Simplified, computationally efficient models are needed to model low-energy flare events in the solar atmosphere. We describe a spatially isothermal model of a chromospheric magnetic flux tube that includes two regions with different temperatures: the initial temperature of the chromosphere and the temperature of the heated flare plasma. The thermal balance equation that takes into account the optically thin radiation, the change in the height of the chromosphere, and the heat exchange between its parts through the anomalous heat flux underlies the model. We analyze the response of our model chromosphere to heating analogous to the F-CHROMA grid of models based on the one-dimensional RADYN radiation hydrodynamics code. For a low heating energy flux, ∼3× 10^7 erg cm ^-2 , the model shows a good correspondence to the one-dimensional code and can be used to model nanoflares.
We consider the possibility of a random walk of protons (when a single acceleration event is the acceleration in one of the ‘‘macro’’-accelerators (magnetic cloud) with its own characteristic time) in stellar atmospheres or galaxies. We show that a set of such macro-accelerators can produce the necessary acceleration chain to reach characteristic energies in the cosmic-ray spectrum. We estimate the proton-accelerating stellar wind and the time it takes for this acceleration for various sources of particles. We show that protons during their propagation can continue to gain energy in fairly weak events for a long time.
We present the results of our optical and spectroscopic observations of the X-ray source SRGe J020254.8403705 carried out in 2023-2025 with the 1.5-m Russian-Turkish telescope (RTT-150). Our photometric data analysis has revealed two periodicities: and min. The short period is reliably detected both from our photometry and from the variability in spectral lines and is interpreted as the white-dwarf spin period. The long period has been found only from the photometric variability and may be associated with the orbital motion of the system. The optical spectra of the source contain a flat continuum with intense emission lines of hydrogen and neutral and ionized helium, including the He II line. The presence of an inverted Balmer decrement, the variability of the line equivalent widths and FWHMs with the white-dwarf spin period, and their antiphase variations point to a possible contribution of magnetically controlled accretion to the emission from the system. The SRG/eROSITA and Swift/XRT spectra of SRGe J020254.8+403705 in the energy range 0.3-10 keV are well described by the model of a hot optically thin plasma with a temperature kT similar to 30 KeV and luminosities L-x approximate to 0.5 & times; 10(33) and approximate to 1 & times; 10(33) erg s(-1), respectively, consistent with accretion onto a magnetic white dwarf. The corresponding estimates of the accretion rates are M approximate to 0.5 & times; 10(10) and approximate to 1 & times; 10(-10) M-circle dot yr(-1). According to our results, SRGe J020254.8403705 is classified as an intermediate polar.
