This proposal aims for taking optical spectra and imaging with Keck/LRIS of 8 drastically fading quasars (by a factor of >∼5 in flux) in rest-UV broad-band brightness over ∼10 years between the SDSS and HSC-SSP observing epochs. The selected quasars are the best candidates of so-called changing-look quasars in which AGN activity shuts down (or becomes obscured) for some reason in a short time scale. The ultimate goal of this proposal is to identify long-lasting shutting-down events in AGN, and to study in great detail what happens in this kind of rapid change in accretion state. With the proposed observations, we mainly measure the flux of the remaining broad component of CIV, CIII], and MgII emission lines (depending on the target redshifts). The new data for these fading quasars after the fading, combined with the previous data before the fading, enable us to achieve the above purposes as well as examination of whether or not obscuration of the accretion disk happens.
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