There are a number of coordinate systems used in the Chandra data products. For the positions of events, one may encounter several different coordinate systems: (RA, Dec), (x,y), (detx, dety), (tg_r, tg_d), etc.

For a complete description of the Chandra coordinate systems, please view the Paper on Chandra Coordinate Systems. You may also find the Coordinate Definitions section of the Using SAOImage ds9 useful.