Search Publications
Spectral and correlated timing behaviour of GX5-1.
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +4 more
We have analyzed the X-ray spectral and fast timing behaviour of the Z-source GX5-1 using X-ray colour-colour diagrams (CDs), hardness-intensity diagrams (HIDs) and power spectra. We used all EXOSAT ME data on GX5-1, a total of seven observations during 1983-1985. We detect, for the first time in GX5-1, secular motion of the well known "Z" pattern…
An X-Ray and Optical Study of the Supernova Remnant W44
Rho, Jeonghee; Hester, J. Jeff; Schlegel, Eric M. +1 more
We report the results of a 8000 s observation of the supernova remnant W44 using the ROSAT Position Sensitive Proportional Counter (PSPC). The image shows the same centrally peaked morphology observed by the Einstein IPC and contrasts with the shell-like radio morphology. The eastern limb shows a lack of X-ray emission within the radio shell, prob…
Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images II. Lithium abundances
Tagliaferri, G.; Pasquini, L.; Pallavicini, R. +2 more
We present high-resolution spectra in the Li I 6708 A region, and multicolor photometry, for a sample of active stars detected serendipitously by the EXOSAT satellite. We analyse the spectral data with a spectral synthesis code and derive Li abundances, rotation rates and metallicities. We use our multicolor photometry to infer the spectral classi…
The Discovery of 8.7 Second Pulsations from the Ultrasoft X-Ray Source 4U 0142+61
Mereghetti, S.; Stella, L.; Israel, G. L.
We discovered a periodicity at about 8.7s from the X--ray sources 4U0142+61, previously considered a possible black hole candidate on the basis of its ultrasoft spectrum. The pulsations are visible only in the 1--4 keV energy range, during an observation obtained with the EXOSAT satellite in August 1984. A search for delays in the pulse arrival ti…
The X-Ray Spectra of Blazars Observed with EXOSAT
Giommi, Paolo; Barr, Paul; Sambruna, Rita M. +3 more
A systematic analysis of the X-ray spectra (0.1-10 keV) of all blazars observed with EXOSAT is presented. The objects include 16 X-ray-selected BL Lac objects (XBLs), five radio-selected BL Lac objects (RBLs), and five highly polarized quasars (HPQs). Comparing the results of single-power-law fits for the different classes, we find that XBLs have …
ROSAT X-ray observations of ten cataclysmic variables.
Verbunt, Frank; van Teeseling, Andre
Ten cataclysmic variables have been observed with the ROSAT PSPC. The x-ray spectra can be fitted with optically thin spectra, but several spectra require more than one component. The high emission measures indicate that the emitting plasma is optically thick in strong resonance lines. Variability in the count rate is discovered in seven systems; …
Elemental Abundances of the Supernova Remnant G292.0+1.8: Evidence for a Massive Progenitor
Singh, K. P.; Hughes, John P.
We present a comprehensive nonequilibrium ionization (NEI) analysis of X-ray spectral data from the Einstein Observatory and EXOSAT for the supernova remnant G292.0+1.8. The spectra are well described by a single-temperature, single-timescale NEI model with kT = 1.64-0.19+0.29 keV and net = (5.55-1.12
The X-Ray Spectra of Blazars: Analysis of the Complete EXOSAT Archive
Giommi, Paolo; Barr, Paul; Sambruna, Rita M. +3 more
We analyzed the 0.1-10 keV spectra of 26 blazars (21 BL Lac objects and 5 highly polarized quasars), on the basis of 93 exposures taken from the EXOSAT archives. Fits were performed first with a single power-law model. Indications are found that better fits can be obtained with models where the slope steepens at higher energies. We therefore consi…
X-ray irradiation of white dwarf atmospehres : the soft X-ray spectrum of AM Herculis.
Paerels, Frits; van Teeseling, Andre; Heise, John
We present model atmosphere calculations of white dwarfs irradiated at the surface by hard x-rays. We use a self-consistent treatment of Compton scattering as a noncoherent scattering process. The opacities include the photoionization edges of all individual subshells of the most abundant ions of 15 elements. Because of an 'inverse' blanketing eff…
X-Ray Emission from a Simulated Cluster of Galaxies
Katz, Neal; Tsai, John C.; Bertschinger, Edmund
Using the 1993 cluster simulation of Katz & White, we analyze the intracluster medium and investigate the accuracy of the standard hydrostatic method for determining cluster masses. We show that the simulated cluster gas is in hydrostatic equilibrium with a subsonic flow toward the center. Inside a radius of ∼100 kpc, this flow is in a steady …