Wallace Tucker

Ionization equilibrium and radiative cooling of a low-density plasma.

Ionization equilibrium and radiative cooling of high temperature low density plasma, noting cosmic gas cooling curve of line emission from oxygen ion transitions

The X‐Ray Universe

Beyond the range of optical perception--and of ordinary imaginings--a new and violent universe lay undetected until the advent of space exploration. Supernovae, black holes, quasars and pulsars--these were the secrets of the highenergy world revealed when, for the first time, astronomers attached their instruments to rockets and lofted them beyond the earths x-ray-absorbing atmosphere. The X-Ray Universe is the story of these explorations and the fantastic new science they brought into being. It is a first-hand account: Riccardo Giacconi is one of the principal pioneers of the field, and Wallace Tucker is a theorist who worked closely with him at many critical periods. The book carries the reader from the early days of the Naval Research Laboratory through the era of V-2 rocketry, Sputnik, and the birth of NASA, to the launching of the Einstein X-Ray Observatory. But this is by no means just a history. Behind the suspenseful, sometimes humorous details of human personality grappling with high technology lies a sophisticated exposition of current cosmology and astrophysics, from the rise and fall of the steady-state theory to the search for the missing mass of the universe.

Radiation from a high-temperature, low-density plasma - The X-ray spectrum of the solar corona

Solar coronal X ray spectrum calculation of high- temperature low-density plasma, considering line emission from electron collisional excitation and radiation

DETECTION OF X-RAYS FROM SN 1987A WITH ROSAT

Soft X‐rays (0.5–2 keV) were detected with the ROSAT PSPC from the direction of SN 1987A which falls within an association in the LMC that is rich in B stars. The emission is consistent with two point sources in the LMC with total luminosity ∼1034 erg/s. The brighter source is identified with SN 1987A on the basis of its positional agreement. We interpret the emission as arising from the interaction of supernova ejecta with the pre‐existing blue giant wind. The second source may be an unidentified Be/X‐ray binary. Another possibility is that the second source is an X‐ray echo from the the supernova outburst. The X‐ray echo interpretation requires that the supernova emitted about 1047 erg in a burst of soft X‐rays.

On a galactic origin for the soft X-ray background.

Previous observations and some new data with high angular resolution are considered in the discussion of the galactic origin for the X-ray background. Aspects of instrumentation are discussed together with the observational results, and the parameters of a possible galactic distribution of point sources that would explain essentially all of the soft X-ray background. The excess flux at the poles is accounted for by the fact that the galactic distribution has a larger scale height than the interstellar gas.

Semiempirical limits on the thermal conductivity of intracluster gas

A semiempirical method for establishing lower limits on the thermal conductivity of hot gas in clusters of galaxies is described. The method is based on the observation that the X-ray imaging data (e.g., Einstein IPC) for clusters are well described by the hydrostatic-isothermal beta model, even for cooling flow clusters beyond about one core radius. In addition, there are strong indications that noncooling flow clusters (like the Coma Cluster) have a large central region (up to several core radii) of nearly constant gas temperature. This suggests that thermal conduction is an effective means of transporting and redistributing the thermal energy of the gas. This in turn has implications for the extent to which magnetic fields in the cluster are effective in reducing the thermal conductivity of the gas. Time-dependent hydrodynamic simulations for the gas in the Coma Cluster under two separate evolutionary scenarios are presented. One scenario assumes that the cluster potential is static and that the gas has an initial adiabatic distribution. The second scenario uses an evolving cluster potential. These models along with analytic results show that the thermal conductivity of the gas in the Coma Cluster cannot be less than 0.1 of full Spitzer conductivity. These models also show that high gas conductivity assists rather than hinders the development of radiative cooling in the central regions of clusters.

A blast-wave model for the Vela X supernova remnant and the origin of the Gum Nebula

Vela X supernova remnant blast wave model and Gum Nebula formation, discussing kinetic and rotational energy transformation into radiation

Astronomical Signatures of Dark Matter

Several independent astronomical observations in different wavelength bands reveal the existence of much larger quantities of matter than what we would deduce from assuming a solar mass to light ratio. They are very high velocities of individual galaxies within clusters of galaxies, higher than expected rotation rates of stars in the outer regions of galaxies, 21 cm line studies indicative of increasing mass to light ratios with radius in the halos of spiral galaxies, hot gaseous X-ray emitting halos around many elliptical galaxies, and clusters of galaxies requiring a much larger component of unseen mass for the hot gas to be bound. The level of gravitational attraction needed for the spatial distribution of galaxies to evolve from the small perturbations implied by the very slightly anisotropic cosmic microwave background radiation to its current web-like configuration requires much more mass than is observed across the entire electromagnetic spectrum. Distorted shapes of galaxies and other features created by gravitational lensing in the images of many astronomical objects require an amount of dark matter consistent with other estimates. The unambiguous detection of dark matter and more recently evidence for dark energy has positioned astronomy at the frontier of fundamental physics as it was in the 17th century.

Mechanisms for the Production of X-Rays in a Cosmic Setting

In this chapter we consider the various physical processes which may give rise to the production of X-rays in a cosmic setting. We shall first consider those mechanisms such as synchrotron radiation and Thomson scattering which can, for most cases of interest, be treated using classical electrodynamics. Then processes such as Coulomb bremsstrahlung and line emission, which are intrinsically quantum processes, will be discussed. The spirit of the discussion is to present simple derivations which we hope provide some insight into the basic physics involved and then to state the exact results in a form useful for applications in the remainder of this book. Unless otherwise indicated, the units used throughout this chapter are cgs Gaussian. The reader will be referred to the original literature and to reviews for rigorous derivations. The processes which absorb X-rays are, in general, just the inverse processes of the emission mechanisms to be considered; however, a short section on the absorption of cosmic X-rays is included. Finally, the appendix to this chapter presents a brief account of the energy distribution of relativistic particles which may be responsible for X-ray emission.

Solar X-Ray Emission

The Sun is the brightest source in the sky between 0.5 and 10 keV. Its X-ray intensity, which is highly variable, can range from 10-4 erg cm-2 s-1 for the quiet Sun to several erg cm-2 s-1 for large flares. It is always at least three orders of magnitude brighter than the strongest extrasolar source, Sco X-l, and can be studied in much more detail than any other source. The surface brightness as seen at 1 AU ranges from 10-9 erg cm-2 s-1 (arc sec)-2 to 1 erg cm-2 s-1 (arc sec)-2.