Date : 7/6 (Wed) [15:00 - 17:00] @ F313
Speaker: Prof. Hiroshi Nagai (National Astronomical Observatory of Japan)
Title : Ultra High Resolution Observation of Gamma-ray-loud Radio Galaxy 3C 84 with VLBI
Abstract: Relativistic jets emanating from SMBHs are one of the primary targets of high energy astrophysics. VLBI is a unique tool to provide very high angular resolution, which allows to resolve the innermost region of relativistic jets where the acceleration, collimation, and production of high energy particles are took place. Due to its brightness and proximity, 3C84 (NGC1275) is one of the best-studied radio galaxies in history. The VLBI observations revealed that a recent increased activity in radio bands originated in the restarted jet activity starting in about 2005 (Nagai et al. 2010). The restarted jet is resolved in the transverse direction and found to be limb brightened (Nagai et al. 2014) as also seen in M87 and other nearby radio galaxies. In 1990s, the jet limb-brightening was not observed even with the observations with a similar spatial resolution and sensitivity (Dhawan et al. 1997). The jet morphology was rather ridge brightening. This change in the jet morphology shows an interesting agreement with the gamma-ray flux increase, i.e., the gamma-ray flux in the 1990s was at least 10 times lower than the current one. In Nagai et al. (2014), we proposed that the change from ridge brightening to limb brightening may be attributed to a change in the transverse velocity structure on the basis of a “spine-sheath” scenario. In this talk, I will review these results and introduce the prospects for upcoming millimeter VLBI observation (PI: H. Nagai) with a possible inclusion of ALMA. I also briefly mention an ongoing work with Fujita-san, as well as a very fresh result from ALMA Cycle 3 observation of another radio galaxy Cen A.

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