A New Method to Use Chandra Data to Resolve the X-Ray Halos Around Point Sources and Its Application to Cygnus X-1

Astrophysics, abstract
astro-ph/0303149

From: Xiaoling Zhang <xizhang@jet.uah.edu>

Date: Thu, 6 Mar 2003 21:23:02 GMT   (96kb)

Authors:
Y. Yao,
S. Nan Zhang,
X. L. Zhang,
Y. X. Feng

Comments: 7 pages, 4 figures, submitted to ApJ Letters

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″ 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′ 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″
region; and (3) the spectrum of the point source is distorted by the halo
contamination, especially in the soft energy band below 3 keV.

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)