arXiv subjects

Yu. A. Shibanov

Publications and source records attributed to Yu. A. Shibanov.

At least 19 recordsLinked to original sources

arXiv2025

Identification of radio and gamma-ray pulsars in X-rays using data from the SRG/eROSITA all-sky survey

Using the data from the all-sky survey in soft X-rays performed by the eROSITA telescope onboard the Spectrum-Roentgen-Gamma observatory we identified known radio and $γ$-ray pulsars in the eastern half of the sky. As a result, new candidate counterparts were found for twelve pulsars of different ages and types at a $\gtrsim$ 3$σ$ confidence level. A comparable number had been previously identified in the western half of the sky. In total, this represents about 12\% of all known pulsars already detected in X-rays. For the new counterparts, we provide estimates of their X-ray fluxes, preliminary characteristics of their X-ray spectra, and brief descriptions of the pulsars' properties. In addition, in the eastern half of the sky eROSITA detected 55 pulsars previously identified in X-rays by other telescopes.

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arXiv2025

Studying the black widow pulsars PSR J0312$-$0921 and PSR J1627$+$3219 in the optical and X-rays

Context. PSR J0312$-$0921 and PSR J1627$+$3219 are black widow pulsars with orbital periods of 2.34 and 3.98 hours. They were recently detected in the radio and $γ$-rays. Aims. Our goals are to estimate the fundamental parameters of both binary systems and their components. Methods. We performed first phase-resolved multi-band photometry of both objects with the 10.4-m Gran Telescopio Canarias and fitted the obtained light curves with a model assuming direct heating of the companion by the pulsar. Archival X-ray data obtained with the Swift and XMM-Newton observatories were also analysed. Results. For the first time, we firmly identified both systems in the optical. Their optical light curves show a rather symmetric single peak per orbital period and a peak-to-peak amplitude of $\gtrsim$2 mag. We also identified the X-ray counterpart to J1627$+$3219, while for J0312$-$0921 we set an upper limit on the X-ray flux. Conclusions. We estimated the masses of the pulsars, companion temperatures and masses, Roche lobe filling factors, orbital inclinations, and the distances to both systems. PSR J0312$-$0921 has a very light ($\approx$0.02 M$_\odot$) companion which possibly has one of the lowest ($\approx$1600 K) `night-side' temperatures among the known black widow systems. We found that the distances to J0312$-$0921 and J1627$+$3219 are about 2.5 and 4.6 kpc, respectively. This likely explains their faintness in X-rays. The X-ray spectrum of PSR J1627$+$3219 can be described by the power-law model, and its parameters are compatible with those obtained for other black widows.

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arXiv2025

MASTER OT J072007.30+451611.6: A Polar with Strong Optical Variability and Suppressed He II Emission

The transient optical source MASTER OT J072007.30+451611.6 has been recently discovered and proposed as a peculiar polar with an unusually high amplitude of the orbital brightness variation in the optical of $\sim$3 mag. To clarify its nature, we performed multiband time-series optical photometry with 1.5-m class telescopes and spectroscopy with the 10.4-m Gran Telescopio Canarias. We also analysed archival data of different optical surveys and detected the source in X-rays with the Spectrum-RG/eROSITA telescope. We confirm the orbital period of $\approx$1.5 h with the high amplitude of the brightness modulation. Compiling survey data, covering $\sim$19 yr, we find high and low brightness states of the object at time scales of years, likely explained by different accretion rates. Our data were obtained in the high brightness state. Optical spectra with hydrogen and helium emission lines, consisting of broad and narrow components, indicate the presence of an accretion stream without disk. The Doppler tomography shows that the narrow component is mainly emitted from the Lagrangian L$_1$ point, while the broad component is from the region where the accretion stream interacts with the white dwarf magnetosphere. The ratio of equivalent widths of HeII 4686 and H$β$ emission lines is $<$0.4, which is curiously low for polars. The X-ray spectrum of the source can be described by the thermal plasma emission model with parameters consistent with values observed for polars.

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arXiv2025

Is the Fermi source 4FGL J1824.2+1231 a transitional millisecond pulsar?

