PhD in Physics
Specialization Astrophysics; CGPA: 4.0/4.0
University of Alberta
Hello world!!
Understanding the enigma of the unknown has always driven man to push his boundaries of knowledge. In this regard, the universe has been the most puzzling and wicked creation — it constrains us from performing experiments, making us mere observers to witness its magic. The curiosity to discern the mysteries of the cosmos has not only increased man's understanding of physics but also carved the path for new technologies. Since the tracking of the motion of the moon and the sun by early man to understand seasons, we have come a long way into building large telescopes and sending satellites into space to study the night sky. With the beginning of a new era of multi-messenger astrophysics and instruments such as Athena waiting for launch, we indeed are in the golden age of astronomy.
Hi!! I am currently a PhD student in physics at the University of Alberta specializing in astrophysics. I work with Prof. Craig Heinke and search for compact "dead" stars (i.e., neutron star and black hole systems) in X-ray catalogs and decipher their properties. My research involves efficiently analyzing the X-ray spectra (i.e., changing flux w.r.t energy of photons) through machine learning methods and/or manually tailored X-ray colors to distinguish different kinds of X-ray sources. Identifying compact objects serendipitously in these catalogs and mapping their distribution across the Galaxy allows us to probe their formation and understand the evolution of our Galaxy. Analyzing the nature of X-ray emission in compact objects allows us to examine the properties of matter at extremely high temperatures and densities, under intense gravitational and magnetic fields. I enjoy the cycle of manipulating large datasets to find and study interesting objects that allow us to further our understanding of the universe. Besides compact object systems (isolated neutron stars and X-ray binaries), I am also interested in accreting white dwarfs, X-ray transients, and instrumentation for X-ray detectors. Please refer my CV for more details.
Education and Training
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Present 2019
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2019 2017
Master of Science in Physics
Specialization Astrophysics; CGPA: 4.0/4.0
University of Alberta
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2017 2013
B.Tech in Aerospace Engineering with Honors
Minor: Physics, Computer Science; CPI: 9.48/10
Indian Institute of Technology Bombay
Honors, Awards and Grants
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2024, 2021, 2020Alberta Graduate Excellence Scholarship
The Alberta Graduate Excellence Scholarship recognizes outstanding academic achievement of the students pursuing graduate studies in Alberta.
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2023Pansy and George Strange Graduate Scholarship
The Pansy and George Strange Graduate Scholarship is awarded annually to outstanding graduate students at the University of Alberta, with preference given to students with undergraduate degree from an accredited university in India.
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2022Ivy A Thompson and William A Thompson Graduate Scholarship
Awarded annually for superior academic achievement to graduate students at the University of Alberta.
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2021Dr. Isaac Yakoub graduate scholarship in Physics
Awarded annually to graduate students in physics for outstanding academic achievement.
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2019Valerie Jagoldas Graduate Scholarship in Science
The Valerie Jagoldas Graduate Scholarship is awarded for superior academic achievement in science streams.
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2019University of Alberta Doctoral Recruitment Scholarship
The University of Alberta Doctoral Recruitment Scholarship recognizes the superior academic and scholarly achievements of incoming PhD students. I was awarded CA$5000 from the Faculty of Graduate Studies (FGSR).
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2017Institute Silver medal, IIT Bombay
Institute silver medal is awarded to the most outstanding student in terms of academic performance within each department. Added to having the highest cumulative grade point in Aerospace Department 2017 batch, I had taken several additional courses thus completing honors in aerospace, and minors in physics and computer science.
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2012Bronze medal, International Olympiad of Astronomy and Astrophysics
IOAA is an annual astronomy and astrophysics competition for high school students which overseas participation from about 50 countries. I represented India at the international level as a part of a five-member team and won a bronze medal for the country. Even during the orientation-cum-selection camp before the internationals, I was awarded for the best theory solution.
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2011Silver medal, International Astronomy Olympiad
IAO is an annual astronomy olympiad organized by the Eurasian Astronomical Society for students of age group 14-18. I was a part of a three-member team that represented India at the international level, and I bagged a silver medal for the nation. During the selection camp for the international event, I was awarded for the best observer.
