RS Oph has returned to quiescence levels in X-rays
ATel #1494; Thomas Nelson (University of Wisconsin at Madison) and Marina Orio (INAF Padova and University of Wisconsin at Madison)
on 29 Apr 2008; 12:16 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)
Subjects: X-ray, Cataclysmic Variable, Nova
We report an XMM-Newton observation of the recurrent nova RS Oph, carried out on 2008 Feb 26, 743.9 days after the 2006 outburst. The observation lasted 17 ks, not including periods of high background. The recurrent nova was detected with the EPIC-pn instrument with a count rate of 0.105+/-0.004 c/s.
The spectrum is quite soft, with essentially no counts above 2 keV. Very little continuum is present, and several emission features are detected at energies corresponding to lines of Ne IX, O VIII, O VII and N VII. Both the EPIC-pn spectra, and the very low S/N RGS spectra show that the X-ray flux is emitted mainly or entirely in emission lines. The iron K alpha lines close to 7 keV, detected in the XMM-Newton observations of 2006 September, are not measured any more. The observed X-ray flux in the range 0.15 to 10 keV is ~1.5 x 10(-13) erg cm(-2) s(-1), a factor of 8 lower than in October 2006.
The EPIC count rates are consistent with the count rate measured in the quiescent ROSAT observations of 1992 (see Orio 1993, A&A, 274, L41). The presence of emission lines seems to indicate that we are observing a wind in quiescence, rather than accretion.
