“Don't ask yourself what the world needs; ask yourself what makes you come alive. And then go and do that. Because what the world needs is people who have come alive”
--- Howard Thurman, Gil Bailie's Violence Unveiled, p. xv (Thanks to Max Tegmark at MIT from whom I first came to know this quote).
A supreme quality of teaching and top level research are symbiotic in nature. This is apparent at the majority of the premier research universities in the world where students get to learn and draw inspiration from the faculty members who are working on cutting-edge research while the faculty members rejuvenate their drive for research through teaching and spirited discussion with students.
Presidency University is trying to provide such an environment to its students and faculty. I am glad to be a part of this endeavour.
My broad research interest is in astrophysics. More specifically I probe the physics of astronomical objects containing black holes, e.g., active galactic nuclei (AGN) and X-ray binaries, primarily by studying their time variability. Below I give a (relatively) non-technical description of my research. More technical details are in the section named Research / Administrative Experience.
All galaxies are believed to contain a super-massive black hole (having a million to a billion times the mass of the Sun) at their center. About 5% of these black holes are actively accreting mass from its surroundings and as a result producing enormous amount of electromagnetic radiation from gamma-ray to radio frequencies. These galaxies are called active galaxies and the bright central part of the active galaxies are called active galactic nucleus.
There are several reasons for which learning more about the nature of AGNs is important:
1. An active galactic nucleus (AGN) is brighter than the rest of the galaxy and sometimes ten thousand times as bright as an average galaxy. Being the most luminous long-lived class of objects in the sky that are more common at high redshifts, their light comes from a very young universe. They are an important tool for the astronomers to probe the distant and early universe.
2. The extremely high luminosities of AGNs are thought to be produced by the accretion of matter on to a supermassive black hole. Hence, AGN is a natural laboratory to test strong field General Relativity.
3. In many cases AGNs produce two oppositely directed jets of magnetized plasma moving at near-light speed that are equally luminous over a large range of wavelengths from radio to gamma rays. Jets are the brightest non-transient objects in the sky. The apparent brightness of jets is amplified by factors of few-10000 if they are pointed toward our line of sight. Hence we can observe them even if they are far away. In some cases, high-energy emission (X-rays, Gamma-rays) from the jets varies by a factor of a few in minutes. To explain how such large amount of emission is generated at such short-timescales is a challenge for the theories of acceleration of particles.
4. It has been established now that the stellar motion near the center of the galaxies is correlated to the mass of the central super-massive black hole (SMBH). In addition, it has been observed that kinetic energy of the jets affect its environment such as the intra-cluster medium. Hence, the formation and evolution of galaxies are influenced by the SMBH and the jets.
5. Considerable progress has been made in our understanding of the nature of active galactic nuclei (AGNs) over the last two decades. But how and why the jets form is not understood. Knowledge about this will be useful for many astrophysical systems containing a jet such as stellar mass black hole X-ray binaries, and young stellar objects as well as active galactic nuclei.
Due to their large distances, AGNs are not spatially resolved with current and near-future technologies except by radio interferometry. However, one of the defining properties of AGNs is time variability, that is, their brightness significantly varies with time due to changes in emission processes and internal dynamics. Hence, these systems can be probed by analyzing the change of its brightness with time at a given wave band (e.g. X-rays) as well as how the change at different wave bands (e.g. optical vs. gamma-rays) compare.
This analysis and its theoretical interpretation is the central theme of my research.
BSc (Honours) Physics (Presidency College, University of Calcutta, 2001)
MSc Physics (IIT Kanpur, 2003)
PhD Astronomy (Boston University, 2009)
Post-doctoral research experience at Yale University (2009-2012) and University of Wyoming (2012-2013).
