Observation and schematic view of the CND. Left panel: HCN contours of the CND as presented in Christopher et al. (2005). The two ellipses highlight the proper CND and the NEA. The red circle marks the position of Sgr A^⋆and the green one the position of the magnetar SGR J1745-2900. Middle panel: a 3D model of the CND. (x, y) is the plane of the sky (RA, Dec). The torus has an inclination of ≃70° with respect to the line of sight (LOS), and ≃20° with respect to the y-axis to match the observed position angle. The star marks the position of Sgr A^⋆. Right panel: the ring is projected in the x-LOS plane (top view). For a transient close to the position of Sgr A^⋆, such as SGR J1745-2900, the two orange highlighted parts of the CND are the first and the last to produce a fluorescence signal. The iso-delay paraboloids Sunyaev & Churazov (1998) are plotted as dashed (six-month delay) and dashed-dotted (nine-year delay) lines, respectively. The time delay measured by the observer is due to the different light paths reported in the same scheme according to the line style used for the parabolas. The solid line is the light path from the transient to the observer.