arXiv subjects
Publications and source records attributed to V. V. Gvaramadze.
The proper motion of massive stars could cause them to explode far from the geometric centers of their wind-driven bubbles and thereby could affect the symmetry of the resulting diffuse supernova remnants. We use this fact to explain the origin of SNRs consisting of two partially overlapping shells (e.g. Cygnus Loop, 3C 400.2, etc.).
We propose an explanation for the origin of hyperfast neutron stars (e.g. PSR B1508+55, PSR B2224+65, RX J0822-4300) based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star (or its helium core) which attained its peculiar velocity (similar to that of the neutron star) in the course of a strong three- or four-body dynamical encounter in the core of a young massive star cluster. This hypothesis implies that the dense cores of star clusters (located either in the Galactic disk or near the Galactic centre) could also produce the so-called hypervelocity stars -- the ordinary stars moving with a speed of ~1000 km/s.
Astrometric data on the pulsars B2020+28 and B2021+51 suggest that they originated within several parsecs of each other in the direction of the Cyg OB2 association. It was proposed that the pulsars share their origin in a common massive binary and were separated at the birth of the second pulsar following the asymmetric supernova explosion. We consider a different scenario for the origin of the pulsar pair based on a possibility that the pulsars were separated before their birth and that they are the remnants of runaway stars ejected (with velocities similar to those of the pulsars) from the core of Cyg OB2 due to strong three- or four-body dynamical encounters. Our scenario does not require any asymmetry in supernova explosions.
The supernova remnant S147 harbors the pulsar PSR J0538+2817 whose characteristic age is more than an order of magnitude greater than the kinematic age of the system (inferred from the angular offset of the pulsar from the geometric center of the supernova remnant and the pulsar proper motion). To reconcile this discrepancy we propose that PSR J0538+2817 could be the stellar remnant of the first supernova explosion in a massive binary system and therefore could be as old as its characteristic age. Our proposal implies that S147 is the diffuse remnant of the second supernova explosion (that disrupted the binary system) and that a much younger second neutron star (not necessarily manifesting itself as a radio pulsar) should be associated with S147. We use the existing observational data on the system to suggest that the progenitor of the supernova that formed S147 was a Wolf-Rayet star (so that the supernova explosion occurred within a wind bubble surrounded by a massive shell) and to constrain the parameters of the binary system. We also restrict the magnitude and direction of the kick velocity received by the young neutron star at birth and find that the kick vector should not strongly deviate from the orbital plane of the binary system.
It is shown that the gravitational potential outside an inhomogeneous ellipsoid of revolution (spheroid) whose isodensity surfaces are confocal spheroids is identical to the gravitational potential of a homogeneous spheroid of the same mass.
A scenario for the origin of the system PSR B1757-24/supernova remnant (SNR) G5.4-1.2 is proposed. It is suggested that both objects are the remnants of a supernova (SN) that exploded within a pre-existing bubble blown-up by a runaway massive star (the SN progenitor) during the final (Wolf-Rayet) phase of its evolution. This suggestion implies that (a) the SN blast centre was significantly offset from the geometric centre of the wind-blown bubble (i.e. from the centre of the future SNR), (b) the bubble was surrounded by a massive wind-driven shell, and (c) the SN blast wave was drastically decelerated by the interaction with the shell. Therefore, one can understand how the relatively young and low-velocity pulsar PSR B1757-24 was able to escape from the associated SNR G5.4-1.2 and why the inferred vector of pulsar transverse velocity does not point away from the geometric centre of the SNR. A possible origin of the radio source G5.27-0.9 (located between PSR B1757-24 and the SNR G5.4-1.2) is proposed. It is suggested that G5.27-0.9 is a lobe of a low Mach number (\simeq 1.7) jet of gas outflowing from the interior of G5.4-1.2 through the hole bored in the SNR's shell by the escaping pulsar. It is also suggested that the non-thermal emission of the comet-shaped pulsar wind nebula originates in the vicinity of the termination shock and in the cylindric region of subsonically moving shocked pulsar wind. The role of magnetized wind-driven shells (swept-up during the Wolf-Rayet phase from the ambient interstellar medium with the regular magnetic field) in formation of elongated axisymmetric SNRs is discussed.
