B and I-band optical micro-variability observations of the BL Lac objects S5 2007+777 and 3C 371

Abstract

We have observed S5 2007+777 and 3C 371 in the B and I bands for 13 and 8 nights, respectively, during various observing runs in 2001, 2002 and 2004. The observations resulted in almost evenly sampled light curves, 6−9 h long. We do not detect any flares within the observed light curves, but we do observe small amplitude, significant variations, in both bands, on time scales of hours and days. The average variability amplitude on time scales of minutes/hours is ∼2.5% and ∼1−1.5% in the case of S5 2007+777 and 3C 371, respectively. The average amplitudes increase to ∼ 5−12% and ∼ 4−6%, respectively, on time scales of days. We find that the B and I band variations are highly correlated, on both short and long time scales. During the 2004 observations, which resulted in the longest light curves, we observe two well defined flux-decay and rising trends in the light curves of both objects. When the flux decays, we observe significant delays, with the B band flux decaying faster than the flux in the I band. As a result, we also observe significant, flux related spectral variations as well. The flux-spectral relation is rather complicated, with loop-like structures forming during the flux evolution. The presence of spectral variations imply that the observed variability is not caused by geometric effects. On the other hand, our results are fully consistent with the hypothesis that the observed variations are caused by perturbations which affect different regions in the jet of the sources.

Simultaneous optical monitoring of BL Lacertae object S5 0716+714 with high temporal resolution

“…Dai et al (2013) found an anticlockwise loop in intra-day color behavior of S5 0716+714. Xilouris et al (2006) have reported the similar pattern in optical band. In other regime like gamma-ray and X-ray, the loop path has been reported frequently (e.g.…”

Multi band optical micro variability of BL Lac objects

“…Our main aim is to study the intra-night flux and energy spectral variations over a period of 3 nights in 2001. The quality of the light curves is similar to those presented by Xilouris et al (2006) in the case of S5 2007+777 and 3C 371.…”

“…In order to detect weak fluctuations we have performed aperture photometry by intergrading counts within a circular aperture of 7.5 arcsec centered on the objects Standard stars from Landolt (1992) were observed during the nights of 5, 6 October 2001 and calibration of 5field stars close to the objects (and subsequently of the sources) to the standard system was made, using DAOPHOT. The calibrated magnitudes of the sources were corrected for galactic reddening using the values of A B =0.269, A R =0.166 and A I =0.120 for PKS 2254+074 and A B =0.214, A R =0.133, A I =0.096 for S5 1803+784, converted into flux and corrected for the contribution of the host galaxy to the measured flux in each band as described in Xilouris et al (2006). The subtraction of the host galaxy contribution was not possible in the case of S5 1803+784 since it was unresolved in Pursimo et al (2002).…”

Program and Results of Investigations Rapid Variability of the BL Lac Object 3C 371 in Radio and Optical Ranges

“…In newer optical observations (filters B, I), it was confirmed that 3C 371 has significant low-amplitude variability on a time scale from several hours to several days. Moreover, there is a strong correlation between the B and I bands on short and long time scales [24].…”