Physics – Plasma Physics
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..dpph4i201a&link_type=abstract
American Physical Society, Division of Plasma Physics Meeting, November 16-20, 1998 New Orleans, LA, abstract #H4I.2.01
Physics
Plasma Physics
Scientific paper
After briefly reviewing the radio, infrared, optical, X-ray and gamma ray observations of rotation powered pulsars (RPPs) and their implications for the basic geometry and magnetization of RPPs, I summarize the current understanding of non-neutral relativistic beam acceleration over the magnetic polar caps of these compact stars. I draw particular attention to general relativistic effects on the electric field, introduced by inertial frame dragging, which make available as much as 20% of the total cross cap voltage drop for beam acceleration, more than an order of magntidude more than was found in earlier thories which included only the effects of general relativity. I then disucss the gamma ray emission from the accelerated beam, and the conversion of the gamma rays into a quasi-neutral pair plasma streaming away from the poles. Some new results on the distribution functions of the pairs will be presented, which show a form f(p) ∝ exp(-p_min /p) (1 + p / p_min)^-s. Here p > 0 is an electron or positron's momnetum parallel to the background magnetic field B_0, s ~ 1.8, p_min ~ 10 MeV/c while p_max depends strongly on pulsar parameters, but for operating radio pulsars is typically on the order of 1 GeV/c. Linear theory is used to show that the steeply rising low energy cutoff drives an instabilty of the subluminous ordinary mode in the plasma within and just above the pair creation zone at very low altidude (heights less than a few km above the surface). The free energy in the distributions is shown to be sufficent to allow this process to be a candidate for the still puzzling origin of pulsar radio emission. Linear theory is also used to evaluate the possibility that higher altidude flow effects in the pair plasma yield a two stream instability, a radio emission source first suggested twenty years ago. If time permits, some results of PIC simulations of these processes will be described, along with some of the propagation effects (refraction, self-modulation and self-focussing, collective cyclotron scattering in the outer magnetosphere) which need to be addressed if a full understanding of pulsar radio emission is to be achieved.
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