The nova-like cataclysmic binary AE Aqr , which is currently understood to be a former supersoft X-ray binary and current magnetic propeller , was observed for over two binary orbits ( 78 ks ) in 2005 August with the High-Energy Transmission Grating ( HETG ) onboard the Chandra X-ray Observatory .
The long , uninterrupted Chandra observation provides a wealth of details concerning the X-ray emission of AE Aqr , many of which are new and unique to the HETG .
First , the X-ray spectrum is that of an optically thin multi-temperature thermal plasma ; the X-ray emission lines are broad , with widths that increase with the line energy , from \sigma \approx 1 eV ( 510 ~ { } km~ { } s ^ { -1 } ) for O viii to \sigma \approx 5.5 eV ( 820 ~ { } km~ { } s ^ { -1 } ) for Si xiv ; the X-ray spectrum is reasonably well fit by a plasma model with a Gaussian emission measure distribution that peaks at \log T ( { K } ) = 7.16 , has a width \sigma = 0.48 , an Fe abundance equal to 0.44 times solar , and other metal ( primarily Ne , Mg , and Si ) abundances equal to 0.76 times solar ; and for a distance d = 100 pc , the total emission measure EM = 8.0 \times 10 ^ { 53 } ~ { } cm ^ { -3 } and the 0.5–10 keV luminosity L _ { X } = 1.1 \times 10 ^ { 31 } ~ { } erg~ { } s ^ { -1 } .
Second , based on the f / ( i + r ) flux ratios of the forbidden ( f ) , intercombination ( i ) , and recombination ( r ) lines of the He \alpha triplets of N vi , O vii , and Ne ix measured by Itoh et al .
in the XMM-Newton Reflection Grating Spectrometer spectrum and those of O vii , Ne ix , Mg xi , and Si xiii in the Chandra HETG spectrum , either the electron density of the plasma increases with temperature by over three orders of magnitude , from n _ { e } \approx 6 \times 10 ^ { 10 } ~ { } cm ^ { -3 } for N vi [ \log T ( { K } ) \approx 6 ] to n _ { e } \approx 1 \times 10 ^ { 14 } ~ { } cm ^ { -3 } for Si xiii [ \log T ( { K } ) \approx 7 ] , and/or the plasma is significantly affected by photoexcitation .
Third , the radial velocity of the X-ray emission lines varies on the white dwarf spin phase , with two oscillations per spin cycle and an amplitude K \approx 160 ~ { } km~ { } s ^ { -1 } .
These results appear to be inconsistent with the recent models of Itoh et al. , Ikhsanov , and Venter & Meintjes of an extended , low-density source of X-rays in AE Aqr , but instead support earlier models in which the dominant source of X-rays is of high density and/or in close proximity to the white dwarf .