Variability as a Probe of Supermassive Black Hole Accretion and Outflow

超大质量黑洞(SMBH)存在于每个大质量星系的中心，包括射手座A*(SgrA*)，这是我们银河系中约400万个太阳质量的黑洞。这些质量聚集的密度如此之大，以至于光无法逃脱其引力的吸引，尽管这些聚集的质量聚集在比我们太阳系更小的结构中，但它们对其宿主星系的形成和结构有着深远的影响。SMBH最常见的生长方式是气体和尘埃通过吸积盘流入。尽管其核心有黑暗的质量，但吸积盘，有时还有相关的喷流或风，可以让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，对吸积的SMBH进行战略性的“时间域”监测可以探索这一独特的强引力区域中的物理支配物质。 SgrA*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，在高能时很弱。在近红外耀斑中，S星云处于静止状态；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，通常持续一个小时左右。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到400倍的静止状态)。可行的物理模型包括从小行星的潮汐分裂到磁重联。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施加更严格的限制。X射线耀斑也可能帮助我们将Sgr A*与整个质谱线上微弱增长的黑洞联系起来。 我是四个批准的钱德拉X射线天文台项目的PI，其中几个项目与同时进行的甚大阵列和XMM牛顿观测相结合，以监测SgrA*和寒冷的尘埃天体G2。在Haggard等人中。(2015)我们将报道从SGR A*观测到的两个最大的X射线耀斑；在这两个耀斑中，我们解决了大尺度和小尺度的耀斑内部可变性，这是一个探测耀斑在吸积流中起源的探测器。在NSERC Discovery Grant的支持下，我将建立一个团队来分析和解释对SGR A*的专有和档案观察。我的团队会 (1)生成SgrA*和G2的Chandra X射线和VLA射电光曲线(和X射线谱)； (2)对S耀斑进行了详细的研究，包括耀斑间和耀斑内的变化； (3)相互关联和解释多波长数据(特别是结合吸积理论和红外/无线电数据)； (4)分析了银河系中心X射线双星、恒星群和延展发射。 通过国际合作，我们还对银河系中心进行了费米、斯威夫特、XMM、哈勃、斯皮策和VLBA的观测，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，以获得识别耀斑机制所需的任何额外同步数据，并将其与LLAGN和XRB变率联系起来。

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.