Multi-colour optical variability of the blazar 3C 454.3 in 2007–2010

Abstract

Context. We present our optical multiband (B and R) observations of the blazar 3C 454.3, which were acquired over 30 nights from August 2007 to December 2010. Aims. We analyse our data to study the optical emission variability properties of 3C 454.3. Methods. The observations were carried out using both the 1 m EOS Telescope (EST) and the 0.8 m Tsinghua-NAOC Telescope (TNT) simultaneously in most nights at the Xinglong Observatory of National Astronomical Observatories, Chinese Academy of Sciences (NAOC). Both telescopes are equipped with the same type of Princeton Instrument CCD and standard Johnson-Cousin UBVRI filters. To reach a similar signal-to-noise ratio (S/N) in different bands with the same exposure time, observations using the larger diameter EST were carried out with B-band filter, while those of the smaller diameter TNT were carried out with R-band filter. Any time differences between the two telescopes were corrected using GPS. The typical sampling rate was one data point per minute, which is the highest time-resolution so far. Results. A multi-peak outburst was observed during November-December 2007, in addition to a later outburst during October 27-November 1, 2010. The brightest magnitudes for 3C 454.3 during our observations were B = 13.77 mag and R = 12.69 mag at JD = 2 454 436.0952 (December 1, 2007). One of the most striking events was detected on December 1, 2007, when a flux increase of about 0.67 mag occurred in 3.2 h. A colour analysis shows that the colour variability processes are apparently complex. A bluer-when-brighter trend, a redder-when-brighter trend (generally in faint states), and no significant colour variance were all detected during the outburst of November-December 2007. Furthermore, the kind of "saturation" effect in the B − R trend is not visible in the bright state (R < 14) during August 12-14, 2007. These trends may be due to the interactive contribution from the accretion disc and the jet components. Meanwhile, intra-night variability in B and R bands was found to be correlated, without any time delay exceeding one minute.

Intra-night optical multiband variability of BL Lacertae during the 2011 outburst

“…Our observations did not detect any noticeable time lags between the intra-night variations in the B and R bands, so that the individual measurements do not indicate a loop path. Similar results were reported by Zhai et al (2011) for the blazar 3C 454.3. However, the loop paths described by the nightly means may suggest that BL Lac has a spectral hysteresis in its inter-night variations (Wu et al 2007).…”

“…The results indicated that no measurable time delay longer than the exposure interval between B and R bands during the four nights. This coincidence of the B and R band variations suggests that the radiation in both wavebands may be similar in active states and arise from the same region in the jet (Zhai et al 2011). …”

“…The read-out noise and gain of the CCD were five electrons and 2.3 electrons/ADU, respectively. The entire CCD chip covers ∼11 × 11 arcmin 2 of the sky, equipped with standard Johnson-Cousin UBVRI filters in a filterwheel (Zhai et al 2011). Exposure times were well chosen to lead to a good compromise between high precision and high temporal density, and the range was 25 to 150 s in B band and 5-30 s in R band.…”

“…Schneider & Weiss 1987), etc. The shock-injet model suggests that the relativistic particle jets cause the IDV phenomenon even on the timescales of less than one hour (Gupta & Joshi 2005;Zhai et al 2011). The most rapid rate of change (as fast as 0.19 mag/h) was detected by Villata et al (2002).…”

Intra-night variability of the blazar CTA 102 during its 2012 and 2016 giant outbursts

“…In this paper, we concentrate on the multicolour intra-night variability of CTA 102 during its 2012 and 2016 maxima. So far, several objects have been multicolour (quasi)-simultaneously monitored on intranight time scales, among which S4 0954+65 (Papadakis et al 2004;Bachev et al 2016), 3C 454.3 (Bachev et al 2011Zhai et al 2011), BL Lacertae (Zhai & Wei 2012), S5 0716+714 (Stalin et al 2009;Wu et al 2012), etc. To the best of our knowledge, this is the first such study for CTA 102.…”