Search Publications
A spectral classification of QPO sources
Hasinger, Guenther
The spectral and power-spectral similarities between different modes of the QPO sources Cyg X-2 and Sco X-1 are emphasized. It is shown that low-mass X-ray binaries in general can be found in three different states, forming a Z-shaped spectral correlation diagram. There is a direct relation between the spectral states and three different QPO modes…
Circinus X-1, as viewed by EXOSAT
Tennant, A. F.
In this paper we review the discoveries made with EXOSAT during observations of Cir X-1. Type 1 X-ray bursts were seen in two observations. During the brightest burst, the energy flux was observed to saturate. If we assume this saturation is due to the Eddington limit then it is possible to estimate a distance to the source from the X-ray data alo…
X-ray bursts - Some recent developments
Lewin, Walter H. G.; van Paradijs, Jan
In this paper we review recent developments in the areas of burst recurrence, and mass-radius relations of neutron stars. We reach the surprising conclusion that the time-averaged X-ray luminosity emitted in type 1 bursts is approximately independent of the persistent X-ray luminosity over a large range (factor of ~30) of the latter. We conclude t…
Coordinated X-ray and ultraviolet observations of the intermediate polar H2215-086
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +6 more
Quasi-simultaneous observations of H2215-086 (=FO Aqr), obtained with Exosat and IUE in 1983 and 1985 are reported. Secular variations in the X-ray flux and in the shape of the rotational light curve are observed. The modulation of the photoelectric absorption cutoff is studied by means of phase resolved X-ray spectra. A possible orbital modulatio…
The flux variability of the Seyfert galaxy NGC6814 as observed with exosat
Branduardi-Raymont, G.; Mittaz, J. P. D.
We present five EXOSAT observations of the Seyfert galaxy NGC6814. The source is found to be variable at both soft (LE) and medium (ME) X-ray energies. The most remarkable characteristics of this variability are the regular recurrence of flares at 12000s intervals during a 1-day long ME observation, a dip in the ME flux by a factor of 2 in ~ 300 s…
Detection of transient periodicity in an EXOSAT observation of NGC4151
Piro, L.; Perola, G. C.; Fiore, F. +1 more
Fourier analysis of an EXOSAT (ME) 30000 s observation of the Seyfert 1 galaxy NGC 4151 revealed a transient periodical phenomenon (period 131 +/- 1 s and duration of a few thousand seconds) with a probability of a chance occurrence of the peak in the power spectrum of 2 10-3. Analysis of short data segments provides further evidence of…
Results of high resolution soft X-ray spectroscopy of hot white dwarfs with EXOSAT
Paerels, Frits; Heise, John
We present the final results of the high resolution X-ray spectroscopy of hot white dwarfs, obtained with the 500 lines mm-1 Transmission Grating Spectrometer on EXOSAT. These data, which are unique in wavelength coverage, spectral resolution, and statistical quality, have offered us the first detailed look at the photospheric X-ray spe…
Spectral and QPO analysis of GX5-1 at very high intensity
Kendziorra, E.; Staubert, R.; Collmar, W.
From a short EXOSAT observation of the bright low mass X-ray binary GX 5-1 we have derived information about the spectral and the QPO behaviour of this source during a very high intensity state. GX 5-1 was found to be on the `horizontal branch' in the hardness ratio/intensity diagram. The X-ray luminosity (1-20 keV) varied from 3.8 *10<…
X-ray time variability and luminosity correlations in BL lacertae objects
Maccagni, D.; Giommi, P.; Garilli, B. +2 more
We present the preliminary results of a study of the soft X-ray properties of a sample of 34 BL Lacertae objects observed with the the EXOSAT Observatory. Strong correlations between the X-ray, optical and radio fluxes have been found in the subsample of X-ray selected objects. X-ray variability is common and has been significantly detected in 14 …
Accretion disc boundary layers with white dwarfs
van der Woerd, Hans
The boundary layer between the accretion disc and white dwarf in non-magnetic cataclysmic variables is the major source of X-rays from these systems. Two modes of X-ray emission exist; at low accretion rates a thermal instability develops in the accreting matter and a hard X-ray emitting corona is formed around the white dwarf; at high accretion r…