Astronomy & Astrophysics Division Seminar
Title : Gaining insight into radiative and variability phenomena of black hole X-ray binaries
Date : 02-04-2024
Time : 16:00:00
Speaker : Nazma Husain
Area : Astronomy & Astrophysics Division
Venue : online: https://meet.google.com/jqv-rbwg-unz
Abstract
Around 72 Black Hole X-ray Binary (BHXB) candidates have been discovered till now, showcasing variety of radiative phenomena and rapid variability in the X-ray lightcurve. This variability manifests itself as Quasi-Periodic Oscillations (QPOs) and broadband noise continuum in the power spectra. These properties offer a unique lens to study extreme gravitational environments in close regions to the black hole. Despite substantial research, our understanding of the origin and energy-dependent behaviour of the variability remains incomplete. I will focus on the modelling of variability, testing its different origins and exploring the spectral behaviour in different accretion regimes, using data from AstroSat, NICER, NuSTAR and Swift. In addition, I will discuss a peculiar case of a highly luminous BHXB, which exhibited non-standard disk behaviour. I will conclude by exploring future prospects to better our understanding of the accretion physics around different compact object systems.
Title : Optical Monitoring of a long-period dynamically new comet C/2020 V2 (ZTF)
Date : 04-04-2024
Time : 16:00:00
Speaker : Goldy Ahuja
Area : Astronomy & Astrophysics Division
Venue : Seminar Room # 113/114 (Thaltej Campus)
Abstract
Comets are the pristine bodies that retain the essential information of the early Solar System. They are mainly placed in two reservoirs, i.e., Kuiper Belt and Oort Cloud. These reservoirs hold a large number of comets. The comets in the Kuiper belt are responsible for the short-period low-inclination known as Jupiter family comets (JFC), while comets in the Oort Cloud account for the long-period comets with different inclinations (as compared to the JFC). Studying the composition of different classes of comets is essential to understanding the formation and evolution of the Solar System. Dynamically New Comet (DNC) is a subcategory of long-period comets with a semi-major axis > 10000 AU. These comets are entering the inner Solar System for the first time, which gives us an excellent opportunity to study their composition. The Zwicky Transient Facility discovered Comet C/2020 V2 (ZTF) in November 2020. It was categorized as a dynamically new comet. In the talk, I will present the different results of this dynamically new comet C/2020 V2 (ZTF) using the photometric observations from TRAPPIST and spectroscopic observations from different observatories in India.
Title : Cloud-Cloud Collision: Formation of Hub-Filament Systems and Associated Gas Kinematics
Date : 12-04-2024
Time : 11:00:00
Speaker : Arup Kumar Maity
Area : Astronomy & Astrophysics Division
Venue : Seminar Room #113/114 (Thaltej Campus)
Abstract
Massive star-forming regions (MSFRs) are commonly associated with hub-filament systems (HFSs) and sites of cloud-cloud collision (CCC). Recent observational studies of some MSFRs suggest a possible connection between CCC and the formation of HFSs. To understand this connection, we analyzed the magneto-hydrodynamic simulation data from Inoue et al. (2018). This simulation involves the collision of a spherical molecular cloud with a plane-parallel sea of dense molecular gas at a relative velocity of about 10 km/s. Following the collision, turbulent and non-uniform cloud undergoes shock compression, rapidly developing filamentary structures within the compressed layer. We found that CCC can lead to the formation of HFSs, which is a combined effect of turbulence, shock compression, magnetic fields, and gravity. The collision between the cloud components shapes the filaments into a cone and drives inward flows among them. These inward flows merge at the vertex of the cone, rapidly accumulating high-density gas, which can lead to the formation of massive star(s). The gas distribution in the position-velocity and position-position spaces highlights the challenges in detecting two cloud components and confirming their complementary distribution if the colliding clouds have a large size difference. However, such CCC events can be confirmed by the position-velocity diagrams presenting gas flow toward the vertex of the cone, which hosts gravitationally collapsing high-density objects, and by the magnetic field morphology curved toward the direction of collision. In this talk, I will present these initial results.
Title : Daksha: Indian Eyes on Transient Skies
Date : 15-04-2024
Time : 11:00:00
Speaker : Prof. Varun Bhalera
Area : Astronomy & Astrophysics Division
Venue : Seminar Room #113/114 (Thaltej Campus)
Abstract
Daksha is a proposed High Energy transients mission that will have higher sensitivity than any other mission in the world. Daksha will comprise of two satellites covering the entire sky from 1 keV to > 1 MeV. The primary objectives of the mission are to discover and characterize electromagnetic counterparts to gravitational wave sources; and to study Gamma Ray Bursts (GRBs). With its broadband spectral response, high sensitivity, and continuous all-sky coverage, it will discover fainter and rarer sources than any other existing or proposed mission. Daksha can make key strides in GRB research with polarization studies, prompt soft spectroscopy, and fine time-resolved spectral studies. In addition, Daksha is a versatile all-sky monitor that can address a wide variety of science cases. Daksha will provide continuous monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy counterparts to Fast Radio Bursts. Using Earth occultation to measure source fluxes, the two satellites together will obtain daily flux measurements of bright hard X-ray sources including active galactic nuclei, X-ray binaries, and slow transients like Novae. Correlation studies between the two satellites can be used to probe primordial black holes through lensing. Daksha will have a set of detectors continuously pointing towards the Sun, providing excellent hard X-ray monitoring data. Closer to home, the high sensitivity and time resolution of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray Flashes. In this talk, I will discuss the scientific impact of Daksha in all these areas