通过ZTF光变曲线中的光学QPOs探测SDSS J1609+1756中的亚pc双黑洞系统
A sub-pc BBH system in SDSS J1609+1756 through optical QPOs in ZTF light curves
AI总结：
本研究通过四种方法分析ZTF光变曲线，在类星体SDSS J1609+1756中探测到周期约340天、置信度高于5σ的光学准周期振荡，结合宽线特征估算出中心存在亚pc双黑洞系统，总质量上限约1.03×10^8太阳质量。
摘要：
光学准周期振荡是活动星系核（AGN）中亚pc双黑洞系统最被期望的标志。本文报告了在红移z=0.347的类星体SDSS J1609+1756中发现的稳健光学QPOs。为了探测可靠的光学QPOs，采用了四种不同方法分析SDSS J1609+1756长达4.45年的ZTF g/r/i波段光变曲线：正弦函数直接拟合、广义Lomb-Scargle周期图、自交叉相关函数和加权小波Z变换方法。这四种方法均得出周期约340天的可靠光学QPOs，置信度高于5σ，以确保SDSS J1609+1756中光学QPOs的稳健性。同时，基于通过CAR过程模拟光变曲线以追踪AGN内禀活动，可以确认置信度高于3σ，表明光学QPOs并非AGN内禀活动的误探测，再次证实了稳健的光学QPOs，并强烈暗示SDSS J1609+1756中心存在亚pc双黑洞系统。此外，基于SDSS J1609+1756宽巴尔末发射线中明显的红移肩部特征，预期中心双黑洞系统的空间间距估计小于107±60光日，接受的总黑洞质量上限约为(1.03±0.22)×10^8太阳质量。因此，通过ZTF光变曲线探测并报告周期约1年的双黑洞系统预期光学QPOs是高效可行的，结合特殊的宽线发射特征，未来有望为宽线AGN中双黑洞系统的空间间距提供更多线索。
英文摘要：
Optical quasi-periodic oscillations (QPOs) are the most preferred signs of sub-pc binary black hole (BBH) systems in AGN. In this manuscript, robust optical QPOs are reported in quasar SDSS J1609+1756 at $z=0.347$. In order to detect reliable optical QPOs, four different methods are applied to analyze the 4.45 years-long ZTF g/r/i-band light curves of SDSS J1609+1756, direct fitting results by sine function, Generalized Lomb-Scargle periodogram, Auto-Cross Correlation Function and Weighted Wavelet Z-transform method. The Four different methods can lead to well determined reliable optical QPOs with periodicities $\sim340$ days with confidence levels higher than 5$σ$, to guarantee the robustness of the optical QPOs in SDSS J1609+1756. Meanwhile, based on simulated light curves through CAR process to trace intrinsic AGN activities, confidence level higher than $3σ$ can be confirmed that the optical QPOs are not mis-detected in intrinsic AGN activities, re-confirming the robust optical QPOs and strongly indicating a central sub-pc BBH system in SDSS J1609+1756. Furthermore, based on apparent red-shifted shoulders in broad Balmer emission lines in SDSS J1609+1756, space separation of the expected central BBH system can be estimated to be smaller than $107\pm60$ light-days, accepted upper limit of total BH mass $\sim(1.03\pm0.22)\times10^8{\rm M_\odot}$. Therefore, to detect and report BBH system expected optical QPOs with periodicities around 1 year is efficiently practicable through ZTF light curves, and combining with peculiar broad line emission features, further clues should be given on space separations of BBH systems in broad line AGN in the near future.
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