Dr Amar Deo Chandra

I am currently a Research Associate at the Aryabhatta Research Institute of Observational Sciences (ARIES). I obtained my PhD at the Center of Excellence in Space Sciences India, IISER Kolkata and Integrated MSc. (Physics) from the UM-DAE Centre for Excellence in Basic Sciences.

Besides research, I am passionate about disseminating science to the masses through popular outreach talks, experimental demonstrations, print and the electronic media. You can find a partial list of outreach efforts I have been involved as a co-founder and an independent volunteer.

Email  /  LinkedIn  /  Astrobreeze

Research

My research interests include developing novel instruments for optical spectroscopy and imaging, beam shaping/adaptive optics using Spatial Light Modulators (SLMs), developing iterative algorithms for generating optimised computer generated holograms, phase reconstruction using iterative algorithms and designing automated pipelines for data analysis.

Some of my other interests include trying to comprehend radio pulsar emission using multi-frequency observations, timing and spectroscopy of X-ray pulsars. I have been priviledged to utilise Giant Metrewave Radio Telescope (GMRT) processed data and data from space missions (AstroSat, Neil Gehrels Swift Observatory and archival Rossi X-ray Timing Explorer) to explore fascinating manifestations of radio and X-ray pulsars respectively. I also have profound interests to explore the strongest magnets in our Universe viz. magnetars and fascinating cosmic objects called Ultraluminous X-ray Pulsars.

Current research interests: Adaptive optics, Hyperspectral imaging, X-ray pulsar timing and spectroscopy, Exploring X-ray transients, Understanding manifestations of radio pulsar emission, disruptive technologies
  • Characterisation of phase modulation properties of a reflective Spatial Light Modulator (SLM)

  • We use a Michelson interferometer setup to characterise the phase response of a reflective SLM. The conventional calibration method is time-consuming and we develop a new method using novel phase-masks which can enable threefold faster measurements without modifying any hardware in the experimental setup. To our knowledge, our method is the first endeavour directed towards enabling rapid phase characterisation of an SLM and can have very useful applications in settings which often require frequent and faster phase calibrations such as in astronomy.

    Chandra and Banerjee, Journal of Modern Optics 67 (7), 628-637, 2020

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  • Development of automated pipelines for analyzing interferograms

  • We have developed a semi-automated pipeline in Python and shell from scratch to analyze all recorded interferograms obtained during our phase calibration experiment of an SLM. The first step in the analysis is to smoothen each interferogram and then make an appropriate 1-D cut in the interferogram at two locations, viz. one in the top half and the other in the bottom half of the interferogram. These values are kept fixed for all interferograms. A peak detection algorithm then detects the number of specified peaks in the fringe pattern and finds the relative shift between the upper half (variable graylevel) and lower half (reference graylevel) of the fringe pattern. We then compute the relative shifts between different graylevels and obtain the calibration curve for our SLM.

    Chandra and Banerjee, Journal of Modern Optics 67 (7), 628-637, 2020


  • Generation of optimised phase masks using Iterative Fourier Transform Algorithms (IFTAs) for diverse beam shaping applications

  • Inherent defects in the SLM such as their pixelated nature, phase change according to the gray scale and edge effects limit the resolution and the diffraction efficiency of the SLM. IFTAs can be used to design the optimised phase distribution of the rectangular grating in 1D and 2D. SLMs are promising candidates to employ such optimised IFTAs wherein precise control and regulation of applied electrical voltages can enable us to manipulate the amplitude or phase of the incident beam. Another advantage of this method is that no additional changes need to be made in the SLM hardware to realise the goals. Thus, one can make up for the inherent limitations of the SLM and use it to maximum advantage. Besides, many of these optimised IFTAs are fast and computationally feasible. An array of 2D uniform spots can be useful for many applications such as optical trapping, adaptive wavefront sensing applications in an AO system etc. We have developed a code for generating optimised phases for 1D or 2D gratings and achieved experimental realisation of this method by generating an array of 1D/2D spots.

