Results of the search (pn data, P = 0.011–1000 s). The frequency range is Δν = 87.72 Hz, the energy band is 0.36–2.2 keV, and the size of the extraction region is 18.85″ (5260 counts). Dashed horizontal lines show confidence levels of from 1σ to 4σ for the detection of a periodic signal, given the frequency range and length of the observation. A periodic signal at P _∗  ~ 18.6 ms is detected at 4σ (left). The periodogram on the right shows the same analysis conducted for a background region (size 52″ and 5322 total counts; see text).