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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Carpet-2 is an air-shower array at Baksan Valley, Russia, equipped with a large-area (175 m2) 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 Eγ > 1 PeV, directionally associated with IceCube high-energy neutrino events, in the data obtained in 3080 days of Carpet-2 live time. [ABSTRACT FROM AUTHOR]

In the data obtained at the Baksan underground scintillation telescope (BUST), electron neutrinos and antineutrinos with energies above 21 MeV have been sought in coincidence with the GW150914, GW151226, GW170104, GW170608, GW170814, and GW170817 gravitational wave events. No neutrino signals from gravitational wave events have been detected in the interval of ±500 s at the Baksan underground scintillation telescope. Bounds on the fluxes of low-energy electron neutrinos and antineutrinos from astrophysical sources of gravitational bursts have been obtained. [ABSTRACT FROM AUTHOR]

Temporal and energy characteristics of the very-high-energy gamma-ray bursts from evaporating primordial black holes have been calculated by assuming that the photospheric and chromospheric effects are negligible. The technique of searching for such bursts on shower arrays is described. We show that the burst time profile and the array dead time should be taken into account to interpret experimental data. Based on data from the Andyrchy array of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences), we have obtained an upper limit on the number density of evaporating primordial black holes in a local region of space with a scale size of ∼10−3 pc. Comparison with the results of previous experiments is made. [ABSTRACT FROM AUTHOR]

Knee formation in the EAS size spectrum as a possible result of some portion of EAS's energy carried away by some missing EAS component is discussed. To explain the absence of the bump in calculated EAS size spectrum for the standard EAS development in the present day experiments, the model of "catastrophic" EAS development was proposed. The hypothesis that all the energy lost for the further shower development ELT finally passes into neutrino (¾ELT) and muons (¼ELT) is shown to be practically excluded by present experimental data. [ABSTRACT FROM AUTHOR]