arXiv subjects

A. A. Lutovinov

Publications and source records attributed to A. A. Lutovinov.

At least 37 records · Page 2Linked to original sources

arXiv2021

Phase-Resolved Spectroscopy of the Magnetar SGR J1745-2900 Based on Data from the NuSTAR Observatory

The magnetar SGR J1745-2900 located in the vicinity of the supermassive black hole Sgr A$^{\star}$ was detected during its X-ray outburst with the Swifht/XRT telescope in April 2013. For several months after its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period $\sim3.76$ s to be recorded. Using these observations, we have studied in detail the dependence of the pulse profile and the pulsed fraction on the energy and intensity of the magnetar. The pulsed fraction in the 3-5 and 5-10 keV energy bands is shown to be 40-50%, slightly increasing with decreasing flux. We have performed phase-resolved spectroscopy for the source in the energy band from 3 to $\sim$40 keV and show that the temperature of the emitting regions remains fairly stable during the pulse, while their apparent size changes significantly with phase.

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arXiv2021

The X-ray pulsar XTE J1858+034 observed with NuSTAR and Fermi/GBM: spectral and timing characterization plus a cyclotron line

Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the spectral and timing behavior of the neutron star can be studied in detail. We analyze a $NuSTAR$ observation of the XRP XTE J1858+034 during its outburst in 2019. The spectrum is fit with a phenomenological, a semi-empirical and a physical spectral model. A candidate cyclotron line is found at $48\,$keV, implying a magnetic field of $5.4\times10^{\rm 12}\,$G at the site of emission. This is also supported by the physical best-fit model. We propose an orbital period of about $81$ days based on the visual inspection of the X-ray outbursts recurrence time. Based on $Fermi$ Gamma-ray Burst Monitor data, the standard disk accretion-torque theory allowed us to infer a distance of $10.9\pm1.0\,$kpc. Pulse profiles are single-peaked and show a pulsed fraction that is strongly energy-dependent at least up to $40$ keV.

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arXiv2018

Optical Identification of X-ray Sources from the 14-Year INTEGRAL All-Sky Survey

We present the results of our optical identifications of several hard X-ray sources from the INTEGRAL all-sky survey obtained over 14 years of observations. Having improved the positions of these objects in the sky with the X-ray telescope (XRT) of the Swift observatory and the XMM-Newton observatory, we have identified their counterparts using optical and infrared sky survey data. We have obtained optical spectra for more than half of the objects from our sample with the RTT-150 and AZT-33IK telescopes, which have allowed us to establish the nature of the objects and to measure their redshifts. Six sources are shown to be extragalactic in origin and to belong to Seyfert 1 and 2 galaxies (IGR J01017+6519, IGR J08215-1320, IGR J08321-1808, IGR J16494-1740, IGR J17098-2344, IGR J17422-2108); we have failed to draw definitive conclusions about the nature of four more objects (IGR J11299-6557, IGR J14417-5533, IGR J18141-1823, IGR J18544+0839), but, judging by circumstantial evidence, they are most likely also extragalactic objects. For one more object (IGR J18044-1829) no unequivocal identification has been made.

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arXiv2018

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the Z and Y Filters of the Vista Sky Surveys and the IRAC Filters of the Spitzer Sky Surveys

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric $Z$ and $Y$ bands of the infrared VVV (VISTA/ESO) survey and the [3.6],[4.5], [5.8] and [8.0] bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: $M_{Z}= -0.20\pm0.04$ and $M_{Y}=-0.470\pm0.045$, $M_{[3.6]}= -1.70\pm0.03$, $M_{[4.5]}= -1.60\pm0.03$, $M_{[5.8]}= -1.67\pm0.03$ and $M_{[8.0]}= -1.70\pm0.03$. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, $[M/H]\simeq0.40$ (${\bf Z} \simeq 0.038$) with an error of $[M/H]\simeq 0.1$ dex, while the effective temperature is $4250\pm150$ K. Stars with an age of 9-10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of $\sim8$ can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200-8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.

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arXiv2017

Peculiarities of super-Eddington flares from the X-ray pulsar LMC X-4 with NuSTAR

We present results of the analysis of super-Eddington flares registered from the X-ray pulsar LMC X-4 by the NuSTAR observatory in the broad energy range 3-79 keV. The pulsar spectrum is well described by the thermal comptonization model both in a quiescent state and during flares, when the peak luminosity reaches values $L_{\rm x} \sim (2-4)\times10^{39}$ erg s$^{-1}$. An important feature, found for the first time, is that the order of magnitude increase in the luminosity during flares is observed primarily at energies below 25-30 keV, whereas at higher energies (30-70 keV) the shape of the spectrum and the source flux remain practically unchanged. The luminosity increase is accompanied by changes in the source pulse profile -- in the energy range of 3-40 keV it becomes approximately triangular, and the pulsed fraction increases with increasing energy, reaching 60-70% in the energy range of 25-40 keV. The paper discusses possible changes in the geometry of the accretion column, which can explain variations in spectra and pulse profiles.

