摘要:

We examine the evolutionary paths of primordial binary systems to the x‐ray binary stage. Although mass and angular momentum losses from the system are likely, the massive x‐ray binaries can be qualitatively described in terms of conservative evolution. On the other hand, low mass x‐ray binaries could not have evolved to their present state by normal evolutionary processes alone. These systems have suffered severe mass and angular momentum losses in a common envelope phase.

ISSN:0094-243X    

DOI:10.1063/1.34523

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Possible scenarios are discussed for the evolution of close binaries characterized primordially by: masses of individual components less than ∼10 M⊙, semimajoraxes A in the range 10≲A/R⊙≲2000, and orbital periodsPorbless than 25 yrs. Final products include double degenerate dwarfs withA≳(3‐5)R⊙, single rapidly rotating dwarfs (Prot≳10 sec), or neutron stars (Prot≳10−3sec), and supernovae of type I (SNeI).We suggest that binary systems consisting of a low mass non‐degenerate component and a neturon star or black hole may be primarily the result of inelastic capture collisions between single neutron stars and single low mass stars or of exchange captures involving the replacement of one component of a low mass binary by a passing neutron star. Tidal capture and exchange capture processes can occur with the necessary frequency (∼10−7yr−1) in high stellar density regions in globular clusters, in the Galactic bulge, and possibly also in the Galactic disk. The evolution of such systems leads ultimately to the formation of massive (≳1.4 M⊙) and rapidly rotating (Prot≳10−3sec) single neutron stars or to binaries containing a neutron star and a degenerate dwarf.A simple conservation law for ‘‘accumulation’’ instabilities accompanying the evolution of low mass binaries is presented. Several accumulation instabilities leading to SNeI and novae, to dwarf novae and X‐ray recurrent bursters, and to X‐ray and &ggr;‐ray bursters are discussed. It is shown that, from considerations both of evolution and of energetics, &ggr;‐ray bursters cannot be explained by systems consisting of a neturon star with a low mass companion. They can, however, be understood in terms of either of two models in which a single young (age ≳107yr) neutron star with a strong magnetic field is accreting matter from (1) the interstellar medium or (2) from the wind emitted by an OB star companion which does not fill its Roche lobe.

ISSN:0094-243X    

DOI:10.1063/1.34512

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The properties of the persistent X‐ray sources (such as X‐ray bursts) are also seen from the transient X‐ray source suggesting that they are related binary systems containing accreting compact objects. The spectral properties of the X‐ray transients are considered and compared with those of the persistent sources. The spectral morphologies of the three classes of persistent source i.e. the X‐ray pulsars, the bulge sources and the accreting black holes also characterise the spectra of the X‐ray transients. A comparative study of the spectra of the transients with those of the persistent sources suggests that two thirds of the transients seen to date result from episodic accretion onto neutron stars with either low magnetic fields (the soft bulge‐like transients) or high magnetic fields (the hard pulsing transients). The remaining transients have unusually soft (ultra‐soft) spectra similar to those of the black hole candidates in their high state.For the systems containing late type lobe filling stars the recurrence interval of the outbursts coupled with the total outburst energy gives time averaged accretion rates of <1016.5gm s−1, well below that required to power the bulge‐like sources. Two transients that after the ourburst became steady sources required accretion rates of ∼1016.5gm s−1, both to power the outburst and the subsequent persistent emission. This suggests that for mass transfer rates below ∼1016.5gm s−1the mass transfer onto compact objects in semi‐detached late type systems becomes intermittent.

ISSN:0094-243X    

DOI:10.1063/1.34536

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

We review some basic characteristics of soft X‐ray transients (rise, decay and recurrence times, maximum luminosity and total outburst energies). Based on a literature search we compare the optical spectra of low‐mass X‐ray binaries with those of catacylsmic variables. A comparison of the properties of soft X‐ray transients with those of dwarf novae shows: 1. The amounts of mass transferred in soft X‐ray transients and large dwarf nova outbursts are of similar order of magnitude. 2. The rise times of soft X‐ray transients are similar to those of dwarf nova outbursts, their decay times are an order of magnitude larger. We suggest that X‐ray irradiation of the disc is responsible for this difference in decay behaviour. 3. Soft X‐ray transients have recurrence times in excess of ∼200 days, whereas most known dwarf novae recur at intervals less than this value. We suggest an explanation for this difference based on the idea that short recurrence times correspond to high mass transfer rates in quiescence: potential soft X‐ray transients with short recurrence times have a quiescent X‐ray luminosity above a cetain critical value, which stabilizes the mass transfer process.