My broad research goal is to probe accreting black hole systems using multi-waveband time variability. As a part of my PhD thesis, I have developed and used robust timing analysis tools to constrain the location and mechanism of high energy emission in individual AGNs. The relationships that I have uncovered between the black hole (BH) and the jet in the radio galaxies provide strong support for the paradigm of universality in the accretion processes in BHs spanning a broad range of masses from 10 to 10^8 solar mass. I have developed a theoretical model of the time variable non-thermal emission spectrum of an AGN jet to facilitate the interpretation of the timing analysis. As a post-doc at Yale, I collaborated with Charles Bailyn, Jerry Orosz, and Michelle Buxton to model the multi-frequency variability and spectra of Galactic BH X-ray binaries in order to constrain their geometric and physical parameters. In collaborations with Krzysztof Nalewajko at University of Colorado, Boulder, Xuhui Chen at , Paolo Coppi at Yale and Giovanni Fossati at Rice University I am modeling the the spectral energy distributions of AGNs with truly simultaneous data. I have extended my time variability related work to gamma-ray variability from the Fermi Gamma-Ray Space Telescope. I am currently working in collaboration with Jo Bovy at Princeton University and Adam Myers at University of Wyoming to develop an algorithm to search for quasars from large all-sky surveys which will include both variability and color information and hence will be superior to previous such efforts. Below, I discuss these projects.
1. Long-Term Multi-Wavelength Time Variability of Blazars:
Blazars are a subclass of AGNs with bright, relativistic jets and violent variability. Time variability across multiple wavebands can be used to probe the location and physical processes related to the emission at very fine resolutions.
I used self-developed robust analysis tools to probe 11-year-long X-ray, optical and radio time variability data of the blazar 3C 279 to show that the emission in the above wavelengths is mostly produced in its jets and the X-ray emission is dominate by the synchrotron self-Compton process.
I have analyzed the time variability properties of a sample of six blazars at optical-IR as well as gamma-ray energies observed as a part of the Yale/SMARTS program during 2008-2010. One of the key results of this project was the longer-term (~months) gamma-ray and optical-IR outbursts in in these blazars are dominated by the crossing timescale of a disturbance and not the radiative cooling timescales.
I showed that the blazar PKS 0208-512 underwent an optical-near-infrared outburst in 2009-10 which did not have any gamma-ray counterpart unlike its other major OIR flares.
Related Papers:
"Correlated Multi-Waveband Variability in the Blazar 3C 279 from 1996 to 2007", 2008, ApJ, 689, 79-94.
"Flaring Behavior of the Quasar 3C 454.3 Across the Electromagnetic Spectrum", 2010, ApJ, 715, 362-384.
"Similarity of the Optical-IR and Gamma-Ray Variability of Fermi Blazars", 2012, ApJ, 749, 191-204.
"SMARTS Optical and Infrared Monitoring of 12 Gamma-Ray bright Blazars", 2012, ApJ, 756, 13-28.
"An Optical-Near-Infrared Outburst with No Accompanying Gamma-Rays in the Blazar PKS 0208-512", 2013, ApJ, 763, L11-L16.
2. Numerical modeling of the Emission Processes in AGN:
Most or all of the X-ray and optical emission originates in the jet in the case of the blazars 3C 279 and PKS 1510 while in the radio galaxies 3C 120 and 3C 111, emission at those wavebands is produced in the accretion disk-corona system. I carried out numerical modeling of the emission processes in a blazar jet and in an accretion disk-corona system. I compared results from those models to the analysis of the multi-wavelength variability described above to draw conclusions about the location and mechanism of emission in these objects.
Related Papers:
"Correlated Multi-Waveband Variability in the Blazar 3C 279 from 1996 to 2007", 2008, ApJ, 689, 79-94.
“Disk-jet Connection in the Radio Galaxy 3C 120”, 2009, ApJ, 704, 1689-1703.
3. Accretion Disk-Jet Connection in the radio galaxies 3C 120 and 3C 111:
Stellar mass black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs) are both powered by accretion on to a black hole (BH) and in many cases, emit radiation over several decades of frequency and have relativistic jets. This has led to the paradigm that these two systems are fundamentally similar with characteristic time and size scales linearly scaled by the mass of the central BH. In BHXRBs, superluminal radio emitting features appear and propagate along the jet shortly after sudden decrease in the X-ray flux.