The association of PSR B1757-24 and the supernova remnant (SNR) G5.4-1.2 was recently questioned by Thorsett et al. (2002) on the basis of proper motion measurements of the pulsar and the "incorrect" orientation of the vector of pulsar transverse velocity [inferred from the orientation of the cometary-shaped pulsar wind nebula (PWN)]. We showed, however, that the association could be real if both objects are the remnants of an off-centred cavity supernova (SN) explosion.
We discuss a concept of off-centred cavity supernova explosion as applied to neutron star/supernova remnant associations and show how this concept could be used to preclude the anti-humane decapitating the Duck (G5.4-1.2 + G5.27-0.9) and dismembering the Swan (Cygnus Loop), as well as to search for a stellar remnant associated with the supernova remnant RCW86.
We report the results of a search for a point X-ray source (stellar remnant) in the southwest protrusion of the supernova remnant G 315.4-2.30 (MSH 14-63, RCW 86) using the archival data of the Chandra X-ray Observatory. The search was motivated by a hypothesis that G 315.4-2.30 is the result of an off-centered cavity supernova explosion of a moving massive star, which ended its evolution just near the edge of the main-sequence wind-driven bubble. This hypothesis implies that the southwest protrusion in G 315.4-2.30 is the remainder of a pre-existing bow shock-like structure created by the interaction of the supernova progenitor's wind with the interstellar medium and that the actual location of the supernova blast center is near the center of this hemispherical structure. We have discovered two point X-ray sources in the "proper" place. One of the sources has an optical counterpart with the photographic magnitude $13.38\pm0.40$, while the spectrum of the source can be fitted with an optically thin plasma model. We interpret this source as a foreground active star of late spectral type. The second source has no optical counterpart to a limiting magnitude $\sim 21$. The spectrum of this source can be fitted almost equally well with several simple models (power law: photon index $=1.87$; two-temperature blackbody: $kT_1 =0.11$ keV, $R_1 =2.34 $ km and $kT_2 =0.71$ keV, $R_2 =0.06$ km; blackbody plus power law: $kT =0.07$ keV, photon index $=2.3$). We interpret this source as a candidate stellar remnant (neutron star), while the photon index and non-thermal luminosity of the source (almost the same as those of the Vela pulsar and the recently discovered pulsar PSR J 0205+6449 in the supernova remnant 3C 58) suggest that it can be a young "ordinary" pulsar.
The possible association of the supernova remnant (SNR) G 343.1-2.3 with the pulsar PSR B 1706-44 (superposed on the arclike "shell" of the SNR) has been questioned by some authors on the basis of an inconsistency between the implied and measured (scintillation) transverse velocities of the pulsar, the absence of any apparent interaction between the pulsar and the SNR's "shell", and some other indirect arguments. We suggest, however, that this association could be real if both objects are the remnants of a supernova (SN) which exploded within a mushroom-like cavity (created by the SN progenitor wind breaking out of the parent molecular cloud). This suggestion implies that the actual shape of the SNR's shell is similar to that of the well-known SNR VRO 42.05.01 and that the observed bright arc corresponds to the "half" of the SNR located inside the cloud. We report the discovery in archival radio data of an extended ragged radio arc to the southeast of the bright arc which we interpret as the "half" of the SN blast wave expanding in the intercloud medium.
