Results of tests in the AO9 (top) and AO11 (bottoms) pn time series. The frequency range is Δν ~ 87.7 Hz. Dashed horizontal lines show confidence levels of 1σ to 4σ (68% to 99.994%) for the detection of a periodic signal, taking the whole frequency range of the search into consideration (see text). The frequency of the highest peak resulting from each search is labelled. Top: the energy band is 0.36−2.25 keV, the size of the extraction region is 18.6′′, and the number of photons is 5188. Bottom: the energy band is 0.37−1.9 keV, the size of the extraction region is 19.7′′, and the number of photons is 5244.