Solar hard X-ray halo from decaying neutrons

DACE/Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK e-mail: a.mackinnon@educ.gla.ac.uk

Received: 31 August 2006
Accepted: 24 October 2006

Abstract

Aims. To quantify the solar X-ray halo resulting from inner bremsstrahlung in beta decay of neutrons generated by cosmic ray bombardment of the solar surface.

Methods.We show analytically how the angular form of this X-ray halo directly reflects the energy distribution of neutrons escaping the Sun. Previous Monte Carlo calculations of solar albedo neutron production are used to normalise an assumed parametric form for the escaping neutron distribution and thus to estimate the halo's intensity. The main remaining assumptions, that neutrons escape radially and that gravitational deceleration may be neglected, affect a negligible fraction of all solar neutrons.

Results.Observations of this halo would have clear diagnostic interest for cosmic ray propagation in the inner heliosphere. Unfortunately it is unlikely to be observable in competition with the cosmic X-ray background.