Speaker
Description
The magnetic fields surrounding supermassive black holes (SMBHs) are crucial to high-energy phenomena such as the initiation of relativistic jets and the formation of hot accretion disk corona that radiates strong X-rays. Various observations have been attempted to assess magnetic fields at the cores of mass-accreting SMBHs (active galactic nuclei; AGNs), but details remain unclear at a scale of tens of Schwarzschild radii (R_s). Here we report the discovery of a rapid flare of millimeter continuum emission from the nearby radio-quiet AGN of the Circinus galaxy. The time-scale of this flare is as short as 3 minutes, corresponding to a source size (radius) of about 12 R_s or less, consistent with the expected spatial scale of the hot corona. The high angular resolution of the data (approximately 1 parsec) and the spectral index analysis enabled to identify the responsible physical mechanism of this flare as coronal synchrotron radiation. We estimated the magnetic field strength as approximately 115 Gauss or higher, which is thousands to millions of times greater than the typical magnetic field strength in star-forming regions of our Galaxy, and is comparable to the values found in general relativistic magneto-hydrodynamic simulations of AGN accretion disk. Our study demonstrates that time-decomposition of high-resolution interferometric data serves as a unique tool to unveil magnetic activities around SMBHs.
