Mukul Bhattacharya
Welcome to my webpage!
Brief biography:
I am working as a Simons Collaboration (SCEECS) Postdoctoral Fellow at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), University of Wisconsin-Madison, USA, since July 2024. Prior to joining the SCEECS Collaboration, I held two postdoctoral positions: as an Eberly Postdoctoral Scholar (2021-2024) in the Department of Physics at Pennsylvania State University, and as a Postdoctoral Research Associate (2020-2021) at the Center for Neutrino Physics, Virginia Tech, Blacksburg.​
I completed my Ph.D. in Physics (thesis) from the University of Texas at Austin in August 2020, under the supervision of Prof. Pawan Kumar. I received my Master of Arts in Physics (thesis) from UT Austin in May 2018. Before joining UT Austin in 2015, I obtained my Bachelor of Science (Research) from the Indian Institute of Science (IISc) at Bangalore, with a major in Physics and minor in Mathematics. I was advised by Prof. Banibrata Mukhopadhyay and Prof. Subroto Mukerjee for my undergraduate thesis project.
Research interests:
My research involves understanding particle acceleration, dynamical evolution, and emission mechanism in energetic astrophysical transients that include fast radio bursts (FRBs), compact binary (BHNS/BNS) mergers, core-collapse supernovae (CCSNe), tidal disruption events (TDEs) and active galactic nuclei (AGNs) by utilizing various messengers such as electromagnetic waves, cosmic rays, neutrinos, and gravitational waves. In addition to building detailed theoretical models to explain the key physical processes operating in these energetic transients, I leverage reliable numerical simulations to predict future observations from the next-generation multi-messenger facilities.
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Collaborators: Pawan Kumar (UT Austin), Kohta Murase (Penn State), Shunsaku Horiuchi (Virginia Tech), David Radice (Penn State), Ke Fang (WIPAC), Wenbin Lu (UC Berkeley), Eric Linder (UC Berkeley), Kazumi Kashiyama (Tohoku U., Japan), Shigeo Kimura (Tohoku U., Japan); Jose Carpio (UNLV), Nick Ekanger (Virginia Tech), Mainak Mukhopadhyay (Penn State), Eduardo Gutierrez (Penn State), Rahul Kashyap (IIT Bombay); Jewel Capili (Cal. Poly. State U.), Yuri Sato (Aoyama Gakuin U., Japan)
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For more information, please visit my research page.​ A pdf version of my updated CV is available here.
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My ongoing research is primarily focused on:
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Magnetar wind nebulae as sources of persistent radio emission in FRBs
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GW-triggered observations of kilonova transients from compact binary mergers
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Particle acceleration and TeV neutrino production in AGN coronal regions
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Effect of intermittent turbulence on the formation of TeV halos
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In the recent past, I have also worked on:
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Synthesis of heavy elements via r-process in magnetized NS outflows
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Production of TeV-PeV neutrinos in relativistic jets launched from magnetars
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Source properties and cosmological applications of FRBs
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Explaining non-thermal GRB prompt spectrum with photospheric emission model
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Long-term evolution of magnetized WDs due to field decay and radiative cooling
Ongoing research projects
FRB persistent emission powered by magnetized wind nebula
Although >30 FRBs have already been localized with arcsecond precision and associated with a host galaxy, only three repeating sources (121102, 190520, 201124) are associated with a luminous persistent radio source (PRS) in their host galaxy. Given that FRBs occur with a high volumetric rate which is comparable to CCSNe, it is possible that these PRS constitute a distinct subclass of extragalactic FRB sources.
Using an emission model for magnetar wind nebulae, I numerically compute the quasi-steady synchrotron emission by accounting for interactions between the baryon/pair-dominated wind and nebular photons. My analysis provides constraints on the source age, magnetic field, spin period and energy density of the environment leveraging current and future radio observations of FRBs.
Relevant publications:
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Bhattacharya M., Murase K., Kashiyama K., 2024, Quasi-steady emission from repeating fast radio bursts can be explained by magnetar wind nebula, under review in MNRAS.
