Abstract Details
| Name: Sunil Chandra Affiliation: PRL Ahmedabad, *currently at TIFR Conference ID: ASI2015_475 Title : Multi-wavelength Study of Variability in Blazars Authors and Co-Authors : Supervisor: Prof. K. S. Baliyan (Physical Research Laboratory, Ahmedabad) Abstract Type : Oral Abstract Category : Thesis Abstract : Active Galactic Nuclei (AGNs) are centers of galaxy, very compact in size but emitting huge energy, sometimes more than hundred times the total energy emitted by a normal galaxy. The mechanism of energy generation is understood to be accretion of mater onto a supermassive black hole ($10^6$ - $10^9$ $M_{\odot}$) through accretion disk. Most of them have jets of magnetized plasma moving at relativistic speed perpendicular to the disk. In a sub-class known as blazars, emission is dominated by the non-thermal radiation from the jet, directed at small angles ($\leq 15^{\circ}$) to the line of sight, ranging from radio to $\gamma$-rays. However, the exact structure of the jet, its origin, acceleration, collimation and the physical mechanisms behind such huge energy output are not clearly understood. The central energy source is too compact to be resolvable by any present day, and even any new facility in near future. However, the variability in flux and polarization, the defining property of blazars, provides one of the important tools to probe the inner regions of AGNs. In the present work we have used variability in multi-frequency flux and optical polarization for several blazars. Optical photometric and polarimetry obervations for more than seven years carried out from Mt Abu Observatory as well as data at UV, X-ray from Swift and high energy $\gamma$-ray from Fermi space observatory are used to explore short and long-term variations and their behaviour at various wavelengths. Shortest time scale variation at a particular wavelength provides information about the size of the emission region. Study of polarization is used to understand the extent of magnetic fields in the emission region. The intra- and inter-night variations in blazar S5 716+714 are used to determine fastest rate of variation and size of the emission region which is very compact ($\sim 10^{15}$ cm). Long term study of the source is used to determine duty cycle of variation which is very high (84 \%). Bluer when brighter nature of flux variations indicates to be shock-in-jet model describing the generation of emission. The work also describes the statistical study on the nature of polarization in blazars and its application in classifying the same. We propose source CGRaBS J0211+1051 to be an LBL based on this and confirm the status by carrying out multiwavelngth study for spectral energy distribution (SED). A detailed study of source PKS 1510-089 using multiwavelength data is made and reasons behind the generation of several outbursts and flares is discussed. The thesis also reports several statistical methods developed/used by me in this study. |