Annotation of the results obtained in 2021
A wide-angle map of the supernova remnant Puppis A at energies above 4 keV has been obtained using the ART-XC Pavlinsky X-ray telescope on-board Spektr-RG. An article describing the work will be published in a peer-reviewed journal. A review of the most important results of the INTEGRAL observatory on sky mapping and cataloguing of X-ray radiation sources has been prepared. The uniqueness of wide-angle X-ray surveys of the Galaxy at energies of the hard X-ray energy range is demonstrated. An overview of the results of measuring the cosmic X-ray background using unique Earth shading maneuvers carried out at the INTEGRAL observatory is also presented. A study of the long-term evolution of the intensity of the massive molecular cloud Sagittarius B2 in the galactic centre was carried out using data from the INTEGRAL observatory in 2003-2019. It is shown that after the previously observed decrease in the reflected radiation flux in 2003-2009, constant radiation at a level of 1 mCrab in the range of 30-80 keV is observed. The X-ray spectrum of Sgr B2 is well described by a power law with a slope Γ = 1.4 and an exponential cutoff at an energy of about 43 keV. The residual radiation of the Sgr B2 molecular cloud in 2011-2019 is in good agreement with the models of a reflected X-ray flare from an external X-ray source, as well as with models of ionization of the cloud's neutral gas by low-energy particles of cosmic rays. However, the latter model predicts the amount of ionization of the interstellar medium, which is not confirmed by other experiments, which makes the model of ionization by cosmic rays less plausible. The data of the Coma cluster observations in the X-ray band with SRG/eROSITA have been analysed. The data cover a ~3°×3° area around the cluster with a typical exposure time of more than 20 ks. The stability of the instrumental background and operation of the SRG observatory in the scanning mode provided us with an excellent data set for studies of the diffuse emission up to a distance of ~1.5R200 from the Coma centre. In this study, we discuss the rich morphology revealed by the X-ray observations (also in combination with the SZ data) and argue that the most salient features can be naturally explained by a recent (ongoing) merger with the NGC 4839 group. The gas in the Coma core went through two shocks, first through the shock driven by NGC 4839 during its first passage through the cluster some gigayear ago and, more recently, through the "mini-accretion shock" associated with the gas settling back to quasi-hydrostatic equilibrium in the core. After passing through the primary shock, the gas should spend much of the time in a rarefaction region, where radiative losses of electrons are small, until the gas is compressed again by the mini-accretion shock. Unlike "runway" merger shocks, the mini-accretion shock does not feature a rarefaction region downstream and, therefore, the radio emission can survive longer. Such a two-stage process might explain the formation of the radio halo in the Coma cluster. A new X-ray-selected supernova remnant (SNR) candidate SRGe J0023+3625 = G116.6-26.1 was found in the SRG/eROSITA all-sky survey. The source features a large angular extent (~4 degrees in diameter), nearly circular shape, and X-ray spectrum dominated by emission lines of helium- and hydrogen-like oxygen. It lacks bright counterparts of similar extent at other wavelengths which could be unequivocally associated with it. Given the relatively high Galactic latitude of the source, |b|~26 degrees, we interpret these observational properties as an indication of the off-disc location of this SNR candidate. Namely, we propose that this object originated from a Type Ia supernova which exploded some 40 000 yr ago in the low density gas of the Milky Way halo at a distance of ~3 kpc from the Sun. The low density of the halo gas implies that the cooling and collisional ionization equilibrium (CEI) time-scales downstream of the forward shock are much longer than the age of the SNR. This results in a relatively soft spectrum, reflecting pre-shock ionization state of the gas, and strong boost in the plasma emissivity (compared to CEI) due to enhanced collisional excitation through the increased electron temperature. If confirmed, such a rare object would provide us with a unique 'in situ' probe of physical conditions (density, temperature and metallicity) near the interface between the Milky Way's disc and the halo. Recently, Medvedev et al. 2020 discovered X-ray emission from the quasar CFHQS J142952+544717 at redshift