The gamma-ray source LSI +61° 303

II. Multiwavelength emission model

Department of Physics, University of Calgary, Calgary, Canada T2N 1N4

Corresponding author: leahy@iras.ucalgary.ca

Received: 2 June 2003
Accepted: 29 September 2003

Abstract

The multi–wavelength spectrum of LSI +61° 303 is summarized. The X-ray to γ-ray luminosity of  erg/s is due to inverse Compton emission from relativistic electrons around a pulsar. The X-ray to γ-ray spectrum determines the electron energy index, which is consistent with the observed radio spectrum if it mainly optically thin. The inverse Compton emission from a compact region of electrons peaks at periastron due to the higher density of stellar photons. This compact region is highly self-absorbed at radio frequencies implying the quiescent radio emission comes from a separate diffuse population of electrons. The number and total energy of electrons in the diffuse region is ~0.1 of that in the compact region (~ electrons, ~ erg). The compact region cannot be static due to its high internal pressure: expansion leading to loss of electrons and injection of new electrons are required. A pulsar with spin period 0.1 s can provide sufficient injection power. A steady diffuse outflow of electrons from the compact region produces too much optically thick synchrotron emission. The alternative is bulk expansion of the compact electron bubble, with dynamic pressure limiting the expansion velocity and resulting in expansion away from the Be star. Injection ends as the bubble wall facing the Be star stalls and the pulsar's orbit takes it out of the bubble. Alternately, the Rayleigh-Taylor instability could cause the bubble to break up before the exit of the pulsar. In either case, energy injection rates of ~ into the bubble result in a detached bubble of size, velocity and electron content similar to the initial conditions used by Peracaula ([CITE]) to model radio outbursts for LSI +61° 303.