    Chandra and Banerjee, Journal of Modern Optics 67 (7), 628-637, 2020


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  • Generation of Laguerre-Gaussian (LG) beams using SLM

  • We have generated Laguerre-Gaussian (LG) beams of higher orders using our reflective SLM. We obtain LG beams whose radial and azimuthal modes are upto (p,l)=(3,3) (check montage showing LG beams of different radial (p) and azimuthal (l) orders generated using an SLM).
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  • Adaptive hyperspectral imaging

  • To measure the spectrum of a cosmic source, one would require an interferometer which measures one wavelength at a time. This method of measuring spectra becomes challenging to study a source whose spectra changes rapidly with time or a transient source which is visible for only short durations. In our work we show in laboratory settings that it is possible to measure multiple wavelengths at a given time using an adaptive Michelson interferometer wherein one of the mirrors is replaced with an adaptive optical element which is a reflective Spatial Light Modulator (SLM). In addition, this novel approach does not involve moving mechanical parts which is very useful for potential spectroscopic applications using space instruments. Potential applications of this method include studying targets whose optical emission and concomitant spectral signature varies quickly on time-scales of a few tens of milli-seconds such as solar dynamic activity, optical emission from compact objects such as neutron stars and transient events such as gamma-ray bursts (GRBs).

    Chandra et al., Optics Express 30 (11), 19930-19943, 2022



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  • Adaptive Optics (AO) using SLM

  • Observations from ground based telescopes are marred by seeing effects and require adaptive optics systems. AO systems usually use deformable mirrors which are expensive and are used only for wavefront correction. SLMs can function as dynamical optical elements and can work both as an adaptive wavefront sensor as well as to compensate for wavefront abberation. AO using SLMs is an active area of research and we are developing an open-loop AO system in laboratory settings using Zernike phase correction.

Publications

List of publications: ADS Library

Ultraluminous X-ray Pulsar (ULXP) Catalogue


Discovery of torque reversal in the Be/X-ray binary pulsar GX 304-1
A. D. Chandra.
Under review.
[PDF]


AstroSat observations of the Be/X-ray binary XTE J1946+274 during 2018 and 2021 outbursts
A. D. Chandra, J. Roy and P. C. Agrawal.
Research in Astronomy and Astrophysics, 23 (4), 045003, 2023.
[PDF]


Adaptive hyperspectral imaging using structured illumination in a spatial light modulator-based interferometer
A. D. Chandra, M. Karmakar, D. Nandy and A. Banerjee.
Optics Express 30 (11), 19930-19943, 2022.
[PDF]


Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?
A. D. Chandra, J. Roy, P. C. Agrawal and M. Choudhury.
Monthly Notices of the Royal Astronomical Society 508 (3), 4429-4442, 2021.
[PDF]

Blog: Taking the pulse of a neutron star for almost five decades finds nearly cyclic spin changes on long time-scales


Efficient beam multiplexing and improving efficiency of a spatial light modulator using an iterative algorithm
A. D. Chandra and A. Banerjee.
SPIE Optics + Photonics 2020, Laser Beam Shaping XX (11486), 2020.
[PDF]


Rapid phase calibration of a spatial light modulator using novel phase masks and optimization of its efficiency using an iterative algorithm
A. D. Chandra and A. Banerjee.
Journal of Modern Optics 67 (7), 628-637, 2020.
[PDF]


Study of recent outburst in the Be/X-ray binary RX J0209.6-7427 with AstroSat: a new ultraluminous X-ray pulsar in the Magellanic Bridge?
A. D. Chandra, J. Roy, P. C. Agrawal and M. Choudhury.
Monthly Notices of the Royal Astronomical Society 495 (3), 2664-2672, 2020.
[PDF]

Press release by the Royal Astronomical Society on our discovery
Ultra-bright X-ray source awakens near a galaxy not so far away

Blog: Detection of a New Ultraluminous X-ray Pulsar in the Magellanic Bridge with AstroSat

