On the characterization of multi-wavelength flaring activity in Blazars; a case of historical flare in S5 0716+714

Blazars are well known to show very frequent variations with time-scales ranging from less

than an hour to few years, over the entire EM spectrum. The understanding of blazar

emission and the corresponding physical processes, has been completely changed with the

six years of unprecedented contribution by Fermi, a space-based γ-ray observatory, launched

in June, 2008. The high energy (MeV-GeV) radiative output is supposed to be attributed to

the inverse Compton scattering (IC) of low energy seed photons. The origin of seed photons

may be either the synchrotron emission in the jet or the external photons form

disk/torus/line-regions etc. Generally, the high energy flares in blazars are associated with

the formation of shock in the jet. However, the origin and nature of the shock and role of

magnetic field are not yet well established. Simultaneous study of observables (lightcurves,

SEDs and polarization), corresponding to a particular flaring activity, is essential in order to

understand the underlying mechanism. 

BL Lac object S5 0716+714 (z~0.31), a highly variable blazar, was extensively observed

during its historical brightened state during the early 2015. A high cadence polarization

observations covering the complete duration were also performed. The dual γ-ray flares,

seen within 3 days apart, were witnessed to be closely followed at X-rays and UV/optical

bands. A significant variations in degree of polarization (DP) and two successive rotation of

180o in position angle (PA) was also observed during the second flare. We modelled the

observed lightcurves, SED and polarization (DP & PA) using the Helical Magnetic Field

Model (HMFM), proposed by Haocheng, et al., (2015), to understand the underlying physics

In this seminar, I will summarize the observations and results obtained from this study.