arXiv subjects

S. B. Popov

Publications and source records attributed to S. B. Popov.

At least 37 records · Page 2Linked to original sources

arXiv2019

On the possibility of registering X-ray flares related to fast radio bursts with the SRG/eROSITA telescope

In this note we discuss the possibility of detecting the accompanying X-ray emission from sources of fast radio bursts with the eROSITA telescope onboard the Spektr-RG observatory. It is shown that during four years of the survey program about 300 bursts are expected to appear in the field of view of eROSITA. About 1\% of them will be detected by ground-based radio telescopes. For a total energy release $\sim~10^{46}$~ergs depending on the spectral parameters and absorption in the interstellar and intergalactic media, an X-ray flare can be detected from distances from $\sim 1$~Mpc (thermal spectrum with $kT=200$~keV and strong absorption) up to $\sim1$~Gpc (power-law spectrum with photon index $Γ=2 $ and realistic absorption). Thus, eROSITA observations might help to provide important constraints on parameters of sources of fast radio bursts, or may even allow to identify the X-ray transient counterparts, which will help to constrain models of fast radio bursts generation.

astro-ph.HE↗

arXiv2019

Planet migration in wind-fed accretion disks in binaries

Planet migration originally refers to protoplanetary disks, which are more massive and dense than typical accretion disks in binary systems. We study planet migration in an accretion disk in a binary system consisting of a solar-like star hosting a planet and a red giant donor star. The accretion disk is fed by a stellar wind. %, disk self-gravity is neglected. We use the $α$-disk model and consider that the stellar wind is time-dependent. Assuming the disk is quasi-stationary we calculate its temperature and surface density profiles. In addition to the standard disk model, when matter is captured by the disk at its outer edge, we study the situation when the stellar wind delivers matter on the whole disc surface inside the accretion radius with the rate depending on distance from the central star. Implying that a planet experiences classical type I/II migration we calculate migration time for a planet on a circular orbit coplanar with the disk. Potentially, rapid inward planet migration can result in a planet-star merger which can be accompanied by an optical or/and UV/X-ray transient. We calculate timescale of migration for different parameters of planets and binaries. Our results demonstrate that planets can fall on their host stars within the lifetime of the late-type donor for realistic sets of parameters.

astro-ph.EP↗

arXiv2018

Fast Radio Bursts

The phenomenon of fast radio bursts (FRBs) was discovered in 2007. These are powerful (0.1-100 Jy) single radio pulses with durations of several milliseconds, large dispersion measures, and record high brightness temperatures suggesting coherent emission mechanism. As of time of writing, 32 FRBs were recorded. There is also one repeating source from which already hundreds of bursts have been detected. The FRB rate is estimated to amount up to several thousand per day over the sky, and their isotropic sky distribution likely suggests a cosmological origin. Since the discovery, different hypotheses on the possible FRB nature have been proposed, however up to now the origin of these transient events remains obscure. The most prospective models treat them as being related to a bursting emission from magnetars -- neutron stars whose activity is due to their magnetic field dissipation, -- or as being analogs of giant pulses observed from several radio pulsars . Future increase in the statistics of the observed FRBs and an improvement upon the FRB population characteristics will make possible to use them as a new tool to probe the intergalactic medium and to test fundamental physical theories.

astro-ph.HE↗

arXiv2018

Fast radio bursts: superpulsars, magnetars, or something else?

We briefly review main observational properties of fast radio bursts (FRBs) and discuss two most popular hypothesis for the explanation of these enigmatic intense millisecond radio flashes. FRBs most probably originate on extragalactic distances, and their rate on the sky is about a few thousand per day with fluences above $\sim$~1~Jy~ms (or with fluxes larger than few tenths of Jy). Two leading scenarios describing these events include strong flares of magnetars and supergiant pulses of young radio pulsars with large rotational energy losses, correspondingly. At the moment, it is impossible to choose between these models. However, new telescopes can help to solve the puzzle of FRBs in near future.

astro-ph.HE↗

arXiv2017

A multi-wavelength study of SXP 1062, the long period X-ray pulsar associated with a supernova remnant

