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Astron. Astrophys. 357, L25-L28 (2000)

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Letter to the Editor

Chandra measurement of the geometrical distance to Cyg X-3 using its X-ray scattering halo

P. Predehl 1, V. Burwitz 1, F. Paerels 2 and J. Trümper 1

1 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany (predehl@mpe.mpg.de)
2 Columbia University, New York, USA

Received 24 March 2000 / Accepted 8 April 2000


Using Chandra-HETGS data of Cyg X-3 we succeeded for the first time in applying a method, developed 27 years ago, to directly determine the geometric distance to X-ray sources. The method implies the existence of a halo of radiation scattered on interstellar dust. Any intensity variations of the source itself appear delayed and smeared out in the halo. By analysing and correlating the X-ray lightcurves at different radial distances from the source, we could determine the distance to Cyg X-3 to be approximately 9 kpc. Even though the statistics in this dataset are meager the usefulness and the possibilities of this method are convincingly demonstrated.

Key words: scattering – stars: binaries: eclipsing – ISM: clouds – X-rays: galaxies – X-rays: ISM

Send offprint requests to: P. Predehl

© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000