GW-triggered observations of kilonovae from BNS/BHNS mergers
NS mergers, including BNS and BHNS mergers, are the prime targeted GW sources with associated EM counterparts. Joint multi-messenger analysis of GW signal and EM emission breaks the degeneracy in GW parameter space to provide better constraints on binary parameters, post-merger remnant and ejecta properties in addition to improving the source localization.
Decay of unstable r-process nuclei can drive quasi-thermal kilonova emission detectable in UVOIR bands. Dynamical ejecta for BHNS mergers tends to be
more anisotropic and neutron-rich as compared to BNS mergers. Subsequently, the formation of heavier r-process nuclei for BHNS mergers increases the ejecta opacity and affects the observable kilonova emission. ​Using the abundance distribution of r-process nuclei synthesized in dynamical ejecta and disk wind, coupled with their specific heating rates and opacity information from the nuclear reaction network SkyNet, we compute the bolometric light curves for kilonova and cocoon shock breakout emission. I include information from early warning alerts of GW detectors which enhances sky localization and allows for low-latency EM observations. With this formalism, I will devise an effective target-of-opportunity follow-up strategy of these sources using the cadence, exposure time and filter information of advanced surveys. ​
Relevant publications:
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Gutierrez E., Bhattacharya M., Radice D., Murase K., Bernuzzi S., 2024, Cocoon shock breakout emission from binary neutron star mergers, under review in PRD, arXiv:2408.15973.
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Ekanger E., Bhattacharya M., Horiuchi S., 2023, Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae, MNRAS, 525, 2040.
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Bhattacharya M., Kumar P., Smoot G., 2018, Mergers of black hole-neutron star binaries and rates of associated electromagnetic counterparts, MNRAS, 486, 5289.
Particle acceleration and neutrino production in AGN coronae
Recent detection of 10-100 TeV neutrinos by IceCube and their association with Seyfert galaxies e.g. NGC 1068 have opened up the prospect of multi-messenger studies of AGNs. Resolving multi-messenger connection between all-sky neutrino flux in TeV and the diffuse isotropic gamma-ray background requires sources of high-energy cosmic neutrinos to be opaque to GeV-TeV gamma rays and also possible cosmic-ray accelerators. Although the core region of AGNs is optically thick to GeV-TeV gamma rays, MeV gamma rays and neutrinos can escape to serve as smoking gun of hidden cosmic-ray acceleration that cannot be probed by X-rays and lower-energy photons.
I evaluate the detectability of GeV-TeV neutrinos with MeV gamma-rays from the nearby bright Seyfert galaxies identifiable by X-ray measurements. As AGN
coronal regions are magnetized and turbulent, particles can be accelerated via magnetic reconnections or plasma turbulence. I utilize disk-corona SED templates from observed galaxies to solve the particle transport equations and compute the cosmic-ray, neutrino and gamma-ray spectra. ​
Effect of intermittent turbulence on the formation of TeV halos
Extended TeV gamma-ray emission has been detected by HAWC around young and middle-aged pulsars such as Geminga and Monogem. The morphology of these TeV halos requires CR diffusion to be locally suppressed by 2-3 orders of magnitude compared to that in Galactic ISM. The physical origin of such small diffusion coefficients is still unknown which raises a question on whether regions of reduced diffusivity are common around pulsar wind nebulae (PWNe).
I consider self-confinement of cosmic rays around supernova remnants due to the excitation of resonant streaming instabilities. The excitation of resonant instability is due to the pairs generated by PWNe. A steep CR gradient generates Alfven waves that resonantly scatter the same CR population, thereby suppressing diffusion within ~20-40 pc of young pulsars (< 100 kyr). I model the
intermittent turbulence and its effect on particle transport to derive constraints on the turbulence spectrum and energy scale of particles. ​
Previous research projects
r-process nucleosynthesis is magnetized NS outflows
Astrophysical production sites for heaviest elements is still widely debated. They are expected to be synthesized through rapid neutron capture process which requires hot, dense and neutron-rich environments. Comparing stellar abundance data to r-process yields in relativistic outflows from rapidly spinning magnetars helps to constrain the properties of these stars and further characterize their emission signatures.
