Simultaneous MITSuMEg′R_CI_Cmonitoring of S5 0716+714

Abstract

We present the results of our intra‐night optical flux monitoring observations of S5 0716+714 done simultaneously in g′, RC and IC filters. The observations were done using the Multicolor Imaging Telescopes for Survey and Monstrous Explosions instrument on the 50 cm telescope at the Okayama Astrophysical Observatory over 30 nights between 2008 March 11 and 2008 May 8. Of these 30 nights, 22 nights have continuous (without any break) observations with the duration ranging from 1 to 6 h and hence were considered for intra‐night optical variability (INOV). The remaining eight nights have continuous observations of less than 1 h and hence were considered only for long‐term optical variability. In total, we have 4888 data points which were simultaneous in g′, RC and IC filters. Of the 22 nights considered for INOV, the object showed flux variability on 19 nights with the amplitude of variability in the IC band ranging from ∼4 per cent to ∼55 per cent. The duty cycle for INOV was thus found to be 83 per cent. A good correlation between the light curves in all the three bands was found. No time lag between different bands was noticed on most of the nights, except for three nights where the variation in g′ was found to lead that of the IC band by 0.3 to 1.5 h. On inter‐night time‐scales, no lag was found between g′ and IC bands. On inter‐night time‐scales as well as intra‐night time‐scales on most of the nights, the amplitude of variability was found to increase towards shorter wavelengths. The flux variations in the different bands were not achromatic, with the blazar tending to become bluer when brighter on both inter‐night and intra‐night time‐scales, and this might be attributed to the larger amplitude variation at shorter wavelengths. A clear periodic variation of 3.3 h was found on 2008 April 1 and a hint for another possible periodic variability of 4 h was found on 2008 March 31. During our 30 days of observations over a 2 month period, the source has varied with an amplitude of variability as large as ∼80 per cent.

The nature of the intra-night optical variability in blazars

“…This blazar has been a target of a number of intra‐night monitoring campaigns. Practically all studies, for example Sagar, Gopal‐Krishna & Mohan (), Nesci, Massaro & Montagni (), Wu et al (), Gu et al (), Montagni et al (), Pollock, Webb & Azarnia (), Gupta et al (), Stalin et al (), Poon, Fan & Fu (), Carini, Walters & Hopper () and Rani et al (), report significant variations, which can typically be described as smooth fluctuations or a sequence of trends, often abruptly changing direction. Some reports even imply the presence of very rapid (tenths of a magnitude) changes within a few minutes (Fan et al ) and/or quasi‐periodic oscillations (Gupta, Srivastava & Wiita ; Rani et al ) on a ∼15‐min time‐scale.…”

The Outburst of the Blazar S5 0716+71 in 2011 October: Shock in a Helical Jet

“…The redshift determinations (z ≈ 0.3) are based on measurements of the size of a marginally detected host galaxy and a location near three galaxies with redshifts of 0.26 (Bychkova et al 2006;Nilsson et al 2008). Optical variability has been studied by many teams; the blazar exhibits persistent activity on both long and short (intraday) timescales, as shown by, e.g., Wagner et al (1996), Ghisellini et al (1997), Hagen-Thorn et al (2006), and Stalin et al (2006Stalin et al ( , 2009, and by the results of several WEBT campaigns (Raiteri et al 2003;Ostorero et al 2006;Villata et al 2008;Chen et al 2008). Violent polarimetric variability of S5 0716+71, among other blazars, was studied by Ikejiri et al (2011).…”

Optical Quasi-periodic Oscillation of the BL Lacertae Object S5 0716+714 during the Faint State

“…Quirrenbach et al (1991) found that the blazar has a possible QPO on the timescale of ∼ 1 day. Stalin et al (2009) presented the results of intra-night optical monitoring of S5 0716+714 who gave evidences for possible quasi-periods ranging from 0.9 to 4.3 h. Gupta et al (2009) found high probabilities (from 95% to >99%) quasi-periodic IDV timescales between ∼25 and ∼ 73 minutes (min), which is the first good evidence for quasi-periodic components in the optical intra-day variable light curves of any blazars. Using several different techniques, Rani et al (2010) discovered an approximately 15 min quasi-period at a > 3σ confidence level for S5 0716+714.…”