SXP 1062 is a Be X-ray binary located in the Small Magellanic Cloud. It hosts a long-period X-ray pulsar and is likely associated with the supernova remnant MCSNR J0127-7332. In this work we present a multi-wavelength view on SXP 1062 in different luminosity regimes. We consider monitoring campaigns in optical (OGLE survey) and X-ray (SWIFT telescope). During these campaigns a tight coincidence of X-ray and optical outbursts is observed. We interpret this as typical Type I outbursts as often detected in Be X-ray binaries at periastron passage of the neutron star. To study different X-ray luminosity regimes in depth, during the source quiescence we observed it with XMM-Newton while Chandra observations followed an X-ray outburst. Nearly simultaneously with Chandra observations in X-rays, in optical the RSS/SALT telescope obtained spectra of SXP 1062. On the basis of our multi-wavelength campaign we propose a simple scenario where the disc of the Be star is observed face-on, while the orbit of the neutron star is inclined with respect to the disc. According to the model of quasi-spherical settling accretion our estimation of the magnetic field of the pulsar in SXP 1062 does not require an extremely strong magnetic field at the present time.

astro-ph.HE↗

arXiv2017

A young contracting white dwarf in the peculiar binary HD 49798/RX J0648.0--4418?

HD 49798/RX J0648.0--4418 is a peculiar X-ray binary with a hot subdwarf (sdO) mass donor. The nature of the accreting compact object is not known, but its spin period $P=13.2$~s and $\dot P =-2.15 \times 10^{-15}$s~s$^{-1}$, prove that it can be only either a white dwarf or a neutron star. The spin-up has been very stable for more than 20 years. We demonstrate that the continuous stable spin-up of the compact companion of HD 49798 can be best explained by contraction of a young white dwarf with an age $\sim 2$~Myrs. This allows us to interpret all the basic parameters of the system in the framework of an accreting white dwarf. We present examples of binary evolution which result in such systems. If correct, this is the first direct evidence for a white dwarf contraction on early evolutionary stages.

astro-ph.HE↗

arXiv2017

Looking for Hall attractor in astrophysical sources

Recently, numerical calculations of the magnetic field evolution in neutron stars demonstrated the possible existence of a Hall attractor, a stage at which the evolution of the field driven by the Hall cascade ends. The existence of such a stage in neutron star magnetic evolution is very important, and can be potentially probed by observations. Here we discuss three types of objects which could have reached this stage. First, we briefly describe the evolution of normal radio pulsars with ages about a few hundred thousand years. Then we analyse in more detail observations of RX J1856.5-3754, one of the Magnificent Seven, focusing on the surface temperature distribution and comparing model predictions with the temperature map inferred from X-ray observations. Finally, we discuss the necessity of the Hall attractor stage to explain the hypothetical existence of accreting magnetars. We conclude that at the moment there is no direct confirmation of the Hall attractor stage in known sources. However, more detailed observations in the near future can demonstrate existence (or absence) of this stage of the crustal magnetic field evolution.

astro-ph.HE↗

arXiv2017

How to make a mature accreting magnetar

Several candidates for accreting magnetars have been proposed recently by different authors. Existence of such systems contradicts the standard magnetic field decay scenario where a large magnetic field of a neutron star reaches $\lesssim$ few$\times 10^{13}$G at ages $\gtrsim 1$ Myr. Among other sources, the high mass X-ray binary 4U0114+65 seems to have a strong magnetic field around $10^{14}$ G. We develop a new Bayesian estimate for the kinematic age and demonstrate that 4U0114+65 has kinematic age 2.4-5 Myr ($95\%$ credential interval) since the formation of the neutron star. We discuss which conditions are necessary to explain the potential existence of magnetars in accreting high-mass binaries with ages about few Myrs and larger. Three necessary ingredients are: the Hall attractor to prevent rapid decay of dipolar field, relatively rapid cooling of the crust in order to avoid Ohmic decay due to phonons, and finally, low values of the parameter $Q$ to obtain long Ohmic time scale due to impurities. If age and magnetic field estimates for proposed accreting magnetars are correct, then these systems set the strongest limit on the crust impurity for a selected sample of neutron stars and provide evidence in favour of the Hall attractor.

