摘要:

Objects with temperatures on the order of 30 eV and luminosities around 1038erg/s have been established as a separate class by the recent ROSAT observations. The prototype supersoft x‐ray source (SSS) is the well‐known x‐ray binary CAL83 in the LMC, which has an orbital period of 1.04d. In the meantime about 10 SSS have been found in the Magellanic Clouds and at least 15 in the Andromeda Nebula. Two uncatalogued galactic supersoft sources have recently been discovered, but also the nova Muscae 1984 could be detected in a supersoft state 9 years after the explosion. In several cases dramatic time variability is found, with x‐ray on‐ and off‐states. The observations are summarized here. Several models have been suggested to explain the high luminosity and low temperature of SSS, all of them require very high mass accretion rates, which are also indicated in some of the optical spectra. In one interpretation the compact object is a neutron star (or black hole) shrouded by super‐Eddington accretion and the large radius and low temperature of the x‐ray photosphere is due to a Compton scattering cloud. If this were true, a large number of undetected supersoft neutron star binaries could help to moderate the millisecond pulsar birthrate problem. In the more likely interpretation, the compact object is a white dwarf burning nuclear fuel on its surface at the Eddington accretion rate. In this case the long‐sought predecessors for SN type‐Ia explosions might be among the class of supersoft sources. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45948

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This article reports on the analysis of the first M31 survey with the ROSAT PSPC performed in July 1991. The spectral characteristics of the 396 individual x‐ray sources detected will be discussed as well as their positional correlation with the 108 individual x‐ray sources detected by the Einstein observatory. The optical identifications of the ROSAT x‐ray sources are the result of a MIT‐MPE‐UvA collaboration. A detailed analysis of the integral flux distribution shows that just two thirds of the detected x‐ray sources in the field of M31 must be background objects. The discovery of a significant absorption of background radiation is discussed, as well as an upper limit for the luminosity of a diffuse emission component. Finally a comparison of the luminosity function of 29 globular clusters sources with the one in our own galaxy reveals a good agreement. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45950

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The Einstein X‐ray Observatory Satellite provided the first detection of isolated x‐ray sources in the Andromeda Galaxy. Recent ROSAT observations have provided observations of the x‐ray binaries in M31 complete toLx∼1034erg sec−1, and are sensitive enough to detect many supernova remnants and other x‐ray sources. Optical identifications are crucial to identify or confirm the identifications of these sources. This article reviews the search for optical counterparts to the Einstein x‐ray sources and discusses the ongoing efforts of the MIT‐UvA‐MPE group to identify optical counterparts to the ROSAT x‐ray sources. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46031

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We propose that the supersoft x‐ray spectra observed in CAL 83, CAL 87, and RX J0527.8‐6954 can be explained as a result of near‐Eddington accretion onto neutron stars. Our model is consistent with a recently proposed unified model for the low‐mass x‐ray binaries (LMXRB). If the luminosity of the source is within 10% of the Eddington value, what determines whether the source appears as a supersoft x‐ray source or as a ‘‘canonical’’ LMXRB is the nature of the accretion flow and its extend. If the radial flow is subsonic and extends toatleasta few thousand neutron star radii the source behaves like a supersoft one. If on the other hand the flow is supersonic and extends toatmosta few hundred neutron star radii, the source exhibits the characteristics of a ‘‘canonical’’ LMXRB. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45951

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present deep pointed observations of ten globular clusters obtained with the ROSAT PSPC, and one with the ROSAT HRI. X‐ray sources are detected in the cores of seven of them, at luminosities of ∼1–6×1032erg s−1. At least two of these are multiple. Four have colors indicating soft spectra, with blackbody temperatureskT≲0.3 keV. Soft spectra can be excluded for the other three sources. The sources outside the cores are probably not associated with the cluster. The most likely counterparts for these sources are soft x‐ray transients (SXTs). ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45952

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Modern stellar evolutionary tracks are used to calculate the evolution of a very large number of massive binary star systems (Mtot≳15M⊙) which cover a wide range of total masses, mass ratios, and starting preparations. Each binary is evolved accounting for mass and angular momentum loss (due to wind mass loss, mass loss during Roche lobe overflow of the primary, mass loss during a common envelope phase should it occur), through the supernova of the primary to the x‐ray binary phase. Using the observed rate of star formation in our galaxy and the properties of massive binaries, we calculated the expected high mass x‐ray binary (HMXRB) population in the Galaxy. We test various massive binary evolutionary scenarios by comparing the resulting predictions to the x‐ray observations. Our principle result is that approximately 70% of the overflow matter is lost from a massive binary system during mass transfer in the Roche lobe overflow phase. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45953

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Single neutron stars were thought of more than 30 years before they were observed (and even then were not instantly recognized). Binary neutron stars, on the other hand, were observed before they had been thought of as a separate, interesting class, and were also not immediately recognized for what they were. The traditional apportionments of credit for the various ideas are not fully supported by contemporaneous publications. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45954

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A summary is given of progress reported at this meeting on six basic questions having to do with x‐ray binaries: which stellar systems create them; what drives mass transfer; the nature of the accretion disk, if one exists; how the x‐rays are made; neutron star life‐cycles; and analogous systems in other galaxies. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45955

出版商:AIP    

年代:1994

数据来源: AIP