Search Publications
An Ionized Accretion Disk in Cygnus X-1
Done, C.; Mulchaey, J. S.; Mushotzky, R. F. +1 more
Results of an analysis of archival Exosat and HEAO 1-A2 observations of Cyg X-1 are presented. It is found, in agreement with Ebisawa (1991), that the X-ray spectrum of Cyg X-1 exhibits a 'high-energy excess' above 8 keV, similar to that seen in Ginga spectra of AGN. It is shown, on the basis of a likelihood ratio test, that the data are significa…
Correlated Hard X-Ray and Ultraviolet Variability in NGC 5548
Nandra, K.; Clavel, J.; Reichert, G. A. +7 more
We present the result of a series of contemporaneous (within one day) hard X-ray (Ginga) and ultraviolet (IUE) observations of the Seyfert 1 galaxy NGC 5548. Nine of these observations were carried out over a period of 51 days in 1990 May-July, and two in 1989. An additional simultaneous IUE-EXOSAT observation obtained on 1984 May 21 is also analy…
The spectral signature of the cooling flow in Abell 478.
Fabian, A. C.; Edge, A. C.; Johnstone, R. M. +1 more
We present X-ray spectra of Abell 478 taken with the Ginga LAC and with the Einstein SSS. The LAC data set an upper limit of ~440 M_sun_ yr^-1^ on the mass deposition rate throughout the whole cluster if a value for the galactic absorption based on 21-cm observations of H I is adopted. The SSS data strongly require an absorbing column density well…
EXOSAT X-Ray Spectra of Quasars
Comastri, Andrea; Setti, Giancarlo; Zamorani, Giovanni +4 more
We have measured the X-ray spectra in the 0.1-10 keV energy range for 17 AGNs (mostly PG quasars) using the EXOSAT Low and Medium Energy arrays. The sample has been selected on the basis of soft X-ray flux and includes all the AGNs in the 1981 Zamorani et al. and 1986 Tananbaum et al. publications with an Einstein flux greater than 6x10^-12^ ergs …
Radio-loud and radio-quiet quasars observed by EXOSAT.
Saxton, R. D.; Turner, M. J. L.; Stewart, G. C. +2 more
We present results from the spectral analysis of EXOSAT data on 31 quasars, 18 radio-loud and 13 radio-quiet. Simple power-law models with fixed (Galactic) absorption give acceptable fits to the spectra obtained in the 2-10 keV band. Using the results from these fits we have compared the distributions of spectral indices α for the radio-loud and r…
Variability pattern from X-ray to IR wavelengths in the active nucleus ofNGC 1566.
Alloin, D.; Pelat, D.; Baribaud, T. +1 more
This study presents the results of a multiwavelength monitoring of the active galactic nucleus in NGC 1566. Data collected in the X-rays, ultraviolet, visible and near-infrared domains have been combined together, in order to disentangle the various components and to better understand the patterns of variability in this active nucleus. At all wave…
X-Ray Luminosity and Spectral Variability of Hard X-Ray--selected Active Galactic Nuclei
Tagliaferri, G.; Giommi, P.; Grandi, P. +2 more
One hundred sixty-one observations archived in the EXOSAT data base are analyzed in order to study time and spectral variability of all 30 sion-line active galactic nuclei (AGNs) in the Piccinotti sample. For each source long-term (from days to months) and short-term (from minutes to hours) luminosity variations were sought using the soft (LE: 0.0…
The EXOSAT obseravtions of SS Cygni.
Watson, M. G.; Jones, M. H.
A series of nine observations of SS Cygni made using Exosat between 1983 November and 1984 September are presented. Distinct soft amd hard X-ray emitting components were spectrally resolved by the LE and ME instruments, respectively. In quiescence the source shows hard X-ray emission with a 2-10 keV luminosity of 1.2 x 10 exp 33 (d/200 pc)-squared…
GINGA and EXOSAT observations of the Perseus cluster of galaxies.
Fabian, A. C.; Allen, S. W.; Edge, A. C. +2 more
We report observations of the Perseus cluster of galaxies made using the Ginga and EXOSAT satellites. Our results from Ginga indicate that the region around the centrally dominant galaxy NGC 1275 is well described by a model incorporating emission from an isothermal, diffuse plasma of temperature ~6.3 keV, metal abundance ~ 0.4 solar, a cooling fl…
Models for the remnants of recurrent novae - III. Comparison with the X-ray observations of RS Ophiuchi (1985).
Bode, M. F.; O'Brien, T. J.; Kahn, F. D.
The X-ray emission predicted by a model for the interaction of ejecta with a circumstellar medium is compared to Exosat observations of the 1985 outburst of the recurrent nova RS Ophiuchi. The model parameters are constrained by fitting the predicted spectrum to the first X-ray observation, made 55 days after the outburst, and are found to be cons…