Astronomy & Astrophysics Division Seminar
Title : Time-Dependent Modeling of Extreme Gamma-Ray Flares of Blazars
Date : 01-05-2025
Time : 16:00:00
Speaker : Anton Dmitriev
Area : Astronomy & Astrophysics Division
Venue : Online
Abstract
Blazar flares offer a unique window into the extreme physics of relativistic outflows, including particle acceleration and the origin of multi-wavelength (MWL) emission. A key approach to studying these processes is physical modeling of varying blazar jet emission. Many numerical codes employ a kinetic framework to track particle spectrum evolution under various physical effects. We have developed EMBLEM (Evolutionary Modeling of BLob EMission), a versatile radiative code based on time-dependent particle (re-)acceleration, escape, radiative cooling, and adiabatic expansion. This code allows us to self-consistently connect low state and flaring emission. Based on a leptonic framework, the code incorporates synchrotron self-Compton (SSC) and external Compton (EC) scenarios. We showcase its application to (1) modeling extreme gamma-ray flares in blazars such as Mrk 421 and 3C 279, and (2) searching for internal gamma-ray opacity signatures in high-redshift blazars.
Title : Atmospheric evaporation from exoplanets
Date : 07-05-2025
Time : 11:00:00
Speaker : Dr. Gopal Hazra
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)
Abstract
The habitability of any planet is decided by a complex evolution of its interior and atmosphere. Recently in many observations, it has been found that close-in exoplanets are going through significant atmospheric evaporation, which could affect the overall evolution of the exoplanet atmosphere. This atmospheric evaporation from exoplanets is very much dependent on the plasma and radiation environment of their parent stars (e.g., stellar radiation, stellar wind, stellar flares, and Coronal Mass Ejections (CMEs). In this talk, I will explain different physical processes (e.g., Jeans escape, hydrodynamic escape) by which an exoplanet can lose its atmosphere. One major process that leads to significant loss of exoplanetary atmosphere is the stellar radiation-driven atmospheric outflow. Once planetary outflow is initiated from the planet by stellar radiation, it further interacts with the stellar wind shaping up the exoplanetary atmosphere (sometimes producing a comet-like structure) and its atmospheric mass-loss rate. Moreover, flares and coronal mass ejections (CMEs) from the star will also have a great impact on planetary evaporation and mass loss. I will present our newly developed 3D radiation magnetohydrodynamics model where we have implemented a self-consistent radiative transfer of incident stellar radiation to simulate planetary outflow and its interaction with the stellar wind, CMEs, and flares. I will show that radiation-driven planetary outflow alone can not explain the observed transit signatures & corresponding mass-loss rate, but the interaction with the stellar wind/coronal mass ejections can explain the observed mass-loss rate and transit for many exoplanets. I will also discuss briefly the effect of stellar and planetary magnetic fields on the atmospheric mass-loss rate and corresponding observational signatures.
Title : The Secret Lives of Galaxies: From Dusty Starbursts to Buried Black Holes
Date : 20-05-2025
Time : 00:16:00
Speaker : Dipanjan Mitra
Area : Astronomy & Astrophysics Division
Venue : Online:https://imeet.vconsol.com/join/9277507210?be_auth=NDc5OTIx
Abstract
Abstract - Galaxies are the building blocks of the Universe, and some of the most massive and mysterious ones formed when the Universe was just a few billion years old. Many of these early galaxies were rich in dust and forming stars at high rates, yet hidden from view in visible light. These dusty star-forming galaxies (DSFGs) played a key role in building today’s giant elliptical galaxies, and understanding them is essential to piecing together the story of galaxy formation. In my recent work, I used data from space and ground-based telescopes (JWST, Euclid, Herschel, and LSST) to show how we can trace the stars, dust, and AGN activity in these galaxies across cosmic time, and developed physical models. In this talk, I shall demonstrated that by combining multi-wavelength data (from ultraviolet to far-infrared) we can get a complete picture of how galaxies evolve, even when they are deeply buried in dust. I shall also discuss the role deep radio surveys in unveiling obscured active galactic nuclei (AGN) at high redshifts.