Spectral characteristics of transient X-ray sources.
Abstract
The subdivision of transient X-ray sources into hard-spectrum sources which show little spectral evolution and soft-spectrum sources which exhibit marked softening in time is discussed in relation to various properties of the following seven sources: Cen X-4, 3U 1543-47, A1524-62, A1118-61, A1743-28, A0535 plus 26, and A0620-00. X-ray spectra are obtained for A1524-62 and A0535 plus 26; their spectral properties are summarized along with those of the other five sources. It is shown that A1118-61 and A0535 plus 26 both have very hard spectra which do not show strong variation with phase, exhibit regular pulsation, and have (high-mass) Be stars as proposed optical counterparts. For the other five sources, there is evidence that the spectra have evolved from a hard to a soft state, pulsation has not been observed, and available optical identifications indicate low-mass companions. It is suggested that a significant correlation exists for X-ray transients among the occurrence of pulsation, hardness of the X-ray spectrum, and association with systems containing bright early-type stars.
- Publication:
-
Nature
- Pub Date:
- September 1976
- DOI:
- 10.1038/263034a0
- Bibcode:
- 1976Natur.263...34M
- Keywords:
-
- Astronomical Spectroscopy;
- Spectrum Analysis;
- X Ray Sources;
- X Ray Spectra;
- Binary Stars;
- Early Stars;
- Pulsars;
- Variable Stars;
- X Ray Stars;
- Astrophysics;
- ASTRONOMICAL SPECTROSCOPY;
- SPECTRUM ANALYSIS;
- X RAY SOURCES;
- X RAY SPECTRA;
- BINARY STARS;
- EARLY STARS;
- PULSARS;
- VARIABLE STARS;
- X RAY STARS