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

Abstract

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 10³¹ergs^-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 × 10³⁰ergs^-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 × 10³²ergs^-1 over the luminosity range of 1 × 10²⁸ergs^-1 and the maximum luminosity of the sample (1.50 × 10³²ergs^-1). The total absolute lower limit for the normalized luminosity per solar mass is 1.81 × 10²⁶ergs^-1M^-1_solar which accounts for ~16 per cent of the total X-ray emissivity of cataclysmic variables as estimated by Sazonov et al.