Long-term X-ray/UV observations of the ultraluminous X-ray source HolmbergII X-1.

Proceedings of The Multifaceted Universe: Theory and Observations - 2022 — PoS(MUTO2022) Pub Date : 2022-09-16 DOI:10.22323/1.425.0056

K. Atapin, A. Vinokurov, M. Safonova, S. Fabrika, O. Bordoloi

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Abstract

Ultraluminous X-ray sources (ULXs) are point-like extra-galactic sources with luminosities ex-ceeding the Eddington limit for stellar-mass black holes. The results of our recent observations of one of these sources – Holmberg II X-1 – with the Astrosat observatory prompted us to look at the long-term brightness and spectral variability of this source using the Swift/XRT observations. We found that after being in the state of low variability ( ≲ 2 times) and hard spectrum ( Γ ∼ 1 . 8) for about ten years, the source returned to the state with high variability ( ≳ 10 times ) and a soft spectrum ( Γ ∼ 2 . 5). Thus, during the time of the Swift monitoring of more than 15 years, the ULX experienced state transitions at least 3 times. Also we found that the period of 27 days observed in the variable state and vanished in the steady state appeared again as the source returned to the variable state. Further analysis and modeling are necessary to shed light on the possible mechanisms of the observed state transitions of Holmberg II X-1. The Multifaceted Universe: Theory and Observations 2022

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超亮x射线源HolmbergII X-1的长期x射线/紫外观测。

超亮x射线源(ULXs)是点状的星系外源，其亮度超过了恒星质量黑洞的爱丁顿极限。我们最近用Astrosat天文台对其中一个光源Holmberg II X-1的观测结果促使我们使用Swift/XRT观测来观察这个光源的长期亮度和光谱变化。我们发现，在处于低变异性(> 2倍)和硬谱(Γ ~ 1)的状态后。8)大约十年后，源恢复到高变异性(约10倍)和软光谱(Γ ~ 2)的状态。5)因此，在超过15年的Swift监测期间，ULX至少经历了3次状态转换。我们还发现，在可变状态下观察到的27天的周期在稳态中消失了，当源返回到可变状态时又出现了。进一步的分析和建模对于阐明Holmberg II X-1观测到的状态转变的可能机制是必要的。《多面宇宙:理论与观测》2022

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Proceedings of The Multifaceted Universe: Theory and Observations - 2022 — PoS(MUTO2022)

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