发表机构
Shanghai Astronomical Observatory, Chinese Academy of Sciences; University of Chinese Academy of Sciences; Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso; Millennium Nucleus on Transversal Research and Technology to Explore Supermassive Black Holes (TITANS); Department of Astronomy, School of Physics, Peking University; Kavli Institute for Astronomy and Astrophysics, Peking University（中国科学院上海天文台; 中国科学院大学; 瓦尔帕莱索大学理学院物理与天文学研究所; 探索超大质量黑洞跨学科研究和技术千年核（TITANS）; 北京大学物理学院天文学系; 北京大学科维理天文与天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用ZTF数据系统研究IMBH候选体的INOV，发现常规PSF测光的表观INOV多为视宁度导致的伪信号，差分图像测光未检测到可靠INOV，ZTF单夜监测对低振幅INOV探测概率仅约1.2%，强调可靠测光方法的重要性。
AI 中文摘要
中等质量黑洞（IMBHs）为研究黑洞族群低质量端的吸积变异性提供了独特的观测窗口，然而它们的夜间内光学变异性（INOV）至今仍缺乏严格约束。我们利用兹威基瞬变巡天（ZTF）的高时间分辨率观测数据，对光学选样的IMBH候选体样本中的INOV开展了系统研究。在由1447个宽Hα选样的候选体构成的母样本中，我们识别出64个IMBH候选体（平均活动星系核贡献比$f_{\rm AGN}\backsimeq0.06$），并开展了163次夜间内监测。通过常规ZTF点扩散函数（PSF）拟合测光识别出的表观INOV信号，大多与视宁度相关的致密核成分和延展宿主星系成分的相对贡献变化有关，这类变化会模拟出本征的短时标变异性。相比之下，差分图像测光未检测到可靠的INOV。覆盖$\bigtriangleup t\backsimeq0.003$至1600天的整体结构函数显示，小部分源存在长期变异性，而夜间内时标下的本征变异性仍未被分辨。蒙特卡洛模拟进一步表明，类似ZTF的单夜监测对长期分析推断出的变异性振幅的INOV探测概率很低，仅约1.2%，探测概率主要由源亮度、AGN贡献比、本征变异性振幅和测光精度控制。这些结果表明，未检测到INOV并不意味着不存在快速吸积变异性，而可能反映了当前观测能力下低振幅信号的探测局限性。我们的发现强调了可靠测光方法对未来低质量吸积黑洞高时间分辨率变异性研究的重要性。
英文摘要
Intermediate-mass black holes (IMBHs) provide a unique regime for studying accretion variability at the low-mass end of the black hole population, yet their intranight optical variability (INOV) remains poorly constrained. We present a systematic investigation of INOV in an optically selected sample of IMBH candidates using high-cadence observations from the Zwicky Transient Facility (ZTF). From a parent sample of 1,447 broad H$α$-selected candidates, we identify 64 IMBH candidates (median $f_{\mathrm{AGN}}\sim0.06$) with 163 intranight monitoring sessions. Apparent INOV signals identified by conventional ZTF PSF-fit photometry are largely associated with seeing-dependent changes in the relative contributions of compact nuclear and extended host components, which can mimic intrinsic short-timescale variability. In contrast, no robust INOV is detected with difference-image analysis. An ensemble structure function spanning $Δt\sim0.003$--$1600$ days reveals long-term variability in a small subsample of sources, whereas intrinsic variability remains unresolved at intranight timescales. Monte Carlo simulations further show that ZTF-like single-night monitoring has a low INOV recovery probability ($\sim1.2%$) for the variability amplitudes inferred from the long-term analysis. The recovery probability is primarily controlled by source brightness, AGN contribution, intrinsic variability amplitude, and photometric precision. These results demonstrate that the absence of detected INOV does not imply the absence of rapid accretion variability, but can reflect the limited detectability of low-amplitude signals under current observing capabilities. Our findings highlight the importance of robust photometric methodologies for future high-cadence variability studies of low-mass accreting black holes.
Comments22 pages, 12 figures, submitted to ApJ. Comments are welcome
