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Vol 49, No 5 (2023)
Articles
Cosmic Abundance of Iron
Abstract
I explore the possibility of estimating an upper limit for the present-day iron abundance in the baryonic matter at which the gamma-ray background from the decay of 56 Ni synthesized in the Universe to date comes into conflict with the observed MeV gamma-ray background. I calculate the brightness of the gamma-ray background from SNe Ia and SNe II by taking into account the gamma-ray scattering and absorption in supernova ejecta. The model brightness of the gamma-ray background is shown to be consistent with the observed MeV gamma-ray background if the iron abundance in the baryonic matter is less than 15% of the solar one.
301-307
Investigation of the Flaring Activity of BL Lac in July–November 2021
Abstract
The source BL Lac exhibited an enhanced activity from August 2020 to July 2022. This activity peaked in July–August 2021. In this period the source reached historic brightness maxima in various energy ranges. Observations of this nonstandard maximum were carried out by the SAI staff of the Crimean Station of SAI and with the telescopes of the Caucasus Mountain Observatory (CMO SAI MSU). Optical and near-infrared photometric data as well as optical polarimetric data were obtained. When investigating the correlation between the optical and gamma-ray fluxes and between the optical and infrared fluxes, its high degree with an almost zero lag was confirmed—this means that the emission regions spatially coincide or are very close together. The degree of linear polarization in the investigated period changed in a wide range, reaching 20 %, with an anticorrelation between the degree of linear polarization and the brightness of the object having been observed. A similar pattern of variation was also observed in the preceding flares of this object. The changes in the electric vector position angle (EVPA) show a dependence on the rate of change of the object’s brightness. The EVPA changed greatly during flares and slowly at the times of a slow change in the intensity.
308-321
Can Observations of 511 keV Line From the M31 Galaxy Shed Light on the AGN Jet Composition? 1 [1]
Abstract
Positron annihilation line at 511 keV is a known component of the gamma-ray diffuse emission. It is believed to be produced in the Galaxy, but there could be possible extragalactic contribution as well. E.g., positrons can be produced in jets of active galactic nuclei (AGN) and after that accumulate and gradually annihilate in hot gaseous halos around galaxies. In this work we test this hypothesis in application to an individual object – the Andromeda galaxy (M31) which is close and has a supermassive black hole in its center, which powered an AGN before. We compute the growth history of the supermassive black hole in M31, relate it to the evolution of jet luminosity and estimate the positron content in its halo. We calculate the 511 keV photon flux due to positron annihilation which should be observed at Earth and find the value of around \(10^{-4}\) photon cm\({}^{-2}\)s\({}^{-1}\). It is very close to the observational limits (\(<10^{-4}\)photon cm\({}^{-2}\)s\({}^{-1}\)) set by the INTEGRAL/SPI in the assumption of the point source, so further observations would be able to constrain leptonic models of the jets and propagation of cosmic rays in the circumgalactic medium of large spiral galaxies.
322-323
Counter-Rotating Gaseous Disk and Star Formation in the S0 Galaxy NGC 934
Abstract
Using long-slit and panoramic spectroscopy at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and by mapping emission lines in a narrow passband of 13 Å with the MaNGaL instrument at the 2.5-m telescope of the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Lomonosov Moscow State University, we have investigated the gaseous component of the giant lenticular galaxy NGC 934. The gas kinematics in the galaxy has turned out to disagree completely with the stellar kinematics, suggesting recent accretion of a large amount of cold gas by the galaxy. Weak star formation proceeds in the accreted gas on the periphery of the galaxy, mainly in a ring of radius 26 kpc, which may promise the buildup of a giant low-surface-brightness stellar disk in this early-type galaxy. The gas metallicity in the star formation ring is nearly solar: the accretion source is most likely the swallowing of a massive gas-rich satellite.
324-334
X-ray Halo of the Pulsar 4U 1538–52 from SRG Data
Abstract
We present the first results of the SRG observation of the pulsar 4U 1538–52 based on ARC-XC and eROSITA data. An extended emission in the form of a halo is detected around the source in the 0.5–8 keV energy band. Our simulation has shown that its surface brightness distribution can be described by a two-component model composed of a flat disk 250 in radius and a b-model with a characteristic size 480. We have constructed a broadband spectrum of 4U 1538–52 in the energy range 0.5–30 keV, which can be fitted by a weakly absorbed (
NH=0,7*1022 cm-2) power law with a high-energy cutoff. In addition, iron emission lines are detected in the pulsar spectrum at 6–7 keV. We show that the observed halo spectrum is considerably softer (a power-law index 2.8) than the pulsar spectrum (a power-law index 0.9), consistent with the predictions of theoretical models for the X-ray scattering by dust.
335-344
Spectral and Temporal Analysis of the Supergiant Fast X-ray Transient IGR J16195–4945 with SRG/ART-XC
Abstract
We present the results of the analysis of the SRG/ART-XC observation of the Supergiant Fast X-ray Transient IGR J16195-4545 performed on March 3, 2021. Six bright flares are present in the light curve, with no significant change in hardness occuring during these flares. The spectrum is described with an absorbed power law model with a high energy exponential cutoff showing heavy absorption, with
NH = (12 ± 2) × 1022ñì−2, and Γ = 0.56 ± 0.15, Ecut = 13 ± 2 keV. Adopting the Bayesian block decomposition of the light curve, we measured the properties of the observed flares (duration, rise time, waiting time, released energy and pre-flare luminosity), which are consistent with the quasi-spherical subsonic accretion model. The stellar wind velocity of the supergiant is estimated to be vw ≈ 500 km s−1.. Additionally, the system was found to have an unusual near-IR variability.
345-352
Properties of the Flare Energy Release in Force-Free Magnetic Flux Ropes
Abstract
A straight cylindrical, electrically shielded magnetic flux rope is considered as the upper part of a weakly curved magnetic loop whose footpoints are fixed in the photosphere. All parameters of the flux rope depend on one variable—the distance r from the axis of its symmetry. As the flux rope rises into the rarefied solar atmosphere, the external pressure keeping the flux rope from lateral expansion drops continuously. At some critical value of it the longitudinal magnetic field of the flux rope vanishes on the magnetic surface where the longitudinal electric current changes its sign in accordance with the requirement for the total current to be shielded. At the same time, the azimuthal current and the force-free parameter near this surface grow indefinitely. Because of this growth, the electron drift velocity near this surface exceeds the ion-sound speed, leading to the excitation of a plasma ion-sound instability as a trigger of flare energy release. The plasma conductivity in the region of plasma turbulence drops by seven orders of magnitude. Rapid magnetic energy dissipation at the anomalous resistivity generates an inductive electric field in the plasma that exceeds considerably the Dreicer limit. This explains the efficient acceleration of particles in the region where the magnetic field weakens rapidly.
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