We propose a new approach for studying the neutron star/supernova remnant associations, based on the idea that the supernova remnants (SNRs) can be products of an off-centered supernova (SN) explosion in a preexisting bubble created by the wind of a moving massive star. A cavity SN explosion of a moving star results in a considerable offset of the neutron star (NS) birth-place from the geometrical center of the SNR. Therefore: a) the high transverse velocities inferred for a number of NSs through their association with SNRs can be reduced; b) the proper motion vector of a NS should not necessarily point away from the geometrical center of the associated SNR. Taking into account these two facts allow us to enlarge the circle of possible NS/SNR associations, and could significantly affect the results of previous studies of associations. The possibilities of our approach are illustrated with some examples. We also show that the concept of an off-centered cavity SN explosion could be used to explain the peculiar structures of a number of SNRs and for searches for stellar remnants possibly associated with them.
We present some arguments in support of the association of the pulsar PSR B1706-44 with the supernova remnant G343.1-2.3, based on the idea that these objects could be the result of a supernova explosion within a mushroom-like cavity (created by the supernova progenitor wind breaking out of the parent molecular cloud). We suggest that in addition to the known bright "half" of G343.1-2.3 there should exist a more extended and weaker component, such that the actual shape of G343.1-2.3 is similar to that of the well-known SNR VRO 42.05.01. We have found such a component in archival radio data.
It is generally accepted that the PSR B1509-58 is associated with the supernova remnant (SNR) MSH 15-52 (G 320.4-01.2). The spin-down age of the pulsar is \simeq 1700 years, while the size and the general appearance of the SNR suggest that this system is much older. A few possible explanations of this discrepancy have been put forward. We offer an alternative one and suggest that the high spin-down rate of the pulsar characterizes only a relatively short period of its (present) spin history, and that the enhanced braking torque is connected with the interaction between the pulsar's magnetosphere and the dense matter of a circumstellar clump (created during the late evolutionary stages of the supernova (SN) progenitor star). Our suggestion implies that the "true" age of PSR B1509-58 could be much larger than the spin-down age, and therefore the SNR MSH 15-52 is a middle-aged remnant similar to the Vela SNR (G 263.9-3.3). We also suggest that the dense (neutral) gas of the circumstellar clump could be responsible for the enhanced neutral hydrogen absorption towards PSR B1509-58, and that the optical emission of an optical counterpart for PSR B1509-58 should rather be attributed to a bow shock around this pulsar than to the pulsar itself.
It is pointed out that a cavity supernova (SN) explosion of a moving massive star could result in a significant offset of the neutron star (NS) birth-place from the geometrical centre of the supernova remnant (SNR). Therefore: a) the high implied transverse velocities of a number of NSs (e.g. PSR B1610-50, PSR B1757-24, SGR0525-66) could be reduced; b) the proper motion vector of a NS should not necessarily point away from the geometrical centre of the associated SNR; c) the circle of possible NS/SNR associations could be enlarged. An observational test is discussed, which could allow to find the true birth-places of NSs associated with middle-aged SNRs, and thereby to get more reliable estimates of their transverse velocities.
Most of middle-aged supernova remnants (SNRs) have a distorted and complicated appearance which cannot be explained in the framework of the Sedov-Taylor model. We consider three typical examples of such SNRs (Vela SNR, MSH 15-52, G 309.2-00.6) and show that their structure could be explained as a result of interaction of a supernova (SN) blast wave with the ambient medium preprocessed by the action of the SN progenitor's wind and ionized emission.
The nature of the Vela X-ray "jet", recently discovered by Markwardt & Ögelman (1995), is examined. It is suggested that the "jet" arises along the interface of domelike deformations of the Rayleigh-Taylor unstable shell of the Vela supernova remnant; thereby the "jet" is interpreted as a part of the general shell of the remnant. The origin of deformations as well as the general structure of the remnant are discussed in the framework of a model based on a cavity explosion of a supernova star. It is suggested that the shell deformations viewed at various angles appear as filamentary structures visible throughout the Vela supernova remnant at radio, optical, and X-ray wavelengths. A possible origin of the nebula of hard X-ray emission detected by Willmore et al. (1992) around the Vela pulsar is proposed.