Search Publications
In situ exploration of the dusty coma of comet P/Halley at Giotto's encounter: Nucleus emission and production rates from temporal variability
McDonnell, J. A. M.; Pankiewicz, G. S.; Perry, C. H.
Flux-time profiles from the DIDSY and PIA experiments, taken at Giotto's encounter with comet P/Halley, are used to study coma dust dynamics and the nucleus emission. A comparison of the data with a `fountain' model, incorporating variable source function and grain type is made. Local enhancements such as jets, envelopes and terminators are analys…
Giotto Comet Halley Dust Impact experiment: Studies of discrete impact events
McDonnell, J. A. M.; Alexander, W. M.; Goad, H. +2 more
Analysis of discrete pulse height data from specific individual events of the Giotto Comet Halley Dust Impact Detectors DID-1 and DID-4 has been completed. The cumulative flux for the mid-size range of this Giotto comet dust experiment has been studied and results are presented. The technique employed in the investigation utilized a constant numbe…
A correlation of energetic particle flux anisotropies with magnetic field variations in- and outside the coma of comet Halley
Neubauer, F. M.; Daly, P. W.; Ip, W. -H. +4 more
Anisotropies and energy spectra of cometary ions (mainly O+, OH+, H2O+) derived from the EPA/EPONA measurements on board of Giotto during the encounter (12-14 March 1986) with comet Halley are used to study the acceleration processes taking place in the vicinity of the comet. Further evidence was found f…
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…
IUE and optical spectrophotometry of the HZ Herculis/Hercules X-1 system
Howarth, I. D.; Raymond, J. C.; Wilson, R. +1 more
Photometric (B-filter) data of HZ Herculis obtained between 1972 and 1974 have been fitted by a model consisting of Roche-lobe-filling star transferring material to a neutron star via a tilted, preccessing, accretion disc. The disc inclination was found to be small, thus avoiding theoretical difficulties experienced with high-inclination discs. We…
Optical and UV observations of the symbiotic star CH Cygni after the jets ejection in 1984
Mikolajewska, J.; Mikolajewski, M.; Tomov, T.
The optical and UV observations of the symbiotic star CH Cyg are discussed in the context of the jet appearance. CH Cygni is an eclipsing binary with a period of 5700 days, consisting of an M 6 giant and a white dwarf surrounded by an accretion disk formed from the cool giant wind. Previous studies of the system are reviewed and emission line prof…
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…