Searcharxiv⌕ Search

arXiv subjects

S. B. Popov

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

At least 91 records · Page 5Linked to original sources
arXiv2006

Neutron star masses: dwarfs, giants and neighbors

We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass ($ M \stackrel{<}{\sim} 1 M_{\odot}$) and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario is given. Secondly, we discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations we derive the mass spectrum of massive ($M > 1.8 M_{\odot}$) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of {\it mass constraint} which can be helpful, in our opinion, in discussing different competive models of the thermal evolution of NSs.

astro-ph↗
arXiv2006

A tale of two populations: Rotating Radio Transients and X-ray Dim Isolated Neutron Stars

We highlight similarities between recently discovered Rotating Radio Transients and X-ray Dim Isolated Neutron Stars. In particular, it is shown that X-ray Dim Isolated Neutron Stars have a birthrate comparable to that of Rotating Radio Transients. On the contrary, magnetars have too low a formation rate to account for the bulk of the radio transient population. The consequences of the recent detection of a thermal X-ray source associated with one of the Rotating Radio Transients on the proposed scenarios for these sources are also discussed.

astro-ph↗
arXiv2005

Be/X-ray binaries and candidates: catalogue

We present a compilative catalogue of Be/X-ray binaries and candidates in the Galaxy and in the Large and Small Magellanic Clouds. This catalogue contains 130 sources and provides information on names and spectral types of optical components, distances, spin characteristics of neutron stars, and on orbital and X-ray properties of binary systems. We give brief comments on each object and provide necessary references to original data.

astro-ph↗
arXiv2005

Nearby young single black holes

We consider nearby young black holes formed after supernova explosions in close binaries whose secondary components are currently observed as the so-called runaway stars. Using data on runaway stars and making reasonable assumptions about the mechanisms of supernova explosions and binary breakup, we estimate the present position of nearby young black holes. For two objects, we obtained relatively small error regions ($\sim 50$-100 deg$^2$). The possibility of detecting these nearby young black holes is discussed.

astro-ph↗
arXiv2005

Soft gamma repeaters outside the Local group

We propose that the best sites to search for SGRs outside the Local group are galaxies with active massive star formation. Different possibilities to observe SGR activity from these sites are discussed. In particular we searched for giant flares from nearby galaxies ($\sim 2$ -- 4 Mpc) M82, M83, NGC 253, and NGC 4945 in the BATSE data. No candidates alike giant SGR flares were found. The absence of such detections implies that the rate of giant flares with energy release in the initial spike above $0.5 \cdot 10^{44}$ erg is less then 1/25 yr$^{-1}$ in our Galaxy. However, hyperflares similar to the one of 27 December 2004 can be observed from larger distances. Nevertheless, we do not see any significant excess of short GRBs from the Virgo galaxy cluster and from galaxies Arp 299 and NGC 3256 with extremely high star formation rate. This implies that the galactic rate of hyperflares with energy release $\sim 10^{46}$ erg is less than $\sim 10^{-3}$ yr$^{-1}$. With this constraint the fraction of possible extragalactic SGR hyperflares among BATSE short GRBs should not exceed few percents. We present a list of short GRBs coincident with galaxies mentioned above, and discuss the possibility that some of them are SGR giant flares. We propose that the best target for observations of extragalactic SGR flares by {\it Swift} is the Virgo cluster.

astro-ph↗
arXiv2005

Magnetars origin and progenitors with enhanced rotation

Among a dozen known magnetar candidates there are no binary objects. As an estimate of a fraction of binary neutron stars is about 10% it is reasonable to address the question of solitarity of magnetars, to estimate theoretically the fraction of binary objects among them, and to mark o probable companions. We present population synthesis calculations of binary systems. Our goal is to estimate the number of neutron stars originated from progenitors with enhanced rotation, as such compact objects can be expected to have large magnetic fields, ie. they can be magnetars. The fraction of such neutron stars in our calculations is about 13-16%. Most of these objects are isolated due to coalescences of components prior to a neutron star formation, or due to a system disruption after a supernova explosion. The fraction of such neutron stars in survived binaries is about 1% or lower. Their most numerous companions are black holes.

astro-ph↗
arXiv2005

A parameter to quantify dynamics of a researcher's scientific activity

I propose the coefficient, $t_h$, and its modification $N_t$ which in a simple way reflect dynamics of scientific activity of an individual researcher. I determine $t_h$ as a time period (from some moment in the past till the present moment) during which papers responsible for 1/2 of the total citation index were published. Parameter $N_t$ represents average of the citation index over this period: $N_t={\mathrm{C.I.}}/2t_h$.

physics.soc-ph↗
arXiv2005

Soft gamma repeaters and starforming galaxies

We propose that the best sites to search for SGRs outside the Local group are galaxies with active star formation. Different possibilities to observe SGR activity from these sites are discussed. In particular we searched for giant flares from M82, M83, NGC 253, and NGC 4945 in the BATSE data. We present a list of potential candidates, however, in our opinion no good candidates alike giant SGR flares were found. Still, hyperflares similar to the one of 27 December 2004 can be observed from larger distances. From the BATSE data we select 5 candidates coincident with the galaxies Arp 299 and NGC 3256 which have very high rate of starformation, and propose that they can be examples of hyperflares; but this result has low statistical significance.

