Maps of the central flash intensity. Left panel: map of the central flash intensity, adopting the 1σ- upper limit ϵ′ = 0.0011 for the apparent oblateness of the flash layer (corresponding to a deprojected oblateness ϵ = 0.0019) (see text for details). The black labels along the iso-intensity contours (in curves) indicate the received stellar flux in units of its unocculted value. The grey diamond-shaped feature near the centre is the caustic curve described by Eq. (4) and corresponding to ϵ′ = 0.0011. In the case considered here, the flash layer is assumed to be aligned with the apparent direction of Triton’s poles, indicated by the dash-dotted line. Neptune’s direction is determined from the position angle 286° of Triton with respect to the planet at the moment of the occultation. Right panel: same, but adopting the oblate solution ϵ = 0.042 found by Elliot et al. (1997) from the shape of a central flash observed during the 14 August 1995 occultation.