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arXiv 2008.13434astro-ph.HE
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Her X-1的回旋线能量:衰变后的稳定性

The cyclotron line energy in Her X-1: stable after the decay

R. Staubert, L. Ducci, L. Ji, F. Fuerst, J. Wilms, R. E. Rothschild, K. Pottschmidt, M. Brumback, F. Harrison

摘要:

我们总结了2012年至2019年期间通过重复NuSTAR观测跟踪Her~X-1回旋加速器线演变的专门努力的结果。之前观察到的回旋加速器线能量的近20年的衰减在2012年左右结束:从那时起,脉冲相位平均通量校正回旋加速器线能量保持稳定并恒定在Ecyc=(37.44+/-0.07)keV的平均值(归一化为6.8 RXTE/ASM-cts/s的通量水平)。2007年发现的Ecyc的通量依赖性现在被高精度地测量,给出的斜率为(0.675+/-0.075)keV/(ASM-cts/s),对应于通量增加两倍时Ecyc增加6.5%。我们还发现,所有的线参数,以及连续参数显示与X射线通量的相关性。虽然现在已知几个吸积双星的Ecyc和X射线通量(正的和负的)之间存在相关性,并对潜在的物理学提出了各种建议,但长期衰变的现象迄今为止只在Her~X-1和Vela~X-1中看到过,其解释远没有那么令人信服。

英文摘要:

We summarize the results of a dedicated effort between 2012 and 2019 to follow the evolution of the cyclotron line in Her~X-1 through repeated NuSTAR observations. The previously observed nearly 20-year long decay of the cyclotron line energy has ended around 2012: from there onward the pulse phase averaged flux corrected cyclotron line energy has remained stable and constant at an average value of Ecyc= (37.44+/-0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts/s). The flux dependence of Ecyc discovered in 2007 is now measured with high precision, giving a slope of (0.675+/-0.075) keV/(ASM-cts/s), corresponding to an increase of 6.5% of Ecyc for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between Ecyc and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her~X-1 and Vela~X-1, with far less convincing explanations.

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