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arXiv2017

Radius of the neutron star magnetosphere during disk accretion

The dependence of the spin frequency derivative $\dotν$ of accreting neutron stars with a strong magnetic field (X-ray pulsars) on the mass accretion rate (bolometric luminosity, $L_{bol}$) has been investigated for eight transient pulsars in binary systems with Be stars. Using data from the Fermi/GBM and Swift/BAT telescopes, we have shown that for seven of the eight systems the dependence $\dotν$ can be fitted by the model of angular momentum transfer through an accretion disk, which predicts the relation $\dotν\sim L^{6/7}_{bol}$. Hysteresis in the dependence $\dotν(L_{bol})$ has been confirmed in the system V 0332+53 and has been detected for the first time in the systems KS 1947+300, GRO J1008-57, and 1A 0535+26. The radius of the neutron star magnetosphere in all of the investigated systems have been estimated. We show that this quantity varies from pulsar to pulsar and depends strongly on the analytical model and the estimates for the neutron star and binary system parameters.

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arXiv2017

Stable accretion from a cold disc in highly magnetized neutron stars

The aim of this paper is to investigate the transition of a strongly magnetized neutron star into the accretion regime with very low accretion rate. For this purpose we monitored the Be-transient X-ray pulsar GRO J1008-57 throughout a full orbital cycle. The current observational campaign was performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV) between two subsequent Type I outbursts in January and September 2016. The expected transition to the propeller regime was not observed. However, the transitions between different regimes of accretion were detected. In particular, after an outburst the source entered a stable accretion state characterised by the accretion rate of ~10^14-10^15 g/s. We associate this state with accretion from a cold (low-ionised) disc of temperature below ~6500 K. We argue that a transition to such accretion regime should be observed in all X-ray pulsars with certain combination of the rotation frequency and magnetic field strength. The proposed model of accretion from a cold disc is able to explain several puzzling observational properties of X-ray pulsars.

astro-ph.HE↗

arXiv2017

Modeling of High-Frequency Variability in X-ray Binaries with Black Holes

The properties of the aperiodic variability in X-ray binaries with black holes are considered. The power spectra of the luminosity variability for a flat accretion disk that is an emission source with a power-law energy spectrum have been modeled. At low frequencies the derived power spectrum has the form of a power law with a slope $ρ\approx-1$ and a cutoff at a frequency approximately equal to the fluctuations characteristic frequency at the disk inner edge; at higher frequencies the power spectrum has a complex form. The high-frequency variability is suppressed due to the arrival time delays of the photons emerging in the different parts of the disk. The presence of azimuthal accretion rate fluctuations in the disk and the azimuthal non-uniformity of the disk surface brightness in the observer's imaginary plane caused by the relativistic effects give rise to an additional variability at frequencies $\sim$200 Hz.

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arXiv2017

SMC X-3: the closest ultraluminous X-ray source powered by a neutron star with non-dipole magnetic field

Magnetic field of accreting neutron stars determines their overall behaviour including the maximum possible luminosity. Some models require an above-average magnetic field strength (> 10^13 G) in order to explain super-Eddington mass accretion rate in the recently discovered class of pulsating ultraluminous X-ray sources (ULX). The peak luminosity of SMC X-3 during its major outburst in 2016-2017 reached ~2.5x10^39 erg/s comparable to that in ULXs thus making this source the nearest ULX-pulsar. SMC X-3 belongs to the class of transient X-ray pulsars with Be optical companions, and exhibited a giant outburst in July 2016 - February 2017. The source has been observed during the entire outburst with the Swift/XRT and Fermi/GBM telescopes, as well as the NuSTAR observatory. Collected data allowed us to estimate the magnetic field strength of the neutron star in SMC X-3 using several independent methods. Spin evolution of the source during and between the outbursts and the luminosity of the transition to so-called propeller regime in the range of (0.3 - 7)x10^35 erg/s imply relatively weak dipole field of (1 - 5)x10^12 G. On the other hand, there is also evidence for much stronger field in the immediate vicinity of the neutron star surface. In particular, transition from super- to sub-critical accretion regime associated with cease of the accretion column, absence of cyclotron absorption features in the broadband X-ray spectrum of the source obtained with NuSTAR and very high peak luminosity favor an order of magnitude stronger field. This discrepancy makes SMC X-3 a good candidate to posses significant non-dipolar components of the field, and an intermediate source between classical X-ray pulsars and accreting magnetars which may constitute an appreciable fraction of ULX population.