Transitional millisecond pulsars (tMSPs) in tight binary systems represent an important evolutionary link between low-mass X-ray binaries and radio millisecond pulsars. To date, only three confirmed tMSPs and a few candidates have been discovered. Most of them are gamma-ray sources. For this reason, searching for multiwavelength counterparts to unassociated Fermi gamma-ray sources can help to find new tMSPs. Here we investigate whether the unassociated gamma-ray source 4FGL J1824.2+1231 belongs to the tMSP family. To find the counterpart to 4FGL J1824.2+1231, we used data from SRG/eROSITA and Swift X-ray catalogues, and from different optical catalogues. We also performed time-series photometric optical observations of the source with the 2.1-m telescope of the Observatorio Astronomico Nacional San Pedro Martir, the 1.5-m telescope of the Maidanak Astronomical Observatory and the 1.5-m Russian-Turkish telescope. In addition, we carried out optical spectroscopic observations with the Russian-Turkish telescope and used archival spectroscopic data obtained with the Gemini-North telescope. Within the position error ellipse of 4FGL J1824.2+1231, we found only one X-ray source which coincides with an optical object. We consider it as a likely multiwavelength counterpart to 4FGL J1824.2+1231. The source shows strong optical variability and significant proper motion. The latter strongly implies that this is a Galactic source. Double-peaked H and He emission lines are detected in its spectrum with a flat continuum, as often observed in accretion disks of compact binary systems. The X-ray spectrum is well fitted by a power law with the photon index 1.7. The derived intrinsic X-ray-to-gamma-ray flux ratio is about 0.2. If the X-ray/optical source is the true counterpart to 4FGL J1824.2+1231, then all its properties suggest that it is a tMSP in the subluminous disk state.

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arXiv2024

4FGL J1544.2$-$2554: a new spider pulsar candidate

Context. Spider pulsars are millisecond pulsars in tight binary systems, in which a low-mass companion star is heated and ablated by the pulsar wind. Their observations allow one to study stellar evolution with formation of millisecond pulsars and physics of superdense matter in neutron stars. However, spiders are rare due to difficulties of their discovery using typical radio search techniques. The Fermi $γ$-ray source 4FGL J1544.2$-$2554 was recently proposed as a pulsar candidate, and its likely X-ray and optical counterparts with the galactic coordinates $l\approx344.\!\!^\circ76$, $b\approx22.\!\!^\circ59$ and the magnitude $G\approx20.6$ were found using the eROSITA and Gaia surveys. Aims. Our goals are to study whether the source is a new spider pulsar and to estimate its fundamental parameters. Methods. We performed the first optical time-series multi-band photometry of the object. We used the Lomb-Scargle periodogram to search for its brightness periodicity and fitted its light curves with a model of direct heating of the binary companion by the pulsar wind. Results. The source shows a strong brightness variability with a period of $\approx$ 2.724 h and an amplitude of $\gtrsim$ 2.5 mag, and its light curves have a single broad peak per period. These features are typical for spider pulsars. The curves are well fitted by the direct heating model, resulting in an orbit inclination of the presumed spider system of $\approx 83^\circ$, a companion mass of $\approx 0.1$ M$_\odot$, its ''day-side'' and ''night-side'' temperatures of $\approx 7200$ K and $\approx 3000$ K, a Roche-lobe filling factor of $\approx 0.65$ and a distance of $\approx 2.1$ kpc. Conclusions. Our findings suggest that 4FGL J1544.2$-$2554 is a spider pulsar. This encourages searches for the pulsar millisecond pulsations in the radio and $γ$-rays to confirm its nature.

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arXiv2024

SRGe J194401.8+284452 -- an X-ray Cataclysmic Variable in the Field of the Gamma-Ray Source 4FGL J1943.9+2841

