Optical Monitoring and Spectral Analysis of OJ 287

Abstract We present a comprehensive multiband optical monitoring and spectral analysis of the blazar OJ 287, conducted using the 1.26 m National Astronomical Observatory–Guangzhou University Infrared/Optical telescope (NGT). During an intensive 17 day observational campaign from 2022 December to 2023 January, we obtained 2716 high-quality photometric observations (929 in the g band, 887 in the r band, and 900 in the i band). The data reveal significant variability across all bands. Our main findings are as follows. (1) Significant magnitude variations were detected: Δ m g = 0.945 ± 0.048 mag ( g band), Δ m r = 0.648 ± 0.023 mag ( r band), and Δ m i = 0.945 ± 0.051 mag ( i band). (2) Numerous intraday variability (IDV) events were identified, with characteristic parameters (Δ m , Δ T , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>V</mml:mi> <mml:mi>R</mml:mi> <mml:mo>=</mml:mo> <mml:mfrac> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>m</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>T</mml:mi> </mml:mrow> </mml:mfrac> </mml:math> ) showing consistent patterns between the g and r bands but distinct behavior in the i band. (3) Successful modeling of intraday light curves using a multi-Gaussian function, yielding brightening ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>b</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ) and dimming ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ) timescales, and revealing an average peak separation of Δ Tc = 42.96 ± 0.99 minutes that appears to be frequency independent. (4) Development of a novel radiation framework suggesting that the observed IDV phenomena originate from multiple components—with the frequency-independent variations attributable to the central black hole, while frequency-dependent variations stem from jet and accretion disk processes.