I use the results of extensive multi-frequency monitoring of the radio galaxy 3C 120 between 2002 and 2007, and 3C 111 between 2004 and 2010 to show that the appearance of new knots in the VLBA images of the jet follow prominent dips in the smoothed X-ray light curve. This demonstrates a connection between events in the jet at parsec scales and those occurring near or in the accretion disk.
We have also shown that the X-ray power spectrum of 3C 111 and 3C 120 contain a break. The best-fit value of the break frequency agrees with the empirical relation between break timescale, BH mass, and accretion rate obtained by McHardy et al.(2006) based on a sample of mainly radio-quiet Seyfert galaxies. This indicates that the accretion process in these two radio galaxies is similar to that of black hole X-ray binaries and Seyfert galaxies, and that there is a possible universality in the accretion processes in BHs spanning a broad range of masses from 10 to 10^8 solar mass.
Related Papers:
“Disk-jet Connection in the Radio Galaxy 3C 120”, 2009, ApJ, 704, 1689-1703.
“Connection between the Accretion Disk and Jet in the Radio Galaxy 3C 111”, 2011, ApJ, 734, 43-58.
4. Study of the Stellar Mass Black Hole Systems:
I have been working on the modeling of ellipsoidal variations in the optical-IR flux of binary systems consisting of a Roche-lobe filling star and an accretion disk around a black hole. Long-term optical-IR monitoring of galactic X-ray binary systems are carried out by the SMARTS consortium. Orbital parameters of these systems can be obtained and the physics of accretion flow can be probed using the theoretical modeling mentioned above along with the long-term light curves.
Related Papers:
"Optical and Near Infrared Monitoring of the Black Hole X-Ray Binary GX 339-4 during 2002-2010", 2012, AJ, 143, 130-145.
Jet Spectral Breaks in Black Hole X-Ray Binaries, 2013, MNRAS, 429, 815-832.
5. Spectral Energy Distribution Modeling of Blazar
Modeling of truly simultaneous time-variable spectral energy distributions (SEDs) from radio to gamma-rays is the holy grail of blazar physics. Such analysis for a large sample of blazars is now possible with data from Fermi and supporting multi-waveband programs. We have modeled the optical-near-infrared (OIR) to gamma-ray SED of the blazar PKS 0208-512 during 2008--2011 to investigate the physical parameters related to its emission.
Related Paper:
Implications of the Anomalous Outburst in the Blazar PKS 0208-512, 2013, ApJ, 771, L25-L30.
Administrative work:
I have published the findings of my research in leading international journals of astrophysics, e.g., Astrophysical Journal, Astronomical Journal, Monthly Notices of the Royal Astronomical Society, and Astrophysical Journal Letters. I am currently carrying out several ongoing projects with collaborators located primarily in the US.
I have served as a referee for several manuscripts submitted to various international journals of astrophysics and have been a member of multiple NASA proposal review panels. I have obtained NASA research grants both as a principal investigator and a co-investigator.
Please see the CV (in pdf) for most recent updates.
