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S. B. Popov

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

At least 109 records · Page 6Linked to original sources
arXiv2003

On the evolutionary states of neutron stars in pre-low-mass X-ray binaries

We present a simple model for the evolutionary states of neutron stars in pre-low-mass X-ray binaries during the main sequence stage of donor stars. It is shown that for typical parameters some of the neutron stars in these systems can not accrete matter from winds of their companions in a stable way. Accretors are found if neutron stars have magnetic fields about $10^{13}$ G and higher and/or in close systems with orbital periods about a few days and shorter.

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arXiv2003

Radioquiet isolated neutron stars: old and young, nearby and far away, dim and very dim

We briefly discuss the evolutionary path and observational appearance of isolated neutron stars (INSs) focusing on radioquiet objects. There are many reasons to believe that these sources are extremely elusive once the star surface has cooled down: their high spatial velocities, the long propeller stage and/or the very low accretion efficiency. We describe recent population synthesis models of close-by young INSs, highlighting the major difficulties encountered in the past by these simulations in reproducing the observed properties of known sources. As we show, a likely possibility is that most of the INSs in the Solar proximity are young (less than few Myrs) neutron stars born in the Gould Belt. To stay hot enough and sustain X-ray emission for a time $\approx 1$ Myr, they probably need to be low- to medium-massive, with $M$ less than$\sim 1.35 M_\odot$.

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arXiv2003

Log N -- Log S distributions of accreting and cooling isolated neutron stars

We model populations of isolated neutron stars in the Galaxy following their orbital and magneto-rotational evolution. It is shown that accretors become more abundant than coolers at fluxes below $\sim 10^{-13}$ erg cm$^{-2}$ s$^{-1},$ and one can predict that about one accreting neutron star per square degree should be observed at the {\it Chandra} and {\it Newton} flux limits of $\sim 10^{-16}$ erg cm$^{-2}$ s$^{-1}.$ The soft ROSAT sources associated with isolated neutron stars can be relatively young cooling objects only if the neutron star birth rate in the Solar vicinity during the last $\sim 10^6$ yr is higher than that inferred from radiopulsar observations.

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arXiv2003

Young isolated neutron stars from the Gould Belt

The origin of the local population of young, cooling neutron stars is investigated with a population synthesis model taking into account the contribution of neutron stars born in the Gould Belt, in addition to those originating in the Galactic disk. We estimate their emission in the soft X-ray band as a function of distance and age and construct the Log N -- Log S distribution. It is shown that the inclusion of neutron stars from the Gould Belt provides a good fit to the observed Log N -- Log S distribution. As the Sun is situated inside the Gould Belt, one can naturally explain the comparative local overabundance of massive progenitors and can remove the difficulty of the deficit of relatively bright ($\ga 0.1$ ROSAT PSPC cts s$^{-1}$) cooling neutron stars previously reported from models where only neutron stars from the Galactic disk were accounted for.

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arXiv2002

Young compact objects in the Solar vicinity

We present Log N -- Log S distribution for close-by young isolated neutron stars. On the basis of this distribution it is shown that the seven ROSAT isolated neutron stars (if they are young cooling objects) are genetically related to the Gould Belt. We predict, that there are about few tens unidentified close-by young isolated neutron stars in the ROSAT All-Sky Survey. The possibility that these seven peculiar sources contain a neutron star less massive and more magnetized then in ordinary radiopulsars is also discussed. In the aftermath of relatively close recent supernova explosions (1 kpc around the Sun, a few Myrs ago), a few black holes might have been formed, according to the local initial mass function. We thus discuss the possibility of determining approximate positions of close-by isolated black holes using data on runaway stars and simple calculations of binary evolution and disruption.

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arXiv2002

Astrophysics of isolated neutron stars: radioquiet neutron stars and magnetars

In this paper we review present state of theoretical and observational exploration of isolated neutron stars. We mainly discuss objects which do not show usual radiopulsar activity. We include into our review the following types of objects: dim X-ray sources in the Galactic disk and in globular clusters; compact X-ray sources in supernova remnants; anomalous X-ray pulsars; soft gamma repeaters; Geminga. Also we briefly discuss related types of objects: isolated black holes, quark stars and supernovae. We review basic physical processes connected with evolution of isolated neutron stars: cooling; magnetic field decay; period evolution; magnetospheric processes, accretion. We discuss populational synthesis of isolated neutron stars of different types.

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arXiv2002

Young close isolated compact objects

We suggest that the seven radio-quiet isolated neutron stars observed with ROSAT are young cooling objects associated to recent near-by supernova explosions which formed runaway stars and the Local Bubble, affecting the topology of the interstellar medium in the vicinity of the Sun (within a few hundred parsecs). In the aftermath of these explosions, a few black holes might have been formed, according to the local initial mass function. We thus discuss the possibility of determining approximate positions of close-by isolated black holes using data on runaway stars and simple calculations of binary evolution and disruption.

