Self-focussed electromagnetic waves and SS 433

Abstract

Voi.25, pp.213-216, 1981. Printed in Great Britain. All rights reserved. 0083-6656/81/020213-04500.50 per page/O Copyright©1981 Pergamon Press Ltd. Vistas in Astronomy, SELF-FOCUSSED ELECTROMAGNETIC WAVES AND SS 433 Gregory Benford,1 Attilio Ferrari 2 and Silvano Massaglia3 IUniversity of California, Irvine, CA 92717, U.S.A. 2Max-Planck-Institut ftlr Physik und Astrophysik, 8046 Garching bei Mtlnchen, F.R.G. 3Istituto di Fisica Genrale dell'Universit~t, 10125 Torino, Italy Double jets of matter emitted by neutron stars (or black holes) have been invoked to explain the periodicity in wavelength shifts in S$ 433. I We attempt to show that the jets need not be beams of particles, 2 but could instead be self-focussed, large-amplitude electromagnetic waves. Our model has several parts: (a) Precession is obtained from a coupling of the wave nozzle to the angle of the accretion disk. frequency waves. (b) The beaming comes from self-focussed low- (c) The two beams strike a screen. creating a hot spot as they go. They bore a hole through this screen, Photons escape the hot spot only along a channel opened by the beam, giving a narrow cone of emission. (d) The Milgrom mechanism accelerates neutral gas bunches, by absorption of these photons, to 8 = 0.28. The 161.7 ± 0.3 day period of the SS 433 Doppler shifts can be explained by precession of long double beams. I Some nutation or more complicated geometry may have to be added to this picture, but it seems essentially correct kinematically. We shall assume the energy source in SS 433 is a spinning young neutron star surrounded by an accretion disk. magnetospheric structure with an accretion disk is complex. 3 star has not been significantly slowed by the disk. through a Roche lobe. The problem of We shall assume the neutron The disk is fed by a large F-star The neutron star emits a low-frequency electromagnetic wave following the standard pulsar models. If the F-star spin axis and orbital angular momentum are not aligned, disk precession will result. We suppose the F-star spin ~ is not aligned with the neutron-star spin ~ also; so as matter from its Roche lobe enters the disk, it induces the plane of the disk to tilt and the neutron-star spin-axis to precess with the 162-day period. Orbital motion of the two stars appears as the |3. l-day period. 4 The magnetized rotating neutron star has a magnetosphere with regions of charge separation within its speed-of-light cylinder. The low-frequency wave affects particle motion at and beyond the light cylinder. In this framework the Crab has been interpreted as characterized by a low-density plasma, in the sense that the large amplitude wave has enough strength to evacuate a large cavity around the pulsar: p wave ~ ~ Pplasma where E o and n E 2 O >> I (I) o are the wave electric-field amplitude and plasma density at the light eylind~ y is the Lorentz factor of the particles accelerated by the interaction with the wave. As shown by Dobrowolny and Ferrari, 5 if E O ~ 105 e.s.u. (corresponding to B o > 10 II G at the