Curent Semester (2020 Even: Jan-May)
1. BSc 2nd Yr (Major): Modern Physics Lab (PHYS 04C9)
Lab Exercises (Computational)
2. BSc 3rd Yr (Major): Astrophysics & Cosmology Elective (PHYS 0603)
Course Introduction
Reading Material
Problem Sets
3. MSc 1st Yr: Computational Physics Lab (PHYS 0891)
Course Introduction
Reading Material
Problem Sets
Class Work
4. PhD Coursework: Research Methodology (PHYC1)
How to Give an Effective Research Talk: Slides
Principles of Statistical Inference: Reading Material, Problem Set
Computational Skills (Python Programming): Problem Set
Courses taught since 2013 Fall
PhD Coursework: Professional Research Training (How to Give an Effective Research Talk), Principles of Statistical Inference, Python Programming
MSc 2nd Yr: Introduction to Astrophysics, Astrophysics Laboratory
MSc 1st Yr: General Laboratory, Computational Physics, Classical Mechanics
BSc 3rd Yr (Major): Electrical and Solid State Laboratory, Compu-
tational Physics, Astrophysics & Cosmology Elective
BSc 2nd Yr (Major): Lagrangian Mechanics
BSc 1st Yr (Major): Newtonian Mechanics, Mechanics Lab, Math Methods Lab (Python based)
BA/BSc 1st Yr (General Education curriculum): Space, Time and the Universe, Physics of Everyday Life
Mentoring Experience (Curricular Research)
2018 Spring: Mr. Sagnick Mukherjee (BSc thesis project titled “Disk-Jet Connec- tion in Blazars").
2018 Spring: Mr. Souradip Bhattacharya (BSc thesis project titled “Comptoniza- tion in Active Galactic Nuclei").
2018 Spring: Mr. Prasun Ranjan Das (BSc thesis project titled “Development of Some Higher Secondary and BSc 1st Yr level Physics Demonstrations and Experiments").
2018 Spring: Mr. Kaustav Mitra (MSc thesis project titled “Turbulence in Blazar Jets").
2018 Spring: Mr. Dhrubajyoti Sengupta (MSc thesis project titled “Broad Line Emission in Low-Luminosity Active Galactic Nuclei"(jointly with Dr. Susmita Chakraborty, IISc).
2017 Spring: Mr. Anwesh Majumder (BSc thesis project titled “Spectral Energy Distribution of Quasars").
2017 Spring: Mr. Tathagata Saha (BSc thesis project titled “Accretion Disk-Corona Interaction in Active Galactic Nuclei").
2017 Spring: Ms. Sukanya Mallik (BSc thesis project titled “Particle Acceleration in the Universe (Reading Course)").
2017 Spring: Ms. Nishat Parveen (MSc thesis project titled “Thermal Emission from Blazars").
2017 Spring: Mr. Faruk Abdulla (MSc thesis project titled “Astrophysical Fluid Dynamics (Reading Course)").
2016 Spring: Mr. Agniva Roychowdury (BSc thesis project titled “Identification and Classification Quasars Using Their Vaiability").
2016 Spring: Mr. Shashwata Ganguly (BSc thesis project titled “Modeling X-ray and Optical Variability in Accertion Disk-Corona System in Active Galactic Nuclei").
2016 Spring: Ms. Namrata Roy (Co-Supervisor: MSc thesis project titled “Char- acteristics of Chromospheric Spectral Lines in Solar Flares"). 2015 Fall: Mr. Ajay Haldar (PhD coursework optional module research project titled “Modeling Stellar Structure").
2015 Spring: Ms. Jhuma Ghosh (MSc thesis project titled “Comparing the Nature of GeV Variability of FSRQ and BL Lac Objects Using Fermi-LAT Data").
2015 Spring: Mr. Pritam Pramanik (MSc thesis project titled “WISE Properties of Type-2 Quasars").
2014 Spring: Mr. Prantik Nandi (MSc thesis project titled “Probing Accretion Disk-Jet Connection Through Gamma-Ray Variability of Blazars"). 2014 Spring: Mr. Somnath Mandal (MSc thesis project titled “Studying the Gamma-Ray vs. X-ray Time variability of Fermi Blazars").
2014 Spring: Mr. Suryasish Ghosh (MSc thesis project titled “Physics of Blazar Jets Using Gamma-Ray vs. Optical-Infrared Time Variability").
American Astronomical Society: 2006-2012.
Refereed Publications
15 refereed publications with more than 750 citations as of 2018 June [from the
SAO/NASA Astrophysics Data System (ADS)].
