Extragalactic background light (EBL), formed by the light radiated and re-radiated by stars, galaxies, and active galactic nuclei throughout the evolution of the Universe, brings the imprint of the history of the rate of the formation of emitting astrophysical objects and the Universe’s expansion. It makes EBL one of the fundamental quantities in cosmology. The optical depth for high-energy emission from the distant active galactic nuclei provides a constraint for the EBL density that is clear from the foreground galactic and other emissions, and, therefore, for the cosmological parameters. In this work, we investigate the high-redshift active galaxy 4C +55.17 (z = 0.902), whose unusually hard and stable high-energy spectrum makes it a valuable probe of EBL-induced absorption effects. Using observations extending from GeV to TeV energies, we reconstruct the optical depth associated with gamma-ray propagation and compare the inferred attenuation with predictions from existing EBL models. The results favor relatively low EBL intensities in the optical and infrared bands, consistent with low-level EBL models and suggesting reduced star formation activity and dust contributions over cosmic evolution. We further explore the cosmological implications of the reconstructed optical depth and derive constraints on the Hubble constant in the range H0≈ 64–74 km s−1 Mpc−1, with an average value of H0=69±4 km s−1 Mpc−1. These findings demonstrate the potential of hard-spectrum, high-redshift gamma-ray sources such as 4C +55.17 as cosmological probes for studying EBL evolution and addressing current tensions in cosmological parameter measurements.

4U 2129+47 is classified as a low-mass x-ray binary containing a neutron star. It is actively studied in the optical and x-ray. It was found that this binary exhibits both the outburst and quiescent states. The spectroscopic investigations of the optical counterpart of the neutron star in this binary system showed that the 4U 2129+47 is a hierarchical triple system. X-ray observations showed the evidence for a spatially extended Accretion Disk Corona. This type of objects is considered as a possible source of high energy emission generated due to the interaction between the wind of the neutron star pulsar and accretion disk. Observations of 4U 2129+47 system with SHALON telescope were performed in the period 1999-2011 years. Weak gamma-ray emission from this object was detected with the significance of 11.6 sigma. An integral flux above > 0.8 GeV was measured. The modulation of detected gamma-ray emission with the orbital period of 5.24 h is found. The hard differential spectrum with the photon index of -1.49 +/- 0.13 has been determined. Detected modulation of TeV gamma-ray flux with orbit together with the hard tail of soft x-rays detected with Chandra can be evidence of active accretion and also may point to the generation of emission through the interaction of the wind and accretion stream.

Blazars are among the most powerful objects in the Universe, whose photon spectrum extends from radio to very high energy gamma-rays (gamma-rays). Spectral energy distribution (SED) of blazars has a two-humped shape, whose low-energy part originates from the leptonic mechanism of synchrotron radiation of relativistic electrons in the blazars' jets. It is generally believed that the high-energy part of the spectral energy distribution is of hadronic and leptonic scenarios, but different localization of the source of emission within the core region or far beyond is considered. Also, blazars' emission is characterized by rapid variability at all wavelengths. The tracking of the flaring events at the radio band to connected ones at higher energies may allow localizing emission regions. High-frequency peaked Bl Lacertae type of blazar objects (HBL) are characterized by multi-wavelength variability and SED peaking at the GeV-TeV energy range. Thus, HBL objects have been considered as the best candidate for the sources of very high gamma-rays. Mkn 180 is the HBL object with the spectrum that has been measured through radio and X-ray bands to high energy gamma-rays. The study of the connection between the outbursts from Mkn 180 viewed from radio to very high energy gamma-rays is presented together with its features at the MeV-TeV energy range. These results can help find the parameters for the models of generation of high-energy gamma-ray emission in Bl Lac-type objects.