EurekAlert, phys.org, Sci-News, Science Daily, IFLscience, UPI.com, ANI news, Spektrum.de, SciTechDaily, Naked Science, Nanowerk, Science springs




Astronomer's Telegram

13. Swift/XRT observation of the X-ray transient SRGA J144459.2-604207
A. D. Chandra.
ATel#16471, 2024.

12. Swift/BAT confirms X-ray brightening of the black hole X-ray binary 4U 1543-47
A. D. Chandra.
ATel#15717, 2022.

11. Swift/XRT observations of GRB 221017A
A. D. Chandra.
ATel#15702, 2022.

10. Swift/XRT confirms brightening of the X-ray transient 2E 1050.8-6200
A. D. Chandra.
ATel#15630, 2022.

9. Rapid X-ray brightening of XTE J1701-462
A. D. Chandra.
ATel#15602, 2022.

8. Swift/XRT confirms outburst of XTE J1701-462
A. D. Chandra.
ATel#15594, 2022.

7. New outburst of GX 339-4 confirmed by Swift/XRT
A. D. Chandra.
ATel#15578, 2022.

6. Swift/XRT observations of XTE J1829-098
A. D. Chandra.
ATel#15555, 2022.

5. Detection of X-ray brightening from the X-ray pulsar XTE J1829-098
A. D. Chandra.
ATel#15551, 2022.

4. Swift/XRT non-detection of the X-ray transient MAXI J1957+032
A. D. Chandra.
ATel#15460, 2022.

3. Swift detects rapid outburst decay from MAXI J1957+032
A. D. Chandra.
ATel#15457, 2022.

2. Swift follow-up of the newly discovered accreting millisecond X-ray pulsar MAXI J1816-195
A. D. Chandra.
ATel#15426, 2022.

1. MAXI/GSC detection of a new X-ray outburst from the Be/X-ray binary pulsar H1145-619
A. D. Chandra.
ATel#15359, 2022.

Observing Time Awarded

AstroSat (total 440 ks awarded as PI)

Neil Gehrels Swift Observatory (total 116 ks awarded as PI)

Neutron star Interior Composition Explorer (total 65 ks awarded as PI)

Technical skills

Programming
Python, C/C++, Fortran, shell scripting (bash), Latex, Mathematica, HTML

Software packages
FTOOLS, XSPEC, XRONOS, LaxpcSoft, GNUPlot, PGPLOT, LightPipes, HTCondor

Operating systems
Linux, Windows

Hardware
Interfacing devices using RS-232, USB and Labview

Other relevant skills
Data reduction of AstroSat, Neil Gehrels Swift Observatory, Neutron star Interior Composition Explorer (NICER) and Rossi X-ray Timing Explorer (RXTE) mission
Experience in developing automated pipelines from scratch for data reduction/analysis

Research experience

Development of a semi-coherent method to search for continuous gravitational waves (Aug-Sept 2014 and Nov-April 2015)
Advisor: Dr. Holger J. Pletsch, PI Emmy Noether group, Max Planck Institute for Gravitational Physics (Albert Einstein Institute)

Spectral studies of X-ray pulsar Vela X-1 using Rossi X-ray Timing Explorer (Aug-Dec 2013)
Advisors: Prof. P. C. Agrawal and Dr. Manojendu Choudhury, UM-DAE CEBS, Mumbai (MSc. thesis project)
Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?
A. D. Chandra, J. Roy, P. C. Agrawal and M. Choudhury.
Monthly Notices of the Royal Astronomical Society 508 (3), 4429-4442, 2021.

Pulse shape variations in pulsars on long time-scales (May-July 2013)
Advisor: Prof. Yashwant Gupta, National Centre for Radio Astrophysics-Tata Instiute of Fundamental Research (NCRA-TIFR), Pune (VSRP summer project)

Timing studies of X-ray pulsar Vela X-1 using Rossi X-ray Timing Explorer (Jan-April 2013)
Advisors: Prof. P. C. Agrawal and Dr. Manojendu Choudhury, UM-DAE CEBS, Mumbai (semester project)
Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?
A. D. Chandra, J. Roy, P. C. Agrawal and M. Choudhury.
Monthly Notices of the Royal Astronomical Society 508 (3), 4429-4442, 2021.