astro-ph.HE↗

arXiv2016

Probing the surface magnetic field structure in RX J1856.5-3754

The evolution of magnetic field in isolated neutron stars is one of the most important ingredients in the attempt to build a unified description of these objects. A prediction of field evolution models is the existence of an equilibrium configuration, in which the Hall cascade vanishes. Recent calculations have explored the field structure in this stage, called the Hall attractor. We use X-ray data of near-by, cooling neutron stars to probe this prediction, as these sources are surmised to be close to or at Hall attractor phase. We show that the source RX J1856.5-3754 might be closer to the attractor than other sources of its class. Our modelling indicates that the properties of surface thermal emission, assuming that the star is in the Hall attractor, are in contradiction with the spectral data of RX J1856.5-3754.

astro-ph.HE↗

arXiv2016

Post fall-back evolution of multipolar magnetic fields and radio pulsar activation

It has long been unclear if the small-scale magnetic structures on the neutron star (NS) surface could survive the fall-back episode. The study of the Hall cascade (Cumming, Arras and Zweibel 2004; Wareing and Hollerbach 2009) hinted that energy in small scales structures should dissipate on short timescales. Our new 2D magneto-thermal simulations suggest the opposite. For the first $\sim$10 kyrs after the fall-back episode with accreted mass $10^{-3} M_\odot$, the observed NS magnetic field appears dipolar, which is insensitive to the initial magnetic topology. In framework of the Ruderman & Sutherland (1975) vacuum gap model during this interval, non-thermal radiation is strongly suppressed. After this time the initial (i.e. multipolar) structure begins to re-emerge through the NS crust. We distinguish three evolutionary epochs for the re-emergence process: the growth of internal toroidal field, the advection of buried poloidal field, and slow Ohmic diffusion. The efficiency of the first two stages can be enhanced when small-scale magnetic structure is present. The efficient re-emergence of high order harmonics might significantly affect the curvature of the magnetospheric field lines in the emission zone. So, only after few $10^4$ yrs would the NS starts shining as a pulsar again, which is in correspondence with radio silence of central compact objects (CCOs). In addition, these results can explain the absence of good candidates for thermally emitting NSs with freshly re-emerged field among radio pulsars (Bogdanov, Ng and Kaspi 2014), as NSs have time to cool down, and supernova remnants can already dissipate.

astro-ph.HE↗

arXiv2016

Rapidly rotating neutron star progenitors

Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, $τ_c$. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 $M_\odot$ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value $τ_c \simeq 5 \times 10^5$ years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being $\sim 0.1-1\%$ of the total core collapses, depending on the common envelope efficiency.

astro-ph.HE↗

arXiv2016

Fast Radio Bursts counterparts in the scenario of supergiant pulses

We discuss identification of possible counterparts and persistent sources related to Fast Radio Bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large spin-down luminosities. In particular, we demonstrate that at least some of sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance ($p$-value $\approx 4\%$) of galaxies in error boxes of FRBs. In the very near future with even modestly increased statistics of FRBs and with the help of dedicated X-ray observations and all-sky X-ray surveys it will be possible to decisively prove or falsify the supergiant pulses model.

astro-ph.HE↗

arXiv2015

Cosmological redshift, recession velocities and acceleration measures in FRW cosmologies

In this methodological note we discuss several topics related to interpretation of some basic cosmological principles. We demonstrate that one of the key points is the usage of synchronous reference frames. The Friedmann-Robertson-Walker one is the most known example of them. We describe how different quantities behave in this frame. Special attention is paid to potentially observable parameters. We discuss different variants for choosing measures of velocity and acceleration representing the Hubble flow, and present illustrative calculations of apparent acceleration in flat $ΛCDM$ model for various epochs. We generalize description of the "tethered" galaxies problem for different velocity measures and equations of state, and illustrate time behavior of velocities and redshifts in the $ΛCDM$ model.

