Search Publications
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…
Detection of energetic electron (E greater than KeV) and ion fluxes (E greater than 97 KeV) from comet P/Halley by the Giotto experiment EPA on 1986 March 13/14
Neubauer, F. M.; Kirsch, E.; O'Sullivan, D. +2 more
Relativistic electron fluxes (greater than 220, greater than 300 KeV) were recorded during the Giotto encounter with comet P/Halley from the inbound to the outbound bowshock. A strong enhancement in the greater than 300 KeV electron flux was measured about 1 hr after the outbound crossing of the bow shock. It is suggested that the electrons were s…
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<…
Giant Starspots and Stellar Flares: The View from Space
Byrne, Patrick B.
Satellite observations of starspots and stellar flares are examined. The properties of sunspots and solar flares are reviewed and the method used to infer the existence of starspots is described. IUE observations of the atmospheres of spotted stars and Exosat X-ray observations of solar flares are discussed. Also, an IUE spectrum of II Peg and a U…
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…IUE Observations of Stars in the Neighborhood of the Lambda Orionis Nebula
Bergoffen, Martin J.; van Buren, Dave
The authors present the results of an IUE archive study of five stars along the line of sight towards the λ Orionis H II region. H I, Fe II, Si II, and Mn II column densities have been found using a profile-fitting technique for H I and the curve-of-growth method for the ions. HD 36861 and HD 36822 lie at or near the center of the H II region, whi…
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.