SRGe J194401.8+284452 is the brightest point-like X-ray object within the position uncertainty ellipse of an unidentified $γ$-ray source 4FGL J1943.9+2841. We performed multi-wavelength spectral and photometric studies to determine its nature and possible association with the $γ$-ray source. We firmly established its optical counterpart with the Gaia based distance of about 415 pc. Our data show that the object is a cataclysmic variable with an orbital period of about 1.5 hours. SRGe J194401.8+284452 exhibits fast spontaneous transitions between the high and low luminosity states simultaneously in the optical and X-rays, remaining relatively stable between the transitions on scales of several months/years. This can be caused by an order of magnitude changes in the accretion rate. The brightness of the source is about 17 mag and 20 mag in the optical range and $5\times 10^{-12}$ and $5\times 10^{-13}$ erg/cm$^2$/s in the $0.3- 10$ keV range in the high and low states, respectively. We constrained the mass of the white dwarf ($0.3 - 0.9$ $M_\odot$) and its temperature in the low state (14750 $\pm$ 1250 K), the mass of the donor star ($\leq$ 0.08 $\pm$ 0.01 $M_ \odot$). In the low state, we detected regular optical pulsations with an amplitude of 0.2 mag and a period of 8 min. They are likely associated with the spin of the white dwarf, rather than with its non-radial pulsations. In the high state, the object demonstrates only stochastic optical brightness variations on time scales of $1 - 15$~minutes with amplitudes of $0.2 - 0.6$~mag. We conclude, that SRGe J194401.8+284452 can be classified as an intermediate polar, and its association with the $γ$-ray source is very unlikely.

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arXiv2024

Two black widow pulsars in the optical and X-rays

Context. Two millisecond pulsars, PSR J1513$-$2550 and PSR J2017$-$1614, with spin periods of about 2.1 and 2.3 ms were recently discovered in the radio and $γ$-rays and classified as black widow pulsars in tight binary stellar systems with orbital periods of about 4.3 and 2.3 h. Aims. Our goals are to reveal fundamental parameters of both systems and their binary components using multi-wavelength observations. Methods. We carried out the first time-series multi-band optical photometry of the objects with the 2.1-metre telescope of the Observatorio Astronómico Nacional San Pedro Mártir, the 6.5-metre \magel-1 telescope, and the 10.4-metre Gran Telescopio Canarias. To derive the parameters of both systems, we fitted the obtained light curves with a model assuming heating of the companion by the pulsar. We also analysed archival X-ray data obtained with the XMM-Newton observatory. Results. For the first time, we firmly identified J1513$-$2550 in the optical and both pulsars in X-rays. The optical light curves of both systems have a single peak per orbital period with peak-to-peak amplitude of $\gtrsim2$ magnitudes. The J2017$-$1614 light curves are symmetric, while J1513$-$2550 demonstrates strong asymmetry whose nature remains unclear. Conclusions. We constrained the orbital inclinations, pulsar masses, companion temperatures and masses, as well as the distances to both systems. We also conclude that J2017$-$1614 may contain a massive neutron star of 2.4$\pm$0.6 M$_{\odot}$. The X-ray spectra of both sources can be fitted by power laws with parameters typical for black widow systems.

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arXiv2023

The black widow pulsar J1641+8049 in the optical, radio and X-rays

PSR J1641+8049 is a 2 ms black widow pulsar with the 2.2 h orbital period detected in the radio and $γ$-rays. We performed new phase-resolved multi-band photometry of PSR J1641+8049 using the OSIRIS instrument at the Gran Telescopio Canarias. The obtained data were analysed together with the new radio-timing observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), the X-ray data from the Spectrum-RG/eROSITA all-sky survey, and all available optical photometric observations. An updated timing solution based on CHIME data is presented, which accounts for secular and periodic modulations in pulse dispersion. The system parameters obtained through the light curve analysis, including the distance to the source 4.6-4.8 kpc and the orbital inclination 56-59 deg, are found to be consistent with previous studies. However, the optical flux of the source at the maximum brightness phase faded by a factor of $\sim$2 as compared to previous observations. Nevertheless, the face of the J1641+8049 companion remains one of the most heated (8000-9500 K) by a pulsar among the known black widow pulsars. We also report a new estimation on the pulsar proper motion of $\approx$2 mas yr$^{-1}$, which yields a spin down luminosity of $\approx$4.87$\times 10^{34}$ ergs s$^{-1}$ and a corresponding heating efficiency of the companion by the pulsar of 0.3-0.7. The pulsar was not detected in X-rays implying its X-ray-luminosity was <3 $\times$ 10$^{31}$ erg s$^{-1}$ at the date of observations.

