Search Publications
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…
The dwarf nova dippers
Sonneborn, G.; Charles, P. A.; Hassall, B. J. M. +1 more
Two previous papers /1,2/ have shown that the dwarf nova OY Car has extensive vertical disc structure during its (~2 week) superoutbursts. This structure is analogous to that seen in the low mass X-ray binaries (LMXBs), in that the whole disc flares towards its edge, and there is a bulge or ``dark spot'' where the mass transfer stream meets the di…
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<…
Energy distribution and variability of BL Lac objects: Recent observations and a theoretical scheme
Maraschi, L.
Spectral properties of X-ray selected and radio-selected BL Lacs are discussed. The results provide a direct indication that the X-ray emission is more isotropic than the radio emission. Recent results of multifrequency observations of the brightest X-ray selected BL Lac object, PKS 2155-304, are reviewed, showing how the fast X-ray variability is…
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 …
SS Cygni: The mass accretion rate behaviour in quiescence and in outburst
Gaudenzi, S.; Giovannelli, F.; Claudi, R. +1 more
From the HeII λ1640 emission line equivalent width values in all good available IUE low resolution spectra, we have deduced the correspondent mass accretion rate values Mdot for SS Cygni, using the optically thick boundary-layer model by Patterson and Raymond 1985. The Mdot behaviour can be distinguished as follows:
1) in the rising and decli…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…
Infrared to UV energy distribution of the black hole candidate LMC X-3: Observation of the accretion disk
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +4 more
LMC X-3 is a binary X-ray source which most probably hosts a black hole. Here, the authors present a preliminary report on observations of the source in the IR, optical, and UV bands. The observations allow to evidentiate the presence of the accretion disk surrounding the black hole.
Simulataneous X-ray and optical observations of LMC X-2
Motch, C.; Beuermann, K.; Pakull, M. +3 more
The X-ray source LMC X-2 was observed with EXOSAT for -8hours on February 2nd, 1984 with simultaneous photometric and spectroscopic optical coverage. The source was seen at a luminosity of Lx ~ 1.5 1038erg.s-1 with a mean X-ray spectrum which can be described equally well by either a superposition of a thermal emis…