The symbiotic star SMC 3
ATel #1379; Andreas Zezas and Marina Orio
on 4 Feb 2008; 09:29 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)
Subjects: X-ray, Binary, Star, Variables
Andreas Zezas and Marina Orio report the XMM-Newton detection
of the supersoft X-ray source (SSS) and symbiotic binary SMC 3,
17 years after the first ROSAT detection, in a 20 ks exposure done
on 2007 October 28. The EPIC pn count rate with the medium filter
was 0.0315+-0.0019 counts/s.
SMC 3 was still a luminous SSS without a significant change in the
effective temperature of about 500,000 K, but the luminosity in the
0.15-1 keV range decreased by more than a factor of 4 since the previous
XMM-Newton observation of 2006 (Orio et al., ApJ 2007, 661, 1105).
The X-ray flux was 3.1 10^{-13} erg/cm^2/s, still about a factor of 10 higher
than the flux measured a previous Chandra ACIS-S observation done
in 2004, exactly 4 years and 8 months earlier. There are no significant
spectral changes since the previous X-ray observations and the new
measurement seems to confirm that SMC 3 undergoes an eclipse in X rays,
lasting a few months and repeating itself with a period of about
4.5 years, as suggested by Kahabka (2004, A&A, 416, 57). In this last
X-ray observation the source was probably just coming out of the eclipse.