ISSN:0094-243X    

DOI:10.1063/1.34556

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Results are presented on observations by HAKUCHO and TENMA satellites on the galactic bulge X‐ray sources. Most of the sources observed showed a positive correlation between intensity and spectral hardness. GX5‐1 has been found to have two characteristic states. Quasi‐periodic pulsations with 106 to 205 seconds have been observed from GX 349+2. Observational results are interpreted in terms of mass accretion onto an unmagnetized neutron star.

ISSN:0094-243X    

DOI:10.1063/1.34571

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Hard X‐ray recurrent transients are intriguing constituents of X‐ray sources. Some of them exhibit flares periodically. Many hard X‐ray transient sources are associated with Be star binaries, which are typically known to have long orbital periods and relatively large eccentricities. The recurrent period seems to be equal to the binary period and the outburst is considered to occur near the periastron passage of the neutron star.Spherically symmetric stellar wind for the case of eccentric binary orbit has been investigated by many authors to explain the transient behaviors. This model requires the extremely large eccentricity (∼0.9) which is inconsistent with observations (0.1∼0.5). Therefore, the simple spherically symmetric wind must be abandoned.If the equatorial plane of the Be star is not coplanar with the binary orbital plane, X‐rays are emitted when the neutron star penetrates through the gas disk around the Be star. In this model the outbursts occur twice in an orbital period and in general there will be two different time intervals between the outbursts if the binary orbit is eccentric. These properties, however, do not seem to be supported by observational evidence.Here the stellar wind with the presence of magnetic field has been studied. The ejected gas can obtain the angular momentum from the rotating primary star through the magnetic field. Hence, the gas will rotate around the star as it moves much slower outwards than the case without the magnetic field. The radial velocity is suppressed this way up to the Alfven radius where the ram pressure of the gas equals the magnetic pressure. Beyond the Alfven radius, the gas will no longer be influenced by the magnetic pressure and escape freely.Now consider the case where the binary orbit is eccentric, and the periastron and the apoastron are inside and outside the Alfven radius, respectively. The mass accretion onto the neutron star is enhanced inside the Alfven radius because of the slower velocity and higher density of the stellar wind in contrast to those outside the Alfven radius. Hence, the outburst occurs near the periastron passage of the neutron star. The required eccentricity is ∼0.3 7 which is consistent with the observations. In this model, furthermore, the change of the light curves of outbursts as observed in 4U0538‐66 can be explained in terms of the variation in the mass loss rate from the primary star.The detail for this study is seen in the Proceedings of a Workshop on Accreting Neutron Stars held at the Max‐Planck‐Institute in Munich (1982).

ISSN:0094-243X    

DOI:10.1063/1.34578

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A systematic search of the HEAO A‐1 Sky Survey Experiment data base for fast (<3 hour) transients is described. Seven new transient or flaring sources were found, all relatively faint (<10 UFU). dMe flare stars are present in two of the error boxes and NGC 1841, a globular cluster in the LMC, lies just outside a third.

ISSN:0094-243X    

DOI:10.1063/1.34579

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The Vela spacecraft, particularly Vela 5B, produced all‐sky X‐ray data of unprecedented length and completeness. Recent re‐analysis has put the data in the form of 10‐day skymaps covering a 7‐year period, which have led to the discovery or confirmation of a number of long‐term periodicities, and have made possible a time‐lapse movie of the X‐ray sky.

ISSN:0094-243X    

DOI:10.1063/1.34580

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Five day light curves of MXB 1916‐05 obtained 6 month apart reveal two modes of behavior. In the fall 1977 the source had several extended periods of low flux as well as generally erratic variability. In the Spring 1978 the flux steadily increased over several days. The 50 minute period was not detected. We interpret the erratic variability as an instability in the accretion disk.

ISSN:0094-243X    

DOI:10.1063/1.34581

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Recurrent soft x‐ray transient sources and dwarf novae have many remarkably similar observational properties. Both classes of cataclysmic variables are thought to be composed of close binaries with one component filling its Roche lobe. These systems undergo considerable luminosity variation on the timescale ranging from weeks to months. The outburst properties in both classes can be adequately described in terms of a model in which the outbursts are regulated by the same basic physical mechanism, i.e., a thermal instability associated with the partially ionized regions of an accretion disk around a compact accreting component of the close binary system. In this contribution, we show how observational properties obtained in these two classes of cataclysmic variables may be combined to provide an understanding of the nature of the outbursts.

ISSN:0094-243X    

DOI:10.1063/1.34582

出版商:AIP    

年代:1984

数据来源: AIP