The intra-night optical variability of the bright BL Lacertae object S5 0716+714

Abstract

Aims. We address the topic of the intra-night optical variability of the BL Lac object S5 0716+714. Methods. To this purpose a long-term observational campaign was carried out, from 1996 to 2003, which allowed the collection of a very large data set, containing 10 675 photometric measurements obtained in 102 nights. Results. The source brightness varied in a range of about 2 mag, although the majority of the observations were performed when it was in the range 13.0 < R < 13.75. Variability time scales were estimated from the rates of magnitude variation, which were found to have a distribution function well fitted by an exponential law with a mean value of 0.027 mag/h, corresponding to an e-folding time scale of the flux τ F = 37.6 h. The highest rates of magnitude variation were around 0.10-0.12 mag/h and lasted less than 2 h. These rates were observed only when the source had an R magnitude <13.4, but this finding cannot be considered significant because of the low statistical occurrence. The distribution of τ F has a well-defined modal value at 19 h. Assuming the recent estimate of the beaming factor δ ∼ 20, we derived a typical size of the emitting region of about 5 × 10 16 /(1 + z) cm. The possibility of searching for a possible correlation between the mean magnitude variation rate and the long-term changes in the velocity of the superluminal components in the jet is discussed.

The 72-h WEBT microvariability observation of blazar S5 0716 + 714 in 2009

“…Thus overall, the rise and decline rates are similar in this segment of light curve. Although the rates are different, the fact that the slopes for the rise and decline are the same agree with the results found by Villata et al (2000) and Montagni et al (2006).…”

“…He studied shots that had a delta function rise and exponential decline and was able to show that a random distribution of such shots yields a 1/ f power spectrum. The shot profiles studied by Lehto (1989) did not resemble the microvariability seen in 0716+714, but visual inspection of over 100 microvariability light curves between 1989 and 2009 (Montagni et al 2006;Humrickhouse & Webb 2008) led Webb et al (2010) to propose that the microvariability curves were indeed shots, but shots with a light curve profile given by Kirk et al (1998;hereafter KRM). KRM calculated the particle acceleration in the shock front for various magnetic field orientations and particle densities assuming a plane shock encounters a cylindrical density enhancement.…”

“…Wu et al (2007) used an objective prism set up to obtain truly simultaneous multicolor observations over several nights. Montagni et al (2006) monitored the source for microvariability between 1996 and 2003 finding the most rapid variations were on the order of 0.1 mag per hour over a period of two hours. They also found no difference between the rise and decline rates.…”

Multi-frequency VLBA study of the blazar S5 0716+714 during the active state in 2004

“…It is highly variable on timescales from hours to months across all observed wavelengths. Intra-day variability (IDV) has been detected in this blazar (Wagner et al 1996;Stalin et al 2006;Montagni et al 2006;Gupta et al 2009). The IDV in radio band is likely to be intrincic to the source because it is either reported to be correlated with the optical band (Wagner et al 1996) or its spectrum is not consistent with the scintillation (Fuhrmann et al 2008), which…”

New blazars from the cross-match of recent multi-frequency catalogs

“…Large-amplitude flux and spectral variability, on short time scales down to a few hours (i.e., Montagni et al 2006;Gupta et al 2008), characterize their emission. In the radio band they appear as core-dominated, flat spectrum sources.…”