Astronomy & Astrophysics

Table 1: Properties of the confirmed (first two rows) and candidate periodic sources. ROSAT coordinates are J2000. The frequency is expressed in mHz. N is the number of photons. $\hat{S}(f)$ is the decimal logarithm of the ${\it FPP}$ corrected for the number of trials. $N_{\rm F}$ is the number of frequencies searched. "ID'' refers to the numbers in Fig. 6. Identifications in italics are tentative.