Yukikatsu Terada, Kaya Mori, Takayuki Hayashi, Gabriel L. Bridges, Manabu Ishida, Axel D. Schwope, Mariko Kimura, Masayoshi Nobukawa, David A. H. Buckley, Solen Balman, Taichi Ichikawa, Atsuto Matsumura, Mai Takeo, Charles J. Hailey, Gavin Ramsay, Antonio Rodriguez, Samantha Walker
Abstract We present XRISM/Resolve high-resolution X-ray spectroscopy of the prototypical magnetic cataclysmic variable AM Herculis. All satellite lines of highly ionized Fe are fully resolved. Lighter-element lines (Si, S, Ca) show 2–3 eV widths consistent with purely thermal broadening, while the broader 6–7 eV Fe lines require additional bulk Doppler broadening. Spin-phase-resolved modulations are clearly detected in the Fe XXV and Fe XXVI lines, with semiamplitudes of 81.8 ± 6 km s −1 and 132.5 ± 9 km s −1 , and mean velocities of 143.6 ± 6 km s −1 and 225.6 ± 8 km s −1 , respectively. After removing these bulk Doppler shifts, we obtain intrinsic Doppler widths of 5.2 3 − 0.15 + 0.16 eV for Fe XXV and 6.2 3 − 0.18 + 0.19 eV for Fe XXVI , directly revealing gradients of bulk velocity and temperature in the cooling-flow plasma. We additionally examined the resonance anisotropy predicted by Terada et al.; the equivalent widths (EWs) of the Fe XXV and Fe XXVI resonance lines increase at the pole-on phase by factors of 1.30–1.35, in positive correlation with their oscillator strengths. Combining XRISM with simultaneous NuSTAR data and PSAC/MCVSPEC plasma models, we derive a self-consistent shock temperature of 24.0 ± 0.1 keV and shock velocity of 1116 ± 2 km s −1 . Radiative transfer simulations of the resonance lines further constrain the shock density to ≈(5–6) × 10 15 cm −3 , providing a new density diagnostic for accretion columns. The resulting accretion-column geometry has a height of 200–300 km and a radius of 200–400 km.