ROSAT Observation of the Old Classical Nova CP Puppis

Abstract

CP PUPPIS is an old classical nova, that had an outburst in 1942 as one of the fastest and brightest novae ever recorded (Δ m=17 mag, t3 = 6.5 days ; V ej ≥ 1000 km/sec, Payne-Gaposhkin 1957 ). We observed it in X-rays with the ROSAT Position Sensitive Proportional Counter in April 1993. The source was detected with a count rate of 0.067 ± 0.004 c/s. The total X-ray flux between 0.1 and 2.4 keV was ~ 2.88 x10-12 ergs s-1 cm-2. The spectrum is best fitted by a thermal bremsstrahlung emission model with temperature ≥ 1 keV. Temperatures as high as 30 keV are allowed within 2σ errors. The X-ray count rates are modulated with the ≃1.5 hrs. spectroscopic and photometric orbital periods (Bianchini et al. 1985; Warner 1985; O’Donoghue et al. 1989; Diaz & Steiner 1991, White et al. 1993). The significance of the modulations at the spectroscopic period detected by White et al., (1993) ( P ~ 5295 s ) was tested by a phase dispersion method and found to be at the 3σ confidence level. Considering the variation of X-ray flux with the orbital period and the possibility of high plasma temperatures in the emitting medium, we favor an intermediate polar interpretation for this system.