* Astronomy

Title: V723 Cassiopeia still on in X-rays: A bright Super Soft Source 12 years after outburst
Authors: J.U-. Ness, G. Schwarz, S. Starrfield, J.P. Osborne, K.L. Page, A.P. Beardmore, R.M. Wagner, C.E. Woodward

We find that the classical nova V723 Cas (1995) is still an active X-ray source more than 12 years after outburst and analyse seven X-ray observations carried out with Swift between 2006 January 31 and 2007 December 3. The average count rate is 0.022±-0.01 cts s^{-1} but the source is variable within a factor of two of the mean and does not show any signs of turning off. We present supporting optical observations which show that between 2001 and 2006 an underlying hot source was present with steadily increasing temperature. In order to confirm that the X-ray emission is from V723 Cas, we extract a ROSAT observation taken in 1990 and find that there was no X-ray source at the position of the nova. The Swift XRT spectra resemble those of the Super Soft X-ray binary Sources (SSS) which is confirmed by RXTE survey data which show no X-ray emission above 2 keV between 1996 and 2007. Using blackbody fits we constrain the effective temperature to between T_eff=(2.6-4.6)x10^5 K and a bolometric luminosity >5x10^35 erg s^-1. In order to confirm that our blackbody fitting technique works, we applied it to a Chandra observation of CAL 83, known to be a Super Soft Source, and obtain results that are consistent with a Non-LTE stellar atmosphere analysis of the same data. We discuss a number of possible explanations for the continuing X-ray activity, including the intriguing possibility of steady hydrogen burning due to renewed accretion.

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