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Fig. 1


The flux limit in the 0.5–2 keV band vs. the area coverage for various surveys. Magenta long dashed lines are the total XRT Deep Serendipitous Survey; black solid lines are medium large not contiguous surveys: A: H2XMM, B: CHAMP, C: SEXSI, D: XMM-BBS, E: AXIS, Q: twoXMM (|b|  > 20); red dot short-dashed lines are the smallest and very deep surveys: F: CDFN, G: CDFS, H: LockmanHole; blue dotted lines are shallow contiguous survey I: CCOSMOS, L: XMMCOSMOS, M: ELAIS-S1, N: ECDFS, O: AEGISX, P: SXDS (for references see Table 1).

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