Search Publications
Radio to X-ray energy distribution of BL Lacertae objects.
Giommi, P.; Micol, A.; Ansari, S. G.
We present multifrequency spectra of a large number of radio and X-ray selected BL Lacertae objects constructed using non-simultaneous archival data. The data were obtained using the European Space Information System (ESIS) and are from several radio and optical catalogues, the IRAS Faint Source Catalogue, the Einstein and the EXOSAT databases. Th…
A detailed X-ray variability study of the Seyfert galaxy NGC 4051
Papadakis, I. E.; Lawrence, A.
We present a detailed and rigorous examination of the X-ray variability characteristics of the Seyfert galaxy NGC 4051, using the 1985 EXOSAT observation and our improved power spectrum modelling techniques. The Medium Energy (ME) power spectrum is adequately fitted by a power-law model, but the Low Energy (LE) spectrum is not. We find an excellen…
Circinus X-1 revisited: fast-timing properties in relation to spectral state.
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +2 more
We have studied the X-ray spectral and fast-timing variations of Cir X-1 by performing a homogenous analysis of all EXOSAT ME data on this source using X-ray hardness-intensity diagrams (HIDs), colour-colour diagrams (CDs), and power spectra. Cir X-1 exhibits a wide range of power spectral shapes and a large variety in X-ray spectral shapes. At di…
Multifrequency Spectra of EXOSAT Blazars
Ghosh, K. K.; Soundararajaperumal, S.
Blazars have been divided into two groups: radio-selected blazars (RBLs) and X-ray-selected blazars (XBLs). Results of the X-ray spectral analysis of 28 such blazars which were observed with EXOSAT are presented in this paper, and in four these are new results which were not published earlier. X-ray results suggest that XBLs are steep-spectrum sou…
Long-term X-ray variability of NGC 4151
Papadakis, I. E.; McHardy, I. M.
We present a new method of estimating the power spectrum in the case of unevenly sampled data, together with its application to the long X-ray light curve of the Seyfert galaxy NGC 4151. This method is based on the Fourier transform of the observed autocovariance function. The method is simple to use and wisely applicable. The long-term power spec…
Evidence for Elemental Variation in the Ejecta of the TYCHO Supernova Remnant
Hughes, John P.; Gorenstein, P.; Vancura, O.
We present an X-ray study of the Tycho supernova remnant utilizing archival data from the high-resolution imagers (HRIs) on Einstein and ROSAT, the low-energy imaging telescopes (LEITs) on EXOSAT, and spectral data from the Broad Band X-ray Telescope (BBXRT). We have made use of the differing HRI bandpasses to construct images of Tycho in two spec…
Burstlike Events in the Z Source Cygnus X-2
van Paradijs, J.; van der Klis, M.; Kuulkers, E.
We have found nine burstlike events in EXOSAT data of the Z source Cyg X-2. Their durations are of the order of several seconds. Within the limited counting statistics we cannot find an indication for cooling during the burstlike events, which would have indicated that they are bona fide type I bursts, i.e., thermonuclear flashes on the surface of…
Dynamic Processes in Be Star Atmospheres. III. Rapid Multiwavelength Variability in gamma Cassiopeiae
Smith, Myron A.
A review of the characteristics of X-ray emission from gamma Cas suggests various weaknesses with conventional scenarios that invoke Be wind interactions with a putative binary companion. To explore whether this emission might arise instead from sporadic high-energy events on the Be star itself, we have examined the temporal behavior of Voyager 1 …
Emission Spectrum Integrated over an Accretion Disk: Comparison with Observations of Active Galactic Nuclei
Shimura, Toshiya; Takahara, Fumio
Emission spectrum from an accretion disk for active galactic nuclei is obtained by solving the vertical structure and radiative transfer self-consistently and by integrating the local spectrum over radii. We found that even for moderate accretion rates, disks emit a significant portion of the total luminosity in UV through soft X-ray range; for th…
The EXOSAT GSPC iron line catalog.
Parmar, A. N.; White, N. E.; Taylor, B. G. +3 more
We report on the global properties of the Fe feature seen in the 6-7keV spectra of X-ray sources observed with the EXOSAT Gas Scintillation Proportional Counter (GSPC). Of a total of 431 spectra extracted from the EXOSAT archive, 205 required the addition of a Gaussian emission line to the continuum spectrum in order to obtain satisfactory fits. T…