16. “Probing the Jets of Blazars Using the Temporal Symmetry of Their Multi-Wavelength
Outbursts”, Roy, Namrata; Chatterjee, Ritaban; Joshi, Manasvita; Ghosh, Aritra sub-
mitted to MNRAS
15. “Possible Accretion Disk Origin of the Emission Variability of a Blazar Jet”, Chat-
terjee, Ritaban; Roychowdhury, Agniva; Chandra, Sunil; Sinha, Atreyee 2018, ApJL,
859, L21
14. “Magnetic Field Amplification and Flat Spectrum Radio Quasars”, Chen, Xuhui;
Chatterjee, Ritaban; Zhang, Haocheng; Pohl, Martin; Fossati, Giovanni; Boettcher,
Markus; Bailyn, Charles D.; Bonning, Erin W.; Buxton, Michelle; Coppi, Paolo; Isler,
Jedidah; Maraschi, Laura; Urry, Meg 2014, MNRAS, 441, 2188
13. “The Black Hole Binary V4641 Sagitarii: Activity in Quiescence”, MacDonald, R. K.
D.; Bailyn, C. D.; Buxton, M.; Cantrell, A. G.; Chatterjee, Ritaban; Kennedy-Shaffer,
R.; Orosz, J. A.; Markwardt, C. B.; Swank, J. H. 2014, ApJ, 784, 2-20.
12. “The X-ray spectrum and spectral energy distribution of FIRST J155633.8+351758: a
LoBAL quasar with a probable polar outflow”, Berrington, Robert C.; Brotherton, Michael
S.; Gallagher, Sarah C.; Ganguly, Rajib; Shang, Zhaohui; DiPompeo, Michael; Chatter-
jee, Ritaban; Lacy, Mark; Gregg, Michael D.; Hall, Patrick B.; Laurent-Muehleisen, S.
A., 2013, MNRAS, 436, 3321-3330.
11. “A Time Resolved Study of the Broad Line Regin in Blazar 3C454.3”, Isler, J. C.;
Urry, C. M.; Coppi, P.; Bailyn, C. D.; Chatterjee, Ritaban; Fossati, G.; Bonning, E. W.;
Maraschi, L.; Buxton, M. 2013, ApJ, 779, 100-109.
10. “Implications of the Anomalous Outburst in the Blazar PKS 0208-512”, Chatterjee,
Ritaban; Nalewajko, Krzysztof; Myers, Adam 2013, ApJ, 771, L25-L30.
9. “An Optical-Near-Infrared Outburst with No Accompanying Gamma-Rays in the Blazar
PKS 0208-512”, Chatterjee, Ritaban; Fossati, G.; Urry, C. M.; Bailyn, C. D.; Maraschi,
L.; Buxton, M.; Bonning, E. W.; Isler, J.; Coppi, P. 2013, ApJ, 763, L11-L16.
8. “Jet Spectral Breaks in Black Hole X-Ray Binaries”, Russell, David; Markoff, Sera;
Casella, Piergiorgio; Cantrell, A. G.; Chatterjee, Ritaban; Fender, Robert; Gallo, Elena;
Gandhi, Poshak; Homan, Jeroen; Maitra, Dipankar; Miller-Jones, James; O’Brien, Kieren;
Shahbaz, Tariq 2013, MNRAS, 429, 815-832.
7. “SMARTS Optical and Infrared Monitoring of 12 Gamma-Ray bright Blazars”, Bon-
ning, E.W.; Urry, C. M.; Bailyn, C.; Buxton, M.; Chatterjee, Ritaban; Coppi, P.; Fossati,
G.; Isler, J.; Maraschi, L. 2012, ApJ, 756, 13-28.
6. “Optical and Near Infrared Monitoring of the Black Hole X-Ray Binary GX 339-4 dur-
ing 2002-2010”, Buxton, Michelle M.; Bailyn, Charles D.; Capelo, Holly L.; Chatterjee,
Ritaban; Dincer, Tolga; Kalemci, Emrah; Tomsick, John A. 2012, AJ, 143, 130-145.