astro-ph.HE↗

arXiv2016

Observations of the X-ray pulsar LMC X-4 with NuSTAR: limit on the magnetic field and tomography of the system in the fluorescent iron line

We present results of the spectral and timing analysis of the X-ray pulsar LMC X-4 with the NuSTAR observatory in the broad energy range 3-79 keV. Along with the detailed analysis of the averaged source spectrum, the high-precision pulse phased-resolved spectra were obtained for the first time. It has been shown that the comptonization model gives the best approximation of the obtained spectra. The evolution of its parameters was traced depending on the pulse phase as well. The search for the possible cyclotron absorption line was performed for all energy spectra in the 5-55 keV energy range. The obtained upper limit for the depth of the cyclotron absorption line $τ\simeq0.15$ ($3σ$) indicates no cyclotron absorption line in this energy range, which provides an estimate of the magnitude of the magnetic field on the surface of the neutron star: $B < 3 \times 10^{11}$ G or $B > 6.5 \times 10^{12}$ G. The latter one is agree with the estimate of the magnetic field obtained from the analysis of the power spectrum of the pulsar: $B \sim 3 \times 10^{13}$ G. Based on results of the pulse phase-resolved spectroscopy we revealed a delay between maxima of the source emission and the equivalent width of the fluorescent iron line. This delay can be apparently associated with the travel time of photons between the emitting regions in the vicinity of the neutron star and the relatively cold regions where this emission is reflected (presumably, at the inflowing stream or at the place of an interaction of the stream and the outer edge of the accretion disk).

astro-ph.HE↗

arXiv2016

Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and V 0332+53

We present the results of the monitoring programmes performed with the Swift/XRT telescope and aimed specifically to detect an abrupt decrease of the observed flux associated with a transition to the propeller regime in two well known X-ray pulsars 4U 0115+63 and V 0332+53 during their giant outbursts in 2015. Such transitions were detected at the threshold luminosities of $(1.4\pm0.4)\times10^{36}$ erg s$^{-1}$ and $(2.0\pm0.4)\times10^{36}$ erg s$^{-1}$ for 4U 0115+63 and V 0332+53, respectively. Spectra of the sources are shown to be significantly softer during the low state. In both sources, the accretion at rates close to the aforementioned threshold values briefly resumes during the periastron passage following the transition into propeller regime. The strength of the dipole component of the magnetic field required to inhibit the accretion agrees well with estimates based on the position of the cyclotron lines in their spectra, thus excluding presence of a strong multipole component of the magnetic field in the vicinity of the neutron star.

astro-ph.HE↗

arXiv2015

IGR J17463-2854, a Possible Symbiotic Binary System in the Galactic Center Region

This paper is devoted to determining the nature of the hard X-ray source IGR J17463-2854 located toward the Galactic bulge. Using data from the INTEGRAL and Chandra X-ray observatories, we show that five point X-ray sources with approximately identical fluxes in the 2-10 keV energy band are detected in the error circle of the object under study. In addition, significant absorption at low energies has been detected in the spectra of all these sources. Based on data from the VVV (VISTA/ESO) infrared Galactic Bulge Survey, we have unambiguously identified three of the five sources, determined the J, H and K magnitudes of the corresponding stars, and obtained upper limits on the fluxes for the remaining two sources. Analysis of the color-magnitude diagrams has shown that one of these objects most likely belongs to a class of rarely encountered objects, symbiotic binary systems (several tens are known with certainty), i.e., low-mass binary systems consisting of a white dwarf and a red giant. Note that all our results were obtained using improved absorption values and an extinction law differing in this direction from the standard one.

astro-ph.HE↗

arXiv2015

On the Possibility of Improving the Orbits of Satellites Based on Observations of Isolated X-ray Pulsars

At present, there is a great worldwide interest in the development of technologies that allow information about the X-ray emission from pulsating cosmic sources to be used to obtain navigation solutions for deep-space spacecraft. In this paper, we illustrate the technique for determining the spatial position of a spacecraft based on the already existing data from the RXTE X-ray space observatory. We show that the spacecraft position toward the Crab pulsar can be determined using an X-ray detector with an effective area of about 0.6 sq.m in the energy range 3-15 keV with an accuracy up to 730 m in a signal integration time of 1000 s. Extending the energy range to 1 keV (the efficiency of the RXTE/PCA spectrometer decreases dramatically at energies below 3 keV) will allow a spacecraft position accuracy of 400-450 m to be achieved at the same effective area and up to 300-350 m when using detectors with an effective area of ~1 sq.m in the energy range 1-10 keV.