Study regarding pulse shape variations in pulsars (May-July 2012)
Advisor: Prof. Yashwant Gupta, National Centre for Radio Astrophysics-Tata Instiute of Fundamental Research (NCRA-TIFR), Pune (Indian Academy of Sciences Summer project)

Teaching experience

Teaching assistant, Modern physics and optics (PH2203), IISER Kolkata (Spring 2019)

Teaching assistant, Advanced Optics Laboratory (PH3204), IISER Kolkata (Spring 2018)

Teaching assistant, Space astronomy (SS4202), CESSI, IISER Kolkata (Spring 2017)

Teaching assistant, Physics Laboratory I (PH1102), IISER Kolkata (Autumn 2016)

Awards and Honors

Measurement Science and Technology: 2022 Outstanding Reviewer Award.

Awarded scholarship in form of full fee waiver to attend the European Virtual Summer School on Adaptive Optics (7-10 June, 2021) .

Awarded SPIE International Day of Light (IDL) micro-grant (funding $1000) for conducting outreach activities during inaugural edition of IDL 2018 (total 14 awardess across the globe).

INSPIRE fellowship, Department of Science and Technology, Government of India, March 2016-present.

Visiting Summer Research Programme (VSRP) fellowship, National Centre for Radio Astrophysics-Tata Instiute of Fundamental Research (NCRA-TIFR), May-July 2013.

Indian Academy of Sciences-Indian National Science Academy-The National Academy of Sciences, India (IASc-INSA-NASI) Summer Research Fellowship 2012.

INSPIRE scholarship, Department of Science and Technology, Government of India, July 2009-July 2014.

Relevant courses

Machine Learning with Python
IBM digital credential

Participated in the Global Initiative for Academic Networks (GIAN) course on A short course on Super-oscillations and Weak Measurement held from 5-12 December, 2016 in IISER Kolkata. The course was taught by Prof. Sir Michael Victor Berry, University of Bristol.

Fluid and Magneto-hydrodynamics (Spring 2016)

Computational Physics (Autumn 2015)

Attended a set of twelve lectures on Experimental astronomy by Prof. Alec Boksenberg (FRS, Former Director, Royal Greenwich Observatory) during February, 2014.

Professional service

Referee for APL Photonics, APL Machine Learning, Applied Physics Letters, Applied Optics, Biomedical Optics Express, Journal of Optics, Journal of Physics Communications, Journal of the Optical Society of America A, Measurement Science and Technology, New Journal of Physics, Optical Engineering, Optics Express, Optics Letters, OSA Continuum, Physica Scripta, Review of Scientific Instruments
Recognized Optica (formerly OSA) reviewer
IOP Trusted Reviewer
Recognized Optical Engineering reviewer

LOC for three day student organised conference "Contemporary Trends in Optics 2019" (CoOpt-2019)
LOC for one day outreach workshop on International Day of Light (IDL) 2018
LOC for three day student organised conference "Contemporary Trends in Optics 2017" (CoOpt-2017)
LOC (lead) for three day workshop on "Space Astronomy and Telescope Making" 2017
LOC (lead) for World Space Week 2015 outreach events

Public outreach (selected events)

Virtual outreach talk: Delivered a popular astronomy talk (including discussions on existing/upcoming astronomy facilities in India + India's participation in International megaprojects SKA, TMT, LIGO and career propsects for engineers in astronomy) to students of Coochbehar Government Engineering College as part of their college fest "Tech-O-Ber" during October, 2021 Recording of virtual talk

Virtual outreach talk: Delivered a popular astronomy talk and discussed career prospects in science for school students after 12th grade on 8 October, 2020. The online talk was organized by Planet Academia based in Dhanbad and the audience included about 100 school and college students.

