High-resolution X-ray Spectra Of The Symbiotic Star SS73 17

Abstract

SS73 17 was an innocuous Mira-type symbiotic star until Integral and Swift discovered its bright hard X-ray emission, adding it to the small class of "hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it emits three bright iron lines as well, with little to no emission in the 0.3-2 keV bandpass. We present here followup observations with the Chandra HETG and Suzaku that confirm the earlier detection of strong emission lines of Fe Kalpha fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray emission. The high resolution spectrum also shows emission lines of other highly ionized ions as Si XIV and possibly S XVI. In addition, a reanalysis of the 2006 Suzaku data using the latest calibration shows that the hard (15-50 keV) X-ray emission is brighter than previously thought and remains constant in both the 2006 and 2008 data. The G ratio calculated from the Fe XXV lines shows that these lines are thermal, not photoionized, in origin. With the exception of the hard X-ray emission, the spectra from both epochs can be fit using thermal radiation assuming a differential emission measure based on a cooling flow model combined with a full and partial absorber. We show that acceptable fits can be obtained for all the data in the 1-10 keV band varying only the partial absorber. Based on the temperature and accretion rate, the thermal emission appears to be arising from the boundary layer between the accreting white dwarf and the accretion disk.

7 pages, 5 figures. Accepted by the Astrophysical Journal

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• Discovery of fast, large-amplitude optical variability of V648 Car (=SS73-17)
• Long-term X-ray Variability of the Symbiotic System RT Cru based on Chandra Spectroscopy
• SU Lyn: diagnosing the boundary layer with UV and hard X-ray data
• Variable Hard X-ray Emission From the Central Star of the Eskimo Nebula
• Detection of X-rays from the symbiotic star V1329 Cyg
• X-ray Variability in the Symbiotic Binary RT Cru: Principal Component Analysis
• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• Revisiting symbiotic binaries with interferometry: II. New PIONIER data