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arXiv2001

The Magnificent Seven: Close-by Cooling Neutron Stars?

We model Galactic populations of accreting and cooling isolated neutron stars in the attempt to explore their link with a new class of dim soft X-ray sources revealed by ROSAT. For accretors we follow the magneto-rotational and dynamical evolution in the Galactic potential and a realistic large scale distribution of the interstellar medium is used. Under standard assumptions old neutron stars enter the accretor stage only if their magnetic field exceeds $\approx 10^{11}$--$10^{12}$ G. We predict about 1 source per square degree for fluxes $\approx 10^{-15}$--$10^{-16}$ erg cm$^{-2}$s$^{-1}$ in the energy range 0.5-2 keV. Cooling neutron stars are explored within a simpler model of local sources, including however interstellar absorption. They are found to be significantly less abundant at low fluxes, $<0.1$ sources per square degree, but dominate over accretors at higher flux levels ($\approx 10^{-12}$--$10^{-11}$ erg cm$^{-2}$s$^{-1}$). We suggest that the faint sources observed by ROSAT may be young cooling neutron stars with typical age $\la 10^6$ yrs, if the total number of young neutron stars in the Solar proximity is $\sim 10$ times higher than inferred from radiopulsars statistics.

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arXiv2001

Evolution of Isolated Neutron Stars

In this paper we briefly review our recent results on evolution and properties of isolated neutron stars (INSs) in the Galaxy. As the first step we discuss stochastic period evolution of INSs. We briefly discuss how an INS's spin period evolves under influence of interaction with turbulized interstellar medium. To investigate statistical properties of the INS population we calculate a {\it census} of INSs in our Galaxy. Then we show that for exponential field decay the range of minimum value of magnetic moment, $μ_b$: $\sim 10^{29.5}\ge μ_b \ge 10^{28} {\rm G} {\rm cm}^3$, and the characteristic decay time, $t_d$: $\sim 10^8\ge t_d \ge 10^7 {\rm yrs}$, can be excluded assuming the standard initial magnetic momentum, $μ_0=10^{30} {\rm G} {\rm cm}^3$, if accreting INSs are observed. It is shown that old accreting INSs become more abundant than young cooling INSs at X-ray fluxes below $\sim 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. The weak {\it ROSAT} sources, associated with INSs, can be young cooling objects, if the NSs birth rate in the solar vicinity during the last $\sim 10^6$ yr was much higher than inferred from radiopulsar observations.

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arXiv2001

Stochastic spin evolution of neutron stars

In this paper we present calculations of period distribution for old accreting isolated neutron stars (INSs). At the age about a few billions years low velocity INSs come to the stage of accretion. At that stage their period evolution is governed by magnetic breaking and accreted angular momentum. Due to turbulence of the interstellar medium (ISM) accreted momentum can both accelerate and decelerate rotation of an INS and spin evolution has chaotic character. Calculations show that for constant magnetic fields INSs have relatively long spin periods, $\ge 10^4$--$10^5$ s, depending on parameters of INSs and an ISM. Due to long periods INSs have high spin up/spin down rates, which should fluctuate on a time scale about a few years.

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arXiv2001

Period distribution of old accreting isolated neutron stars

In this paper we present calculations of period distribution for old accreting isolated neutron stars (INSs). After few billion years of evolution low velocity INSs come to the stage of accretion. At this stage INS's period evolution is governed by magnetic braking and angular momentum accreted. Since the interstellar medium is turbulized accreted momentum can either accelerate or decelerate spin of an INS, therefore the evolution of period has chaotic character. Our calculations show that in the case of constant magnetic field accreting INSs have relatively long spin periods (some hours and more, depending on INS's spatial velocity, its magnetic field and density of the surrounding medium). Such periods are much longer than the values measured by {\emph ROSAT} for 3 radio-silent isolated neutron stars. Due to long periods INSs should have high spin up/down rates, $\dot p$, which should fluctuate on a time scale of $\sim 1$ yr.

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arXiv2001

Evolution of isolated neutron stars in globular clusters: number of Accretors

With a simple model from the point of view of population synthesis we try to verify an interesting suggestion made by Pfahl & Rappaport (2001) that dim sources in globular clusters (GCs) can be isolated accreting neutron stars (NSs). Simple estimates show, that we can expect about 0.5-1 accreting isolated NS per typical GC with $M=10^5 M_{\odot}$ in correspondence with observations. Properties of old accreting isolated NSs in GCs are briefly discussed. We suggest that accreting NSs in GCs experienced significant magnetic field decay.

