Search Publications
A Catalog of Intracluster Gas Temperatures
Forman, W.; Jones, C.; Vrtilek, S. D. +3 more
We have searched the Einstein Monitor Proportional Counter (MPC) data base for observations of clusters of galaxies. The MPC was a nonfocal plane instrument on board the Einstein Observatory and accumulated data during all pointed observations with the four focal plane instruments. By co-adding the MPC spectra obtained during all pointed observati…
X-Ray Variability of Active Galactic Nuclei: A Universal Power Spectrum with Luminosity-dependent Amplitude
Papadakis, I.; Lawrence, A.
We present power-law model fits to the power spectra of 12 high- quality "long look" observations of AGNs from the EXOSAT data base. The AGNs concerned differ in X-ray luminosity L_x_, over a range 10^4^. The results are consistent with all objects having a power spectrum index equal to the mean value α = 1.55. There is no correlation with L_x_, s…
On the nature of rapid X-ray variability in active galactic nuclei.
McHardy, I. M.; Lehto, H. J.; Green, A. R.
We systematically analyse all (110) EXOSAT AGN medium-energy light curves of length greater than 20 ks to search for and quantify their flux variability. We also perform extensive simulations to quantify the selection effects (such as the source brightness or the length of observation) that might prevent the detection of variability. We quantify v…
ROSAT studies of the composition and structure of DA white dwarf atmospheres.
Barstow, M. A.; Koester, D.; Sansom, A. E. +7 more
We present here a detailed study of a sample of hot I)A white dwarfs detected in the EUV and soft X-ray bands by ROSAT during its all-sky survey. The survey data are combined with additional ROSAT pointed-phase observations, earlier EXOSAT results and the available optically determined effective temperatures and gravities. We show that the spectra…
Further probing of the X-ray source in NGC 4151 : new constraints on the nuclear geometry.
Sokoloski, J. L.; Yamauchi, M.; Warwick, R. S. +4 more
We report on the results of new Ginga observations of the archetypal Seyfert galaxy, NGC 4151, performed over an 18-month period between early 1990 and mid-1991. The present programme complements earlier extensive monitoring of this source in the medium-energy X-ray band by both EXOSAT and Ginga to give a combined data set of some 36 separate obse…
X-Ray Observations of the Warm Absorber in NGC 3783
Nandra, K.; Turner, T. J.; Fabian, A. C. +2 more
We present a high signal-to-noise ROSAT position sensitive proportional counter (PSPC) observation of the Seyfert 1 galaxy NGC 3783. The 0.1-2.5 keV spectrum shows strong evidence for an absorption edge most likely associated with O VII-VIII. Such a feature, which has now been detected in a number of PSPC spectra (Nandra et al.; Nandra & Pound…
The EXOSAT Medium Energy (ME) Sample of Dwarf Novae
Mukai, K.; Shiokawa, K.
We present our analysis of the EXOSAT medium energy (ME) archival data on dwarf novae. Many dwarf novae were observed with EXOSAT; unfortunately, a significant fraction resulted in nondetection or marginal detection with the ME instrument. Our analysis of the brightest dwarf nova, SS Cyg, shows little correlation between the count rate and the har…
The Quasi-periodic Oscillations and Very Low Frequency Noise of Scorpius X-1 as Transient Chaos: A Dripping Handrail?
Scargle, Jeffrey D.; Steiman-Cameron, Thomas; Young, Karl +3 more
We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time s…
GINGA Observations of the Coma Cluster and Studies of the Spatial Distribution of Iron
Hughes, John P.; Tanaka, Yasuo; Butcher, Jackie A. +1 more
The large area counters on the Japanese satellite Ginga have been used to determine the X-ray spectrum from the central region of the Coma cluster of galaxies over the energy range from 1.5 to 20 keV. The spectrum is well represented by an isothermal model of temperature 8.21+/-0.16 keV and a heavy element (iron) abundance of 0.212+/-0.027 relativ…
Analysis of the DA white dwarf HZ 43A and its companion star.
Werner, K.; Jordan, S.; Barstow, M. A. +3 more
The DA white dwarf HZ 43 A (WD 1314+293) is analyzed based on a newly obtained optical spectrogram. We demonstrate that the derived parameters Teff = 49.000 K and log g = 7.7 are in agreement with the observed Ly-alpha line, the slope of the UV continuum, and the measured trigonometric parallax. The EXOSAT spectrograms of Paerels et al.…