Suzaku Observation of the Intermediate Polar V1223 Sagittarii

Abstract

Abstract We report on the Suzaku observation of the intermediate polar V1223 Sagittarii. Using a multi-temperature plasma emission model with its reflection from a cold matter, we obtained the shock temperature to be 37.9 $^{+5.1}_{-4.6}\ $ keV. This constrains the mass and the radius of the white dwarf (WD) in the ranges 0.82 $^{+0.05}_{-0.06}\ M_\odot$ and (6.9 $\ \pm\ $ 0.4) $\times$ 10 $^{8}\ $ cm, respectively, with the aid of a WD mass–radius relation. The solid angle of the reflector viewed from the post-shock plasma was measured to be $\Omega/$ 2 $\pi$$=$ 0.91 $\ \pm\ $ 0.26. A fluorescent iron K $\alpha $ emission line was detected, whose central energy was discovered to be modulated with the WD rotation for the first time in magnetic-CVs. Detailed spectral analysis indicates that the line comprises a stable 6.4 keV component and a red-shifted component, the latter of which appears only around the rotational intensity-minimum phase. The equivalent width ( $EW$ ) of the former stable component, $\sim\ $ 80 eV, together with the measured $\Omega$ indicates that the major reflector is the WD surface, and the shock height is not more than 7% of the WD radius. Comparing this limitation to the height predicted by the Aizu model (Aizu, 1973, Prog. Theor. Phys., 50, 344), we estimated the fractional area onto which the accretion occurs to be $<\ $ 7 $\times$ 10 $^{-3}$ of the WD radius, which is the most severe constraint in non-eclipsing IPs. The red-shifted iron line component, on the other hand, can be interpreted as emanating from the pre-shock accretion flow via fluorescence. Its $EW$ (28 $^{+44}_{-13}\ $ eV) and the central energy (6.30 $_{-0.05}^{+0.07}\ $ keV) at the intensity-minimum phase are consistent with this interpretation.