arXiv subjects

Ilya A. Mereminskiy

Publications and source records attributed to Ilya A. Mereminskiy.

12 recordsLinked to original sources

arXiv2026

SRGA J115215.0$-$510656: an unusual long-period eclipsing dwarf nova with disc wind signatures

We present the first detailed optical study of the cataclysmic variable SRGA J115215.0$-$510656, based on new time-resolved photometric and spectroscopic observations complemented by long-baseline Transiting Exoplanet Survey Satellite (TESS) data. The TESS light curve reveals deep, recurring eclipses consistent with a high-inclination geometry and an orbital period of 0.43567659(9)d. The eclipse morphology during outburst is consistent with a possible 'inside-out' type outburst and supports classification of the system as a U Gem-type dwarf nova. By combining eclipse phase width and ellipsoidal modulation, we constrain the system geometry to a narrow locus in the $(q,i)$ plane, with allowed mass ratios $0.28 \lesssim q \lesssim 0.84$ and inclinations $i$ $\simeq$75$-$84$^{\circ}$. The persistence of single-peaked Balmer lines during outburst, together with strong He II emission and a flattened Balmer decrement, points towards emission arising in a disc wind or vertically extended regions above the disc. Absorption features from a late-type secondary star (approximately K3) are detected, contributing roughly 30 per cent of the red optical flux. Comparison with main-sequence expectations suggests that the donor star is moderately inflated, consistent with a mildly evolved secondary. With its long orbital period, modest outburst amplitude, and emission-line characteristics, SRGA J115215.0$-$510656 appears to be a rare and compelling example of a bright, long-period dwarf nova whose optical properties are influenced by disc-wind processes during outburst.

astro-ph.SR↗

arXiv2024

Flickering pulsations in bright X-ray pulsars: the evidence of gravitationally lensed and eclipsed accretion column

It is expected that extreme mass accretion rate onto strongly magnetised neutron star results in appearance of accretion columns above stellar surface. For a distant observer, rotation of a star results in periodic variations of X-ray flux. Because the mass accretion rate fluctuates around the average value, the pulse profiles are not stable and demonstrate fluctuations as well. In the case of bright X-ray pulsars, however, pulse fluctuations are not solely attributed to variations in the mass accretion rate. They are also influenced by the variable height of the columns, which is dependent on the mass accretion rate. This study delves into the process of pulse profile formation in bright X-ray pulsars, taking into account stochastic fluctuations in the mass accretion rate, the corresponding variations in accretion column geometry and gravitational bending. Our analysis reveals that potential eclipses of accretion columns by a neutron star during their spin period should manifest specific features in pulse profile variability. Applying a novel pulse profile analysis technique, we successfully detect these features in the bright X-ray transient V0332+53 at luminosities $\gtrsim 2\times 10^{38}\,{\rm erg\,s^{-1}}$. This detection serves as compelling evidence for the eclipse of an accretion column by a neutron star. Detection of the eclipse places constraints on the relation between neutron star mass, radius and accretion column height. Specifically, we can establish an upper limit on the accretion column height, which is crucial for refining theoretical models of extreme accretion.

astro-ph.HE↗

arXiv2024

Nature of the diffuse emission sources in the H I supershell in the galaxy IC 1613

We present a study of the nearby low-metallicity dwarf galaxy IC 1613, focusing on the search for massive stars and related feedback processes, as well as for faint supernova remnants (SNR) in late stages of evolution. We obtained the deepest images of IC 1613 in the narrow-band Hα, He II and [S II] emission lines and new long-slit spectroscopy observations using several facilities (6-m BTA, 2.5m SAI MSU, and 150RTT telescopes), in combination with the multi-wavelength archival data from MUSE/VLT, VLA, XMM-Newton, and Swift/XRT. Our deep narrow-band photometry identifies several faint shells in the galaxy, and we further investigate their physical characteristics with the new long-slit spectroscopy observations and the archival multi-wavelength data. Based on energy balance calculations and assumptions about their possible nature, we propose that one of the shells is a possible remnant of a supernova explosion. We study five out of eight Wolf-Rayet (WR) star candidates previously published for this galaxy using the He ii emission line mapping, MUSE/VLT archival spectra, and new long-slit spectra. Our analysis discards the considered WR candidates and finds no new ones. We found P Cyg profiles in Hα line in two stars, which we classify as Luminous Blue Variable (LBV) star candidates. Overall, the galaxy IC 1613 may have a lower rate of WR star formation than previously suggested.

astro-ph.GA↗

arXiv2023

Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431

We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January--February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar's geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind.