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arXiv2023

Nature of 4FGL J1838.2+3223: a flaring `spider' pulsar candidate

An unidentified $γ$-ray source 4FGL J1838.2+3223 has been proposed as a pulsar candidate. We present optical time-series multi-band photometry of its likely optical companion obtained with the 2.1-m telescope of Observatorio Astronómico Nacional San Pedro Mártir, Mexico. The observations and the data from the Zwicky Transient Facility revealed the source brightness variability with a period of $\approx$4.02 h likely associated with the orbital motion of the binary system. The folded light curves have a single sine-like peak per period with an amplitude of about three magnitude accompanied by fast sporadic flares up to one magnitude level. We reproduce them modelling the companion heating by the pulsar. As a result, the companion side facing the pulsar is strongly heated up to 11300$\pm$400 K, while the temperature of its back side is only 2300$\pm$700 K. It has a mass of 0.10$\pm$0.05 ${\rm M}_\odot$ and underfills its Roche lobe with a filling factor of $0.60^{+0.10}_{-0.06}$. This implies that 4FGL J1838.2+3223 likely belongs to the `spider' pulsar family. The estimated distance of $\approx$3.1 kpc is compatible with Gaia results. We detect a flare from the source in X-rays and ultraviolet using Swift archival data and another one in X-rays with the eROSITA all-sky survey. Both flares have X-ray luminosity of $\sim$10$^{34}$ erg s$^{-1}$ which is two orders of magnitude higher than the upper limit in quiescence obtained from eROSITA assuming spectral shape typical for spider pulsars. If the spider interpretation is correct, these flares are among the strongest flares observed from non-accreting spider pulsars.

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arXiv2023

Optical spectral observations of three binary millisecond pulsars

We present the results of optical spectroscopy of stellar companions to three binary millisecond pulsars, PSRs J0621$+$2514, J2317$+$1439 and J2302$+$4442, obtained with the Gran Telescopio Canarias. The spectrum of the J0621$+$2514 companion shows a blue continuum and prominent Balmer absorption lines. The latter are also resolved in the spectrum of the J2317$+$1439 companion, showing that both are DA-type white dwarfs. No spectral features are detected for the J2302$+$4442 companion, however, its broadband magnitudes and the spectral shape of the continuum emission imply that this is also a DA-type white dwarf. Based on the spectral analyses, we conclude that the companions of J0621$+$2514 and J2317$+$1439 are relatively hot, with effective temperatures $T_{\rm eff}$$=$8600$\pm$200 and 9600$\pm$2000~K, respectively, while the J2302$+$4442 companion is significantly cooler, $T_{\rm eff}$$<$6000~K. We also estimated the distance to J0621$+$2514 of 1.1$\pm$0.3 kpc and argue that its companion and the companion of J2317$+$1439 are He-core white dwarfs providing constraints on their cooling ages of $\lesssim$2 Gyr.

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arXiv2023

A new redback pulsar candidate 4FGL J2054.2+6904

The Fermi catalogue contains about 2000 unassociated $γ$-ray sources. Some of them were recently identified as pulsars, including so called redbacks and black widows, which are millisecond pulsars in tight binary systems with non- and partially-degenerate low-mass stellar companions irradiated by the pulsar wind. We study a likely optical and X-ray counterpart of the Fermi source 4FGL J2054.2+6904 proposed earlier as a pulsar candidate. We use archival optical data as well as Swift/XRT and SRG/eROSITA X-ray data to clarify its nature. Using Zwicky Transient Facility data in $g$ and $r$ bands spanning over 4.7 years, we find a period of $\approx$7.5 h. The folded light curve has a smooth sinusoidal shape with the peak-to-peak amplitude of $\approx$0.4 mag. The spectral fit to the optical spectral energy distribution of the counterpart candidate gives the star radius of 0.5$\pm$0.1$R_\odot$ and temperature of 5500$\pm$300 K implying a G2--G9-type star. Its X-ray spectrum is well fitted by an absorbed power law with the photon index of 1.0$\pm$0.3 and unabsorbed flux of $\approx 2\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. All the properties of 4FGL J2054.2$+$6904 and its presumed counterpart suggest that it is a member of the redback family.