z = 6.18 in the SRG/eROSITA all-sky survey. We obtained additional observations of CFHQS J14+54 using the XMM-Newton orbital observatory. A detailed analysis of the data performed in Medvedev et al. 2021 has shown that the X-ray luminosity of this quasar is ~ 10 ^ 46 erg/sec and turns out to be hundreds of times higher than the luminosity of known quasars at redshifts z > 6. In this work, we estimated the mass of a supermassive black hole (SMBH) in CFHQS J14+54 at the level of > 2 x 10^9 solar masses. How SMBHs with such great masses appeared in the early Universe (the quasar redshift corresponds to the age of the Universe of ~ 1 billion years) is still one of the most intriguing questions in astrophysics today. The found quasar is "radio-loud", that means it has powerful emission in the radio range. It is commonly believed that such radiation is generated by relativistic charged particles produced in jets of quasars. However, CFHQS J14+54 is unlikely to be a blazar, so its high X-ray luminosity is unlikely to be related to the Doppler boosting effect. We put forward the hypothesis that the extreme X-ray properties of CFHQS J14+54 could be associated with the inverse Compton scattering of cosmic microwave background photons (at z = 6.18) off relativistic electrons in the jets. If so, CFHQS J14+54 along with SRGe J170245.3+130104, recently discovered in the SRG/eROSITA all-sky survey (z = 5.5, Khorunzhev et al 2021), might be the tip of the iceberg of high-z quasars with enhanced X-ray emission. X-ray reflection off dense molecular clouds in the Galactic Centre region has established itself as a powerful probe for the past activity record of the supermassive black hole Sgr A* on a timescale of a few hundred years. Detailed studies of the reflection signal from individual clouds allow us to estimate parameters of the brightest flare(s) and explore properties of the dense gas distribution inside and around them. On the other hand, wide area surveys covering the full Central Molecular Zone are crucial to spot brightening of the new clouds and long-term decay of the flux from the once bright ones. We present and discuss the data obtained by the SRG/eROSITA telescope in the course of its commissioning observations in late 2019 in regard to the X-ray reflection off CMZ clouds located to the East of Sgr A*. We measure the 4-8 keV flux from the currently brightest (in reflected emission) molecular complex Sgr A and derive upper limits for other molecular complexes. We confirm that the Sgr A complex keeps being bright at the level of 4e-13 erg/s/cm2/arcmin2, making it an excellent target for the deep forthcoming high resolution imaging and polarimetric observations. We also describe distinct features of the reflected emission from the clouds for which the primary illumination front has already passed away and the observed signal is dominated by multiply scattered radiation. The ionization state of the circumbinary material in symbiotic systems was studied with the help of the two-dimensional photoionization calculations based on the CLOUDY code and their emission-line spectra were predicted. The simulations are parameterised via the orbital parameters of the binary and the wind mass-loss rate of the donor star, while the mass accretion rate, temperature and luminosity of the white dwarf are computed self-consistently. The parameter space of symbiotic binaries was explored and luminosities of various astrophysically important emission lines computed. The line ratios were compared with traditional diagnostic diagrams used to distinguish symbiotic binaries from other types of sources, and it is shown how the binary system parameters shape these diagrams. In the significant part of the parameter space, the wind material is nearly fully ionized, except for the ‘shadow’ behind the donor star, so the white dwarf emission is typically freely escaping the system. The X-ray emission from the counterparts of historical classical novae in our Galaxy is studied. For this purpose, the data from three SRG/eROSITA sky surveys were used. We obtained distributions of the accretion rate of classical novae and stationary supersoft sources, and showed that these two classes of accreting white dwarfs occupy different, non-intersecting intervals in the accretion rate. Several super soft X-ray sources have been discovered that are associated with the post-nova supersoft X-ray emission. The X-ray spectra of sources of classical novae in a quiescent state have been investigated and it has been demonstrated that some of them are close in their X-ray properties to intermediate polars.

