耀变体的准周期振荡研究

Blazars, an extreme subclass of active galactic nuclei (AGN), are characterized by luminous and rapidly variable continuum emissions across all wavelengths. The presence of quasi-periodic oscillations (QPOs) has been claimed in a small number of blazars at present, on the basis of the time series analysis of light curves of blazars. QPOs in light curves of blazars may be related to the binary black holes system, precession in the jet, instabilities developing within the accretion disk and other effects, which is essential for investigating the theoretical modes and emission mechanisms of blazars. However, there are still inadequacies in some fields, such as sample size, correlations between QPOs at different frequencies, QPOs on short-term timescales and confidence analysis assuming the red noise. In this project, we focus on the multiwavelength QPOs of blazars. The purposed works can be summarized as follows: (1) We will study systematically the distributions of the QPOs for the whole sample from the separate database of Fermi, Swift, OVRO and SMARTS projects, the correlation among QPOs, redshifts, masses of black holes and Doppler factors, authenticities of QPOs for the whole sample. (2) We will search for and identify the QPOs on short-term timescales, investigate physical mechanisms of QPOs and correlations among QPOs in different wavebands and on diverse timescales. (3) In the field of QPO on short-term timescales, we will actively develop the research of periodicity searching algorithms based on the big data and deep learning technologies, and promote the research of the adaptive algorithms.

耀变体是活动星系核的一个重要子类，高光度、快速大幅度光变是其显著的观测特征。目前对耀变体光变的时序分析表明，仅有少量的源可能存在准周期振荡（QPO）现象。QPO可能和双黑洞、喷流的进动、吸积盘的不稳定性等有关，对耀变体的辐射机制和理论模型等研究有重要作用。然而，目前的研究主要集中在少数天体的中长时标范围，在样本大小、多波段QPO的相关性、短时标QPO、红噪声背景下的置信度分析等方面仍有所不足。项目的主要研究内容为：（1）QPO在Fermi、Swift、OVRO和SMARTS项目数据库的整体样本中的分布情况，QPO与红移、黑洞质量、多普勒因子等的相关性，样本层面QPO的真实性；（2）寻找和认证耀变体的短时标QPO，并分析不同波段、不同时标QPO的物理驱动机制及相关性；（3）在短时标QPO领域，积极开展基于大数据分析和深度学习技术的周期提取算法及自适应算法方面的研究。

耀变体的多波段光变可能存准周期振荡（QPO）现象。QPO现象的认证、理论解释以及光变周期提取算法的相互促进，有力地推动了耀变体研究领域的发展。耀变体的QPO研究对黑洞物理、喷流物理、天体辐射机制和宇宙高能伽马辐射等的研究有重要意义。本项目使用耀变体的多波段观测数据开展了大样本和部分耀变体QPO的认证和分析，获取了几个研究成果：1）在OT 081的射电4.8、8和14.5 GHz波段的光变曲线中发现了一个大小约为850天的QPO信号，可以用超大质量双黑洞模型和螺旋喷流模型进行解释；2）在PKS 1510-089射电4.8、8和14.5 GHz波段的光变曲线中发现了QPO存在的证据，在射电37 GHz波段的光变曲线中发现了一个大小约为1330天的QPO信号；3）在S5 0716+714 37 GHz波段的光变曲线中发现了一个大小约为1330天的QPO信号，发现S5 0716+714是研究引力波辐射的候选体；4）在MOJAVE数据库518个耀变体的大样本中发现了4个源存在QPO信号，且其置信度大于99%；5）发现ARIMA(7,0,6)模型可以很好地拟合S5 0716+714射电37 GHz波段光变曲线；6）在S5 0716+714和PKS 1510-089的伽马射线辐射中没有高置信度的QPO信号存在的证据。