Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A279 | |
Number of page(s) | 12 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361/202450012 | |
Published online | 17 October 2024 |
The correlation between dip width and peak flux in Cir X-1
1
Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing, People’s Republic of China
2
Dongguan Neutron Science Center, 1 Zhongziyuan Road, Dongguan 523808, People’s Republic of China
3
School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, 210023 Nanjing, People’s Republic of China
4
University of Chinese Academy of Sciences, Chinese Academy of Sciences, 100049 Beijing, People’s Republic of China
5
Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, People’s Republic of China
6
Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Eberhard Karls, Universität, Sand 1, D-72076 Tübingen, Germany
Received:
18
March
2024
Accepted:
6
August
2024
In this work we analyzed the long-term X-ray variation of Cir X-1 and its NICER spectra. The dip width and the peak flux after periastron are obtained. Our findings show a negative correlation between the dip width and the peak flux. A new scenario is introduced to explain the correlation. The disk height is higher at a larger radius in the standard model. When the neutron star (NS) moves away from periastron, the contraction of the equipotential surface causes the height of the outer disk to increase significantly. It blocks the X-ray emission near the NS. Subsequently, the height of the outer disk gradually decreases due to the viscosity. The viscous timescale is inversely proportional to the height of the disk, and the height of the outer disk is proportional to the mass transferred from the companion near periastron, thus the peak flux. Consequently, the duration of the obscuring, corresponding to the dip width, is inversely proportional to the peak flux. Moreover, we introduce a new ephemeris MJD(N) = 43075.0 + 16.5843N − 4.778 × 10−5N2 based on the dip-in phases (ingress phase of the dip).
Key words: accretion / accretion disks / binaries: general / stars: individual: Cir X-1
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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