astro-ph.HE↗

arXiv2015

Determining the Nature of Faint X-Ray Sources from the ASCA Galactic Center Survey

We present the results of the identification of six objects from the ASCA Galactic center and Galactic plane surveys: AXJ173548-3207, AXJ173628-3141, AXJ1739.5-2910, AXJ1740.4-2856, AXJ1740.5-2937, AXJ1743.9-2846. Chandra, XMM-Newton, and XRT/Swift X-ray data have been used to improve the positions of the optical counterparts to these sources. Thereafter, we have carried out a series of spectroscopic observations of the established optical counterparts at the RTT-150 telescope. Analysis of X-ray and optical spectra as well as photometric measurements in a wide wavelength range based on optical and infrared catalogs has allowed the nature of the program sources to be determined. Two X-ray objects have been detected in the error circle of AXJ173628-3141: one is a coronally active G star and the other may be a symbiotic star, a red giant with an accreting white dwarf. Three sources (AXJ1739.5-2910, AXJ1740.5-2937, AXJ1743.9-2846) have turned out to be active G-K stars, presumably RS CVn objects, one (AXJ1740.4-2856) is an M dwarf, and another one (AXJ173548-3207) may be a low-mass X-ray binary in its low state. The distances and corresponding luminosities of the sources in the soft X-ray band have been estimated; analysis of deep INTEGRAL Galactic Center observations has not revealed a statistically significant flux at energies higher 20 keV from any of them.

astro-ph.HE↗

arXiv2015

Transient X-ray pulsar V0332+53: pulse phase-resolved spectroscopy and the reflection model

We present the results of the pulse phase- and luminosity-resolved spectroscopy of the transient X-ray pulsar V0332+53, performed for the first time in a wide luminosity range (1-40)x10^{37} erg/s during a giant outburst observed by the RXTE observatory in Dec 2004 - Feb 2005. We characterize the spectra quantitatively and built the detailed "three-dimensional" picture of spectral variations with pulse phase and throughout the outburst. We show that all spectral parameters are strongly variable with the pulse phase, and the pattern of this variability significantly changes with luminosity directly reflecting the associated changes in the structure of emission regions and their beam patterns. Obtained results are qualitatively discussed in terms of the recently developed reflection model for the formation of cyclotron lines in the spectra of X-ray pulsars.

astro-ph.HE↗

arXiv2014

Spin-up/spin-down of neutron star in Be-X-ray binary system GX 304-1

We analyze spin-up/spin-down of the neutron star in Be X-ray binary system GX\,304-1 observed by \textit{Swift}/XRT and \textit{Fermi}/GBM instruments in the period of the source activity from April 2010 to January 2013 and discuss possible mechanisms of angular momentum transfer to/from the neutron star. We argue that the neutron star spin-down at quiescent states of the source with an X-ray luminosity of $L_x\sim 10^{34}$~erg s$^{-1}$ between a series of Type I outbursts and spin-up during the outbursts can be explained by quasi-spherical settling accretion onto the neutron star. The outbursts occur near the neutron star periastron passages where the density is enhanced due to the presence of an equatorial Be-disc tilted to the orbital plane. We also propose an explanation to the counterintuitive smaller spin-up rate observed at higher luminosity in a double-peak Type I outburst due to lower value of the specific angular momentum of matter captured from the quasi-spherical wind from the Be-star by the neutron star moving in an elliptical orbit with eccentricity $e\gtrsim 0.5$.

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arXiv2014

An influence of the matter distribution on the positional accuracy of reference sources

We consider an influence of a non-stationary gravitational field of the Galaxy on the visible positions of extragalactic sources. A contribution of the baryonic component of the galactic matter as well as of the hidden matter (including a population of brown dwarfs) were took into account. The observed variations of the deflection angle of light rays in a gravitational field of randomly moving point-like masses can be considered as a stochastic process. Using such an approach we constructed an autocorrelation function of studied stochastic process and found that its relative changes are about 15% for one year and about 35% for ten years.

astro-ph.CO↗

arXiv2013

Gravitational lens system B0218+357: constraints on lens model and Hubble constant

The possibility to use observations of lensed relativistic jets on very small angular scales to construct proper models of spiral lens galaxies and to independently determine the Hubble constant is considered. On the example of the system B0218+357 it is shown that there exists a great choice of model parameters adequately reproducing its observed large-scale properties but leading to a significant spread in the Hubble constant. The jet image position angle is suggested as an additional parameter that allows the range of models under consideration to be limited. It is shown that the models for which the jet image position angles differ by at least 40 deg can be distinguished between themselves during observations on very small angular scales. Observations with the space interferometer RadioAstron-Earth is proposed to determine the jet orientation.

astro-ph.CO↗