V723Cassiopeia still on in X-rays: A bright super soft source 12 years after outburst

J. U. Ness, G. Schwarz, S. Starrfield, J. P. Osborne, K. L. Page, A. P. Beardmore, R. M. Wagner, C. E. Woodward

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Abstract

We find that the classical nova V723Cas (1995) is still an active X-ray source more than 12 years after outburst, and analyze 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 2 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 V723Cas, 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 = (2.8 - 3.8) × 105 K and a bolometric luminosity ≳5 × 10 36 erg s-1 and caution that luminosities from blackbodies are generally overestimated and temperatures underestimated. 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.

Original languageEnglish (US)
Pages (from-to)1328-1333
Number of pages6
JournalAstronomical Journal
Volume135
Issue number4
DOIs
StatePublished - Apr 1 2008

Keywords

  • Novae, cataclysmic variables
  • Stars: individual (V723 Cas)

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    Ness, J. U., Schwarz, G., Starrfield, S., Osborne, J. P., Page, K. L., Beardmore, A. P., Wagner, R. M., & Woodward, C. E. (2008). V723Cassiopeia still on in X-rays: A bright super soft source 12 years after outburst. Astronomical Journal, 135(4), 1328-1333. https://doi.org/10.1088/0004-6256/135/4/1328