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Y Yao, S. Nan Zhang, X. L. Zhang, Y. X. Feng (UAH/NSSTC)
The excellent angular resolution, good energy resolution and broad energy band make Chandra ACIS the best instrument for studying the X-ray halos around some galactic X-ray point sources caused by the dust scattering of X-rays in the interstellar medium, but the direct images of bright sources obtained with ACIS usually suffer from severe pile-up. Making use of the fact that an isotropic image could be reconstructed from its projection on any direction, we can reconstruct the images of the X-ray halos from the data obtained with the regular HETGS and/or the CC mode. These data are nearly or totally pile-up free and enable us to take full advantage of the excellent angular resolution of Chandra. With the reconstructed high resolution images, we can probe the X-ray halos as close as 1 arcsecond to their associated point sources. Applying this method to Cygnus X-1 observed with Chandra HETGS in CC mode, we derive an energy dependent radial halo flux distribution and conclude that, for a 1 arcminute region around the point source: (1) relative to the total intensity, the fractional halo intensity in Cygnus X-1 is about 35% at about 1 keV and drops to about 10% at around 6 keV; (2) about 50% of the halo photons is within less than 30 arcseond region; and (3) the spectrum of the point source is distorted by the halo contamination, especially in the soft energy band below 3 keV.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.