An auroral precipitation model for the rapid X-ray burster

Abstract

It is suggested that rotating magnetospheres can be separated into two catgories according to their rotation speeds. Fast rotators such as pulsars, and perhaps Jupiter, are dominated by gravitational and centrifugal effects and have flattened, distended magnetopheres. The dominant forces in slowly rotating magnetospheres: of which the Earth is an example: are gravitational, electric, and magnetic. Because the outer regions of slowly rotating magnetospheres are subject mainly to electric and magnetic forces, magnetospheric substorms and other types of unstable behavior are expected to occur frequently. It is proposed that the rapid X-ray burster may be a slow rotator, whose magnetospheric activity should resemble the Earth's. Moreover, if all X-ray bursters were slow rotators there should be few X-ray bursters that are also pulsars: in accord with the observational data. The proposed relaxation oscillator that turns the rapid bursters on-and-off has a terrestrial analog in pulsating aurorae. Repeated bursts of particle precipitation ( e.g., pulsating aurorae) from a magnetospheric trapping region are expected when particle injection in a substorm results in saturation of the trapping region with more matter than it can contain in equilibrium. Saturation leads to rapid growth of plasma waves, which are turned off again when the resonantmore » particles are removed by precipitation. If there is a continual source of ''accreting'' matter of sufficient strength, the wave growth and precipitation episodes repeat semiregular intervals, leading to ''pulsations'' or ''bursts'' of radiation when the precipitating particles are stopped in the atmosphere. The predicted repitition periods for the rapid burster: in the range 8 to 24 s: are within the uncertainties of the calculation. It is argued that a saturation-resonant interaction-wave growth-precipitation model fits the observations better than models based on hydromagnetic instabilities.« less