Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Karl Gebhardt. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis--Copenhagen. / On spine: Stochastic processes and cosmic radiation. "Dansk resumé": p. 232-234. "List of references": p. 235-236.

The discovery of cosmic rays with energies greater than 1014e V has posed a question that has not, as yet, been answered: where are particles accelerated to such high energies? A possible answer to this question came in 1983 with the claim made by Samorski and Stamm of an excess number of cosmic rays from the direction of Cygnus X-3. This result was then confirmed by Lloyd-Evans et al. (1983). The excess was taken to be gamma-rays as the galactic magnetic fields result in charged particles being greatly deflected. These claims led to the birth of Pe V gamma-ray astronomy and the building of numerous instruments designed to search for point sources of Pe V gamma-ray emission. One such instrument was the GREX extensive air shower array built at Haverah Park which began collecting data in March 1986. This thesis describes the GREX array and the methods of analysis used to reconstruct the size and arrival direction of the incident cosmic rays from the detected air showers. The methods used to search for potential point sources are then described. These methods have been applied to data recorded by the GREX array between 6 March 1986 and 18 December 1990. Particular attention has been paid to Cygnus X-3 and 8 other candidate sources. No evidence for steady, periodic or sporadic emission has been found for any of the 9 potential sources. In addition, an all-sky survey has failed to discover any unknown point sources of emission in the Northern sky. Observations made by other groups of Cygnus X-3 and the 8 other candidate sources at 10 12 and 10 15 eV are discussed. Cassiday et al. (1989) claimed to have observed an excess of cosmic rays from Cygnus X-3 with energies greater than Sx10 17 eV. A claimed confirmation of this result was made by the Akeno group (Teshima et al. 1990). A search for emission of 5x10 17 eV cosmic rays from Cygnus X-3 has been made using data from the Haverah Park 12km 2 array and is described in this thesis. The upper limit to the flux from Cygnus X-3 in this search is significantly lower than the claimed flux, even during periods of contemporaneous observations.

No description available.

In 2013 March and 2014 May, Voyager-1 (V1) experienced small but significant increases in the flux of galactic cosmic rays (GCRs) in the hundred MeV/n range. Additionally, V1 also saw episodic depletion of GCR flux around perpendicular pitch angles. We discuss the pitch-angle distribution and the time profiles of these events. In a previous paper, we interpreted the 2013 "bump" as the GCRs remotely sensing a shock that reached the magnetic field line passing through V1: particles gained energy as they were reflected on the approaching region of the stronger magnetic field of the disturbance. Here, we point out that energy gain is not restricted to reflected particles -GCRs passing through the disturbance also gain energy. The effect should be present in a broad range of pitch angles with the maximum increase of GCR intensity predicted to occur at the critical reflection angle. In this paper, the shock is not step-like, but a gradual increase of the magnetic field strength, B, taking a few days, in agreement with V1 measurements. This smoothens the profile of the predicted bump in the GCR flux. We also address the linear episodic decreases seen around perpendicular pitch angles. These events are interpreted in terms of adiabatic cooling behind the shock due to the slow weakening of B. We present simple numerical model calculations and find that a gradual shock followed by a slow decrease of B, as observed, may account for both the episodic increases and the anisotropic depletion of GCR fluxes.

No description available.

Dynamical models of Seyfert nuclei and quasi-stellar objects are presented. The central energy source often postulated for these active objects provides a means of heating and ionizing the nuclear gas, and also exerts an outward force on the gas. Since the gas will be fully ionized, it will be nearly transparent to X-rays, while cosmic rays will interact strongly with it. Preliminary calculations of this "ionization" pressure on discrete clouds show that photons are unlikely to produce the high gas velocities relative to the nucleus which are indicated by the emission line profiles in Seyfert nuclei and the blueshifted quasar absorption lines, but that cosmic rays can accelerate the clouds up to these velocities. A more detailed calculation taking into account the dynamics of the gas is called for. A computer code was written to solve the spherically symmetric hydrodynaraic equations numerically. It uses a finite difference, implicit Eulerian scheme to solve the time dependent equations. As well as the mass conservation and momentum transfer equations, the numerical system includes an energy equation which allows for ionization and Coulomb heating, and radiative cooling. The code was used to obtain a set of nuclear evolutionary models. These models involve a static gas surrounding a quiescent energy source which turns on suddenly. A range of input physical parameters is represented: for sizes 0.1 to 1 pc, a total cosmic ray flux from 10⁴³ ergs s⁻¹ to 10⁴⁸ ergs s⁻¹, a gas density of 10⁴ to 10⁸ cm⁻³, a lowest particle energy in a power law spectrum of 0.1 to 10.0 MeV, and a central mass of 10⁸ or 10⁹ M⃙. Such soft cosmic rays have a very short absorption length in the nuclear gas. This means a narrow region in radial extent will gain the momentum of the cosmic ray beam, and an outward moving shell will form. It snowplows the cooler gas ahead of it and leaves a less dense, hot cavity behind. This thin cavity reaches temperatures of 10⁸ K, and the dense shell reaches an equilibrium temperature in the range 10⁴-10⁵ K. The shell velocities increased as the cosmic ray flux was increased, ranging from 500 to 8000 km s⁻¹. The lifetime of this phenomenon is the time for the shell to escape the nuclear region, which is only a few parsecs across. At these velocities, the timescale is only 10³ to 10⁴ years. This suggests repetitive rather than continuous activity of the central source. A quiescent phase would allow replenishment of the gas from extra-nuclear stellar sources. The interface between the hot cavity and the shell is Rayleigh-Taylor unstable with a fragmentation time approximately equal to the shell escape time. This may explain the cloud structure observed in these objects. Thermal instabilities may also arise if the central source turns off. Prediction of the sources of the permitted and forbidden emission lines is dependent on the behavior of the instabilities. The very dense shell suggests a physical distinction between the regions producing the two types of spectra, which may explain the wider permitted lines in some sources. The hot gas near the energy source will produce thermal X-rays. The luminosity and temperature predicted for the X-rays is consistent with observations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.