Research Summary
Massive stars end their lives through supernova explosions leaving behind supernova remnants (SNRs) and can form compact neutron stars (NSs) and black holes (BHs). These compact objects allow us to probe the behavior of matter at extreme densities (1014–1015 g/cm3), very high temperatures (>106 K), under intense gravity (>1014 cm/s2), and large magnetic fields (108–1014 G) and push the limits of modern physics. However, our knowledge of these compact objects and supernova remnants is limited to only a few bright ones. While modern X-ray telescopes have detected hundreds of thousands of X-ray sources in the sky, we have not studied the X-ray spectra of most of these sources, which could contain valuable insights into the nature of X-ray emission. Hardness ratios that compare the X-ray flux in soft and hard energy bands have been used to characterize the slope of X-ray spectra. However, these fail to capture moderate resolution features like emission lines, and can lead to confusion in the nature of X-ray emission (Hebbar et al. 2019).
I am currently developing data-mining algorithms to identify line emission in the X-ray spectra without the need for detailed X-ray spectral analysis. I intend of apply this to X-ray catalogs from XMM-Newton (4XMM-DR14, ~600,000 sources), Chandra (CSC v2.1, ~400,000 sources) and eROSITA (eRASS1, ~930,000 sources). Hebbar & Heinke (2023) showed than supervised artificial neural networks (ANNs) could be trained on simulated spectra generated with known source property distributions and distinguish the line-dominated spectra of stars from the continuum dominated spectra of active galactic nuclei (AGN). We have also used manually tailored X-ray colors to detect iron line emissions in X-ray sources in the Galactic Bulge and separate candidate millisecond pulsars (MSPs) and X-ray binaries from accreting white dwarfs (cataclysmic variables). This will help us constrain the population of MSPs close to the galactic center which will in turn allow us to verify if the excess gamma rays from the galactic center is from dark matter or MSPs (Hebbar et al., in prep).
In my masters, I studied faint X-ray sources where Poisson statistics from low photon counts, high background and the detector response could greatly affect the X-ray spectra and light curve and thus the inferred source properties. I analyzed — binary MSP 47 Tuc W to show the continuation of orbital X-ray variability and to understand the nature and geometry of the intra-binary shock, candidate (AGN) in Henize 2–10 and NGC 4178 and identified the X-rays to be from supernova remnants (SNRs), and argued for the presence of neutron star in SNR 1E 0102.2-7219 and studied its properties. I also like to follow research in other areas of astrophysics. I have also developed back-end algorithms to automatically detect short gamma-ray bursts from AstroSAT CZTI data, and processed Plank data to search for B-mode polarization. I also closely follow research in time domain astronomy that investigate the nature of X-ray transients. Please look into my CV for further details.
Research Interests
- Classification of X-ray sources in catalogs
- X-ray emission from central compact objects and other young neutron stars.
- Neutron star and black hole X-ray binaries
- Millisecond pulsars in Globular clusters
- Accreting white dwarfs
- Time domain astronomy, especially X-ray transients
- Instrumentation in high energy
Selected Projects and Publications
Below is a select list of my research projects. I have included my refereed papers and important conference presentations.
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Machine Learning Applied to X-Ray Spectra: Separating Stars in Orion Nebula Cluster from Active Galactic Nuclei in CDFS
Journal PapersMay 2023, ApJ, 949, 1, 12
Abstract
Modern X-ray telescopes have detected hundreds of thousands of X-ray sources in the universe. However, current methods to classify these sources using the X-ray data themselves suffer problems-detailed X-ray spectroscopy of individual sources is too time consuming, while hardness ratios often lack accuracy, and can be difficult to use effectively. These methods fail to use the power of X-ray CCD detectors to identify X-ray emission lines and distinguish line-dominated spectra (from chromospherically active stars, supernova remnants, etc.) from continuum-dominated ones (e.g., compact objects or active galactic nuclei, AGN). In this paper, we probe the use of artificial neural networks (ANN) in differentiating Chandra spectra of young stars in the Chandra Orion Ultradeep Project (COUP) survey from AGN in the Chandra Deep Field South (CDFS) survey. We use these surveys to generate 100,000 artificial spectra of stars and AGN, and train our ANN models to separate the two kinds of spectra. We find that our methods reach an accuracy of ~92% in classifying simulated spectra of moderate-brightness objects in typical exposures, but their performance decreases on the observed COUP and CDFS spectra (~91%), due in large part to the relatively high background of these long-exposure data sets. We also investigate the performance of our methods with changing properties of the spectra such as the net source counts, the relative contribution of background, the absorption column of the sources, etc. We conclude that these methods have substantial promise for application to large X-ray surveys.
