2025-11-20 マサチューセッツ工科大学（MIT）
A smaller white dwarf star (left) pulls material from a larger star into a swirling accretion disk. The pair is called an “intermediate polar,” and MIT astronomers used powerful telescopes to measure the system’s X-ray polarization for the first time, revealing key features at the center of its hottest, most extreme regions.Credits:Image: Jose-Luis Olivares, MIT
＜関連情報＞
- https://news.mit.edu/2025/first-look-innermost-region-white-dwarf-system-1120
- https://iopscience.iop.org/article/10.3847/1538-4357/ae11b5
降着する白色矮星のX線偏光測定：EXうみへび座の事例研究 X-Ray Polarimetry of Accreting White Dwarfs: A Case Study of EX Hydrae
Sean J. Gunderson, Swati Ravi, Herman L. Marshall, Dustin K. Swarm, Richard Ignace, Yael Nazé, David P. Huenemoerder, and Pragati Pradhan
The Astrophysical Journal Published: 2025 November 10
DOI:10.3847/1538-4357/ae11b5
Abstract
We present the first first X-ray polarization measurements of a white dwarf (WD), the intermediate polar EX Hya. We measured significant polarization only in the 2–3 keV energy band with a polarization degree of 8% at a 3σ significance. No significant polarization was detected above 3 keV, which we attribute to the higher energy bands having lower signal to noise. We found that the scattering surface detected by the Imaging X-ray Polarimetry Explorer appears to be nearly perpendicular to the optical scattering plane, showing that the X-ray scattering surface is the WD and close to the base of the accretion column. Finally, we show how the polarization can be used to estimate the height of the accretion shock above the WD’s surface.