For rapidly spinning young protomagnetars, I estimated the thermodynamic properties such as entropy, density, expansion timescale and electron fraction to show that 1st and 2nd r-process peak nuclei can be synthesized in winds from magnetorotational SNe in contrast to just 1st r-process nuclei from thermal SNe. Smaller entropy coupled with intermediate expansion timescales
of these magnetized outflows facilitates the efficient formation of nuclei that are significantly heavier than Fe.
However, CCSNe outflows fail to achieve the production of elements that are heavier than lanthanides. With the comparison of r-process yields from BNS and BHNS mergers with that from CCSNe, we showed that compact binary mergers are likely to provide dominant contribution in the production of lanthanides and actinides. The predictions of our nucleosynthesis model agree very well with the solar abundance data and that from a metal poor star HD222925. Reliable estimates of the relative contributions from different source classes such as BNS/BHNS mergers, CCSNe, Type Ia SNe, AGB stars, exploding WDs and BBN helps us trace the Galactic chemical evolution, which involves explaining the evolution of nuclei abundance over time within our own Galaxy.
Relevant publications:
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Zhang B. T., Murase K., Ekanger N., Bhattacharya M., Horiuchi S., 2024, Ultraheavy Ultrahigh-Energy Cosmic Rays, under review in Physical Review Letters, arXiv:2405.17409.
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Bhattacharya M., Horiuchi S., Murase K., 2022, On synthesis of heavy nuclei in protomagnetar outflows and implications for ultra-high energy cosmic rays, MNRAS, 514, 6011.
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Ekanger E., Bhattacharya M., Horiuchi S., 2022, Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows, MNRAS, 513, 405.
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Ekanger N., Bhattacharya M., Murase K., Horiuchi S., 2024, Survival of heavy r-process nuclei in protomagnetar outflows, in preparation for PRD.
Production of high-energy neutrinos in relativistic PNS jets
Relativistic jets with large values of magnetization can break out uncollimated from the stellar envelope of compact WR stars or extended blue/red supergiants. Synthesized r-process nuclei and disintegrated protons can continuously interact with the ambient jet photons that leak from the jet-head region. This leads to photomeson interactions which generates pions that eventually decay to produce TeV-PeV neutrinos. Emission of these TeV-PeV neutrinos at late times, 30 sec < t < 100 sec, contributes to detectability as absorption from source environment is weakest at that stage. We showed that magnetized jets are among the most
promising sources for the detection of these high-energy neutrinos as > 10 events/year with energy > 1 TeV can be detected from extended progenitors like blue/red supergiants with next-generation detectors such as IceCube-Gen2 for a source located at a distance of ~100 Mpc.
Relevant publications:
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Bhattacharya M., Carpio J. A., Murase K., Horiuchi S., 2023, High-energy neutrino emission from magnetized jets of rapidly rotating protomagnetars, MNRAS, 521, 2391
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Carpio J. A., Ekanger N., Bhattacharya M., Murase K., Horiuchi S., 2024, Quasithermal GeV neutrinos from neutron-loaded magnetized outflows in core-collapse supernovae: spectra and light curves, Phys. Rev. D, 110, 083012.
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Carpio J. A., Bhattacharya M., Murase K., 2024, Quasithermal neutrinos from magnetised jets in core-collapse supernovae, in preparation for PRD.
Source properties and cosmological applications of FRBs
FRBs are millisecond duration pulses of energetic radio emission located at cosmological distances as evidenced by their large dispersion measure (DM). Characterizing the underlying source population helps optimize future search strategies and provides valuable insights regarding their progenitor models, source environment and host galaxy properties. Detection of FRB 200428 associated with the Galactic magnetar SGR 1935+2154 has confirmed the prediction of our coherent curvature radiation model, where we showed that episodic outbursts of coherent radiation can be produced by the forced reconnection of strong magnetic fields in the magnetospheres of young NS.
I developed a detailed Monte Carlo framework to model the intrinsic luminosity function, host galaxy DM and comoving number density of FRBs. Using this general model, I constrained the properties of near-source medium and the host galaxy morphology. I showed that most FRBs likely originate from galaxies with DM structure similar to Milky Way and intrinsic pulse width is broadened by dispersive smearing in ionized IGM. I also showed that FRB progenitors are young NS with a steep power-law luminosity function. We utilized the statistical ensemble of FRB DM distributions to extract information about their cosmological distances and probe the He reionization history. We showed that a fluence-limited survey with ~10,000 sources can differentiate between different He reionization histories at ~6σ confidence level using FRB DM distribution.
