Optical Monitoring of BL Lacertae Object S5 0716+714 with a Novel Multipeak Interference Filter

Abstract

We at first introduce a novel photometric system, which consists of a Schmidt telescope, an objective prism, a CCD camera, and, especially, a multi-peak interference filter. The multi-peak interference filter enables light in multi passbands to pass through it simultaneously. The light in different passbands is differentially refracted by the objective prism and is focused on the CCD separately, so we have multi "images" for each object on the CCD frames. This system enables us to monitor blazars exactly simultaneously in multi wavebands on a single telescope, and to accurately trace the color change during the variation. We used this novel system to monitor the BL Lacertae object S5 0716+714 during 2006 January and February and achieved a very high temporal resolution. The object was very bright and very active during this period. Two strong flares were observed, with variation amplitudes of about 0.8 and 0.6 mags in the V ′ band, respectively. Strong bluer-when-brighter correlations were found for both internight and intranight variations. No apparent time lag was observed between the V ′and R ′ -band variations, and the observed bluer-when-brighter chromatism may be mainly attributed to the larger variation amplitude at shorter wavelength. In addition to the bluer-when-brighter trend, the object also showed a bluer color when it was more active. The observed variability and its color behaviors are consistent with the shock-in-jet model.

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

“…14, fast flares exhibited a strong bluerwhen-brighter (BWB) trend in inter-night variation (bottom panel), but it is messy in the intra-night variation (top panel). This is consistent with the common trend for blazars when they are in active states (Gu et al 2006;Wu et al 2007). According to Hu et al (2006), the colour results are not strongly affected by the host galaxy, since it has similar colours to the AGN.…”

“…Wu et al (2007) mention that, if the variation at high frequency precedes that at low frequency, a BWB chromatism can be observed. If the fluxes at different frequencies vary simultaneously, but the amplitude is greater at the higher frequency than at the lower one, a BWB chromatism can also be observed.…”

“…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 intra-night variations in active states can be determined by a "strongly-chromatic" short-term component, which may be caused by intrinsic phenomena, such as particle acceleration from shock-in-jet events (Villata et al 2004).…”

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

“…When the source is brighter than R ∼ 14 mag, a bluer-when-brighter trend is detected in our observation. This is consistent with the common trend for blazars, which usually have a bluer-when-brighter chromatism when they are in active states (Gu et al 2006;Wu et al 2007). The high and fast INOV in active states can be determined by a "stronglychromatic" short-term component, which may be caused by intrinsic phenomena, such as particle acceleration from shock-injet events .…”

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

“…Wu et al (2005) performed nearly simultaneous multi-frequency monitoring over a span of seven days and time series analysis of their microvariability observations yielded no repeatable periodicities common in the light curves. 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.…”