Abstract:

Compton scattering of low-frequency photons in a converging flow of cold plasma is studied. The equation of radiative transfer in the case of spherical near-critical steady state accretion onto a neutron star is solved analytically. The inner boundary condition is that the neutron star surface is completely reflective, or that there is a magnetopause with an empty cavity inside it. The photons escape diffusively and electron scattering is the dominant source of opacity. The energy gain of the photon comes entirely from the bulk motion of the converging flow of the accreting gas. The spectrum observed at infinity is a power law at high frequencies with photon number spectral index essentially -1. This spectrum is significantly flatter than that found for accretion into black holes.

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