Mkn 180 is the BL Lac object with the spectrum that has been measured through radio and x-ray band to high energy gamma-rays. This object is considered as a potential candidate for the source of high-energy leptonic and/or hadronic cosmic-ray acceleration. Also, it has been proposed to be a GeV-TeV gamma-ray source. The very high energy gamma-rays from Mkn 180 were detected due to the trigger switched on by an optical burst. Mkn 180 was monitored in the optical wave band and in the high and very high energy gamma-rays for a long period and its light curve was obtained. The spectral energy distribution of Mkn 180 blazar was obtained in the wide energy range as well. The spectral energy distributions of blazars consist of two broad peaks. The first, lower frequency peak occurring between radio and soft x-ray energies is due to the synchrotron emissions of relativistic electrons population. Leptonic and hadronic emission mechanisms are considered to describe the second, higher frequency spectrum part between x-ray and VHE gamma-ray energies. The Inverse Compton emissions of the same electrons (synchrotron self-Compton model) or combined with an external Compton mechanism originating from the broad-line region, or the accretion disk are considered in the leptonic scenario. Also, the high energy spectrum part is supposed to be generated due to the processes of photohadronic or hadronuclear interactions of cosmic rays with radiation or matter in the AGN's jet emission region. The multiwavelength observations of Mkn 180 including the GeV-TeV energy data can help to clarify the dominant mechanism of generation of high-energy gamma-ray emission in this object (and whether it can be the source of UHECRs).

G166.0 + 4.3 (VRO 42.05.01) is a mixed-morphology supernova remnant (SNR) having a different spatial distribution of emission viewed in radio and X-rays. A sharp edge-brightened circular shape of the shell and wing component is visible in radio wavelength, whereas X-ray emission is dominated by a bright spot in the wing, without any edge-brightened structures. The observed shape of this SNR, looking like a shock propagation through the medium of different densities, can be a result of the shock encountering the density discontinuity in the interstellar medium, which makes favorable conditions for the particles' acceleration up to very high energy. Thus, the G166 + 4.3 SNR became a candidate for the investigation of particle acceleration in SNR shocks at high- and very-high energies. At TeV energies, the SHALON telescopes discovered extended emission, with the main contribution to the very-high-energy gamma-ray fluxes given by the regions correlated with the shells visible in the radio energies. But the main contribution to the TeV gamma-ray flux comes from the west part of the SNR, where the maximum of X-ray emission is located. The origin of the very-high-energy gamma-ray emission from G166 + 4.3 SNR is explored.

Active galactic nucleus (AGN) phenomenon and role of jets, powered by the central black hole of AGN, in the feedback of the surroundings on different scales is a matter of detailed multi-wavelength investigations. The long-term observations of AGN are used to reveal the processes taking place in the very proximity to the super-massive black holes. One of the approaches to such studies is to detect the launching of jet components viewed in the radio range and then link it with flaring events detected at higher energy ranges. Tracking the jet-initiated variability events through multiwavelength observations as well as their cross-identification from radio frequencies up to high-energy gamma-rays allows one to locate the regions responsible for the generation of observable features, which can lead to the exploration of the mechanism of jet launching and the origin of emission in the Active Galactic Nucleus. Being nearby and bright, NGC 1275 is one of the extensively studied AGN. This object is very active in the timescales of decades. Multiwavelength long-term observations of NGC 1275 resulted in the detection of different timescale variability from this AGN. For the case of NGC 1275, the cross-correlation of the activity at radio, X-ray, and very high-energy gamma-rays is investigated. The time dependence of the activity of NGC 1275 in the wide energy range was found, which allows one to localize the sites of the emission generation, including one of the very high energies. These multiwavelength long-term studies are highly important for the further advance of the AGN's black hole research and investigations of mechanisms of jet formation.

It is widely considered that the processes of an interaction between the energy and radiation, which are generated in the active galactic nuclei (AGN) by accretion onto their central massive black hole with the gas in the host galaxy, take a great part in the evolution of the galaxies at all development stages. Such “feedback” of the galaxy environment by AGN including the role of their jetted outbursts generally has no evidence through the multiwavelength observations. Only a few objects are suitable for these purposes. The Perseus cluster of galaxies with the central galaxy NGC 1275 is a perfect laboratory for studying both the physics of AGN’s relativistic jets and the feedback role of the central galaxy. Here, the most complete long-term observations across the electromagnetic spectrum from radio up to very-high-energy gamma rays are collected. The multiwavelength light curve provides evidence for the variability of NGC 1275 on decade timescales in the whole energy range and points to the connection of the observed activity with the launch of the features of the relativistic jets from the NGC 1275 core. The relation of multiwavelength emission components is demonstrated with spectral energy distribution and emission maps of the central part of the Perseus cluster. The evidence of the interaction of cosmic rays and magnetic fields generated in the jets at the galactic center with the gas of the Perseus cluster is obtained.

