Esha Kundu

Research Associate, Department of Physics & Astronomy
Location: 4208 Biomed Phys Sci


#Biographical Information

August 2021 - present: Research Associate, Department of Physics and Astronomy, Michigan State University, USA
January 2019 - March 2021: Research Associate, International Centre for Radio Astronomy Research, Curtin University, Australia
February 2019: Ph.D., Department of Astronomy, Stockholm University, Sweden 

# Research Interest

My current research involves the studies of compact objects, especially black hole binaries, in globular clusters, radio emissions from supernovae, and fast radio bursts.  

##Compact objects in globular clusters:

Owing to their old ages and high central densities, globular clusters (GCs) are factories for the formation of compact binaries: those containing a white dwarf, neutron star, or black hole. Some classes of these systems have been long known in GCs (such as accreting neutron star X-ray binaries, and their progeny millisecond pulsars), while others have only been revealed in the last few years (binaries containing stellar-mass black holes). My research involves carrying out a multiwavelength (radio, X-ray, and optical) study of the compact variable sources in Milky Way GCs to unravel the nature of those compact sources. We have observed a significant number (50) of Galactic globular clusters at radio wavelengths through MAVERIC survey using the Very Large Array and Australia Telescope Compact Array. I image globular clusters at radio wavelengths using the Common Astronomy Software Applications. On each image, radio sources with different significance levels are searched using the Aegean source-finding tool. The associations of variable radio sources with X-ray and optical counterparts are examined by cross-matching the location of these candidates with sources on our published X-ray catalog/Chandra and Hubble space telescope images. For radio variable sources with X-ray and/or optical counterparts, we examine their spectra at all observed wavelengths. In my current investigation, I have found many interesting compact sources, including black hole binaries in a subset of these GCs, the draft of which is under preparation now (Kundu et al. in preparation). This study will allow the first statistical determination of the presence of accreting black holes in GCs, and improve our understanding of unusual neutron star and white dwarf binaries. 

## Fast radio bursts (FRBs):

The other area of my active research includes the investigation of progenitors of fast radio bursts by studying radio emissions and the surrounding of these events. Fast radio bursts are transient intense radio pulses of unknown origin. The detection rate of fast radio bursts indicates that these events are overabundant in the universe (more than 1000 events per sky every day), however, we still lack an understanding of the progenitors and emission mechanisms of these objects. Analyzing the evolution of the dispersion measure and rotation measure through the merged material of a white dwarf binary, we showed that, at least for some of the fast radio bursts, the merger of two white dwarfs was a potential channel that formed the fast radio burst sources [Kundu & Ferrario 2020, MNRAS, 492, 3753]( Recently, the source of a non-repeating fast radio burst, FRB 191001, has been localized to the spiral arm of a starburst galaxy. Applying the model developed in my previous paper and performing a statistical analysis on the location of supernovae in the spiral arm of their host galaxies, I established that FRB 191001 was most likely the outcome of a core-collapse supernova [Kundu 2022, MNRAS Letters, 512, L1-L5](

Among fast radio bursts, a substantial number of bursts, mainly those from repeating sources, have shown a drift in frequency and time in their spectra. We found that the free-free absorption in relativistic shocks could produce the observed drifts in the spectra of some of the fast radio bursts [Kundu and Zhang 2021, MNRAS Letters, 508, L48-L52] (

## Supernovae (SNe):

The third 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. 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] (  

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 ] (

Besides, I do frequent radio observations of nearby core-collapse supernovae using Australia Telescope Compact Array (ATCA) in Australia to understand the very last evolutionary stages of massive stars that lead to the collapse. 

## High energy emissions from extragalactic objects:

Other than the above three areas, I have done theoretical modeling of gamma-ray emission from extragalactic objects. The inverse Compton scattering of the cosmic microwave background radiations was found to overproduce the gamma-ray emission, observed by FERMI LAT in 2013, at GeV energies from the large-scale jet of quasar 3C 273. Considering a broken power-law spectrum of the accelerated protons in the jet we showed that the synchrotron emission from this population could explain the observed X-ray to the gamma-ray flux from knot A [Kundu and Gupta 2014b, MNRAS Letters, 444, L16 - L19] (  

Another popular gamma-ray source is Cen A. In 2013, a new component in the gamma-ray spectrum from the core of this object was reported in the energy range of 4 GeV to tens of GeV. We showed that this new component and the HESS detected spectrum of gamma-rays from the core at higher energy had possibly a common origin in the photo-disintegration of heavy nuclei [Kundu and Gupta 2014a, JCAP, 04] ( 

# Publication
My publications can be found here: - [ADS] (