 

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Annotation of the results obtained in 2019
Galaxy clusters Moderately strong shock waves at the periphery of clusters have been shown to explain the nature of the observed radio relics. Methods have been developed for the joint analysis of data from interferometers and traditional telescopes (as applied to the millimeter wavelength range). Using these methods, the distribution of thermal pressure in the rich cluster of galaxies RX J1347.5-1145 was reconstructed and restrictions were imposed on the parameters of the shock wave in the Bullet cluster. Using observations of galaxy clusters in the X-ray range, it is shown that the viscosity of hot gas in clusters is suppressed by at least several orders of magnitude compared to a plasma in which the viscosity is determined by purely Coulomb collisions. The Galactic Center Possibility of determining the characteristics of supersonic turbulence inside molecular clouds irradiated with a short burst of X-ray radiation from Sgr A * by the measured distribution function of the surface brightness of the reflected signal has been demonstrated. Using IBIS/INTEGRAL data, we obtained the image of the supernova remnant RX J1713.7-3946 and performed the detailed analysis at energies up to 120 keV. It is shown that the available observational data are in a good agreement with the theoretical model of particle acceleration in young supernova remnants assuming the Bohm diffusion limit. The diffuse continuum of the inner region of the Galactic bulge was studied according to the NUSTAR telescope. It is shown that dwarf novae dominate in the bulge. A three-dimensional model of the ionization of the stellar wind of a giant star by ultraviolet and soft x-ray radiation of an accreting white dwarf with nuclear burning on the surface is constructed. Observations of a number of super-soft sources in the Magellanic Clouds with a spatial spectrometer WiFeS 2.3-meter telescope of the Australian National University were performed.

 

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Annotation of the results obtained in 2020
We systematically analysed heretofore the largest sample of spectra from black hole and neutron star X-ray binaries in the hard state. We found that the black holes and neutron stars occupy distinctly different regions in the y − kTe plane with neutron stars being characterised by systematically lower values of y-parameter and electron temperature. Observations of the symbiotic binary system LIN 358 were carried out and a 2D photo-ionisation model describing the observational data was constructed. The dependence of populations of soft and super-soft X-ray sources on the morphological type of the host galaxy was explored. Within the framework of the program for the joint study of the history of the activity of the supermassive black hole Sgr A* and the characteristics of the distribution of dense interstellar gas in the center of our Galaxy 1) predictions of properties of the X-ray echo of Sgr A*'s historical flares were obtained depending on the polarization properties of the primary flare radiation. 2) a proposal has been prepared and submitted for deep observations of the currently brightest (in reflected emission) molecular complex Sgr A by Chandra X-ray observatory. The proposal has been fully approved, the observations will be carried out in 2021. Chandra Proposal 22910118 “Unique X-ray Window into Internal Structure of the Cold Gas in Dense Molecular Clouds”, PI: Alexey Vikhlinin, https://cxc.harvard.edu/target_lists/cycle22/cycle22_approved_bpp.html 3) preparation for deep observations of the Sgr A molecular complex by the first imaging X-ray polarimeter IXPE (scheduled for launch in 2021) has been started. Within the framework of the program for the theoretical and numerical study of shock waves formed during the merging of galaxy clusters, 1) We show that merger shocks in galaxy clusters can take over regular accretion shocks and form a new baryonic boundary of a cluster. 2) We suggest that a newly discovered Mpc-size contact discontinuity in the periphery of the Perseus cluster (Abell 426) is the result of a collision between the merger and accretion shocks. 3) We argue that in the process of galaxy clusters merger, a pair of shocks is formed (one closer to the center and one much farther away). Formation of these shocks bears some similarity to nonlinear evolution of shocks, which produce so-called N-waves. 4) The feasibility of using Atacama Compact Array for validation of distant galaxy cluster candidates has been studied. This is in particular important for ongoing search of clusters with the SRG observatory. 5) The structure of the magnetic fields in the hot intra-cluster medium (ICM) and the ICM transport coefficients (e.g.,thermal conductivity) are poorly known. Here we suggest a new method for measuring these properties by studying the characteristic of weak shocks propagating through the ICM. 6) There are examples of compact sources, in particular, stellar mass black holes, which accrete matter at a rate exceeding the Eddington limit. Such systems drive outflows with sub-relativistic velocities. Observations suggest that the outflowing matter can recombine. We consider the consequences of having a fast beam of neutral particles of the ISM heating. It has been shown that Compton scattering by electrons of hot intergalactic gas in galaxy clusters should lead to distortions of the cosmic background X-ray and soft gamma radiation: namely, to an increase in its brightness at energies <60–100 keV and a fall at higher energies. A quantity is proposed that can be estimated from X-ray observations and which correlates well with the depth of the potential well of galaxy clusters. It is shown that the function of gravitational potentials is sensitive to the density of matter in the Universe and the amplitude of the mean-square fluctuations of the density of matter on a scale of 8 Mpc.

 

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