Active galactic nuclei (AGN) especially of blazar type are among the most luminous objects that have been detected through the whole range of the electromagnetic spectrum. It is generally believed that the powered by the central black hole AGN jets are responsible for the observed features like highly variable non-thermal emission characterized by spectral energy distribution extending from radio frequencies up to very high energy gamma-rays. The investigations of the physical properties of jets as well as the mechanisms of jet launching and localization of emissions in AGN are carried out with multi-wavelength observations of active galaxies at the different activity states to trace the temporal changes of fluxes and spectral behavior. NGC 1275 is one of the nearest and extensively studied active galaxies at the energy range from radio band to very high energy gamma-rays. Its multi-wavelength long-term observations resulted in the broadband spectral energy distribution of NGC 1275 obtained simultaneously or quasi-simultaneously and revealed the short-term and long-term timescale variability of emission fluxes from this AGN. Modeling of the NGC 1275 spectral energy distribution at the different activity states was made to estimate the jet physical parameters which may help to understand the changes in the temporal and spectral behavior of NGC 1275 active galactic nucleus.

Cosmic rays are a very valuable tool of multi-messenger astrophysics, as they provide a very different picture of the sky. During the past decades, a large number of active astrophysical objects in our Galaxy and beyond have been discovered through the detection of gamma-rays with Cherenkov telescopes. Cosmic rays, neutrinos have been successfully supplementing the astronomical view. Also, cosmic rays may offer to investigation of the elementary particle properties. Neutrino telescope detects the Cherenkov radiation generated in water or ice by the passage of relativistic charged particles produced by neutrino collisions with nucleons in the detector volume. Some alternative approaches have been proposed. One of them is using earth matter or mountains as a target volume for the conversion of neutrinos to leptons which then initiate extensive air showers (EAS) in the atmosphere, then showers can be detected by the Cherenkov telescope. Investigations with SHALON Cherenkov telescope have included observations of EAS from the sub-horizontal direction Theta=97 degrees$$ \Theta ={97}<^>{{}<^>{\circ}} $$. Five EAS of similar to 10 TeV energies were detected with SHALON from the sub-horizontal directions in the conditions with the zero expected number of showers. These events may be caused by the decay of a long-lived penetrating particle entering the atmosphere from the ground and decaying in front of the telescope. As a possible explanation, two scenarios with an unstable neutrino of mass m approximate to 0.5$$ m\approx 0.5 $$ GeV and c tau approximate to 30$$ c\tau \approx 30 $$ m is discussed. Remarkably, one of these models has been proposed to explain an excess of electron-like neutrino events at MiniBooNE.

The investigation of very high energy gamma-ray sources touches on the problem of the cosmic ray origin and the role of the Galaxy in their generation. The SHALON observations have yielded the results on gamma Cygni SNR Galactic supernova remnant. The observation results are presented with spectral energy distribution and emission map by SHALON in comparison with other experiment data obtained by ROSAT in x-ray energy range, radio-data by CGPS, and also observations of GeV-TeV gamma-rays by Fermi LAT. The overall gamma Cygni SNR characteristics detected in radio, x-rays, and GeV-TeV gamma-rays can be a result of the shocks at the interaction of the supernova ejecta and the surrounding medium. The collected experimental data help to make clear the origin of TeV gamma-ray emission in the gamma Cygni SNR. The density of target material in the SNR surroundings is enough to produce the observable TeV gamma-ray flux via the shock acceleration of hadrons in the detected regions. The detection of gamma-ray emission at 0.8-60 TeV from the North-West and South-East shells of gamma Cygni SNR by SHALON would favor the hadronic origin of the gamma-rays in this supernova remnant.

