Core-collapse and Thermonulclear explosions
Explosion of a massive star and the creation of Crab nebula.
White dwarf accreting matter from a non-degenerate companion and exploding via thermonuclar explosion (Type Ia supernova).
The second area of my research involves the study of radio and X-ray emissions from supernovae to unravel the progenitors of these explosions. Supernovae are massive destruction of stars. The supernova shocks are often bright at radio and X-ray wavelengths which provide crucial information about the ambient medium where the explosion occurred. The circumstellar medium is shaped by the pre-supernova mass-loss history of the progenitor star. As various kinds of stars undergo mass loss at different rates, the circumstellar media carry the signature of the progenitor stars.
Theoretical Study: I have done detailed theoretical modeling of radio emission from nearby supernova Type Ia which enabled us to put stringent constraints on possible progenitor systems of these explosions (Kundu et al. 2017, ApJ, 842, 17 ; Lundqvist, Kundu, et al. 2020, ApJ, 890, 159 ). Moreover, the study of this emission allowed us to gain a deeper insight into the microphysics of shock acceleration (Kundu et al. 2017, ApJ, 842, 17 ).
Hydrodynamical simulation: In general, the interaction between supernova ejecta and ambient medium is described by a self-similar structure. However, it can be quite different from a self-similar structure if the circumstellar medium and/or ejecta profiles are complex. In this situation, one needs numerical simulations to estimate the structure. To evaluate the shock structures properly, I performed hydrodynamical simulations of supernova and circumstellar interaction using the publicly available FLASH code, which I modified accordingly to meet our requirements. With the help of numerical simulations, radio, and X-ray modeling we did a comprehensive study of the mass-loss history of the two core-collapse supernovae, SN 1993J and SN 2011dh (Kundu et al. 2019, ApJ, 875 ).
Observational Study: Among various kinds of SNe, the Type IIn ejects a large amount of material in the ambient medium before the explosion. Due to this fact, the radio emission from this kind of event gets detectable around a year after the SN goes off. However, in the case of one of our Type IIn events, which resides in a dwarf galaxy, the radio emission was detected soon after the explosion, though for a brief period of time. While this object was not luminous at radio frequencies, the X-ray flux detected from this event makes it one of the brightest SNe ever detected at X-rays. The observed X-ray variability of this source shows peculiar features. We are closely monitoring this SN at radio and X-ray wavelengths, and whenever required doing simultaneous observations at both frequencies using X-ray telescopes and the Australia Telescope Compact Array (ATCA) (Kundu et al. in preparation).
Since the SN is bright and displays strange features, to understand the origin of these features in detail we will study this event at multiwavelength in the future as well.
Telescopes used for my multiwavelength study:
Radio wavelength: Very Large Array, USA; Australia Telescope Compact Array, Australia; upgraded Giant Metrewave Radio Telescope, India
X-ray wavelength: Space-based SWIFT telescope.
For details on radio emission from supernova shocks, you are welcome to visit my Ph.D. thesis: Radio emission from supernovae !!