Minute-scale Rapid Variability of Mrk 501 by Multi-band Photometric Monitoring from 2010 to 2017

Abstract

Mrk 501 is one of our long-term photometric monitoring objects with the optical telescopes at Yunnan Astronomical Observatory (YAO). In this work, observations were performed from 2010 March 11 to 2017 June 7 in the BVRI bands. We detected minute-scale rapid variabilities in the optical multi-band light curves. Durations of these rapid variabilities are from 5 to 77 minutes. The minimal decay timescale is about 3 minutes (2.330 ± 1.572 minutes on 2012 May 22 and 3.172 ± 1.626 minutes on 2017 May 20). After subtracting the host-galaxy component, The minimal decay timescale was about 8 minutes on 2017 June 3, and the corresponding duration is about 10 minutes. This fast variability requires the strength of the co-moving magnetic field in the jet larger than 38.60 G (19.69 G for corrected results, with Doppler factor δD ∼ 3). The discrete correlation function (DCF) analysis between B and I band short-term light curves show significant correlated variability; however, no significant time lags are detected. The color–magnitude variation shows significant negative correlation on intranight timescales, which is due to the superposition of multiple components.