstorms is given. It is shown that these experiments can be a useful tool for studying very interesting physical effects in the electrically disturbed atmosphere. The main emphasis is laid on the experimental verification of the runaway breakdown theory and on the role of cosmic rays in the processes of lightning initiation.

At present an experiment for measuring the flux of cosmic diffuse gamma rays with energy higher than 100 TeV (experiment "Carpet-3") is being prepared at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences. The preparation of the experiment implies considerable enlargement of the area of both muon detector and surface part of the shower array. At the moment the plastic scintillation counters with a total continuous area of 410 m2 are installed in the muon detector (MD) underground tunnels, and they are totally equipped with electronics. Adjusting of the counters and their electronic circuits is in progress. Six modules of shower detectors (out of twenty planned to be installed) have already been placed on the surface of the MD absorber. A new liquid scintillation detector is developed for modules of the ground –surface part of the array, whose characteristics are presented. It is shown that the "Carpet-3" air shower array will have the best sensitivity to the flux of primary gamma rays with energies in the range 100TeV – 1PeV, being quite competitive in gamma-ray astronomy at such energies.

On 23 February 1989 an apparent burst of ultra-high energy gamma-rays was observed from the direction of the Crab Nebula by the Baksan Air Shower Array. The result of checking and reanalysis of these data is reported. The excess in the number of events above background has a reduced statistical significance but this is compensated for by a phase analysis with respect to the Crab pulsar cycle which shows the excess to favour one phase bin. The agreement of the evidence from other arrays is discussed.

Probabilities for positrons in cascades of runaway electrons produced by secondary cosmic rays in the strong electric field of thunderclouds to become runaway particles in the direction opposite to that of acceleration of electrons are calculated using modified GEANT4 code. Different electric field strengths and primary energies of electrons generating cascades are investigated.

The 23rd European Cosmic Ray Symposium (ECRS) took place in Moscow at the Lomonosov Moscow State University (3–7 July 2012), and was excellently organized by the Skobeltsyn Institute of Nuclear Physics of the Lomonosov Moscow State University, with the help of the Russian Academy of Sciences and the Council on the Complex Problem of Cosmic Rays of the Russian Academy of Sciences. The first symposia were held in 1968 in Lodz, Poland (high energy, extensive air showers and astrophysical aspects) and in Bern (solar and heliospheric phenomena) and the two 'strands' joined together in 1976 with the meeting in Leeds. Since then the symposia, which have been very successful, have covered all the major topics with some emphasis on European collaborations and on meeting the demands of young scientists. Initially, a driving force was the need to overcome the divisions caused by the 'Cold War' but the symposia continued even when that threat ceased and they have shown no sign of having outlived their usefulness. 2012 has been an important year in the history of cosmic ray studies, in that it marked the centenary of the discovery of enigmatic particles in the perilous balloon ascents of Victor Hess. A number of conferences have taken place in Western Europe during the year, but this one took place in Moscow as a tribute to the successful efforts of many former USSR and other Eastern European scientists in discovering the secrets of the subject, often under very difficult conditions. The symposium covers a wide range of scientific issues divided into the following topics: PCR-IPrimary cosmic rays I (E 1015 eV) MNCosmic ray muons and neutrinos GAGeV and TeV gamma astronomy SHEnergetic particles in the heliosphere (solar and anomalous CRs and GCR modulation) GEOCosmic rays and geophysics (energetic particles in the atmosphere and magnetosphere of the Earth) On a personal note, as I step down as co-founder and chairman of the International Advisory Committee, I should like to thank those very many colleagues and friends with whom I have had the pleasure of working over the past 45 years. These thanks are extended to the present organizers. The organizers are very grateful to the Russian Foundation of Basic Research and to the Dynasty non-profit foundation for financial support. Arnold Wolfendale

Variations of the intensity of cosmic ray muons during thunderstorms are investigated. Linear and quadratic coefficients of regression of the muon flux with near-ground electric field are calculated and compared to the experimental data obtained with the Carpet air shower array in the Baksan Valley, North Caucasus. Based on correlations with the near-ground field, estimates are made of regression coefficients with the mean potential difference in the stratosphere, between the effective level of muon production and the ionosphere. It is shown that maximum observable muon effects (variations with amplitudes of 1%) correspond to a mean potential difference in the stratosphere of about 200 MV.

The brightest events with enhancements of the intensity of the soft component of secondary cosmic rays observed during thunderstorms in the Baksan Valley are analyzed. These experimental data were obtained during thunderstorm seasons of 2003-2008. Assuming bremsstrahlung photons from cascades of runaway electrons to be the main source of the enhancements, the height of generation level is estimated for every event. It is shown that for a half of all events the region of particle generation is located in the stratosphere.

Recent experiments with satellite gamma-ray telescopes Fermi-LAT and AGILE in which bursts of gamma-rays from the Crab Nebula were detected in the energy range around 100 MeV have aroused keen interest, if not sensation. However, as long ago as more than 20 years from now the data on a possible burst in the Crab Nebula at much higher energies, about 100 TeV, were published. Characteristics of transient and stationary fluxes of gamma rays from the Crab Nebula in various energy ranges are discussed in this paper, and it is shown that the old data obtained at ultra-high energy can be reasonably consistent with the modern pattern of burst activity of the source.

Launched on the 15th of June 2006, the space experiment PAMELA is providing data showing interesting features in cosmic rays that might change our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the galaxy. In addition, PAMELA measurements of cosmic antiproton and positron fluxes are setting strong constraints to the nature of Dark Matter. PAMELA is also testing cosmic rays acceleration and propagation models through precise measurements of light nuclei and their isotopes. The determination of fluxes and secondary-to-primary ratios is possible for nuclei up to Oxygen in the energy range 200MeV/n – 150 GeV/n. To investigate this important item, PAMELA can use measurements from three main detectors: the magnetic spectrometer, the calorimeter and the Time-of-Flight system. Analysis strategy and performance for nuclei studies using the detectors in stand-alone configuration will be discussed in this work.

Using data taken by the Pamela experiment during 5 years of operation we studied the anisotropy in the arrival direction of cosmic ray electrons and positrons with energy above 40 GeV. We report on a study of anisotropy in the e�� flux at different angular scales extending from 30��up to 90��, furthermore a directional analysis has been performed around the Sun direction. The observed distribution of arrival directions is consistent with the isotropic expectation at any angular scale used in this study and no significant evidence of strong anisotropies has been observed, also the analysis around the Sun direction did not show any significant excess.