RR Pic (1925): A Chandra X-ray view

Abstract

We present the Chandra ACIS-S3 data of the old classical nova RR Pic (1925). The source has a count rate of 0.067 +/- 0.002 count s(-1) in the 0.3 - 5.0 keV energy range. We detect the orbital period of the underlying binary system in the X- ray wavelengths. We also find that the neutral hydrogen column density differs for orbital minimum and orbital maximum spectra with values 0.25(-0.18)(+0.23) x 10(22) and 0.64(-0.14)(+ 0.13) x 10(22) cm(-2) at 3 sigma confidence level. The X- ray spectrum of RR Pic can be represented by a composite model of bremsstrahlung with a photoelectric absorption, two absorption lines centered around 1.1 - 1.4 keV and five Gaussian lines centered at emission lines around 0.3 - 1.1 keV corresponding to various transitions of S, N, O, C, Ne and Fe. The bremsstrahlung temperature derived from the fits ranges from 0.99 to 1.60 keV and the unabsorbed X-ray flux is found to be 2.5(-1.2)(+0.4) x 10(-13) erg cm(-2) s(-1) in the 0.3 - 5.0 keV range with a luminosity of 1.1 +/- 0.2 10(31) erg s(-1) at 600 pc. We also detect excess emission in the spectrum possibly originating from the reverse shock in the ejecta. A fit with a cooling flow plasma emission model shows enhanced abundances of He, C, N, O and Ne in the X- ray emitting region indicating existence of diffusive mixing.