Search Publications
Missions
Journals
Publication Years
The Discovery of 0.2 HZ Quasi-periodic Oscillations in the X-Ray Flux of the Transient 42 Second Pulsar EXO 2030+374
Stella, L.; Parmar, A. N.; Angelini, L.
The discovery of about 0.2 Hz quasi-periodic oscillations (QPOs) in the 1-15 keV X-ray flux of the transient 42 s pulsar EXO 2030 + 375 is reported. The detection of QPOs in the power spectra of this pulsar was made possible by the application of a newly developed technique to decouple the power spectrum peaks. QPOs were detected during an outburs…
Spectral characteristics of low-frequency plasma turbulence upstream of comet P/Halley
Coates, A. J.; Glassmeier, K. -H.; Neubauer, F. M. +4 more
Spectral characteristics of low-frequency plasma turbulence in a cometary environment have been determined using cross-spectral analyses of magnetic field and plasma measurements made on board the Giotto spacecraft upstream of comet P/Halley. Two upstream regions have been identified, where the mean solar wind magnetic field was approximately para…
An EXOSAT X-Ray Observation of One Orbital Cycle of 4U 1700-37/HD 153919
Haberl, F.; White, N. E.; Kallman, T. R.
Exosat observations of close to one complete binary cycle of 4U 1700-37/HD 153919 are presented, and X-ray absorption variations are determined as a function of orbital phase in order to study the properties of the stellar wind of the companion HD 153919. The decrease noted in absorption between eclipse egress and phase 0.5 may be due to X-rays fr…
The Kinematics of Milky Way Halo Gas. I. Observations of Low-Ionization Species
Danly, Laura
Ultraviolet interstellar line day observed with the IUE toward 70 halo stars and four extragalactic sight lines are analyzed in a study of the large-scale kinematic properties of the Milky Way halo gas. The motions of the low-ionization gas is focused on. Large systematic velocities are found, and a pronounced asymmetry in the absorption character…
The nucleus of comet Halley: Surface structure, mean density, gas and dust production
Rickman, H.
The relation between the mass of a cometary nucleus, its gas production curve, the mean outflow velocity, and the nongravitational delay of the comet is discussed, emphasizing the properties of gaseous outflow from comet Halley. The importance of knowledge about the rotational state of the nucleus is stressed, and it is argued that the likely wobb…
X-Ray Observations of the Starburst Galaxy M82
Pietsch, W.; Schaaf, R.; Kronberg, P. P. +2 more
We report here on long (~ 10^5^ s) X-ray observations of the starburst galaxy M82 with the European X-ray satellite EXOSAT. The observations with the low-energy imaging instrument confirm that there is extended X-ray emission from above and below the disk, with an overall extent perpendicular to the disk of almost 6' corresponding to 6 kpc. We pre…
Iron features in the X-ray spectra of three Seyfert galaxies.
Nandra, K.; Pounds, K. A.; Stewart, G. C. +1 more
Ginga X-ray spectra are presented for three Seyfert type 1 galaxies, each one showing evidence for a significant iron K-emission line. This line is interpreted as fluorescence from cold material, apparently lying close to the plane of the host galaxy, for NGC 5548 (near face-on) and NGC 3227 (~60^deg^ inclination). The additional detection of a la…
EXOSAT observations of X 1822-371 : modelling of the accretion disc rim.
Hellier, Coel; Mason, Keith O.
Data from three Exosat observations have been used to model X1822-371 as an X-ray emitting accretion disk corona (ADC) which is partially obscured by an optically emitting disk whose height varies with azimuthal angle. Using a system inclination of 85 + or - 3 deg and a disk structure parameterized by as few as two straight lines, the model is abl…
Evaluation of cometary dust parameters from numerical simulations: comparison with an analytical approach and the role of anisotropic emissions.
Fulle, M.
A numerical method is developed which models cometary dust tails by means of sample grains. The orbital motion of the grains is rigorously computed, avoiding any Finson-Probstein hypersonic condition and dust shell geometry approximation. The model is applied to the dust tails of Comet Seki-Lines 1962III and Comet Kohoutek 1973XII. The results sho…
Detection of iron features in the X-ray spectrum of the Seyfert I galaxy MCG -6-30-15.
Nandra, K.; Fabian, A. C.; Pounds, K. A. +2 more
The spectra analysis of an extended (~2 d) EXOSAT observation of the Seyfert l galaxy MCG-6-30-15 has revealed significant difference from the previous simple power-law description. In particular, evidence is found for both emission and absorption features from cold iron, indicating a large column density of material possibly located close to the …