Tomoki Morokuma

Abstract: Time Domain Astronomy has been getting popular especially in optical astronomy, mainly using wide-field imaging instruments. Hyper Suprime-Cam (HSC) on the 8.2-m Subaru telescope currently has the best survey capability in terms of survey speed. We have been conducting transient surveys with Subaru/HSC in various time scales from minutes to years since its first light in 2014. I will summarize several main results from our transient surveys. In the latter part of my talk, I focus on one distant active galactic nucleus (AGN) showing a very large decline in brightness over 20 years. This object is interpreted as a rare phenomena in an AGN where its accretion activity has been almost shut down.