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arXiv 2305.16144astro-ph.HEastro-ph.GA
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OJ 287的光谱变化:最低X射线态光谱——在光学-紫外波段延伸且在X射线波段变硬

On the Spectral Changes of OJ 287: The Lowest X-ray state Spectrum -- extended at Optical-UV and Hard at X-rays

Pankaj Kushwaha

AI总结:

本研究分析OJ 287最低X射线态的光谱,发现光学-紫外延伸至X射线的幂律谱,X射线谱最硬,支持同步辐射为主要驱动,并暗示大尺度喷流发射。

摘要:

在BL Lac天体OJ 287的低和中等X射线通量状态下,光学-紫外同步辐射光谱被认为是其大部分X射线光谱变化的主要驱动因素。在此,我们聚焦于Swift设施记录的OJ 287最低X射线通量状态,并报告发现一个光子谱指数为$\rm 2.71\pm0.03$的幂律光学-紫外光谱,该光谱延续至X射线波段。考虑到这一点,在X射线波段,我们发现光子谱指数为$\rm 1.22\pm0.20$的幂律X射线光谱,当考虑其他具有相似X射线光谱的观测时,该指数改善为$\rm 1.29\pm0.06$。这是所报道的最硬X射线光谱(0.3-10 keV),与所报道的Swift-BAT硬X射线光谱一致。我们进一步表明,当与低和中等通量状态下的相应光学-紫外连续谱结合时,该X射线光谱可以重现大部分平坦的X射线光谱,从而强化了同步辐射作为该源LBL状态下大部分X射线光谱变化的主要驱动因素。结合亮态期间光学-紫外光谱的急剧变陡/截断,延伸光谱表明存在一个相对较大的发射区域,可能是大尺度喷流发射。光学-紫外光谱暗示高能幂律粒子谱指数约为$\rm \sim4.4$,而X射线则暗示硬低能粒子谱指数为$\rm 1.3-1.6$,这可能是真实的,也可能源于粒子谱中较高的低能截断。

英文摘要:

Optical-UV synchrotron spectrum has been argued to be the primary driver of the majority of X-ray spectral changes in the BL Lacertae object OJ 287 during its low and intermediate X-ray flux state. Here, we focus on the lowest recorded X-ray flux state of OJ 287 by the Swift facility and report the finding of a power-law optical-UV spectrum with a photon spectrum of $\rm 2.71\pm0.03$ continuing into X-rays. Considering this at X-rays, we found a power-law X-ray spectrum of photon spectral index $\rm 1.22\pm0.20$ that improves to $\rm 1.29\pm0.06$ when considering other observations with similar X-ray spectra. This is the hardest reported X-ray spectrum (0.3-10 keV) and is consistent with the reported Swift-BAT hard X-ray spectrum. We further show that this X-ray spectrum can reproduce most of the flat X-ray spectra when combined with the corresponding optical-UV continuum during the low and intermediate flux states strengthening synchrotron as the primary driver of most of the X-ray spectral changes in the LBL state of the source. Combined with sharp-steepening/cutoff of the optical-UV spectrum during bright phases, the extended-spectrum indicates a comparatively larger emission region and could be the large-scale jet emission. The optical-UV spectrum implies a high-energy power-law particle spectrum of $\rm \sim4.4$ while X-ray implies a hard low-energy particle spectrum of $\rm 1.3-1.6$ which could be the real or can result from a higher low-energy cut-off in the particle spectrum.

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