On the vanishing X-ray variablity in eclipsing MSP 47 Tuc W
Journal Paper January 2021, MNRAS, 500, 1, pp. 1139-1150
Abstract
Redback millisecond pulsars (MSPs) typically show pronounced orbital variability in their X-ray emission due to our changing view of the intrabinary shock (IBS) between the pulsar wind and stellar wind from the companion, Some redbacks (“transitional” MSPs) have shown dramatic changes in their multiwavelength properties, indicating a transition from a radio pulsar state to an accretion-powered state. The redback MSP 47 Tuc W showed clear X-ray orbital variability in Chandra ACIS-S observations in 2002, which were not detectable in longer Chandra HRC-S observations in 2005– 06, suggesting that it might have undergone a state transition. However, Chandra observations of 47 Tuc in 2014–15 show similar X-ray orbital variability as in 2002. We explain the different X-ray light-curves from these epochs in terms of two components of the X-ray spectrum (soft X-rays from the pulsar, vs. harder X-rays from the IBS), and different sensitivities of the X-ray instruments observing in each epoch. However, when we use our best-fit spectra with HRC response files to model the HRC lightcurve, we expect a more significant and shorter dip than that observed in the 2005–06 Chandra data. This suggests an intrinsic change in the IBS of the system. We use the ICARUS stellar modelling software, including calculations of heating by an IBS, to model the X-ray, optical, and UV light-curves of 47 Tuc W. Our best-fitting parameters point towards a high-inclination system (i ∼ 60 deg), which is primarily heated by the pulsar radiation, with an IBS dominated by the companion wind momentum.
X-ray spectroscopy reveals the nature of compact object in SNR 1E0102.2-7219
Journal PaperJanuary 2020, MNRAS, 491, 1585
Abstract
We re-analysed numerous archival Chandra X-ray observations of the bright supernova remnant (SNR) 1E 0102.2-7219 in the Small Magellanic Cloud, to validate the detection of a neutron star (NS) in the SNR by Vogt et al. (2018). Careful attention to the background is necessary in this spectral analysis. We find that a blackbody + power-law model is a decent fit, suggestive of a relatively strong B field and synchrotron radiation, as in a normal young pulsar, though the thermal luminosity would be unusually high for young pulsars. Among realistic NS atmosphere models, a carbon atmosphere with B = 10^12G best fits the observed X-ray spectra. Comparing its unusually high thermal luminosity (Lbol = 0.6-2.7 × 10^34 ergs s−1) to other NSs, we find that its luminosity can be explained by decay of an initially strong magnetic field (as in magnetars or high B-field pulsars) or by slower cooling after the supernova explosion. The nature of the NS in this SNR (and of others in the Magellanic Clouds) could be nicely confirmed by an X-ray telescope with an angular resolution like Chandra, but superior spectral resolution and effective area, such as the Lynx concept.X-ray spectroscopy of candidate AGN in Henize 2-10 and NGC 4178: Likely supernova remnants
Journal PapersJune 2019, MNRAS, 485, 5604
Abstract
Black holes in dwarf/bulgeless galaxies play a crucial role in studying the co-evolution of galaxies and their central black holes. Identifying massive black holes in dwarf galaxies suggests that the growth of black holes could precede that of galaxies. However, some of the most intriguing candidate AGN in small galaxies have such low luminosities that the sample is vulnerable to contamination by other sources, such as supernova remnants. We re-analysed Chandra X-ray Observatory observations of candidate active galactic nuclei (AGN) in Henize 2-10 and NGC 4178, considering the potential signals of emission lines in the minimally-binned X-ray spectra. We find that hot plasma models, which are typical of supernova remnants, explain the observed spectra much better than simple power-law models, which are appropriate for AGN. We identify clear signals of X-ray lines in the faint X-ray source identified with the radio source in Henize 2-10 by Reines et al. 2016. Combining our work with the MUSE measurement of the ionization parameter in this region by Cresci et al. 2017 indicates that this radio and X-ray source is more likely a supernova remnant than an AGN. A similar analysis of the low-count X-ray spectrum of a candidate AGN in NGC 4178 shows that a hot plasma model is about seventeen times more probable than a simple power-law model. Our results indicate that investigation of X-ray spectra, even in a low-count regime, can be a crucial tool to identify thermally-dominated supernova remnants among AGN candidates.
