Evidence for the detection of X-ray scattering from interstellar dust grains
Abstract
Overbeck1 has shown that small angle scattering of X rays by interstellar dust will tend to increase the apparent size of a point celestial X-ray source, the result being the formation of a halo around the source image. Although the exact description of this halo, which depends on the detailed properties of the dust and of the source, has been discussed2-6 no direct observational evidence for the existence of such haloes has been presented, although dust scattering has been invoked to explain the diffuse soft X-ray emission observed around the Crab Nebula during a lunar occultation7.I report here data obtained by the imaging proportional counter on board the Einstein Observatory8 of the bright X-ray source GX339-4 (4U1658-48). These data show a faint but apparently real X-ray halo around GX339-4. The principal uncertainty in the intensity distribution of the halo arises from the poorly determined spectrum of GX339-4 and it is likely that the parameters of the halo and of the derived model of the scattering dust grains may be improved in a future analysis using revised Einstein spectral calibration data; however, the range of allowed spectra leaves the reality of this first detection of an interstellar dust halo unchanged.
- Publication:
-
Nature
- Pub Date:
- March 1983
- DOI:
- 10.1038/302046a0
- Bibcode:
- 1983Natur.302...46R
- Keywords:
-
- Cosmic Dust;
- Interstellar Matter;
- X Ray Scattering;
- X Ray Sources;
- Brightness Distribution;
- Halos;
- Heao 2;
- Astronomy