A Reverberation Mapping Study of a Highly Variable Active Galactic Nucleus 6dFGS gJ022550.0-060145

We use LCOGT observations (MJD 59434-59600) with a total exposure time of similar or equal to 50 hr and a median cadence of 0.5 day to measure the interband time delays (with respect to u) in the g, r, and i continua of a highly variable active galactic nucleus (AGN), 6dFGS gJ022550.0-060145. We also calculate the expected time delays of the X-ray reprocessing of a static Shakura-Sunyaev disk according to the source's luminosity and virial black hole mass; the two parameters are measured from the optical spectrum of our spectroscopic observation via the Lijiang 2.4 m telescope. It is found that the ratio of the measured time delays to the predicted ones is 2.6-1.3+1.3 . With optical light curves (MJD 53650-59880) from our new LCOGT and archival Zwicky Transient Facility, Pan-STARRS, Catalina Sky Survey, and ATLAS observations, and Wide-field Infrared Survey Explorer (WISE) data (MJD 55214-59055), we also measured time delays between WISE W1/W2 and the optical emission. W1 and W2 have time delays (with respect to V), 9.6-1.6+2.9x102 days and 1.18-0.10+0.13x103 days in the rest frame, respectively; hence, the dusty torus of 6dFGS gJ022550.0-060145 should be compact. The time delays of the W1 and W2 bands are higher than the dusty torus size-luminosity relationship of Lyu et al. By comparing the infrared and optical variability amplitude, we find that the dust-covering factors of the W1 and W2 emission regions are 0.7 and 0.6, respectively. Future broad emission-line reverberation mapping of this target and the results of this work enable us to determine the sizes of the AGN main components simultaneously.