The operation of a small-size Cherenkov gamma-ray telescope TAIGA-IACT with camera on SiPMs OnSemi MicroFJ-60035 has been modelled by multiparticle Monte Carlo (MC) methods. The model implies that telescope camera is equipped with two specific types of filters of 290-590 nm (visible+NUV) and 220-320 nm (MUV+UVB)-bands, each covering half of the camera pixels in some uniform order. This allows one to measure the fraction of UV-radiation in total amount of Cherenkov radiation of an extensive air shower (EAS), that can be used for efficient gamma-hadron separation. The corresponding quality factor takes values up to 5.07 in the 10-100 TeV range depending on the distance to EAS axis and camera orientation.

Results are presented from Monte Carlo calculations of the effective areas and count rates of the TAIGA–IACT Cherenkov telescope with an upgraded SiPM OnSemi MicroFJ-60035 camera equipped with SL 290–590 and SL 280–390 filters. It is shown that the threshold energy (by triggering cosmic gamma-quanta) of the TAIGA–IACT telescope with a SiPM camera and an SL 290–590 filter is ≈0.4 TeV, slightly lower than that of the current TAIGA–IACT configuration with a PMT camera (0.5 TeV). The threshold energy of the TAIGA–IACT telescope with a SiPM camera and an SL 280–390 filter is ≈0.7 TeV, which is quite acceptable for Cherenkov telescopes with a mirror area of 10 m2. These results, plus the expected stability of the SiPM design with excessive illumination and the ability to use UV filters (which allow observations at twilight and on moonlit nights without raising the trigger threshold signal appreciably), indicate that the TAIGA–IACT telescope with a SiPM camera is a promising instrument for observing cosmic gamma radiation in the TeV range.

ABSTRACT We present the results of current observations of the young compact cluster of massive stars Westerlund 2 (Wd2) with the Mikhail Pavlinsky ART-XC telescope aboard the Spectrum-Roentgen-Gamma (SRG) observatory which we analysed together with the archival Chandra data. In general, Wd2 was detected over the whole electromagnetic spectrum including high-energy gamma rays, which revealed a cosmic ray acceleration in this object to the energies up to tens of TeV. The detection of Wd2 with ART-XC allowed us to perform a joint spectral analysis together with the high resolution Chandra observations of the diffuse emission from a few selected regions in the vicinity of the Wd2 core in the 0.4–20 keV range. To fit the Wd2 X-ray spectrum above a few keV one needs either a non-thermal power-law emission component, or a hot plasma with temperatures ∼ 5 keV. Our magnetohydrodynamic modelling of the plasma flows in Wd2 shows substantially lower electron temperatures in the system and thus the presence of the non-thermal component is certainly preferable. A kinetic model of the particle acceleration demonstrated that the non-thermal component may originate from the synchrotron radiation of multi-TeV electrons and positrons produced in Wd2 in accordance with the TeV photons detection from the source.

We present modeling of effective area and count rates of a TAIGA-IACT Cherenkov gamma-ray telescope unit with an upgraded camera based on semiconductor photo detectors (SiPM) OnSemi MicroFJ-60035 and optical filters SL 290-590 and SL 280-390. In comparison with the current configuration of TAIGA-IACT where classic vacuum photomultipliers are employed, the threshold detection energy of cosmic gamma-quanta by a TAIGA-IACT unit equipped with a SIiPM-based camera and a wide-band optical filter SL 290590 would be reduced down to about 0.4 TeV, and with a narrower filter SL 280-390 down to about 0.7 TeV. Application of semiconductor photo detectors, which are stable against excess illumination, and optical filters of the near-UV band allows one to substantially increase the duty cycle of a Cherenkov gamma-ray telescopes due to the possibility to carry out observations during moonlit nights and at twilight even without a need to substantially increase the trigger threshold. Hence, one may conclude that a TAIGA-IACT unit with an upgraded camera with SiPM detectors will be an efficient instrument for studies of TeV-range emission from space gamma-ray objects.

An Erratum to this paper has been published: https://doi.org/10.3103/S1062873823360017

Young massive stars in compact stellar clusters could end their evolution as core-collapse supernovae a few million years after the cluster was built. The blast wave of a supernova propagates through the inner cluster region with multiple stellar winds of young luminous stars. We present the results of 3D magnetohydrodynamic simulations of the plasma flows produced by a supernova event inside a cluster with a population of massive stars similar to that in Westerlund 1. We followed its evolution over a few thousand years (i.e. a few shock crossing times). The plasma temperature, density, and magnetic field, which are highly disturbed by supernova event, relax to values close to the initial over the studied period. The relaxation time of a cluster is a few thousand years, which is a sizeable fraction of the period between the successive supernova events for a massive cluster of a few million years age. The spectra of the cluster diffuse X-ray emission simulated here should be representative for the galactic and extragalactic young massive clusters. The resultant magnetic fields are highly intermittent, so we derived the volume filling factors for a set of magnetic field ranges. Highly amplified magnetic fields of magnitude well above 100 mu G fill in a few per cent of the cluster volume, but still dominate the magnetic energy. The structure of the magnetic fields and high-velocity plasma flows with shocks in the system are favourable for both proton and electron acceleration to energies well above TeV.

