Prasanta Bera
Visiting Fellow
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA
Status: Left
Main Research Areas: Magnetic degenerate stars; Accretion in binary stellar systems; Magnetic instability; Mean field dynamos; Numerical magnetohydrodynamics.
Biography:
Prasanta Bera obtained his B.Sc. in Physics from the University of Calcutta in 2010, and his M.Sc. in Physics from the Indian Institute of Technology, Kanpur, in 2012. He then moved to the Inter-University Centre for Astronomy and Astrophysics for his doctoral research. He submitted his Ph.D. thesis to the Jawaharlal Nehru University, Delhi, in 2017, and then moved to NCRA-TIFR as a Visiting Fellow.Research description:
My research work is broadly related to magnetic field in astrophysical systems.
A. Strongly magnetic degenerate stars and their stability:
The mass of a non-magnetic, non-rotating white dwarf is bounded by the Chandrasekhar mass limit (1.4 solar masses). The characteristic light curve of Type-Ia supernovae is attributed to the direct consequence of crossing this maximum mass-limit in an accreting binary system. We study the strongly magnetized white dwarf configurations in a self-consistent manner, as progenitors of over-luminous Type-Ia supernovae. We find evidence for a modification of the white dwarf mass-radius relation caused by the magnetic field. The equilibrium study suggests a maximum white dwarf mass of about 1.9 solar masses may be supported if the interior poloidal field is as strong as approximately 10^10 Tesla. A perturbative analysis shows that these strongly magnetized axisymmetric configurations are sensitive to magnetic instabilities where the perturbations grow at the corresponding Alfvén time scales. Hence, we conclude that long-lived magnetically supported massive magnetic white dwarfs are unlikely to arise in nature.
The mass of a non-magnetic, non-rotating white dwarf is bounded by the Chandrasekhar mass limit (1.4 solar masses). The characteristic light curve of Type-Ia supernovae is attributed to the direct consequence of crossing this maximum mass-limit in an accreting binary system. We study the strongly magnetized white dwarf configurations in a self-consistent manner, as progenitors of over-luminous Type-Ia supernovae. We find evidence for a modification of the white dwarf mass-radius relation caused by the magnetic field. The equilibrium study suggests a maximum white dwarf mass of about 1.9 solar masses may be supported if the interior poloidal field is as strong as approximately 10^10 Tesla. A perturbative analysis shows that these strongly magnetized axisymmetric configurations are sensitive to magnetic instabilities where the perturbations grow at the corresponding Alfvén time scales. Hence, we conclude that long-lived magnetically supported massive magnetic white dwarfs are unlikely to arise in nature.
B. QPOs from accretion column of binary accretion:
Quasi-periodic oscillations (QPOs) with frequency about a Hz are detected in many optical observations of a few accreting magnetic white dwarfs. Local thermal instability due to the efficient cooling from the highly dense region causes the temporal variability. We model the dynamical evolution of the radiative accretion column, which indicates the presence of QPOs in optical/UV (due to cyclotron emission) as well as in X-rays, arising from the bremsstrahlung process. These characteristics of the post-shock region are consistent with the available observed properties of these kinds of systems. Currently we are studying the accretion process by observing the sources in optical/UV and X-ray energy bands to constraint the model further.
Quasi-periodic oscillations (QPOs) with frequency about a Hz are detected in many optical observations of a few accreting magnetic white dwarfs. Local thermal instability due to the efficient cooling from the highly dense region causes the temporal variability. We model the dynamical evolution of the radiative accretion column, which indicates the presence of QPOs in optical/UV (due to cyclotron emission) as well as in X-rays, arising from the bremsstrahlung process. These characteristics of the post-shock region are consistent with the available observed properties of these kinds of systems. Currently we are studying the accretion process by observing the sources in optical/UV and X-ray energy bands to constraint the model further.
Selected publications:
1. Quasi-periodic oscillations from post-shock accretion column of polars (P. Bera & D. Bhattacharya 2018, MNRAS, 474, 1629) 2. A perturbation study of axisymmetric strongly magnetic degenerate stars : the case of super-Chandrasekhar white dwarfs (P. Bera & D. Bhattacharya 2017, MNRAS, 465, 4026) 3. Mass–radius relation of strongly magnetized white dwarfs: nearly independent of Landau quantization (P. Bera & D. Bhattacharya 2014, MNRAS, 445, 3951)
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