Leftpanel: Fe-K_α emission line map of the GC region. The data have been background subtracted and vignetting corrected. The position of Sgr A* is marked by a green star. The dashed white ellipse shows the AC region. Rightpanel: a zoom into the AC region. The position of the AC is indicated by the blue ellipse at l ~ 0.12°, b ~ 0.02°. Bright 6.4-keV knots are highlighted by dashed black circles (labelled N and S) and white ellipses (labelled SN at b ~ 0.015° and DX at b ~ 0.07°). The region used for background accumulation is shown by the two yellow ellipses (bkg). The dashed yellow box shows the sky region studied in Wang et al. (2006, Fig. 14). The galactic coordinate grid is shown in red.