Deriving an X-ray luminosity function of dwarf novae based on parallax measurements

We have derived an X-ray luminosity function using parallax-based distance measurements of a set of 12 dwarf novae, consisting of Suzaku, XMM–Newton and ASCA observations. The shape of the X-ray luminosity function obtained is the most accurate to date, and the luminosities of our sample are concentrated between ∼1030 and 1031 erg s−1, lower than previous measurements of X-ray luminosity functions of dwarf novae. Based on the integrated X-ray luminosity function, the sample becomes more incomplete below ∼3 × 1030 erg s−1 than it is above this luminosity limit, and the sample is dominated by X-ray bright dwarf novae. The total integrated luminosity within a radius of 200 pc is 1.48 × 1032 erg s−1 over the luminosity range of 1 × 1028 erg s−1 and the maximum luminosity of the sample (1.50 × 1032 erg s−1). The total absolute lower limit for the normalized luminosity per solar mass is 1.81 × 1026 erg s−1 M−1⊙ which accounts for ∼16 per cent of the total X-ray emissivity of cataclysmic variables as estimated by Sazonov et al.

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