Relevant publications:
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Bhattacharya M., Kumar P., Linder E. V., 2021, Fast Radio Burst Dispersion Measure Distribution as a Probe of Helium Reionization, PRD, 103, 103526.
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Bhattacharya M. & Kumar P., 2020, Population Modeling of Fast Radio Bursts from Source Properties, ApJ, 899, 124.
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Bhattacharya M., 2019, Constraining FRB progenitors from the observed brightness distributions, arXiv:1907.11992.
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Radice D., Ricigliano G., Bhattacharya M., Perego A., Fattoyev F. J., Murase K., 2023, What if GW190425 did not produce a black hole promptly?, MNRAS, 528, 5836.
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Kumar P., Lu W., Bhattacharya M., 2017, Fast radio burst source properties and curvature radiation model , MNRAS, 468, 2726.
GRB photospheric emission explains non-thermal prompt spectrum
Although GRB prompt emission spectra is modeled using Band function, the underlying radiation mechanism responsible for its distinct non-thermal nature remains elusive. I developed the first Monte Carlo Radiative Transfer (MCRaT) code with photon-to-electron number ratio ~100,000 to model the sub-photospheric Comptonisation of fast cooled synchrotron photons with thermal electrons, electron-proton Coulomb collisions and electron-positron pair processes. I showed that the observed GRB prompt spectrum is generated by the electron-proton Coulomb collisions in addition to ~10-100 episodic events that can inject ~(2500-4000) x electron rest mass energy. Sub-photospheric Comptonization at moderate optical depths ~20-40 determines photon spectral shape as electrons are accelerated in jets with bulk Lorentz factor ~30-100.
Relevant publications:
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Bhattacharya M. & Kumar P., 2020, Explaining GRB prompt emission spectrum with sub-photospheric dissipation and Comptonization, MNRAS, 491, 4656.
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Bhattacharya M., Lu W., Kumar P., Santana R., 2018, Monte Carlo Simulations of Photospheric Emission in Relativistic Outflows, ApJ, 852, 24.
Evolution of magnetized WDs due to field decay and cooling
I studied the thermal properties of strongly magnetized white dwarfs (BWDs), where the cooling evolution occurs due to radiative losses from photon diffusion through the non-degenerate surface layers. I showed that the cooling rates of these BWDs can be suppressed significantly for large magnetic fields, indicating that they will remain practically hidden in an observed H-R diagram due to their low luminosities. We numerically validated the results of our semi-analytical model with the detailed stellar evolution code STARS to infer the mass-radius relationships for these MWDs. We showed that these BWDs can dynamically retain larger masses during the course of their evolution.
Relevant publications:
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Mukhopadhyay B. & Bhattacharya M., 2022, Formation, Possible Detection and Consequences of Highly Magnetized Compact Stars, Particles, 5, 493
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Bhattacharya M., Hackett A. J., Gupta A., Tout C. A., Mukhopadhyay B., 2022, Evolution of Highly Magnetic White Dwarfs by Field Decay and Cooling: Theory and Simulations, ApJ, 925, 133.
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Bhattacharya M., Mukhopadhyay B., Mukerjee S., 2018, Luminosity and cooling of highly magnetized white dwarfs: suppression of luminosity by strong magnetic fields, MNRAS, 477, 2705.