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arXiv2000

Spin and magnetism in old neutron stars

The thermal, spin and magnetic evolution of neutron stars in the old low mass binaries is first explored. Recycled to very short periods via accretion torques, the neutron stars lose their magnetism progressively. If accretion proceeds undisturbed for 100 Myrs these stars can rotate close to break up with periods far below the minimum observed of 1.558 ms. We investigate their histories using population synthesis models to show that a tail should exist in the period distribution below 1.558 ms. The search of these ultrafastly spinning neutron stars as pulsars can help discriminating among the various equations of state for nuclear matter, and can shed light into the physics of binary evolution. The evolution of isolated neutron stars in the Galaxy is explored beyond the pulsar phase. Moving through the tenuous interstellar medium, these old solitary neutron stars lose their rotational energy. Whether also their magnetism fades is still a mystery. A population synthesis model has revealed that only a tiny fraction of them is able to accrete from the interstellar medium, shining in the X-rays. There is the hope that these solitary stars will eventually appear as faint sources in the Chandra sky survey. This might give insight on the long term evolution of the magnetic field in isolated objects.

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arXiv2000

Isolated Neutron Stars in the Galaxy

In this article we briefly review our recent results on evolution and properties of isolated neutron stars (INSs) in the Galaxy. As the first step we calculate a {\it census} of INSs in our Galaxy. We infer a lower bound for the mean kick velocity of NSs, $ \sim $(200-300) ${\rm km s^{-1}}$. The same conclusion is reached for both a constant magnetic field ($B\sim 10^{12}$ G) and for a magnetic field decaying exponentially with a timescale $\sim 10^9$ yr. These results, moreover, constrain the fraction of low velocity stars, which could have escaped pulsar statistics, to $\sim$few percents. Then we show that the range of minimum value of magnetic moment, $μ_b$: $\sim 10^{29.5}\ge μ_b \ge 10^{28} {\rm G} {\rm cm}^3$, and the characteristic decay time, $t_d$: $\sim 10^8\ge t_d \ge 10^7 {\rm yrs}$, can be excluded assuming the standard initial magnetic momentum, $μ_0=10^{30} {\rm G} {\rm cm}^3$, if accreting INSs are observed. For these parameters an INS would never reach the stage of accretion from the interstellar medium even for a low space velocity of the star and high density of the ambient plasma. The range of excluded parameters increases for lower values of $μ_0$. It is shown that old accreting INSs become more abundant than young cooling INSs at X-ray fluxes below $\sim 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. We can predict that about one accreting INS per square degree should be observed at the {\it Chandra} and {\it Newton} flux limits of $\sim 10^{-16}$ erg cm$^{-2}$ s$^{-1}.$ The weak {\it ROSAT} sources, associated with INSs, can be young cooling objects, if the NSs birth rate in the solar vicinity during the last $\sim 10^6$ yr was much higher than inferred from radiopulsar observations.

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arXiv2000

Ultra-strong Elelctric Fields and Vacuum Breakdown: Search for an Astrophysical Scenario

In some models of $γ$-ray bursts super-strong electric fields ($E\sim 10^{14} {\rm statvolt cm}^{-1}$) have been surmized. Such large fields may provide copious pair production through vacuum polarization. Here we examine various astrophysical scenarios where huge electric field can be present. It is shown that when the conditions for quantistic vacuum breakdown are met, pair creation through conventional processes is likely to be always more important. Although of great physical interest, quantum pair production seems therefore of little astrophysical relevance.

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arXiv2000

Constrains on parameters of magnetic field decay for accreting isolated neutron stars

The influence of exponential magnetic field decay (MFD) on the spin evolution of isolated neutron stars is studied. The ROSAT observations of several X-ray sources, which can be accreting old isolated neutron stars, are used to constrain the exponential and power-law decay parameters. We show that for the exponential decay the ranges of minimum value of magnetic moment, $μ_b$, and the characteristic decay time, $t_d$, $\sim 10^{29.5}\ge μ_b \ge 10^{28} {\rm G} {\rm cm}^3$, $\sim 10^8\ge t_d \ge 10^7 {\rm yrs}$ are excluded assuming the standard initial magnetic moment, $μ_0=10^{30} {\rm G} {\rm cm}^3$. For these parameters, neutron stars would never reach the stage of accretion from the interstellar medium even for a low space velocity of the stars and a high density of the ambient plasma. The range of excluded parameters increases for lower values of $μ_0$. We also show, that, contrary to exponential MFD, no significant restrictions can be made for the parameters of power-law decay from the statistics of isolated neutron star candidates in ROSAT observations. Isolated neutron stars with constant magnetic fields and initial values of them less than $μ_0 \sim 10^{29} {\rm G} {\rm cm}^3$ never come to the stage of accretion. We briefly discuss the fate of old magnetars with and without MFD, and describe parameters of old accreting magnetars.

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arXiv2000

Restrictions on parameters of power-law magnetic field decay for accreting isolated neutron stars

In this short note we discuss the influence of power-law magnetic field decay on the evolution of old accreting isolated neutron stars. We show, that, contrary to exponential field decay (Popov & Prokhorov 2000), no additional restrictions can be made for the parameters of power-law decay from the statistics of isolated neutron star candidates in ROSAT observations. We also briefly discuss the fate of old magnetars with and without field decay, and describe parameters of old accreting magnetars.

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