EP-FXT observations of the cool-core cluster Abell 478 out to R200: Thermodynamic properties and azimuthal asymmetry
Abstract
We use deep observations from the Einstein Probe Follow-up X-ray Telescope (EP-FXT) to investigate the gas distribution and thermodynamic properties of the cool-core galaxy cluster Abell 478 (A478) from the center out to R200, and to examine its azimuthal asymmetry and the influence of local dynamical disturbances on hydrostatic mass estimates. We derive the surface-brightness, temperature, electron-density, pressure, entropy, and total mass profiles. The surface-brightness distribution is well described by a double-β model, while the temperature profile shows the characteristic cool-core behavior, with a cool center, a rise toward intermediate radii, and a gradual decline in the outskirts. The hydrostatic mass profile is well fitted by a Navarro-Frenk-White model, yielding R200=2082±95 kpc and M200=(1.12±0.15)×1015 M⊙, indicating that the cluster is close to quasi-static equilibrium on global scales. Despite the globally regular structure, clear azimuthal asymmetry is present. The SW sector shows lower temperatures, higher densities, and lower entropies at intermediate and large radii, together with signatures consistent with a cold-front candidate. Combined with the two-dimensional temperature distribution, these features suggest local dynamical disturbance, likely associated with gas sloshing. A478 is therefore globally relaxed but locally disturbed, demonstrating that nonequilibrium structures can still affect thermodynamic measurements and hydrostatic mass estimates even in an apparently regular cool-core cluster.
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BibTeX
@misc{sun2026epfxt,
title = {{EP-FXT observations of the cool-core cluster Abell 478 out to R200: Thermodynamic properties and azimuthal asymmetry}},
author = {J. X. Sun and Y. Chen and S. M. Jia and C. K. Li and J. Zhang and X. J. Yang and H. Yu and A. Liu and X. Y. Zheng and W. W. Cui and D. W. Han and H. S. Zhao and X. F. Zhao and J. J. Xu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23631},
eprint = {2609.23631},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23631},
}
RIS
TY - UNPB
TI - EP-FXT observations of the cool-core cluster Abell 478 out to R200: Thermodynamic properties and azimuthal asymmetry
AU - J. X. Sun
AU - Y. Chen
AU - S. M. Jia
AU - C. K. Li
AU - J. Zhang
AU - X. J. Yang
AU - H. Yu
AU - A. Liu
AU - X. Y. Zheng
AU - W. W. Cui
AU - D. W. Han
AU - H. S. Zhao
AU - X. F. Zhao
AU - J. J. Xu
PY - 2026
DA - 2026/09/20
PB - arXiv
DO - 10.48550/arxiv.2609.23631
UR - https://arxiv.org/abs/2609.23631
AB - We use deep observations from the Einstein Probe Follow-up X-ray Telescope (EP-FXT) to investigate the gas distribution and thermodynamic properties of the cool-core galaxy cluster Abell 478 (A478) from the center out to R_200, and to examine its azimuthal asymmetry and the influence of local dynamical disturbances on hydrostatic mass estimates. We derive the surface-brightness, temperature, electron-density, pressure, entropy, and total mass profiles. The surface-brightness distribution is well described by a double-β model, while the temperature profile shows the characteristic cool-core behavior, with a cool center, a rise toward intermediate radii, and a gradual decline in the outskirts. The hydrostatic mass profile is well fitted by a Navarro-Frenk-White model, yielding R_200=2082±95 kpc and M_200=(1.12±0.15)×10^15 M_⊙, indicating that the cluster is close to quasi-static equilibrium on global scales. Despite the globally regular structure, clear azimuthal asymmetry is present. The SW sector shows lower temperatures, higher densities, and lower entropies at intermediate and large radii, together with signatures consistent with a cold-front candidate. Combined with the two-dimensional temperature distribution, these features suggest local dynamical disturbance, likely associated with gas sloshing. A478 is therefore globally relaxed but locally disturbed, demonstrating that nonequilibrium structures can still affect thermodynamic measurements and hydrostatic mass estimates even in an apparently regular cool-core cluster.
ER -