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*），我们银河系中的400万太阳质量黑洞。这些质量的集合如此密集，以至于光无法逃脱它们的引力，对它们的宿主星系的形成和结构产生了深远的影响，尽管它们被包装成比我们太阳系更小的结构。SMBH的生长通常是通过气体和尘埃流入吸积盘。尽管在它的核心有黑暗的质量，吸积盘，有时还有相关的喷流或风，可以使整个宿主星系黯然失色。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SMBH的战略性“时域”监测可以探索在这种独特的强引力状态下控制物质的物理学。 Sgr A* 是一个明亮的射电和亚毫米波源，但由于其极低的吸积率和效率，在高能量下是微弱的。频繁的耀斑打断了Sgr A* 的平静;在近红外波段，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射线耀斑机制仍然不确定（尽管X射线通量达到10至400静止）。可行的物理模型从小行星的潮汐破裂到磁场重联。这些截然不同的机制促使观察者对爆发的时间和多波长特性进行更严格的限制。X射线耀斑也可以帮助我们将Sgr A* 与整个质谱中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PI，其中几个项目与超大型阵列和XMM牛顿观测同时进行，以监测Sgr A* 和寒冷的尘埃物体G2。在Haggard等人（2015）中，我们将报告从Sgr 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化，这是对耀斑在吸积流中起源的探测。在NSERC发现资助的支持下，我将建立一个团队来分析和解释Sgr A* 的专有和档案观测。我的团队将 (1)生成Sgr A* 和G2的钱德拉X射线和VLA射电光变曲线（和X射线光谱）; (2)对Sgr A* 的X射线耀斑进行详细的研究，包括耀斑间和耀斑内的变化; (3)对多波长数据进行相互关联和解释（特别是结合吸积理论和红外/无线电数据）; (4)分析银河系中心的X射线双星，恒星的人口，和扩展发射。 通过国际合作，我们还有费米，斯威夫特，XMM，哈勃，斯皮策和银河系中心的VLBA观测，这将加强这些研究。根据我们的发现，我们将积极开展联合观测计划，以获得确定耀斑机制所需的任何额外的同步数据，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.