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 δ D ∼ 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.

Photometric Monitoring of Blazar 3C 66A with the Yunnan University Astronomical Observatory 1 m Telescope

“…These timescales were consistent with the results of ΔT = 23.18 − 344.02 minutes (with Amp = 13.2%-92.8%) by Fan et al (2018) and ΔT = 10-32 minutes (with ΔB = 0 by Xie et al (1992). Considering that the non-thermal radiation in the optical band is dominated by synchrotron radiation, we can estimate the strength of the magnetic field as Zeng et al (2018Zeng et al ( , 2019, Yan et al (2018). The radiation cooling timescale (in the observer frame) of typical particles emitting synchrotron radiation can be defined as (Chiaberge & Ghisellini 1999):…”

“…4 Aperture photometry radii of the source and comparison stars are performed with the same value in each frame, which is determined by the FWHM of the source. As in our previous work, we concentrate on an aperture radius of about 1.5 FWHM for our analysis, which always provides the best signal-to-noise ratio (S/N) (Zeng et al 2017(Zeng et al , 2018(Zeng et al , 2019. We used the three comparison stars, star "2," star "3" and star "5" listed in Table 1, to obtain magnitudes for 3C 66A, and then calculated the average and corresponding standard deviation as the magnitude of 3C 66A in each photometric observation.…”