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arXiv2022

Likely optical counterpart of the cool middle-aged pulsar J1957+5033

The 840 kyr old pulsar PSR J1957+5033, detected so far only in $γ$- and X-rays, is a nearby and rather cool neutron star with a temperature of 0.2--0.3 MK, a distance of $\la$1 kpc, and a small colour reddening excess $E(B-V) \approx 0.03$. These properties make it an ideal candidate to detect in the optical to get additional constraints on its parameters. We thus performed the first deep optical observations of the pulsar with the 10.4-meter Gran Telescopio Canarias in the $g'$ band and found its possible counterpart with $g'=27.63\pm 0.26$. The counterpart candidate position is consistent with the X-ray coordinates of the pulsar within the 0.5 arcsec accuracy. Assuming that this is the real counterpart, we analysed the pulsar X-ray spectrum together with the derived optical flux density. As a result, we found that the thermal emission from the bulk surface of the cooling neutron star can significantly contribute to its optical flux. Our multi-wavelength spectral analysis favours the pulsar nature of the detected optical source, since it provides physically adequate parameters of the pulsar emission. We show that the optical data can provide new constraints on the pulsar temperature and distance.

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arXiv2021

Kinematics, structure and abundances of supernova remnant 0540-69.3

The structure, elemental abundances, physical conditions of the LMC supernova remnant (SNR) 0540-69.3 and its surroundings were investigated using [O III] imaging and spectroscopy. Several new spectral lines are identified, both in central filaments and in interstellar clouds shocked by the supernova blast wave. The central lines are redshifted by $440\pm80$ km s$^{-1}$ with respect to the LMC, and the [O III] emission displays a symmetry axis of ring-like structures which could indicate that the pulsar shares the same general redshift as the central supernova ejecta. [O II], [S II], [Ar III] and H$β$ have more compact structures than [O III], and possibly [Ne III]. The average [O III] temperature is $23\,500 \pm 1\,800$ K, and the electron density from [S II] is typically $10^3$ cm$^{-3}$. By mass, the relative elemental abundances of the central shocked ejecta are ${\rm O:Ne:S:Ar} \approx 1:0.07:0.10:0.02$, consistent with explosion models of $13-20$ solar mass progenitors, and similar to that of SN 1987A, as is also the mixing of hydrogen and helium into the center. [O III] is also seen in freely coasting ejecta outside the pulsar-wind nebula out to well above $2\,000$ km s$^{-1}$. From this a pulsar age of $\approx 1\,200$ years is estimated. Four filaments of shocked interstellar medium with a wide range in degree of ionization of iron are identified. One was observed in X-rays, and another has a redshift of $85\pm30$ km~s$^{-1}$ relative to LMC. From this the electron density of the [O III]-emitting gas is estimated to be $10^3$ cm$^{-3}$. The line of the most highly ionized ion, [Fe XIV] $λ$5303, likely comes from an evaporation zone in connection with the radiatively cooled gas emitting, e.g., [O III].

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arXiv2020

Thermal luminosities of cooling neutron stars

Ages and thermal luminosities of neutron stars, inferred from observations, can be interpreted with the aid of the neutron star cooling theory to gain information on the properties of superdense matter in neutron-star interiors. We present a survey of estimated ages, surface temperatures and thermal luminosities of middle-aged neutron stars with relatively weak or moderately strong magnetic fields, which can be useful for these purposes. The catalogue includes results selected from the literature, supplemented with new results of spectral analysis of a few cooling neutron stars. The data are compared with the theory. We show that overall agreement of theoretical cooling curves with observations improves substantially for models where neutron superfluidity in stellar core is weak.

