README.XRT	The Astro-E2 XRT team	June, 2004

This file describes the calibration status of the ray-tracing program
used to produce XRS/XIS ARFs released for AO1 proposers in 2004 June.
The same program is called in the XRT+XRS simulator "xrssim".


 A) The Bore-sight Point Spread Function
 We adopted the angular resolution of 2 arcmin at 4.5 keV, which is
 corresponding to the largest value inferred from ground-based calibrations
 of XRT-T1, the first-build telescope of Astro-E2 XRT-I. 

 B) Optical Constant
 We adopted the optical constants by Henke et al. (1997).

 C) Off-axis Response
 The off-axis response is taken into consideration but is not yet tuned.
 Within the XRS field of view, the uncertainty of vignetting may be as
 small as 10%. 

 D) Stray Light
 Stray light response was tuned at a monochromatic energy at 1.49 keV.
 Therefore, the stray light flux at lower energies is underestimated
 while that at higher energies is overestimated by orders. Therefore, it is
 highly recommended not to simulate the stray light at 20 arcmin off or
 larger. The stray light routine is under development.

 E) Alignment
 The center of a focal plane detector is assumed to be precisely
 aligned at the focal position of the XRT on boresight, i.e., the boresight
 is corresponding to the aimpoint.