The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma-rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma-ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non-thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of 10(14)-10(15) eV. Whereas, the forward shock model predicts the spectral characteristics of the TeV-gamma-emission corresponding to ones detected at 800 GeV-40 TeV that are the evidence of acceleration of the hadronic cosmic rays in shells of SNRs up to 10(17) eV

Blazars are the subclass of active galactic nuclei (AGNs) which includes the Flat Spectrum Radio Quasars (FSRQ) and BL Lacertae (BL Lac) objects. Variability on the short- and long-time scale in all the wide energy ranges from radio up to gamma-ray emission is a special characteristic of blazars. Multi-wavelength studies of the flaring activity and variability of blazars can serve as a tool to probe the physical properties of the near the core regions and processes responsible for the observed features. 3C 454.3 is a bright FSRQ that is intensively studied through the wide range of electromagnetic spectrum. It has shown remarkably high activity since 2000. The long-term observations of 3C 454.3 at 800 GeV-100 TeV energies with the SHALON telescope were started in 1998 year. A number of activity periods were found. The most significant flaring state of 3C 454.3 at TeV energies was detected in the SHALON observational period of November-December 2010. This increase is correlated with the flares at a lower energy range in observations of Fermi-LAT. The direct association of the significant changes of gamma-ray flux with strong core radio flares are not clear but observed correlations and lags in multi-wavelength activity may point to the complexity of the emission processes in blazars connected with disturbance propagating in the jet.

Cygnus Region contains many objects that are bright in all wavelengths, including one of the most powerful active star formation regions: Cyg OB2, pulsars, and supernova remnants. Some of the sources have been detected at high and very high energies. One of them was discovered due to the proximity to well-known microquasar Cyg X-3. It is an object TeV J2032 + 4130. This object is still of unresolved nature and is being intensively studied in different energy ranges. Numerous X-ray point sources and diffuse X-ray emission regions were found within the TeV J2032 + 4130 region by Chandra and Suzaku. Intensities detected in X-rays from these regions may favor a scenario with the dominantly nucleonic, not electronic origin of TeV emission. The results of the 20-year observations of TeV J2032 + 4130 object by the SHALON experiment are presented. Collected experimental data on fluxes, spectrum shape, and morphology of TeV J2032 + 413 can help determine an object nature.

The investigation of very high energy (VHE) γ -ray sources by any methods, including mirror Cherenkov telescopes, touches on the problem of the cosmic-ray origin and, accordingly, the role of the Galaxy in their generation. The SHALON observations have yielded the results on Galactic supernova remnants (SNR) of different ages. Among them are: the shell-type SNRs Tycho's SNR, Cas A, IC 443, γ Cygni SNR, G166.0+4.3. For each of SNRs, the observation results are presented with spectral energy distribution by SHALON in comparison with other experiment data and images by SHALON in together with data from X-ray by Chandra and radio-data by CGPS. The experimental data presented here have confirmed the prediction of the theory about the hadronic generation mechanism of VHE 800 GeV–100 TeV γ -rays in Tycho's SNR, Cas A and IC 443, and also the collected experimental data help to make clear the origin of TeV γ -ray emission in the older SNRs like γ Cygni SNR and G166.0+4.3.

OJ 287 is one of the most studied BL Lac objects with very long optical measurements whose spectrum has been well measured through radio to X-ray band. The most outstanding characteristic of OJ 287 is its 12-year period, which is discovered in the optical range and has also been confirmed in the X-ray band. OJ 287 is supposed to be a binary black hole system in which a secondary black hole passes the accretion disk of the primary black hole and produces two impact flashes per period. It has also been proposed to be a GeV-TeV source. Observations of OJ 287 in the GeV-TeV energy range reveal the variable gamma-ray connected with the flare activity of this object. The spectral energy distributions of blazars consist of two broad peaks. The first, lower frequency peak is due to the synchrotron emissions of relativistic electrons in the jet. Leptonic and hadronic emission mechanisms are considered to describe the second, higher frequency spectrum part. The inverse Compton emissions of the same electrons (synchrotron self-Compton model) or combined with an external Compton mechanism are considered in the leptonic scenario. The last one supposes the existence of the external to jet photon cloud. The high-energy spectrum part is also supposed to be generated due to the acceleration of the cosmic ray hadrons in shock produced by outflow, which expands and then collides with the wind of the primary black hole. The detection of GeV-TeV energy fluxes can help find the parameters of the configuration of the two-black hole system.