The search for fast transients with CZTI
Journal PaperJuly 2021, Journal of Astrophysics and Astronomy, 42, 73
Abstract
The Cadmium–Zinc–Telluride Imager on AstroSat has proven to be a very effective All-Sky monitor in the hard X-ray regime, detecting over three hundred GRBs and putting highly competitive upper limits on X-ray emissions from gravitational wave sources and fast radio bursts. We present the algorithms used for searching for such transient sources in CZTI data, and for calculating upper limits in case of non-detections. We introduce CIFT: the CZTI Interface for Fast Transients, a framework used to streamline these processes. We present details of 87 new GRBs detected by this framework that were previously not detected in CZTI.From Stellar Death to Cosmic Revelations: Zooming in on Compact Objects, Relativistic Outflows and Supernova Remnants with AXIS
White PaperNovember 2023
Abstract
Compact objects and supernova remnants provide nearby laboratories to probe the fate of stars after they die, and the way they impact, and are impacted by, their surrounding medium. The past five decades have significantly advanced our understanding of these objects, and showed that they are most relevant to our understanding of some of the most mysterious energetic events in the distant Universe, including Fast Radio Bursts and Gravitational Wave sources. However, many questions remain to be answered. These include: What powers the diversity of explosive phenomena across the electromagnetic spectrum? What are the mass and spin distributions of neutron stars and stellar mass black holes? How do interacting compact binaries with white dwarfs - the electromagnetic counterparts to gravitational wave LISA sources - form and behave? Which objects inhabit the faint end of the X-ray luminosity function? How do relativistic winds impact their surroundings? What do neutron star kicks reveal about fundamental physics and supernova explosions? How do supernova remnant shocks impact cosmic magnetism? This plethora of questions will be addressed with AXIS - the Advanced X-ray Imaging Satellite - a NASA Probe Mission Concept designed to be the premier high-angular resolution X-ray mission for the next decade. AXIS, thanks to its combined (a) unprecedented imaging resolution over its full field of view, (b) unprecedented sensitivity to faint objects due to its large effective area and low background, and (c) rapid response capability, will provide a giant leap in discovering and identifying populations of compact objects (isolated and binaries), particularly in crowded regions such as globular clusters and the Galactic Center, while addressing science questions and priorities of the US Decadal Survey for Astronomy and Astrophysics (Astro2020).Identifying neutron stars in Galactic Bulge with X-ray data
PosterHEAD 2024 conference, Horseshoe Bay, Texas, US
Abstract
Fermi observations of the inner degree of the Milky Way Galaxy show an excess of gamma-rays in addition to the expected emission from cosmic ray interactions. This gamma-ray excess (GCE) could be from dark-matter annihilation or an underlying population of millisecond pulsars (MSPs). X-ray observations from XMM-Newton and Chandra, which have higher angular resolution than Fermi, can detect the X-ray emission from bright MSPs and constrain the fraction of GCE that could be explained from MSPs. However, the Galactic Bulge also contains a population of bright intermediate polars and X-ray binaries that emit X-rays. We use deep (> 100 ks) XMM-Newton observations of the Galactic Bulge to study 838 sources with NH,Gal > 5×1022 cm-2. We compare the (6.2–7.2) keV emission with the surrounding (5.8–6.2) keV and (7.2–7.6) keV emission to distinguish continuum sources from sources that show significant 6.4 keV fluorescence Fe emission (such as X-ray binaries and active galactic nuclei) or Fe-K emission at 6.7 and 7.0 keV (such as cataclysmic variables). The high diffuse background emission allows us to use this methodology only on sources with more than 100 counts. Using this approach, we select 32 sources which show emission consistent with a continuum source. Further spectral analysis shows that 11 of these sources do not show evidence of any Fe lines. One source, 4XMM J174501.0-291045, has an extended radio counterpart and could be a possible young neutron star with a pulsar wind nebula. Follow-up observations, especially in high-frequency radio wavelengths, will allow us to reveal the nature of these sources.Designing and Analysis Using ANSYS for "Pratham"-Student Satellite of IIT Bombay"
Conference Paper 65th International Astronautical Congress 2014, Toronto, Canada
Abstract
'Pratham' is the first satellite under the Indian Institute of Technology Bombay (IIT Bombay) Student Satellite Project. This paper provides a brief overview of thermal subsystem. The objective of the sub-system is to ensure the temperature management of the satellite so that it survives under different thermal loads.