astro-ph↗
arXiv2004

Trans-sonic propeller stage

We follow the approach used by Davies and Pringle (1981) and discuss the trans-sonic substage of the propeller regime. This substage is intermediate between the supersonic and subsonic propeller substages. In the trans-sonic regime an envelope around a magnetosphere of a neutron star passes through a kind of a reorganization process. The envelope in this regime consists of two parts. In the bottom one turbulent motions are subsonic. Then at some distance $r_\mathrm{s}$ the turbulent velocity becomes equal to the sound velocity. During this substage the boundary $r_\mathrm{s}$ propagates outwards till it reaches the outer boundary, and so the subsonic regime starts. We found that the trans-sonic substage is unstable, so the transition between supersonic and subsonic substages proceeds on the dynamical time scale. For realistic parameters this time is in the range from weeks to years.

astro-ph↗
arXiv2004

Formation of massive skyrmion stars

As it is well known for stiff equations of state an existence of neutron stars with masses $\ga 2 M_{\sun}$ is possible. Especially interesting possibility is opened if the equation of state based on the Skyrme theory is realized in nature. This equation of state was proposed recently by Ouyed and Butler. We discuss different channels of formation of massive rapidly rotating neutron stars. We use a population synthesis code to estimate numbers of massive neutron stars on different evolutionary stages. A neutron star increases its mass by accretion from a secondary companion. Significant growth of a neutron star mass due to accretion is possible only for certain values of initial parameters of the binary. In this paper we show that significant part of massive neutron stars with $M\ga 2 M_{\sun}$ can be observed as millisecond radio pulsars, as X-ray sources in pair with white dwarfs, and as accreting neutron stars with very low magnetic fields.

astro-ph↗
arXiv2004

Population synthesis in astrophysics

We briefly describe different astrophysical applications of a population synthesis method. In some details we discuss the population synthesis of close binary systems and of isolated neutron stars.

astro-ph↗
arXiv2004

Constraints on the photon charge based on observations of extragalactic sources

Using modern high-resolution observations of extragalactic compact radio sources we obtain an estimate of the upper bound on a photon electric charge at the level $e_γ \lesssim 3 \cdot 10^{-33}$ of elementary charge (assuming the photon charge to be energy independent). This is three orders of magnitude better than the limit obtained with radio pulsar timing. Also we set a limit on a photon charge in the gamma-ray band (energies about 0.1 MeV). In future the estimate made for extragalactic sources can be significantly improved.

hep-ph↗
arXiv2004

Age-Distance diagram for close-by young neutron stars

An age--distance diagram for close-by young isolated neutron stars of different types is introduced and discussed. It is shown that such a diagram can be a useful tool for studying of populations of sources if their detectability strongly depends on age and distance.

astro-ph↗
arXiv2004

Be/X-ray stars and candidates: catalogue

Here we present a compilation of data on Be/X-ray binaries. On the whole we include 90 objects into our catalogue. Brief comments on each object are provided.

astro-ph↗
arXiv2004

Young close-by neutron stars: the Gould Belt vs. the Galactic disc

We present new population synthesis calculations of close young neutron stars. In comparison with our previous investigation we use a different neutron star mass spectrum and different initial spatial and velocity distributions. The results confirm that most of ROSAT dim radioquiet isolated neutron stars had their origin in the Gould Belt. Several tens of young neutron stars can be identified in future in ROSAT data at low galactic latitudes and some of them also can be EGRET unidentified sources.

astro-ph↗
arXiv2004

On the nature of bimodal initial velocity distribution of neutron stars

We propose that the bimodal nature of the kick velocity distribution of radio pulsars is connected with the dichotomy between hadronic stars ({\it i.e.} neutron stars with no quark matter content) and quark stars. Bimodality can appear due to different mechanisms of explosion which leads to the formation of two types of compact stars or due to two different sets of parameters mastering a particular kick mechanism. The low velocity maximum (at $\sim 100$ km s$^{-1}$) is connected with hadronic star formation, whereas the second peak corresponds to quark stars. In the model of delayed collapse of hadronic stars to quark stars (Berezhiani et al. 2003\nocite{bbd2003}) quark deconfinement leads to a second energy release, and to a second kick, in addition to the kick imparted to the newly formed hadronic star during the supernova explosion. If the electromagnetic rocket mechanism can give a significant contribution to pulsar kicks, then the high velocity peak can be connected with the shorter initial spin periods of quark stars with respect to hadronic stars. We discuss {\it pro et contra} of these scenarios.

astro-ph↗
arXiv2004

On the mechanism of low-mass compact object formation

We suggest that low-mass compact objects (hadron stars, quark stars) with $M<1 M_{\odot}$ can appear only due to fragmentation of rapidly rotating proto-neutron stars. Such low-mass stars receive large kicks due to an explosion of a lighter companion in a pair of fragments, or due to dynamical ejection of one of the lighter components in the case when three bodies are formed. As far as low-mass compact objects are expected to be slowly cooling in all popular models of thermal evolution possible candidates are expected to be found among hot high velocity sources.

astro-ph↗