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The symbiotic star SMC 3

ATEL # 1379; Andreas Zezas and Marina Orio
on 4 Feb 2008; 9:29 UT
Password Certification: Marina Orio (

Subjects: X-ray, Binaries, Variables, Stars

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.

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