Large Source Size Research Articles

Differences of observed characteristics between impulsive bursts and post-burst increases

The change of source characteristics during the transition from the impulsive phase to the post-burst phase is investigated for cm bursts on a statistical basis. The results are the following: (1) The sudden decrease of the circular polarization degree is found almost invariably at the transition; typically from 20–30% down to a few percent. (2) Some bursts show remarkable source expansions in the post-burst phase. There are no cases in which impulsive bursts have larger source size than the associated post-burst increases. (3) Type III bursts which are indicative of non-thermal phenomena are associated with the impulsive phase but not with the post-burst phase. Implications of these observed results are discussed.

Some remarks on the hypothesis of relativistic beaming of pulsar emission

The hypothesis of the relativistic beaming of pulsar emission is discussed in connection with objections advanced by Manchesteret al. (1973). It is shown that the same pulse duration of some pulsars with the non-power-law spectrum over a wide frequency interval may be associated either with large source sizes in longitude, or with location of the emitting source at various distances from the rotation axis of the neutron star (depending on the emission frequency).

Design of a high-resolution electron diffraction camera

The conditions governing high resolving power in electron diffraction cameras are discussed, and, in particular, those determining the quality of resolution of the fine-structure in single-crystal reflexions. Limitation of resolution may arise from large source size, instability of electrical supplies, misalinement of the electron-optical system, interference from mechanical vibration and stray magnetic fields, grain in the photographic emulsion or too high an operating gas pressure in the camera. A camera designed to minimize these limitations is described, and its performance illustrated. Detailed fine structure, such as the subsidiary maxima of the shape transforms for small crystals, has been resolved.