gr-qc↗

arXiv2015

Origin of magnetars in binary systems

I review several scenarios of magnetar formation in binary systems via spin-up of a progenitor due to interaction with its companion. Mostly, these evolutionary channels lead to formation of isolated magnetars, and indeed, all well-established sources of this class are single objects. However, some binaries can survive, and several candidates to accreting magnetars have been proposed. I discuss this issue, and conclude that new accretion models can explain properties of the proposed candidates without large magnetic field in correspondence with models of magnetic field evolution.

astro-ph.HE↗

arXiv2015

Magneto-rotational and thermal evolution of young neutron stars

After a brief review of population synthesis of close-by cooling neutron stars, I focus on the interpretation of dichotomy of spin periods of near-by coolers. The existence of two well separated groups -- short period ($\sim$0.1-0.3 s) radio pulsars and long period ($\sim$3-10 s) radio quiet sources, aka the Magnificent seven, -- can not be easily explained in unified models developed recently (Popov et al. 2010, Gull{ó}n et al. 2014). I speculate that the most natural solution of the problem can be in bimodal initial magnetic field distribution related to the existence of an additional mechanism of field generation in magnetars.

astro-ph.HE↗

arXiv2015

Magnetic field decay in normal radio pulsars

We analyse the origin of the magnetic field decay in normal radio pulsars found by us in a recent study. This decay has a typical time scale $\sim 4 \times 10^5$~yrs, and operates in the range $\sim 10^5$~--~few$\times 10^5$~yrs. We demonstrate that this field evolution may be either due to the Ohmic decay related to the scattering from phonons, or due to the Hall cascade which reaches the Hall attractor. According to our analysis the first possibility seems to be more reliable. So, we attribute the discovered field decay mainly to the Ohmic decay on phonons which is saturated at the age few$\times 10^5$~yrs, when a NS cools down to the critical temperature below which the phonon scattering does not contribute much to the resistivity of the crust. Some role of the Hall effect and attractor is not excluded, and will be analysed in our further studies.

astro-ph.HE↗

arXiv2015

Central compact objects in Kes 79 and RCW 103 as "hidden" magnetars with crustal activity

We propose that observations of "hidden" magnetars in central compact objects can be used to probe crustal activity of neutron stars with large internal magnetic fields. Estimates based on calculations by Perna \& Pons (2011), Pons \& Rea (2012) and Kaminker et al. (2014) suggest that central compact objects, which are proposed to be "hidden" magnetars, must demonstrate flux variations on the time scale of months-years. However, the most prominent candidate for the "hidden" magnetars --- CXO J1852.6+0040 in Kes 79, -- shows constant (within error bars) flux. This can be interpreted by lower variable crustal activity than in typical magnetars. Alternatively, CXO J1852.6+0040 can be in a high state of variable activity during the whole period of observations. Then we consider the source 1E161348-5055 in RCW103 as another candidate. Employing a simple 2D-modeling we argue that properties of the source can be explained by the crustal activity of the magnetar type. Thus, this object may be supplemented for the three known candidates for the "hidden" magnetars among central compact objects discussed in literature.

astro-ph.HE↗

arXiv2014

Settling accretion on to isolated neutron stars from interstellar medium

We apply the model of subsonic settling accretion on to isolated neutron stars accreting from the interstellar medium (AINS). We show that in this regime the expected mean X-ray luminosity from AINS turns out to be 2-3 orders of magnitude as small as the maximum possible Bondi value, i.e. $10^{27}-10^{28}$~erg s$^{-1}$. The intrinsically unstable character of settling accretion due to long plasma cooling time leads to regular appearance of X-ray flares with a duration of about one hour and a maximum luminosity of about the Bondi value, $\sim10^{31}$~erg~s$^{-1}$. This feature can be used to distinguished AINS from other dim X-ray sources. With the sensitivity of the forthcoming all-sky X-ray surveys the expected number of the potentially detectable AINS can be from a few to ten.

astro-ph.HE↗