Delivered a popular astronomy talk on "Lifecycle of Stars" and existing/upcoming astronomy facilities in India on 8 June, 2018 to Jagadis Bose National Science Talent Search (JBNSTS) junior scholars during the science workshop organised in IISER Kolkata. This workshop was attended by about 50 junior scholars.

Co-organised PARADIGM-cultivating innovation... on 2nd February, 2018 during INQUIVESTA 2018--annual science fest of IISER Kolkata. I also delivered a popular astronomy talk on "Lifecycle of Stars " and existing/upcoming astronomy facilities in India during the outreach session. I was also responsible for maintaining social media portals for the event.

Co-organised outreach activities on the occasion of "Super Blue Blood Moon Eclipse" on 31 January, 2018. I delivered one of the curtain raiser talks titled "What is a Super-Blue-Blood Moon Eclipse?" and co-led the total lunar eclipse viewing party using a 6-inch reflecting telescope. The skygazing session was a memorable one and witnessed a huge turnout of 500+ participants.

Co-organised a half-day special outreach session on "A career in science after 12th class" in our alma mater JVM Shyamali on 27 December, 2017. This event was co-led by another alumni Shashikant Singh, Scientist, Semi-Conductor Laboratory ISRO. The outreach event was attended by about 100 students and their guardians.

Delivered a popular astronomy talk on "Our solar system" to 9th grade school students during the Salters Chemistry Camp organized by IISER Kolkata along with Royal Society of Chemistry and Government of West Bengal. This camp was held in IISER Kolkata from 19-21 December, 2017 and was attended by 66 school students.

Co-organised an experimental demonstration session for school students from Ek-Pehal on the occasion of Children's day on 14 November, 2017.

Co-organised three day workshop on "Space Astronomy and Telescope Making" from 24-26 March, 2017. The student driven workshop involved active participation from the student community and twenty-five 4-inch reflecting telescopes were built during this period. I also maintained social media portals for this workshop.

Co-organised World Space Week 2015 events including painting competition, quiz, experimental demonstration events, public talks etc.

Organised Supermoon skygazing event using a 6-inch telescope on 28 September, 2015 for Ek-Pehal students and undergraduate students of IISER Kolkata. The event witnessed a turnout of more than three hundred participants.

Popular science interviews

Co-produced popular science interviews with some like-minded research students. The main aim of interviewing scientists was to know how they got into science and their research areas aimed for a layman. We hope these conversations would inspire young students to get excited about science and take up scientific research as a career.

Interview with Prof. David Hilditch, now at CENTRA, Portugal

Interview with Prof. Dipanjan Mukherjee, now at IUCAA, Pune

Interview with Prof. A. N. Ramaprakash, IUCAA, Pune and Associate Program Director, Thirty Meter Telescope-India

Interview with Prof. K. L. Sebastian, Indian Institute of Science, Bangalore

Interview with Prof. Sir Michael Victor Berry (FRS), University of Bristol, England

Interview with Prof. Dipankar Banerjee, Indian Institute of Astrophysics, Bangalore

Popular science articles

Taking the pulse of a neutron star for almost five decades finds nearly cyclic spin changes on long time-scales

Detection of a New Ultraluminous X-ray Pulsar in the Magellanic Bridge with AstroSat

Understanding "Surya"-the gigantic plasma ball in our neighbourhood I-V

ASTROSAT Celebrates 2nd Birthday Among the Stars! A Look at Its Achievements!

Aditya L1: What India's Maiden Space Mission to Study the Sun Will Look For

Hawaii Will Soon Get One of the World's Largest Telescopes, and India Has a Big Role in the Project!

Introduction to Cosmic lighthouses: Pulsars

Collaborators

Prof. Ayan Banerjee, IISER Kolkata (PhD advisor)
Dr. Jayashree Roy, IUCAA Pune
Prof. P. C. Agrawal, Senior professor (retired), TIFR Mumbai (MSc. thesis advisor)
Dr. Sayan Pal, former graduate student, S. N. Bose National Centre for Basic Sciences
Prof. Yashwant Gupta, NCRA-TIFR Pune

References

Available upon request


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