astro-ph.HE↗

arXiv2023

A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375

Accreting X-ray pulsars (XRPs) are presumably ideal targets for polarization measurements, as their high magnetic field strength is expected to polarize the emission up to a polarization degree of ~80%. However, such expectations are being challenged by recent observations of XRPs with the Imaging X-ray Polarimeter Explorer (IXPE). Here we report on the results of yet another XRP, EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT and SRG/ART-XC. In line with recent results obtained with IXPE for similar sources, analysis of the EXO 2030+375 data returns a low polarization degree of 0%-3% in the phase-averaged study and variation in the range 2%-7% in the phase-resolved study. Using the rotating vector model we constrain the geometry of the system and obtain a value for the magnetic obliquity of ~$60^{\circ}$. Considering also the estimated pulsar inclination of ~$130^{\circ}$, this indicates that the magnetic axis swings close to the observer line of sight. Our joint polarimetric, spectral and timing analysis hint to a complex accreting geometry where magnetic multipoles with asymmetric topology and gravitational light bending significantly affect the observed source behavior.

astro-ph.HE↗

arXiv2022

First characterization of a new High Mass X-ray Binary in LMC eRASSU J050810.4$-$660653 with SRG/ART-XC, NuSTAR and Swift

We report results of the first detailed spectral and temporal studies of the recently discovered Be/X-ray binary eRASSU J050810.4$-$660653 in LMC based on the data from the SRG/ART-XC, NuSTAR and Swift/XRT instruments obtained in December 2021 - May 2022 in a wide energy range of 0.5-79 keV. Pulsations with the period of $40.5781 \pm 0.0004$ s were found in the source light curve with the pulsed fraction monotonically increasing with the energy. An estimate of the orbital period of $\sim38$ days was obtained based on the long-term monitoring of the system. The source spectrum can be well approximated with a power-law model modified by an exponential cutoff at high energies. The pulse phase-resolved spectroscopy shows a strong variation of spectral parameters depending on the phase of a neutron star rotation. We have not found any features connected with the cyclotron absorption line both in the phase-averaged and phase-resolved spectra of eRASSU J050810.4$-$660653. However, the neutron star magnetic field was estimated around several $10^{13}$ G using different indirect methods. Discovered variations of the hardness ratio over the pulse phase is discussed in terms of physical and geometrical properties of the emitting region.

astro-ph.HE↗

arXiv2021

SRG/ART-XC, Swift, NICER and NuSTAR study of different states of the transient X-ray pulsar MAXI J0903-531

The results of the broadband spectral and timing study of the recently discovered transient X-ray pulsar MAXI J0903-531 in a wide range of luminosities differing by a factor of ~30 are reported. The observed X-ray spectrum in both states can be described as a classical pulsar-like spectrum consisting of the power-law with the high-energy cutoff. We argue that absence of the spectrum transformation to the two-hump structure expected at low fluxes points to a relatively weak magnetic field of the neutron star below (2-3)$\times10^{12}$ G. This estimate is consistent with other indirect constraints and non-detection of any absorption features which can be interpreted as a cyclotron absorption line. Timing analysis of the NuSTAR data revealed only slight variations of a single-peaked pulse profile of the source as a function of the energy band and mass accretion rate. In both intensity states the pulsed fraction increases from 40% to roughly 80% with the energy. Finally we were also able to obtain the orbital solution for the binary system using data from the Fermi/GBM, NICER and NuSTAR instruments.

astro-ph.HE↗

arXiv2021

15 years of Galactic surveys and hard X-ray Background measurements

The INTEGRAL hard X-ray surveys have proven to be of fundamental importance. INTEGRAL has mapped the Galactic plane with its large field of view and excellent sensitivity. Such hard X-ray snapshots of the whole Milky Way on a time scale of a year are beyond the capabilities of past and current narrow-FOV grazing incidence X-ray telescopes. By expanding the INTEGRAL X-ray survey into shorter timescales, a productive search for transient X-ray emitters was made possible. In more than fifteen years of operation, the INTEGRAL observatory has given us a sharper view of the hard X-ray sky, and provided the triggers for many follow-up campaigns from radio frequencies to gamma-rays. In addition to conducting a census of hard X-ray sources across the entire sky, INTEGRAL has carried out, through Earth occultation maneuvers, unique observations of the large-scale cosmic X-ray background, which will without question be included in the annals of X-ray astronomy as one of the mission's most salient contribution to our understanding of the hard X-ray sky.

astro-ph.HE↗

arXiv2019

Observational constraints on the magnetic field of the bright transient Be/X-ray pulsar SXP 4.78