Extremely low-frequency magnetic fields are thought to be capable of modulating the resistance of plants to adverse factors, particularly drought. Magnetic fields in this frequency range occur in nature in connection with so-called Schumann resonances, excited by lightning discharges in the Earth–ionosphere cavity. The aim of this work was to identify the influence of a magnetic field with a frequency of 14.3 Hz (which corresponds to the second Schumann harmonic) on the transpiration and photosynthesis of wheat plants under the influence of drought. The activity of photosynthesis processes, the crop water stress index, relative water content and leaf area were determined during drought intensification. At the end of the experiment, on the 12th day of drought, the length, and fresh and dry weight of wheat shoots were measured. The results obtained indicate a protective effect of the magnetic field on plants in unfavorable drought conditions; the magnetic field delayed the development of harmful changes in the transpiration and photosynthesis processes for several days. At the same time, in the absence of the stressor (drought), the effect of the electromagnetic field was not detected, except for a decrease in relative transpiration. In favorable conditions, there were only minimal modifications of the photosynthetic processes and transpiration by the magnetic field.

The overall observations of plerions from radio to the very high energy gamma-rays could provide information about the evolution of PWN from the young Crab-like to the older stages. The extended MeV-TeV emission from Geminga middle-aged pulsar of ~ 3.4 × 105 year age in SHALON, Milagro, HAWC observations, and Fermi-LAT detection could arise from the PWN associated with the Geminga SNR. The TeV γ-ray emission from 3C 58 PWN whose estimated age varies from ~ 800 to (5 − 7) × 103 years was first detected in year 2011 by SHALON. The overall spectral energy distribution and information about the extension of PWN from radio to GeV-TeV energies from Fermi-LAT and SHALON observations can contribute to particle transport models and also to the understanding of the mechanisms of PWN expanding, which is, in turn, can shed light on the age of 3C 58 and the history of progenitor SN explosion.

Results from ground level and underground experiments on cosmic rays with energy 1012 to 1020eV are reviewed. They show that the energy spectrum has two significant features, a ‘knee’ and an ‘ankle’. The arrival directions of these cosmic rays at the solar system are anisotropic, features of the anisotropy appearing to be correlated with features of the spectrum. Detailed interpretation of this information awaits conclusive evidence regarding the composition of these cosmic rays. New results and prospective new results on the composition are described and discussed.

Cygnus Region contains many objects that are bright in all wavelengths, including one of the most powerful active star formation regions: Cyg OB2, pulsars, and supernova remnants. Some of the sources have been detected at high and very high energies. One of them was discovered due to the proximity to well-known microquasar Cyg X-3 is object TeV J2032+4130. This object is still of unresolved nature and is being intensively studied in the different energy ranges. The numerous X-ray point sources and diffuse X-ray emission regions were found within the TeV J2032+4130 region by Chandra and Suzaku. Intensities detected in X-rays from these regions may favor a scenario with the dominantly nucleonic, not electronic origin of TeV emission. The results of the twenty-year observation of TeV J2032+4130 object by the SHALON experiment are presented. The collected experimental data on fluxes, spectrum shape, and morphology of TeV J2032+413 can help determine an object type and shed light on the source nature.

OJ 287 is one of the most studied BL Lacs with very long optical measurements which spectrum has been well measured through radio to X-rays. OJ 287 is supposed to be a binary black hole system. Its secondary black hole passes the accretion disk of the primary black hole and produces two impact flashes per 12-year period. Observations of OJ 287 in the GeV – TeV energy range reveal the variable γ-ray flux connected with the flare activity of this object. The spectral energy distributions of BL Lac objects consist of two broad peaks. The Inverse Compton emission of the relativistic electrons in the jet or combined with an external Compton mechanism are considered in the leptonic scenario of second, higher frequency spectrum part generation. The last one supposes the existence of the external to jet photon cloud. Also, the second spectrum part is supposed to be generated due to the acceleration of the cosmic ray hadrons in expanding shock produced by outflow, which then collides with the wind of the primary black hole. The detection of GeV – TeV energy fluxes can help find the configuration parameters of the two-black hole system.