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…
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…
High-Energy Spectrum of Cygnus X-1 Revisited
Done, C.; Fabian, A. C.; Matt, G. +1 more
The X-ray spectrum of Cyg X-1 is probably produced by thermal Comptonization in an accretion disk corona. Photons reflected from the disk are also Comptonized, so the predicted reflection spectrum is dependent on the optical depth and temperature of the scattering medium. Thus, observations of reflection in the 2-20 keV energy range can constrain …
EGRET Limits on High-Energy Gamma-Ray Emission from X-Ray-- and Low-Energy Gamma-Ray--selected Seyfert Galaxies
Michelson, P. F.; Nolan, P. L.; Thompson, D. J. +13 more
A sample of 22 Seyfert galaxies, 11 type 1 and two type 2 galaxies selected according to their X-ray fluxes in the AGN survey catalogs of EXOSAT and Ginga, two additional type 1 galaxies for which detections in low-energy gamma rays have been reported in the past, plus six more type 1 galaxies and one unclassified Seyfert that have been studied by…
The Luminosity Dependence of the X-Ray Spectrum of the Transient 42 Second Pulsar EXO 2030+375
Parmar, A. N.; White, N. E.; Reynolds, A. P.
We report on the evolution in the X-ray spectrum of the transient X-ray pulsar EXO 2030 + 375 during part of an outburst in 1985 May-August. The overall continuum spectral shape is similar to that of other accreting pulsars and can be represented by a power-law spectrum modified at low energies by significant absorption and at high energies either…
An X-Ray Excited Wind in Centaurus X-3
Stevens, Ian R.; Day, C. S. R.
We propose a new interpretation of the behavior of the notable X-ray binary source Centaurus X-3. Based on both theoretical and observational arguments (using EXOSAT data), we suggest that an X-ray excited wind emanating from the O star is present in this system. Further, we suggest that this wind is responsible for the mass transfer in the system…