The 1979 X-ray outburst of Cen X-4

X-ray observations of the first major outburst (since its initial discovery in 1969) of the "classical" transient X-ray source Cen X-4 were obtained with the Ariel 5 All-Sky Monitor. The flare light curve exhibits a double-peaked maximum at a level of approximately 4 times the Crab nebula, and its duration and characteristic decay time scale are the shortest yet observed from the class of "soft" X-ray transients. A total X-ray output of approximately 3 x 10 to the 43rd power ergs, a factor of approximately 20 less than that of the 1969 outburst is estimated. In addition, evidence is found for a regular modulation of the flux during the decline phase at a period of 8.2 plus or minus 0.2 hours. The existing data are consistent with a source model involving episodic mass exchange from a late-type dwarf onto a neutron star comparison in a relatively close binary system

Accretion powered X-ray pulsars

A unified description of the properties of 14 X-ray pulsars is presented and compared with the current theoretical understanding of these systems. The sample extends over six orders of magnitude in luminosity, with the only trend in the phase averaged spectra being that the lower luminosity systems appear to have less abrupt high energy cutoffs. There is no correlation of luminosity with power law index, high energy cutoff energy or iron line EW. Detailed pulse phase spectroscopy is given for five systems

Two component X-ray emission from RS CVn binaries

A summary of results from the solid state spectrometer on the Einstein Observatory for 7 RS CVn binaries is presented. The spectra of all require two emission components, evidenced by line emission characteristic of plasma at 4 to 8 x 10 to the 6th power and bremsstrahlung characteristic of 20 to 100 x 10 to the 6th power K. The data are interpreted in terms of magnetic coronal loops similar to those seen on the Sun, although with different characteristic parameters. The emission regions could be defined by separate magnetic structures. For pressure less than approximately 10 dynes/sq cm the low temperature plasma would be confined within the stellar radii, while the high temperature plasma would, for the synchronous close binaries, fill the binary orbits. However, for loop pressures exceeding 100 dynes/sq cm, the high temperature components would also be confined to within the stellar radii, in loops covering only small fractions of the stellar surfaces. While the radio properties and the occurrence of X-ray flares suggest the larger emission regions, the observations of time variations leave the ambiguity unresolved

OSO-8 X-ray observations of AM Herculis

Hard X-ray observations of the binary system AM Her were coincident with soft X-ray and ground-based optical measurements. In the 2-60 KeV band, variability was detected with an eclipse during phases 0.5 to 0.7 with respect to the 0. d 12892 period optical minima, synchronous with the known soft X-ray eclipse. The 2-60 KeV uneclipsed flux was 9.5 x 10 to the minus 10th power erg sq cm/sec, of which 86% lies above 10 keV. Thus AM Her contains a hard source located near the similarly eclipsed soft X-ray source. The X-ray data are interpreted in terms of thermal bremsstrahlung from accretion onto a white dwarf

X-radiation from clusters of galaxies: Spectral evidence for a hot evolved gas

OSO-8 observations of the X-ray flux in the range 2-60 keV from the Virgo, Perseus, and Coma Clusters provide strong evidence for the thermal origin of the radiation, including iron line emission. The data are adequately described by emission from an isothermal plasma with an iron abundance in near agreement with cosmic levels. A power law description is generally less acceptable and is ruled out in the case of Perseus. Implications on the origin of the cluster gas are discussed

The 35-D X-ray profile of Her X-1

Substantial X-ray emission as reported by Ariel 5 from Her X-l midway through the extended low-state portion of its 35-day cycle is examined. A similar feature during another cycle measured from UHURU satellite is also examined. It is proposed that this feature should occur regularly, consistent with some models for the mass accretion disc which have been reported in the literature. The results of the analysis of 500 days of Ariel-5 All-Sky Monitor data are reported which support the view that the feature occurs regularly in the 35-day cycle

X-ray observations of H1908+050 (=SS433?)

The X-ray source H1908+50 (=4U1908+05=A1909+4) was observed for three 6 day periods in 1977 and 1978 with the HEAO A-2 experiment. The unusual emission line object and variable radio source SS433 was suggested as the optical counterpart. The X-ray of the source varied by a factor of about 2 on a time scale of 6 months, and the spectrum of the object is consistent with either a power law of photon index of 2.1 or with 14.3 keV thermal bremsstrahlung emission with about 575 eV equivalent width iron line. These X-ray characteristics argue against the source being extragalactic. The measurements are consistent with emission from a white dwarf, but are also similar to the X-ray emission sometimes seen from Cir X-1. A search was made for X-ray emission from similar radio sources

Does Electoral Competition create Incentives for Political Parties to collect Information about the Pros and Cons of Alternative Policies?

A well-known rationale for representative democracy is that direct democracy leads to a free-rider problem as to the collection of information. A problem with this rationale is that it takes for granted that representatives collect information. In this paper we examine whether or not electoral competition induces political parties or candidates to collect information about policy consequences. We show that the answer to this question depends on the cost of information collection. More surprisingly, we find that endogenizing information may lead to divergence of policy platforms