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Dr. Krishna Mohana A
Date and Time of Talk
Online Zoom Talk

Blazars are a class of active galaxies whose multi-band emission is dominated by non-thermal radiation
originating from their relativistic jet pointing towards Earth. They exhibit extreme variations ranging from all the
time-scale from minutes to years across the electromagnetic band. Considering the time-scale of the observed
flux variation, the variability can be classified as short-term (time-scale of minutes to hours to days to weeks) and
long-term variability (variations with months to years time-scale). My primary research interests lie in understanding
the blazar emission processes responsible for such observed variabilities using multi-band spectral and timing studies.
In this talk, I will present the results of our recent work on radio variability of the blazar 3C 279. More than a decade of
radio data were collected at seven different frequencies ranging from 2 GHz to 230 GHz. The multi-band radio light curves
show variations in flux, with the prominent flare features appearing first at higher-frequency and later in lower-frequency bands.
This behavior is quantified by cross-correlation analysis, which finds that the emission at lower-frequency bands lags that at
higher-frequency bands. We discuss these flux variations in conjunction with the evolution of bright moving knots seen in
multi-epoch VLBA maps to suggest possible physical changes in the jet that can explain the observational results. Some of the
variations are consistent with the predictions of shock models, while others are better explained by a changing Doppler beaming
factor as the knot trajectory bends slightly, given a small viewing angle to the jet.  I will also discuss the results of our ongoing
works to understand the blazar variability via multi-band spectral study.

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Dr. Krishna Mohana is a postdoctoral fellow (RA-I) at ARIES. He works in the field of active galaxies to understand their
emission processes using multi-wavelength spectral and timing studies. For his research, he uses multi-wavelength
observations (gamma-ray to radio) from various ground and space-based observatories (Fermi-LAT, Swift-BAT; XRT; UVOT, AstroSat, etc.)
and carries out temporal, spectral, and associated theoretical modeling to identify the possible physical mechanism for the observed emission.


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