Chandra High Resolution X-ray Spectroscopy of AM Her

Abstract

We present the results of high resolution spectroscopy of the prototype polar AM Herculis observed with Chandra High Energy Transmission Grating. The X-ray spectrum contains hydrogen-like and helium-like lines of Fe, S, Si, Mg, Ne and O with several Fe L-shell emission lines. The forbidden lines in the spectrum are generally weak whereas the hydrogen-like lines are stronger suggesting that emission from a multi-temperature, collisionally ionized plasma dominates. The helium-like line flux ratios yield a plasma temperature of 2 MK and a plasma density 1 - 9 x10^12 cm^-3, whereas the line flux ratio of Fe XXVI to Fe XXV gives an ionization temperature of 12.4 +1.1 -1.4 keV. We present the differential emission measure distribution of AM Her whose shape is consistent with the volume emission measure obtained by multi-temperature APEC model. The multi-temperature plasma model fit to the average X-ray spectrum indicates the mass of the white dwarf to be ~1.15 M_sun. From phase resolved spectroscopy, we find the line centers of Mg XII, S XVI, resonance line of Fe XXV, and Fe XXVI emission modulated by a few hundred to 1000 km/s from the theoretically expected values indicating bulk motion of ionized matter in the accretion column of AM Her. The observed velocities of Fe XXVI ions are close to the expected shock velocity for a 0.6 M_sun white dwarf. The observed velocity modulation is consistent with that expected from a single pole accreting binary system.

arXiv comment6 figures, AASTEX style, accepted for publication in ApJ

References in corpus (11)

• The Chandra High Energy Transmission Grating: Design, Fabrication, Ground Calibration and Five Years in Flight
• X-ray photoionized plasma diagnostics with Helium-like ions. Application to Warm Absorber-Emitter in Active Galactic Nuclei
• Effects of Gravity on the Structure of Postshock Accretion Flows in Magnetic Cataclysmic Variables
• The Coronae of AR Lac
• On the iron Kalpha complex in magnetic cataclysmic variables
• The K-alpha complex of He-like iron with dielectronic satellites
• Two-temperature accretion flows in magnetic cataclysmic variables: Structures of post-shock emission regions and X-ray spectroscopy
• The Radial Velocity and Mass of the White Dwarf of EX Hydrae Measured with Chandra
• Ionisation Structure in Accretion Shocks with a Composite Cooling Function
• X-Ray Beaming due to Resonance Scattering in the Accretion Column of Magnetic Cataclysmic Variables
• ORFEUS II Far-UV Spectroscopy of AM Herculis

Cited by in corpus (10)

• X-ray Emissions from Accreting White Dwarfs: a Review
• Numerical simulations of high-energy flows in accreting magnetic white dwarfs
• A new soft X-ray spectral model for polars with an application to AM Herculis
• The various accretion modes of AM Herculis: Clues from multi-wavelength observations in high accretion states
• On the importance of satellite lines to the He-like K ALPHA complex and the G ratio for calcium, iron, and nickel
• Phase-resolved X-ray spectroscopy and spectral energy distribution of the X-ray soft polar RS Caeli
• X-ray observation of AM Herculis in a very low state with Suzaku
• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• Confirmation of SRGt 062340.2-265751 as a nova-like cataclysmic variable with a possible magnetic nature
• Detailed ROSAT X-ray Analysis of the AM Her Cataclysmic Variable VV Pup