Scattering of Pulsar X-ray Radiation by Interstellar Dust Particles

Abstract

INTERSTELLAR extinction for the Crab nebula corresponding to a distance of 2 kpc (ref. 1) may be as large as A_v = 2 magnitudes in the visual region, and with the wavelength dependence measured by Stecher² it may reach 4–5 magnitudes in ultraviolet. Thus only several per cent of the optical flux from the Crab nebula pulsar NP 0532 is unaffected by interstellar dust particles. The rest is partly absorbed but mostly scattered into a wide angle and contributes to the diffuse interstellar light. Dielectric particles, of a size comparable to the wavelength, are thought to be involved. Van de Hulst considered ice grains of radii about 0.5 micron, while more refined models which give better agreement with the far ultraviolet measurements deal with graphite particles of radii 0.05–0.07 micron, surrounded by “dirty-ice” mantles of radii 0.16 micron (ref. 3). This article shows that interstellar dust particles may strongly affect the pulsed X-ray radiation^4,5 from NP 0532.