Search Publications
Two patterns of correlated X-ray timing and spectral behaviour in low-mass X-ray binaries.
van der Klis, M.; Hasinger, G.
Exosat data are used to study the power spectra of 16 LMXBs as a function of their behavior in X-ray color-color diagrams. The study confirms the existence of a class of sources with three-branched Z-shaped colour-colour diagrams characterized by a temporal behavior that is strongly dependent on the position of the source on the Z. Evidence for an…
Spectral classification of low-mass X-ray binary (LMXB) energy spectra with color-color diagrams.
Hasinger, G.; Truemper, J.; Schulz, N. S.
In this article we describe spectral variations of a large sample of low-mass X-ray binaries (LMXBs). The observations are done with the European X-ray Observatory EXOSAT. We decomposed the measured X-ray spectrum into three energy bands and plotted them into color-color and hardness-intensity diagrams. Correlations are compared with a few templat…
The X-ray flare and the quiescent emission from Algol as detected by EXOSAT.
Mewe, R.; van den Oord, G. H. J.
The Algol system was observed on August 18/19,1983 with different combinations of three instruments aboard EXOSAT: the low-energy channel multiplier array, the medium-energy proportional counters, and the transmission grating spectrometer. The X-ray flare observed on August 19 was analyzed and the decay phase was studied. It is shown that during t…
The X-ray ephemeris of Cygnus X-3.
van der Klis, M.; Bonnet-Bidaud, J. M.
A set of 17 measurements of the arrival time of the 4.8-hr period of the X-ray binary Cygnus X-3 over an interval of 2.3 yr are derived from Exosat data. These measurements are combined with previous data to study the period of Cygnus X-3 for the period 1970-1985. A cubic ephemeris with a 99.9 percent confidence fit to the data is presented with a…
EXOSAT observations of the X-ray burst source 4U 1608-52.
van Paradijs, J.; Lewin, W. H. G.; Tan, J. +2 more
The results of an analysis of two Exosat observations (July 1984, May 1986) of the highly variable X-ray burst source 4U 1608-52 are presented. During both observations the persistent X-ray flux was low (quiescence), and the persistent X-ray spectrum could be well fitted with a power-law model, with approximately the same index, but a somewhat dif…
Soft and hard X-ray variability from the accretion disk of NGC 5548.
Kaastra, J. S.; Barr, P.
EXOSAT observations of the Seyfert galaxy NGC 5548 confirm previous detections of a soft X-ray excess above a power law component. Both components show correlated variability on a typical time scale of half a day. There is evidence for a delay of the hard X-rays with respect to the soft X-rays of 1-2h. The spectral data can be explained in terms o…
EXOSAT observations of five luminous globular cluster X-ray sources.
Stella, L.; Parmar, A. N.; Giommi, P.
Exosat observations are used to search for orbital modulations in the X-ray light curves of five luminous globular cluster X-ray sources in NGC 1851, NGC 6441, NGC 6712, Terzan 1, and Terzan 2. Upper limits to possible short-period orbital modulation are presented. Two or three intensity dips are observed in the light curve of NGC 6441. The result…
Soft X-ray observations of the VELA pulsar PSR 0833-45.
Oegelman, H.; Zimmermann, H. -U.
X-ray maps produced from Exosat observations of the Vela pulsar in the 0.03-2.4 keV range confirm the components discussed by Harnden et al. (1985). Restricting the central source to a neutron star with an 8-15 km radium emitting blackbody-like radiation suggests a surface temperature in the 600,000 to 1,000,000 K. It is found that the observed bl…
One-pole and two-pole X-ray emission in the AM Herculis binary BL Hyi.
Beuermann, K.; Schwope, A. D.
This paper reports the results of extensive X-ray observations of BL Hyi = H0139-68 with the Exosat satellite when the source was in states of low and intermediate brightness. In the low state, X-rays were observed only between orbital phases phi = 0.0 and about 0.4, coincident with the orbital hump of cyclotron emission from the main pole. In the…
Coordinated observations of a large impulsive flare on UV Ceti.
Heise, J.; van Genderen, A. M.; Waelkens, C. +16 more
The characteristics of the major flare observed on UV Ceti on Decemmber 1985 at 01:26 UT during an international observing campaign are described. X-ray observations were obtained with Exosat in the 0.06-0.3 keV bands and 1-6 keV bands; optical photometry was obtained in 11 wavelength bands, and spectra were recorded in the wavelength range 3500 t…