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arXiv2020

Atacama Compact Array Observations of the Pulsar-Wind Nebula of SNR 0540-69.3

We present observations of the pulsar-wind nebula (PWN) region ofSNR 0540-69.3. The observations were made with the Atacama Compact Array (ACA) in Bands 4 and 6. We also add radio observations from the Australia Compact Array (ATCA) at 3 cm. For 1.449 - 233.50 GHz we obtain a synchrotron spectrum $F_ν \propto ν^{-α_ν}$, with the spectral index $α_ν = 0.17\pm{0.02}$. To conclude how this joins the synchrotron spectrum at higher frequencies we include hitherto unpublished AKARI mid-infrared data, and evaluate published data in the ultraviolet (UV), optical and infrared (IR). In particular, some broad-band filter data in the optical must be discarded from our analysis due to contamination by spectral line emission. For the UV/IR part of the synchrotron spectrum, we arrive at $α_ν = 0.87^{+0.08}_{-0.10}$. There is room for $2.5\times10^{-3}$ solar masses of dust with temperature $\sim 55$ K if there are dual breaks in the synchrotron spectrum, one around $\sim 9\times10^{10}$ Hz, and another at $\sim 2\times10^{13}$ Hz. The spectral index then changes at $\sim 9\times10^{10}$ Hz from $α_ν = 0.14\pm0.07$ in the radio, to $α_ν = 0.35^{-0.07}_{+0.05}$ in the millimetre to far-IR range. The ACA Band 6 data marginally resolves the PWN. In particular, the strong emission 1.5" south-west of the pulsar, seen at other wavelengths, and resolved in the 3-cm data with its 0.8" spatial resolution, is also strong in the millimeter range. The ACA data clearly reveal the supernova remnant shell 20-35 arcsec west of the pulsar, and for the shell we derive $α_ν = 0.64\pm{0.05}$ for the range $8.6-145$~GHz.

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arXiv2020

Optical identification of binary system millisecond pulsar J1045-4509 with the VLT

We analyse archival optical data on the binary companion to the millisecond pulsar \j1045\ obtained with the Very Large Telescope. A possible optical counterpart candidate %source position coincides with the pulsar coordinates is found at the pulsar position. Its magnitudes are $V>26.4$, $R=25.7(2)$ and $I=25.4(2)$. The data are compared with white dwarf evolutionary models. Depending on still poorly known distance to the pulsar, two alternative interpretations are possible. For the radio timing parallax distance, the candidate can be a very cool and old white dwarf with the hydrogen atmosphere and the temperature of $< 3000$ K and the age of $> 5$ Gyr. The dispersion measure distance suggests a younger ($\sim$ 2 Gyr) and hotter ($\sim$ 6000 K) white dwarf, whose atmosphere composition remains unknown.

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arXiv2020

Studying the $γ$-ray pulsar J1932+1916 and its pulsar wind nebula with Chandra

We report on the results of Chandra X-ray observations of the $γ$-ray radio-quiet pulsar J1932+1916. We confirm the previous detection of the pulsar counterpart and its pulsar wind nebula in X-rays from low spatial resolution data obtained by Suzaku and Swift. The Chandra data with much better spatial resolution resolved the fine structure of the nebula in the pulsar vicinity, which can be interpreted as jets bent by the ram pressure. The size of this compact part is about 30'', and it is surrounded by a weak asymmetric diffusive emission extended up to $\approx$ 2.8'. The X-ray spectra of the pulsar, the compact and extended parts of the nebula can be described by the power-law models with photon indexes of 0.44, 2.34 and 2.14, respectively. The actual pulsar's X-ray flux is several times weaker than it was obtained with Suzaku and Swift where it was dominated by the unresolved nebula. We discuss possible associations of J1932+1916 with the nearby supernova remnant G54.4-0.3.

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arXiv2020

Searching for optical companions to four binary millisecond pulsars with the Gran Telescopio Canarias

We report on multi-band photometric observations of four binary millisecond pulsars with the Gran Telescopio Canarias. The observations led to detection of binary companions to PSRs J1630+3734, J1741+1351 and J2042+0246 in the Sloan g', r' and i' bands. Their magnitudes in the r' band are $\approx$24.4, 24.4 and 24.0, respectively. We also set a 3$σ$ upper limit on the brightness of the PSR J0557+1550 companion in the r' band of $\approx$25.6 mag. Combining the optical data with the radio timing measurements and white dwarf cooling models, we show that the detected companions are cool low-mass white dwarfs with temperatures and ages in the respective ranges of (4-7)$\times 10^3$ K and 2-5 Gyr. All the detected white dwarfs are found to likely have either pure hydrogen or mixed helium-hydrogen atmospheres.

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