Publications
Links to all publications in: ADS, astro-ph, Google Scholar
A pdf version of my publication list is available here (as of 10/2024)
13 first author papers, 10 co-authored papers (5 led by mentored students/postdocs),
3 papers currently in preparation [total citations >500, h-index > 10, i10-index > 10]
Most significant papers
(Reverse chronological order)
1. Quasi-steady emission from repeating fast radio bursts can be explained by magnetar wind nebula
Bhattacharya M., Murase K., Kashiyama K., 2024, under review in MNRAS
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2. Cocoon shock breakout emission from binary neutron star mergers
Gutierrez E., Bhattacharya M., Radice D., Murase K., Bernuzzi S., 2024, under review in Phys. Rev. D [arXiv:2408.15973]
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3. Two-component off-axis jet model for radio flares of tidal disruption events
Sato Y., Murase K., Bhattacharya M., Carpio J. A., Mukhopadhyay M., Zhang B. T., 2024, Phys. Rev. D, 110, L061307
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4. High-energy neutrino emission from magnetized jets of rapidly rotating protomagnetars
Bhattacharya M., Carpio J. A., Murase K., Horiuchi S., 2023, MNRAS, 521, 2391
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5. Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae
Ekanger E., Bhattacharya M., Horiuchi S., 2023, MNRAS, 525, 2040
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6. On the synthesis of heavy nuclei in protomagnetar outflows and implications for ultra-high energy cosmic rays
Bhattacharya M., Horiuchi S., Murase K., 2022, MNRAS, 514, 6011
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7. Evolution of Highly Magnetic White Dwarfs by Field Decay and Cooling: Theory and Simulations
Bhattacharya M., Hackett A. J., Gupta A., Tout C. A., Mukhopadhyay B., 2022, ApJ, 925, 133
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8. Fast Radio Burst Dispersion Measure Distribution as a Probe of Helium Reionization
Bhattacharya M., Kumar P., Linder E. V., 2021, Phys. Rev. D, 103, 103526
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9. Explaining GRB prompt emission spectrum with sub-photospheric dissipation and Comptonization
Bhattacharya M. & Kumar P., 2020, MNRAS, 491, 4656
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10. Population Modeling of Fast Radio Burst from Source Properties
Bhattacharya M. & Kumar P., 2020, ApJ, 899, 124
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11. Mergers of black hole-neutron star binaries and rates of associated electromagnetic counterparts
Bhattacharya M., Kumar P., Smoot G., 2018, MNRAS, 486, 5289
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12. Fast radio burst source properties and curvature radiation model
Kumar P., Lu W., Bhattacharya M., 2017, MNRAS, 468, 2726
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Outreach
Recent talks
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Department of Physics, Indian Institute of Technology (IIT), Hyderabad 9/2024
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TeV Particle Astrophysics (TeVPA) meeting, University of Chicago 8/2024
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National Centre for Radio Astrophysics (NCRA) – TIFR, Pune 7/2024
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Department of Astronomy & Astrophysics (DAA), TIFR, Mumbai 7/2024
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Department of Physics, Indian Institute of Technology (IIT), Mumbai 7/2024
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Indian Institute of Science Education & Research (IISER), Pune 7/2024
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Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune 7/2024
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Department of Particle Physics & Astrophysics, Weizmann Institute of Science 5/2024
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Neutrino Focus Session, Institute of Gravitation & Cosmos (IGC), Penn State 5/2024
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6th Neighborhood Workshop, Institute of Gravitation & Cosmos (IGC), Penn State. 4/2024
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Teaching
I have conducted weekly recitations, graded homework, held office hours, and oversaw course communication for the following classes (all at University of Texas, Austin, USA):​
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AST 103L: Astronomical Observations Fall 2016 - Spring 2019​
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PHY 303L: Engineering Physics Summer 2018 ​
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AST 309N: Lives & Deaths of Stars Spring 2016
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AST 301: Introductory Astronomy Spring 2016​
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PHY 103N: Electromagnetism & Optics lab Fall 2015 ​​​​​
Mentoring
I have mentored four Ph.D. students and two Masters students as a postdoctoral scholar:​
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Ph.D. Students​
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Yuri Sato, Dept. of Physical Sciences, Aoyama Gakuin University, Japan 2023 - present
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Jose Carpio, Department of Physics, Penn State University, USA 2021 - 2023
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Alexander Hackett, Institute of Astronomy, University of Cambridge, UK 2020 - 2022 ​
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Nick Ekanger, Department of Physics, Virginia Tech, USA 2020 - present​
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Masters Students​
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Jewel Capili, California Polytechnic State University, USA 2022 - 2023
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Abhay Gupta, Indian Institute of Science, Bangalore 2019 - 2020
Contact
Mailing Address
WIPAC, 222 West Washington Avenue,
5th floor, Room 5309, Madison, WI 53703, USA
Primary: mukulbhattacharya1993@gmail.com
Work: mbhattachar5@wisc.edu​