Search

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., 5 pages, 3 figures, JETPL.cls; V2: references added, version accepted by JETP Letters

Using data of the Baksan Underground Scintillation Telescope (BUST) we have made a search for muon neutrinos and antineutrinos with energies above 1 GeV coinciding with the gravitational wave event GW170817 that was recorded on August 17, 2017 by the Advanced LIGO and Advanced Virgo observatories. This is a 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 GRB170817A accompanying this event is an 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 BUST in the interval $\pm 500$ 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., Submitted to JETP Letters

Carpet is an air-shower array at Baksan, Russia, equipped with a large-area muon detector, which makes it possible to separate primary photons from hadrons. We report first results of the search for primary photons with energies E>100 TeV. The experiment's ongoing upgrade and future sensitivity are also discussed., 8 pages, 5 figures, ICRC 2019

We discuss recently published results of two-dimensional measurements of the cosmic ray anisotropy in the energy range 1-100 TeV. It is demonstrated that, in spite of pretence of the authors to measure the anisotropy in more detail than it was done in one-dimensional measurements of the first harmonic of CR intensity in sidereal time, new measurements give nothing essentially new. Moreover, two-dimensional picture is misleading creating an illusion that the true direction of the anisotropy is observed, while, as before, only the projection of the anisotropy onto the equatorial plane is measured and the phase of the anisotropy remains to be the only directly measured parameter. The sophisticated interpretations of the results of 2D measurements made by their authors are invalid, since they are based on the false assumption that the equatorial excess and deficit of CR intensity seen on the difference maps represent the real anisotropy., Comment: 13 pages, 12 figures

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.

The pre-lightning enhancements of the soft component of cosmic rays were detected in the experiment with the Baksan air shower array. The pictures of two brightest events of this type were published, giving evidence of a big difference in duration of the enhancement depending on the lightning polarity. Now we study the lightning effect statistically. The variance of counting rate is calculated excluding time intervals around lightning from the analysis. This processing results in a decrease of the variance. The value of this decrease is studied in some detail for various selection criteria.

The experiment made with the Baksan air shower array discovered two types of pre-lightning enhancements of the soft component of cosmic rays. We present the preliminary results of an experiment in which the distance to lightning events associated with such enhancements is estimated acoustically using a simple microphone system. During observations in the autumn of 2002, we have succeeded in finding some events, for which it was possible to measure minimum distances to lightning channels. These distances turned out to be fairly large.

The results of studying the correlation of the hard component of cosmic rays with the electric field of the atmosphere during thunderstorm periods are presented. The data at several energy thresholds are examined using the liquid scintillators of the the Baksan air shower array and the plastic scintillators of the muon detector with a threshold of 1 GeV. It is demonstrated that the quadratic effect (changing intensity of muons at the electric field of any sign) is the most pronounced for soft muons.

The results of studying the correlation of the soft component of cosmic rays (10-30 MeV) with the electric field of the atmosphere during thunderstorm periods are presented. The uncovered scintillators of the Baksan air shower array are used as detectors of the soft component, and the data for three seasons (2000--2002) are included into the analysis. It is shown that both linear and quadratic effects of the electric field are present in the soft component intensity. In this case, the linear term is rather stable and independent of the selection criteria, while the quadratic term is subject to significant variations.