We report results of the spectral and timing analysis of the Be/X-ray pulsar SXP 4.78 using the data obtained during its recent outburst with NuSTAR, Swift, Chandra and NICER observatories. Using an overall evolution of the system luminosity, spectral analysis and variability power spectrum we obtain constraints on the neutron star magnetic field strength. We found a rapid evolution of the variability power spectrum during the rise of the outburst, and absence of the significant changes during the flux decay. Several low frequency quasi-periodic oscillation features are found to emerge on the different stages of the outburst, but no clear clues on their origin were found in the energy spectrum and overall flux behaviour. We use several indirect methods to estimate the magnetic field strength on the neutron star surface and found that most of them suggest magnetic field $B \lesssim 2 \times10^{12}$ G. The strictest upper limit comes from the absence of the cyclotron absorption features in the energy spectra and suggests relatively weak magnetic field $B < 6 \times 10^{11}$ G.

astro-ph.HE↗

arXiv2019

Investigation of the Outburst Activity of the Black Hole Candidate GRS 1739-278

We have performed a joint spectral and timing analysis of the outburst of GRS 1739-278 in 2014 based on Swift and INTEGRAL data. We show that during this outburst the system exhibited both intermediate states: hard and soft. Peaks of quasi-periodic oscillations (QPOs) in the frequency range 0.1-5 Hz classified as type-C QPOs have been detected from the system. Using Swift/BAT data we show that after the 2014 outburst the system passed to the regime of mini-outburst activity: apart from the three mini-outbursts mentioned in the literature, we have detected four more mini-outbursts with a comparable (~20 mCrab) flux in the hard energy band (15-50 keV). We have investigated the influence of the accretion history on the outburst characteristics: the dependence of the peak flux in the hard energy band in the low/hard state on the time interval between the current and previous peaks has been found (for the outbursts during which the system passed to the high/soft state).

astro-ph.HE↗

arXiv2018

Studying temporal variability of GRS1739-278 during the 2014 outburst

We report a discovery of low-frequency quasi periodic oscillation at 0.3-0.7 Hz in the power spectra of the accreting black hole GRS1739-278 in the hard-intermediate state during its 2014 outburst based on the ${\it NuSTAR}$ and Swift/XRT data. The QPO frequency strongly evolved with the source flux during the NuSTAR observation. The source spectrum became softer with rising QPO frequency and simultaneous increasing of the power-law index and decreasing of the cut-off energy. In the power spectrum, a prominent harmonic is clearly seen together with the main QPO peak. The fluxes in the soft and the hard X-ray bands are coherent, however, the coherence drops for the energy bands separated by larger gaps. The phase-lags are generally positive (hard) in the 0.1-3 Hz frequency range, and negative below 0.1 Hz. The accretion disc inner radius estimated with the relativistic reflection spectral model appears to be $R_{\rm in} < 7.3 R_{\rm g}$. In the framework of the relativistic precession model, in order to satisfy the constraints from the observed QPO frequency and the accretion disc truncation radius, a massive black hole with $M_{\rm BH} \approx 100$M$_\odot$ is required.

astro-ph.HE↗

arXiv2016

INTEGRAL/IBIS deep extragalactic survey: M81, LMC and 3C 273/Coma fields

We present results of deep surveys of three extragalactic fields, M81 (exposure of 9.7 Ms), LMC (6.8 Ms) and 3C 273/Coma (9.3 Ms), in the hard X-ray (17-60 keV) energy band with the IBIS telescope onboard the INTEGRAL observatory, based on 12 years of observations (2003-2015). The combined survey reaches a $4σ$ peak sensitivity of 0.18 mCrab (2.6$\times$10$^{-12}$ erg s$^{-1}$ cm$^{-2}$) and sensitivity better than 0.25 and 0.87 mCrab over 10% and 90% of its full area of 4900 deg$^{2}$, respectively. We have detected in total 147 sources at $S/N>4σ$, including 37 sources observed in hard X-rays for the first time. The survey is dominated by extragalactic sources, mostly by active galactic nuclei (AGN). The sample of identified sources contains 98 AGN (including 64 Seyfert galaxies, 7 LINERs, 3 XBONGs, 16 blazars and 8 AGN of unclear optical class), two galaxy clusters (Coma and Abell 3266), 17 objects located in the Large and Small Magellanic Clouds (13 high- and 2 low-mass X-ray binaries and 2 X-ray pulsars), three Galactic cataclysmic variables, one ultraluminous X-ray source (ULX, M82 X-1) and one blended source (SWIFT J1105.7+5854). The nature of 25 sources remains unknown, so that the surveys identification is currently complete at 83%. We have constructed AGN number-flux relations ($\log{N}$-$\log{S}$) and calculated AGN number densities in the local Universe for the entire survey and for each of the three extragalactic fields.

astro-ph.HE↗