Abstract Details
| Name: sameer Affiliation: physical research laboratory Conference ID: ASI2016_767 Title : Decade long optical monitoring of Blazar 3C66A Authors and Co-Authors : K.S.Baliyan,Physical Research Laboratory Navpreet Kaur, Physical Research Laboratory S. Ganesh, Physical Research Laboratory Abstract Type : Poster Abstract Category : Extragalactic astronomy Abstract : Blazars are radio loud AGNs with their relativistic jets pointed close to line of sight of the observer boosting their emission due to relativistic beaming. They show rapid and strong variability spanning the entire electromagnetic spectrum, high and variable polarization in radio and optical regimes and dominant non thermal emission from radio to high energy gamma-rays. These also show long term variations with varying time scales. It would be interesting to see if the short term variations have any relationship with the long term trends. Keeping this in mind, we have been monitoring a set of blazars from Mt Abu IR Observatory (MIRO) for more than 10 years now. In this presentation, we would like to discuss this program, with specific study of BL Lac Object 3C66A. The monitoring of blazar 3C66A, from 2005 November 06 to 2015 October 23, in the BVRI broad bands using 1.2m telescope of MIRO was carried out using LN2 cooled CCD. Blazar 3C66A exhibited significant variations in optical flux on short and long term time scales. However it showed a IDV duty cycle of about 16% only. Our statistical study, using structure function, discrete correlation functions and L-S periodogram suggests time scales of intra- night variability from ~ 30 min to about 3.5 hours, and, in at least one case existence of quasi-perodic oscillations with a period of ~ 30 min. The IDV amplitudes in R-band were found to vary from 0.02 mag to as high as 1.1 mag. The typical rate of flux variation was estimated to be ~0.06 mag/hr in both the rising and falling phases. The shortest timescale of variation results in setting an upper limit of 8.1 x 10 14 cm for emitting region size and about 4.3 x 108 Msun as mass of black hole. The long-term study suggests a mild bluer-when- brighter behaviour, typical for blazars, with a large number of short term flares superimposed on the slowly varying brightness flux. The long-term study also gives an indication of a periodicity of about 2.48 years but large gaps in the data forbid us to state it confidently.It means that every 2.48 years, a major flare occurs in the jet, caused by, perhaps, fresh injection of plasma in the jet. Another interesting aspect of the long term study reveals, though not strong, larger intra-day variability amplitudes during the nights when the source is relatively fainter. Normally, one would expect high variability activity with larger amplitude of variation during the bright, flaring phases of the source when highly turbulent jet plasma is expected to interact with frequent shock formations leading to its rapid acceleration and subsequent radiative cooling. More data are required to arrive at a better analysis of the long term behavior of blazar 3C66A. |