Full-particle massive modeling of physical processes in the Earth’s atmosphere leading to generation of Cherenkov radiation in γ-ray- and proton-induced extensive air showers (EASs), as well as Monte Carlo modeling of photon transport in small-size Cherenkov telescope and signal registration with a camera based on OnSemi MicroFJ type semiconductor photomultiplier (SiPM) detectors have been performed. Calculations have been carried out for primaries with energies in the 0.3–30 TeV range and a Cherenkov telescope with an ≃10 m2 mirror similar to that employed at the TAIGA observatory. It is shown that, even with strict selection criteria ensuring high-quality EAS images, the threshold detection energy of the SiPM-based camera would not exceed 0.8 TeV, which is about twice as low as the detection threshold (≃1.5 TeV) of a small-size TAIGA-IACT telescope camera based on vacuum photomultipliers.

The fast stellar winds of massive stars, along with supernovae, determine the dynamics within the star-forming regions. Within a compact star cluster, counterpropagating supersonic MHD shock flows associated with winds and supernova remnants can provide favorable conditions for efficient Fermi I particle acceleration up to energies > 10 PeV over a short timescale of several hundred years. To model the nonthermal spectra of such systems it is necessary to know the complex structure of colliding supersonic flows. In this paper using the PLUTO code we study on a subparsec scale a 2D MHD model of the collision of a core-collapse supernova remnant with a magnetized wind of a hot rotating O-star. As a result the detailed high resolution (~ 10−4 pc) maps of density, magnetic field, and temperature during the the wind - supernova shell interaction are presented.

Full-particle modeling of gamma-ray and proton induced extensive air showers (EASs) in the Earth's atmosphere as well as Monte Carlo modeling of photon transport in a small size Cherenkov telescope and signal registration with its camera based on the OnSemi MicroFJ SiPM detectors have been performed. Calculations have been carried out for primaries within the 0.3 - 30 TeV range and a telescope with a 10 m(2) mirror similar to the unit employed at the TAIGA observatory. It has been shown that even with strict selection criteria aimed at high quality EAS images, the threshold detection energy of the SiPM-based camera would not exceed 0.8 TeV - about twice as low as the current threshold of the TAIGA-IACT camera based on vacuum photomultipliers.

We have modeled propagation of source signal and noise for a future camera of TAIGA-IACT Cherenkov gamma-ray telescope, which will be based on silicon photomultipliers sensitive in the 240 -- 600 nm range. It has been shown that employment of such detectors instead of traditional vacuum photomultipliers will allow one to decrease the energy threshold by a factor of about 2.5: from ~ 1.5 TeV down to ~ 0.6 TeV. We have also shown that application of a standard ultraviolet filter ZWB3 will decrease the source signal by a factor of 3, while the noise signal from the night sky will be decreased by a factor of 6. In this way the duty cycle of the telescope can be extended (the telescope will be able to operate during moonlit nights and during twilight) and the energy threshold further decreased down to ~ 0.3 TeV. A narrow 260 -- 300 nm filter can be employed to improve gamma-hadron separation of primary cosmic particles in the ~ 25 -- 50 TeV band.

Source and noise signals in a new camera of the TAIGA-IACT Cherenkov γ-ray telescope based on silicon photomultipliers (SiPM) have been simulated. It is shown that application of modern silicon photomultipliers as detecting elements of TAIGA-IACT (instead of the currently used conventional vacuum photomultipliers) will make it possible to reduce the threshold detection energy of cosmic γ quanta by a factor of about 2.5 (from ≃1.5 to ≃0.6 TeV). It is also shown that employment of a standard ZWB3 UV filter mask in the TAIGA-IACT camera would reduce the average signal level by a factor of about 3 and the noise (background) level from the night sky by a factor of about 6, which would allow one to extend the duty cycle of the telescope (in particular, to carry out observations during moonlit nights and twilights) and to additionally reduce the threshold detection energy down to ≃0.3 TeV. The application of a narrower UV filter of 260–300 nm bandwidth can increase the efficiency of determining the primary particle type (γ-hadron separation) in the energy range from ~25 up to ~50 TeV.

For most elements, the isotopic ratios seen in cosmic rays (CRs) are similar to those in the solar wind. The most important exception to this is 22 Ne/ 20 Ne where the CR value is ∼ 5 times that of the solar wind. According to most recent models of nucleosynthesis, a large amount of 22 Ne is generated in Wolf-Rayet (WR) stars. In the winds of carbon sequence of WR stars, i.e., WC stars, the isotopic ratio 22 Ne/ 20 Ne can be much larger than in the solar wind. Here, we consider CRs produced by 22 Ne-enriched WR winds in young massive star clusters assuming the acceleration occurs from an ensemble of shock waves from the massive stars’ winds. We estimate the fraction of all Galactic CRs such sources may produce for a given set of parameters.

Fast stellar winds of young massive stars and supernovae play an essential role in the evolution of the interstellar medium in the Milky Way. They dominate the dynamics of the active starforming regions in starburst galaxies and in particularly their non-thermal radiation. The non-thermal emission from starburst galaxies NGC 253, M82, NGC 1068 was detected from radio to gamma-rays. To model the observed radiation, one needs to know the complex structure of the flows and magnetic fields in the starforming regions. In this work a 2.5D magnetohydrodynamic (MHD) simulation (i.e., we consider 3D vector fields, but assume a 2D axisymmetric geometry) of the interaction between a stellar wind and a supernova remnant shock wave is carried out using the MHD module of the code PLUTO. The structure of the flows in the collision region is obtained taking into account the magnetic fields of the rotating source stars. We present the profiles of the bulk plasma velocity, density and magnetic field in the collision region. The amplification of regular magnetic fields in such systems is studied.