Analysis of Optical Long-period Light Variation and Study of Color Index Variation in FSRQ 0208-512

Abstract

The observational data of optical B, V, and R bands of the Flat Spectral Radio Quasar (FRSQ) 0208-512 are collected from the Small and Moderate Aperture Research Telescope System (SMARTS) database. The data span nearly a decade from February 2008 to August 2017, which includes 627, 639, and 634 sets of data in the B, R, and V bands, respectively. The datasets are fully analyzed by the Weighted Wavelet Z Transform (WWZ) and the Monte-Carlo Simulation Lomb-Scargle Periodogram (LSP) method, the conclusions are as follows: (1) a 396 d period is obtained in all three optical bands, which is about 1.08 yr; (2) a positive correlation is found between the B-band magnitude (B) and the optical-band color index (B−V), namely the smaller the magnitude B the smaller the color index (B−V), this is the so called Bluer-When-Brighter; (3) using the 1.08 yr long-period light variation obtained from the 3 optical bands, the central black hole mass M is derived to be 0.12×106M⊙, and the corresponding radius of the radiation region is RM=1.052×108km, here M⊙ is the solar mass.