Spectroscopic Redshift Determination for a Sample of Distant Quasars Detected by the SRG Observatory Based on RTT-150 Observations. II

Astronomy Letters - Results of the spectroscopic observations at the 1.5-m Russian–Turkish telescope for another group of 12 X-ray sources discovered by the eROSITA telescope onboard the SRG...     

Spectroscopic Redshift Measurements for Galaxy Clusters from the Lockman Hole Survey with the eROSITA Telescope Onboard the SRG Observatory

Astronomy Letters - We present the first results of our program of optical observations for galaxy clusters from the Lockman Hole X-ray survey with the eROSITA telescope onboard the SRG space...     

Diffusion of elements in the interstellar medium in early-type galaxies

The role of diffusion in the redistribution of elements in the hot interstellar medium of earlytype galaxies is considered. It is well known that gravitational sedimentation can affect significantly the abundances of helium and heavy elements in the hot intergalactic gas of massive galaxy clusters. The universal temperature profile in cool-core clusters and the theoretical mass–temperature relation suggest that the maximum effect of sedimentation must take place in the most massive virialized objects in the Universe. However, observational data from the Chandra and XMM-Newton observatories demonstrate more complex scaling relations between the masses of early-type galaxies and other parameters, such as the mass fraction and temperature of the interstellar gas. An important fact is that the radial temperature profile can have both falling and rising patterns. We have calculated the diffusion based on the observed gas density and temperature distributions for 13 early-type galaxies that have different envelope types and cover a wide range of X-ray luminosities. To estimate the maximum effect of sedimentation and thermal diffusion, we have solved the full set of Burgers equations for a non-magnetized interstellar plasma. The results obtained demonstrate a considerable increase of the He/H ratio within one effective radius for all galaxies of our sample. For galaxies with a falling or constant temperature profile the average increase of the helium abundance is 60% in one billion years of diffusion. The revealed effect can introduce a significant bias into the metal abundance estimate based on X-ray spectroscopy and can affect the evolution of stars that could be formed from a gas with a high helium abundance.     

Optical and X-ray observations of thermonuclear bursts from GS 1826-24 during September–October 2003

The results of optical (the RTT-150 telescope) and X-ray (the RXTE observatory) observations of the burster GS 1826-24 are presented. Emphasis was placed on analyzing the emissions during thermonuclear bursts. The results obtained allowed the size of the accretion disk in GS 1826-24 and the inclination of this binary to be estimated.     

On the X-ray time-lags in the black hole candidates

It is shown that the energy dependence of the time-lags in Cygnus X-1 excludes any significant contribution of the standard reflected component to the observed lags. The conclusion is valid in the     frequency range where time-lags have been detected with sufficient significance. In fact, the data hint that the reflected component is working in the opposite direction, reducing the lags at energies where the contribution of the reflected component is significant.
We argue that the observed logarithmic dependence of time-lags on energy could be due to the small variations of the spectral index in the frame of a very simple phenomenological model. We assume that an optically thin flow/corona, emitting a power law like spectrum, is present at a range of distances from the compact object. The slope of the locally emitted spectrum is a function of distance, with the hardest spectrum emitted in the innermost region. If perturbations with different time-scales are introduced to the accretion flow at different radii, then X-ray lags naturally appear, caused by the inward propagation of perturbations on the diffusion time-scales.     

Constraints on the luminosity of the central source in SNR 1987A

We obtained constraints on the luminosity of the central source in SNR 1987 A using XMM-Newton and INTEGRAL data. XMM-Newton yields an upper limit on the SNR luminosity in the 2–10 keV energy band, L_X ? 5 × 10³⁴ erg s^?1. Since the optical depth of the envelope is still large in the XMM-Newton energy band, this constraint carries no useful information about the luminosity of the central source. The optical depth is expected to be small in the hard (20–200 keV) X-ray band of the IBIS telescope aboard the INTEGRAL observatory. We detected no statistically significant emission from SNR 1987 A in the INTEGRAL data and obtained an upper limit of L_X ? 1.1 × 10³⁶ erg s^?1 on the luminosity of the central source in the 20–60 keV band. We also obtained an upper limit on the mass of radioactive ⁴⁴Ti, M(⁴⁴Ti) ? 10^?3M_⊙.     

Optical Spectroscopy of SRG/eROSITA Objects with 2.5-m Telescope at the Caucasus Mountain Observatory of the SAI MSU

Astronomy Letters - Based on observations with the new transient double-beam spectrograph (TDS) at the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU, we have determined the types...     

Optical Spectroscopy of Quasars Discovered by SRG/eROSITA with a 2.5-m Telescope at the Caucasus Mountain Observatory of SAI MSU

Astronomy Letters - Based on observations with the transient double-beam spectrograph (TDS) at the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU, we have determined the redshifts...