The physical mechanism for two rapid changing-look AGNs: SDSS J0225+0030 and SDSS J1723+5504

Abstract

SDSS J0225+0030 and SDSS J1723+5504 are two turn-on changing-look active galactic nuclei (CL AGNs) with transition timescales shorter than one year. Such short timescales pose a challenge for the current physical models of CL AGNs. We investigate this issue by exploring two possible mechanisms in this work. First, we consider the effect of a large-scale magnetic field on the viscous timescale, which can increase the radial velocity of the accretion disk. However, it is found that the timescale given by this model remains significantly longer than one year. Second, we improve the model of \citet{2025ApJ...988..207L}, which proposed that the inner thin disk in the bright state may form through the collapse of an advection-dominated accretion flow (ADAF) in the dim state, rather than being replaced by the advection of the outer thin disk. We re-estimate the transition radius $R_{\rm tr}$ between the inner ADAF and the outer thin disk through the observed variation of optical flux between the bright state and dim state. It is found that $R_{\rm tr}$ can be significantly reduced in these two objects owing to the lower gas temperature in the inner disk region (of the order of $10^4$ K), resulting from their large black hole masses ($\sim 10^9 M_{\odot}$) and small Eddington-scaled mass accretion rates ($\sim 0.01$). The cooling timescales given by the revised model in these two objects are found to be comparable to the observed transition timescales.