Origin of Black Hole Short-Term Variability Investigated by the High-Speed Photometry System

黑洞物体的辐射表现出剧烈的活动。本项目旨在观测时间分辨率小于0.1秒的短期光变，以阐明其潜在的物理机制。通过三年的研究，我们获得了以下成果：1)高速测光系统的构建和观测通过使用CCD相机（e2v公司生产的CCD87芯片），我们可以拍摄33张照片/秒，我们构建了高速测光系统。该系统安装在东广岛天文台1.5米（直径）的“Kanata”望远镜上，用于观测一个原型黑洞Cygnus X-1。观测是成功的，我们发现了一种持续时间小于1秒的新型耀斑。2)模拟磁流体动力学（MHD）流动的短期变化。我们从一个带极向磁场的环面开始进行了全球的MHD模拟。然后，环形磁场在中心周围产生并积累，产生膨胀的磁结构（磁塔），从而驱动强质量和磁场流出（射流）。我们还根据模拟数据计算了辐射光谱，发现了光学光源的短期变化。3)一个简单的黑洞可变性模型我们提出了一个新的黑洞物体可变性元胞自动机模型。描述模型计算过程的元胞自动机规则以感应方程为基础，包括磁场波动输入和磁能以磁重联形式耗散两个过程。该模型能较好地再现黑洞变异性的基本观测特征，如非周期波动光曲线、1/f型波动功率谱、对数正态通量分布等。这一成功有力地表明磁场是产生黑洞可变性的根源。

Black hole objects show violent activities in their radiation. The aim of this project is to observe short-term optical variability with the time resolution of less than 0.1 sec so as to clarify its underlying physical mechanism. Through three-year research, we have obtained the following results :1)Construction of the high-speed photometry system and observationsBy using the CCD camera (CCD87 chip made by e2v co.), which enables us to take 33 pictures/sec, we have constructed a high-speed photometry system. This system was attached to the 1.5m (diameter) "Kanata" telescope at the Higashi-Hiroshima Observatory and was used to observe a prototype black hole, Cygnus X-1. The observations was successful and we found a new type of flares with duration less than a sec.2)Short-term variations from simulated magnetohydrodynamical (MHD) flowWe have performed global, MHD simulations starting with a torus threaded with poloidal magnetic fields. Then, the toroidal magnetic fields are created and accumulated around the center, producing an inflated magnetic structure (magnetic tower), which drives strong mass and magnetic field outflows (jets). We also calculated radiation spectra based on the simulation data, finding short-term variability in optical lights.3)A simple model of black hole variabilityWe proposed a new cellular-automaton model for variability of black-hole objects. The cellular-automaton rule which describes the procedure of model calculations is based on the induction equation and consists with two processes: input of fluctuation in the magnetic field and dissipation of magnetic energy in the form of magnetic reconnection. This model can well reproduce the basic observational features of the black-hole variability, such as aperiodic fluctuation light curves, 1/f-type fluctuation power spectra, and lognormal flux distribution. The success strongly indicates magnetic fields being the origin of producing black-hole variability.