Variability as a Probe of Supermassive Black Hole Accretion and Outflow

超大质量黑洞（SMBH）位于每个大质量星系的中心，包括人马座A* (Sgr A*)，这是我们银河系中约400万太阳质量的黑洞。这些质量的集合，密度如此之大，以至于光无法逃脱它们的引力，对宿主星系的形成和结构产生了深远的影响，尽管它们的结构比我们的太阳系还小。SMBHs通常通过吸积盘流入的气体和尘埃生长。尽管吸积盘的核心是黑暗的物质，但它有时会伴随着喷流或风，使整个宿主星系都黯然失色。由于这种动态结构的每一部分都随时间而变化，因此对吸积的SMBHs进行战略性的“时域”监测可以探测这种独特的强重力状态下控制物质的物理。****人马座A*是一个明亮的射电和亚毫米源，但由于其极低的吸积率和效率，在高能量时是微弱的。频繁的耀斑打破了人马座A*的平静；近红外耀斑大约每小时发生一次，而x射线耀斑大约每天上升一次，通常持续约一小时。近红外耀斑与同步辐射有关，但X射线耀斑的机制仍然不确定（尽管X射线通量达到10到400倍的静止）。可行的物理模型范围从小行星的潮汐破坏到磁重联。这些截然不同的机制促使观测者对爆发的时间和多波长特性施加更严格的限制。x射线耀斑也可以帮助我们将Sgr A*与质谱上的弱吸积黑洞联系起来。****我是四个经批准的钱德拉x射线天文台项目的负责人，其中几个项目与超大阵列和XMM牛顿天文台同时进行观测，以监测Sgr A*和寒冷，多尘的物体G2。在Haggard et al.（2015）中，我们将报道从人马座A*观测到的两个最大的x射线耀斑；其中我们解决了大尺度和小尺度的耀斑内变异性，在吸积流中探测耀斑的起源。在国家科学研究委员会发现基金的支持下，我将建立一个团队来分析和解释Sgr a *的专有和存档观测结果。我的小组将****(1)生成钱德拉x射线和VLA射电光曲线（和x射线光谱）的Sgr A*和G2；***(2)对Sgr A*的x射线耀斑进行详细的研究，包括耀斑之间和耀斑内部的变化；***(3)交叉相关和解释多波长数据（特别是结合吸积理论和红外/无线电数据）；和***(4)分析银河系中心x射线双星、恒星群和扩展发射。****通过国际合作，我们也有费米、斯威夫特、XMM、哈勃、斯皮策和VLBA对银河系中心的观测，这将加强这些研究。基于我们的发现，我们将积极开展联合观测计划，以获得任何额外的同步数据，以确定耀斑机制，并将其与LLAGN和XRB变化联系起来

A supermassive black hole (SMBH) resides at the heart of every massive galaxy, including Sagittarius A* (Sgr A*), the ~4 million solar-mass black hole in our Milky Way. These collections of mass, so dense that light cannot escape their gravitational pull, have a profound impact on the formation and structure of their host galaxies, despite being packed into structures smaller than our Solar System. SMBHs grow most often via gas and dust inflowing through an accretion disk. Despite the dark mass at its core, the accretion disk, and sometimes an associated jet or wind, can outshine the entire host galaxy. Since every part of this dynamic structure varies with time, strategic "time-domain" monitoring of accreting SMBHs can probe the physics governing matter in this unique strong-gravity regime.****Sgr A* is a bright radio and submm source, but is faint at high energies due to its extremely low accretion rate and efficiency. Frequent flares punctuate Sgr A*'s quiescence; in the near NIR flares occur approximately hourly, while X-ray flares rise about once per day and typically last about an hour. The NIR flares are associated with synchrotron emission, but the X-ray flare mechanism remains uncertain (despite X--ray fluxes reaching 10 to 400 × quiescence). Viable physical models range from the tidal disruption of asteroids to magnetic reconnection. These vastly different mechanisms motivate observers to place tighter constraints on the timing and multiwavelength properties of the outbursts. X-ray flares may also help us relate Sgr A* to weakly accreting black holes across the mass spectrum.****I am PI of four approved Chandra X-ray Observatory programs, several joint with simultaneous Very Large Array and XMM Newton observations, to monitor Sgr A* and the cold, dusty object G2. In Haggard et al. (2015) we will report the two largest X-ray flares ever observed from Sgr A*; in which we resolve large and small scale intra--flare variability, a probe of the flares' origin within the accretion flow. With NSERC Discovery Grant support, I will build a team to analyze and interpret proprietary and archival observations of Sgr A*. My group will****(1) generate Chandra X-ray and VLA radio light curves (and X-ray spectra) for Sgr A* and G2;***(2) perform detailed studies of Sgr A*'s X-ray flares, including inter- and intra-flare variability;***(3) cross-correlate and interpret the multiwavelength data (incorporating accretion theory and IR/radio data, in particular); and***(4) analyze Galactic Center X-ray binaries, stellar populations, and extended emission.****Through international collaborations we also have Fermi, Swift, XMM, Hubble, Spitzer, and VLBA observations of the Galactic Center, which will enhance these studies. Based on our findings, we will actively pursue joint observatory programs to obtain any additional simultaneous data required to identify the flare mechanism and to link it to LLAGN and XRB variability.**