Left and middle: background-subtracted lightcurves, with a 1 ks bin and for different energy bands, recorded with the three EPIC cameras and with the RGS (MOS1 in black, MOS2 in red, pn in green, combination of both RGS and both orders in blue) extracted in a circular region around π Aqr. The EPIC data extracted in an annular source region (see Sect. 2) are similar, but noisier. Right: background-subtracted lightcurve with a 10 s bin recorded for pn, along with its Fourier periodogram (Heck et al. 1985). The green dotted line indicates the typical ± 1σ error around each data point. The short-term variations clearly are larger than this, demonstrating the presence of flares.