5. “Similarity of the Optical-IR and Gamma-Ray Variability of Fermi Blazars”, Chat-
terjee, Ritaban; Bailyn, C.; Bonning, E. W.; Buxton, M.; Coppi, P.; Fossati, G.; Isler, J.;
Maraschi, L.; Urry, C. M. 2012, ApJ, 749, 191-204.
4. “Connection between the Accretion Disk and Jet in the Radio Galaxy 3C 111”, Chat-
terjee, Ritaban; Marscher, Alan P.; Jorstad, Svetlana G.; Markowitz, Alex; Rivers, Eliz-
abeth; Rothschild, Richard E.; McHardy, Ian M.; Aller, Margo F.; Aller, Hugh D.; Lähteen-
mäki, Anne; Tornikoski, Merja; Harrison, Brandon; Agudo, Iván; Gómez, José L.; Taylor,
Brian W.; Gurwell, Mark 2011, ApJ, 734, 43-58.
3. “Flaring Behavior of the Quasar 3C 454.3 Across the Electromagnetic Spectrum”, Jorstad,
Svetlana G.; Marscher, Alan P.; Larionov, Valeri M.; Agudo, Iván; Smith, Paul S.; Gur-
well, Mark; Lähteenmäki, Anne; Tornikoski, Merja; Markowitz, Alex; Arkharov, Arkadi
A.; Blinov, Dmitry A.; Chatterjee, Ritaban; D’Arcangelo, Francesca D.; Falcone, Abe D.;
Gómez, José L.; Hagen-Thorn, Vladimir A.; Jordan, Brendan; Kimeridze, Givi N.; Kon-
stantinova, Tatiana S.; Kopatskaya, Evgenia N.; Kurtanidze, Omar; Larionova, Elena
G.; Larionova, Liudmilla V.; McHardy, Ian M.; Melnichuk, Daria A.; Roca-Sogorb, Mar;
Schmidt, Gary D.; Skiff, Brian; Taylor, Brian; Thum, Clemens; Troitsky, Ivan S.; Wiese-
meyer, Helmut 2010, ApJ, 715, 362-384.
2. “Disk-jet Connection in the Radio Galaxy 3C 120”, Chatterjee, Ritaban; Marscher,
Alan P.; Jorstad, Svetlana G.; Olmstead, Alice R.; McHardy, Ian M.; Aller, Margo F.; Aller,
Hugh D.; Lähteenmäki, Anne; Tornikoski, Merja; Hovatta, Talvikki; Marshall, Kevin;
Miller, H. Richard; Ryle, Wesley T.; Chicka, Benjamin; Benker, A. J.; Bottorff, Mark C.;
Brokofsky, David; Campbell, Jeffrey S.; Chonis, Taylor S.; Gaskell, C. Martin; Gaynullina,
Evelina R.; Grankin, Konstantin N.; Hedrick, Cecelia H.; Ibrahimov, Mansur A.; Klimek,
Elizabeth S.; Kruse, Amanda K.; Masatoshi, Shoji; Miller, Thomas R.; Pan, Hong-Jian;
Petersen, Eric A.; Peterson, BradleyW.; Shen, Zhiqiang; Strel’nikov, Dmitriy V.; Tao, Jun;
Watkins, Aaron E.; Wheeler, Kathleen 2009, ApJ, 704, 1689-1703.
1. “Correlated Multi-Waveband Variability in the Blazar 3C 279 from 1996 to 2007”, Chat-
terjee, Ritaban; Jorstad, Svetlana G.; Marscher, Alan P.; Oh, Haruki; McHardy, Ian M.;
Aller, Margo F.; Aller, Hugh D.; Balonek, Thomas J.; Miller, H. Richard; Ryle, Wesley T.;
Tosti, Gino; Kurtanidze, Omar; Nikolashvili, Maria; Larionov, Valeri M.; Hagen-Thorn,
Vladimir A. 2008, ApJ, 689, 79-94.
Presidency University Students Corner