Optical monitoring and IDV analysis of the blazars S50716+714 and 3C 273

S50716+714 and 3C 273 are frequently studied blazars,which show obvious optical variabilities with different timescales.Using the 1.0 m telescope at the Yunnan Observatory,we monitored the two sources.For S50716+714,we report 990 observations during the monitoring duration from JD 2458536 to JD 2458540.For 3C 273,there are 884 observations during the monitoring duration from JD 2458539 to JD2458542.Based on those observations,we obtain the following results.(1)For S50716+714,there lie intraday optical variabilities(IDVs),with timescales from 0.31 hours to 2.64 hours.For 3C 273,it is possible that there lie IDVs,with timescales from 0.36 hours to 0.49 hours.(2)The time delay of S50716+714 isτRI=3.46 min between R and I bands,and the time delay of 3C273 isτIV=6.42 min between I and V bands.(3)We find that,for S50716+714,there lies a suspected intra-day period,P≈185.78 min;for 3C273,there lie intra-day periods,which are about~60 min and~80 min.

Constraining evolution of magnetic field strength in the dissipation region of two BL Lac objects

With the assumption that the optical variability timescale is dominated by the cooling time of the synchrotron process for BL Lac objects,we estimate time dependent magnetic field strength of the emission region for two BL Lac objects.The average magnetic field strengths are consistent with those estimated from core shift measurement and spectral energy distribution modelling.Variation of magnetic field strength in the dissipation region is discovered.Variability of flux and magnetic field strength shows no clear correlation,which indicates the variation of magnetic field is not the dominant reason of the variability origin.The evolution of magnetic field strength can provide another approach to constrain the energy dissipation mechanism in jets.

New statistical results on the optical IDV data of BL Lac S5 0716+714

This paper reports on the statistical behavior of the optical Intraday Variability of BL Lac S5 0716＋714. Available Intraday Variability data in the opti- cal are tested to see whether or not the magnitude is lognormally distributed. Our results consistently indicate that this is not the case. This is in agreement with a previ- ous discussion about data for the same object but in a different observational period. Simultaneously, the spectral slope of the light curves is calculated. The implications of these findings on models that describe both the location and source of Intraday Variability are presented.

Evolution of optical spectral index and variability properties of S5 0716+714

We analyze the spectral variability and spectral evolution in the optical en- ergy region by using multiband （BVRI） optical observations of S5 0716＋714 spanning 1994 to 2005. The spectrum hardens when the source becomes brighter, which is con- sistent with general BL Lac objects. The spectral evolution parameter implies that the spectral variability is small in optical bands over 10 years. A simple model represent- ing the variability of a synchrotron component can explain the spectral changes. In addition, we employ the z-transformed discrete correlation function （ZDCF） to ana- lyze the optical multiband flux correlation. The long-term light curve behavior reveals that the variability time scales are 3.5 yr in the B-band, 3.3 yr in the V-band, 3.4 yr in the R-band and 3.5 yr in the/-band. The time lags between any two optical bands were not found when considering statistical errors.

The long-term optical behavior of BL Lac object S5 0716+714

BL Lac object S5 0716+714 is a well-studied object.In this paper,the available optical(BVRI) data of this source are compiled,and the B-,V-,R-and I-band light curves are constructed.Each of them is analyzed by means of the discrete correlation function(DCF) method,the structure function(SF) method and the z-transformed discrete correlation function(ZDCF) method.The results imply that there is a possible periodic variation of 1211 days in each passband light curve.The source varies violently and complicatedly,and exhibits a brightening trend in the light curves.