Search Publications
A Study of BL Lacertae--Type Objects with EXOSAT. I. Flux Correlations, Luminosity, Variability, and Spectral Variability
Maccagni, D.; Giommi, P.; Garilli, B. +2 more
Results are presented from a uniform and systematic analysis of more than 200 X-ray observations of 36 BL Lacertae objects obtained from the EXOSAT archive. All but two objects were detected at least once. Strong luminosity variability, which reached a factor of 30 in one case, was a common property of these objects. Variability was usually more p…
X-Ray Eclipse Mapping of AR Lacertae
Parmar, A. N.; White, N. E.; Culhane, J. L. +2 more
Exosat data of the binary cycle of the eclipsing RS CVn system AR Lac are studied. The data reveal that at energies of less than 1 ke V a factor of 2 intensity modulation is detected and at energies greater than 1 ke V no orbital modulation is observed. The chi-squared and maximum entropy methods are used to model low-energy modulation. The relati…
The X-Ray Absorption Spectrum of VELA X-1
Haberl, F.; White, N. E.
Exosat observations of the massive X-ray binary Vela X-1 are spectrally analyzed. The absorbing column density shows erratic factor of 10 increases up to 5 x 10 to the 23rd H/sq cm that can occur at any orbital phase and last from minutes to many hours. These variations occur on top of a base level of absorption that increases from 3 x 10 to the 2…
Correlation of X-Ray Burst Properties with Source State in the ``Atoll'' Source 4U/MXB 1636-53
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +3 more
A series of Exosat observations of the 'atoll' source 4U/MXB 1636 - 53 shows that duration and temperature of the X-ray bursts strongly correlate with the X-ray spectral and fast variability characteristics of the persistent emission of the source. This implies that spectral shape, fast variability, and burst duration and temperature all correlate…
Period Measurements of the 50 Millisecond Pulsar PSR 0540-69 with the EXOSAT Satellite
Hasinger, Guenther; Oegelman, Hakki
The period of the 50 ms pulsar PSR 0540 - 69 in the Large Magellanic Cloud was determined using five separate X-ray observations with the Exosat satellite in the interval August 12, 1984 to June 30, 1985. Together with Einstein observations and contemporaneous optical data, the Exosat periods can be fitted well to a quadratic curve yielding a brak…
The Complex 0.4--12 keV X-Ray Spectrum of Cygnus X-1
van der Woerd, H.; Barr, P.
Simultaneous observations of the 0.4-2 keV and 2-12 low-state spectrum of Cygnus X-1, made with the low-energy transmission grating spectrometer and gas scintillation proportional counter on board EXOSAT, are presented. At least four spectral components are required to describe the data: a hard (energy spectral index alpha about 0.4) power law dom…
EXOSAT Observations of Cygnus X-2 Continuum and Line Spectrum
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +7 more
An analysis of five Exosat observations of Cyg X-2, taken around a full binary orbit is presented. The data were obtained using all instrumentation (1000 lines/mm Transmission Grating Spectrometer, Channel Multiplier Array + filters, Medium-Energy experiment, and Gas Scintillation Proportional Counter) simultaneously, and span the full energy rang…
X-Ray and Ultraviolet Observations of the Seyfert Galaxy MCG 8-11-11
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +4 more
MCG 8-11-11 was observed in the 0.5-8 keV band with the EXOSAT observatory at 9 epochs in 1983-1986. Quasi-simultaneous UV observations were obtained in all but one case. The X-ray spectra are well fitted by absorbed power laws (N_H_ ~ 1.5 x 10^21^ cm^-2^, α_ph_ ~ 1.7). Small variations of the spectral shape are found with softening of the source …
EXOSAT Observations of the Blazar PKS 1510-089
Singh, K. P.; Rao, A. R.; Vahia, M. N.
A detailed study of X-ray emission from the high-polarization quasar PKS 1510-089, also known as a blazar, is presented, based on the EXOSAT observations in 1984 and 1985. The data were obtained from the EXOSAT archives. There is no evidence for any variations in the X-ray intensity on hourly time scales during either of the two observations. The …
Search for Millisecond X-Ray Pulsations from the Galactic Bulge X-Ray Source GX 9+1
Michelson, P. F.; Norris, J. P.; Wood, K. S. +2 more
The recent discoveries of millisecond radio-pulsars with small period derivatives and quasi-periodic oscillations in bright Galactic X-ray sources have given rise to theories which predict that low-mass X-ray binaries should have low-amplitude X-ray pulsations with short, possibly millisecond, periods. Most previous searches for these pulsations s…