Einstein Probe discovery of the short-period intermediate polar EP J115415.8−501810

作者：Y. Xiao, Mingyu Ge, N. Rea, F. J. Lu, Hua Feng, Lian Tao, D. de Martino, F. Coti Zelati, A. Marino, E. Kuulkers, W. Yuan, Chichuan Jin, H. Sun, J. Wu, N. Hurley-Walker, S. J. McSweeney, D. A. H. Buckley, B. Zhang, S. Zhang, S. Scaringi, Kaya Mori, Zehao Yu, X. T. Hou, Yunfei Xu · 发表于：Astronomy and Astrophysics · 年份：2025 · DOI：10.1051/0004-6361/202554876 · 被引用次数：3 · 研究领域：Astrophysical Phenomena and Observations、Astronomical Observations and Instrumentation、Pulsars and Gravitational Waves Research

The X-ray transient source EP240309a/EP J115415.8−501810 was first detected by the Wide-field X-ray Telescope on board the Einstein Probe (EP) instrument during the commissioning phase. Subsequent optical observations confirmed it as a cataclysmic variable of the intermediate polar type with a 238.2 s spinning white dwarf on a ∼3.76 h orbit. We report the source discovery and follow-up studies carried out with the EP’s Follow-up X-ray Telescope. A periodic variation of 231 s was detected in the 0.3−2 keV band, while no obvious pulsation appeared in the 2−10 keV band. The spectral analysis showed that the X-ray emission could be described by an absorbed bremsstrahlung model with kT > 11 keV. The partial covering absorption, with a hydrogen column density N H = 2.0 × 10 22 cm −2 and covering fraction of around 0.9, is much higher than the interstellar absorption along the line of sight. According to the distance of d = 309.5 pc obtained from the Gaia parallax, we estimated that the luminosity of this source in the 0.3−10 keV range is ∼2 × 10 32 erg s −1 . In addition, a phase-resolved spectral analysis revealed that the detected periodic variation is mainly caused by the change in the absorption column density. In this scenario, the spin modulation arises due to absorption from the pre-shock accretion flow of the X-ray emitting pole, while the optical radiation is modulated at the orbital side band ( ω spin − Ω orbit ) due to the reprocessing in regions within the binary sys...