The design approach has been briefly explained. A CAD model of the satellite is prepared and it is then meshed to obtain Transient Thermal analysis in ANSYS. Different loads of heat flux and internal heat generation and solar radiation is applied. Some of the features like Multilayer Insulation (MLI) and Optical Solar Reflector (OSR) window have been incorporated for thermal control.
All satellite sides will be black anodized from inside. Heat sink is used for power amplifier in telemetry and beacon boards. 4 sides are to be covered by MLI blankets. High dissipation components are placed on the PCB using thermal filler materials. Solar panels back side will be covered with low emittance tape. Monopole holder is covered with MLI blanket. Monopole is polished without applying any coating. OSR requirement for the satellite is on the anti-sun side panel. Heat shrinkable tubes between holder and monopole are used.
The analyses were done in steps. In the first step a simple hollow cube with heat flux and radiation is applied. This model helps to understand the interface of ANSYS and basics of simulation. Next steps model used the complete satellite model with removed those minor parts which did not contribute to thermal coupling to reduce the analysis time. Second model gave approximate result in less time which helped in different frequent design iteration. The final design was modeled and analyzed with complete thermal condition which finally gone through different iteration depending on constrained by other subsystems.
The thermals sub-system has started a new initiative called as virtual laboratory which is openly available on the website of Pratham. Virtual laboratory gives the data of solar heat flux for different orbital altitude and inclination. All the thermal analysis were done in ANSYS and IDEA-S using the parallel processing feature on server to reduce the analysis time. Using the thermal field obtained thermal stress was analyzed.
Project Summary
We implemented a Particle-in-Cell approach to computationally model unmagnetized collisionless shocks, and understand its stucture. We used the 2-dimensional space, 3-dimensional velocity open source code, WARP for our simulations. Through our results, we showed the development of magnetic fields along the shock through Wiebel instabilities in the shock. We also analyzed the affect of different velocities and composition of plasmas on the properties of the shock.
Teaching
I have been a teaching assistant (TA) for several courses during my undergraduate and graduate studies. I have completed Levels 1 and 2 of the Graduate Teaching and Learning (GTL) at the university of Alberta.
Graduate Teaching Experience
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November 2022
Graduate Teaching and Learning program: Level 2
The course aims at teaching the creation of learning objects & outcomes, lesson plans, teaching goals, and teaching philosophy and deepening classroom management skills through practice
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August 2018
Graduate Teaching and Learning (GTL) program: Level 1
I have succesfully completed level one of GTL program by attending 21 hours of lectures during the GTL week. The lectures dealt with a various topics including making the first impression, effective teaching in lab, ethical conduct, planning lessons and active learning.
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2024 2017
Teaching Assistant
Tutored and graded courses — Stellar Astrophysics (I and II) and introductory courses on astronomy of solar system, stars and galaxies; electromagnetism; particles and waves, and modern physics
Undergraduate Teaching Experience
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2017 2014
PH 108: Introduction to Quantum Mechanics
This course introduced the concepts of special relativity, quantum mechanics and condensed matter to first year undergraduates. Overr the course of my undergraduate studies, I was appointed as a TA for this course four times. As a TA I held weekly tutorials, where we solved numerical problems based on the concepts learnt in the lectures. I also proctured and graded the quizzes, mid-term and end-term examinations
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2017 2015
MA 104: Introduction to Numerical Analysis
This course discusses the numerical ways to solve linear and differential equations and dealing with the corresponding numerical errors. I was appointed as the TA for this course thrice during my undergraduate studies. As a TA I was in-charge of weekly tutorials, where we revised the topics learnt in class and solved numerical problems based on those topics. I also invigilated and graded the examinations.
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2014
BB 101: Introduction to Biology
This is an introductory course meant to give the flavour of biology, biotechnology and bio-engineering to first year undergaduates. As a TA, I was responsible for weekly tutorials, where we discussed various applications of engineering in biology and how several engineering systems were inspired from biological systems in living organisms.
Contact & Meet Me
I would be extremely happy to discuss on my research and other topics in physics. I personally prefer e-mail for conversations and official appointments. In case you don't prefer that, you can drop by my office. Also, feel free to contact me through other means, though I might be slower at responding in such situations.
- Office: hebbar@ualberta.ca
- Personal: rpavanhebbar1996@gmail.com
- hebbar1996pavan
- CCIS 2-108, Dept. of Physics, University of Alberta, Edmonton, AB T6G 2E9
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