Observational Cosmology - HI 21 cm
Epoch of Reionization
PI: Abhirup Datta
The research in this group includes cosmological observations at low radio frequency with uGMRT, VLA, ATCA and in future SKA. Dr. Datta is a science team board member for Epoch of Reionziation key science project in International SKA collaboration from India. His current interest in this field is in foreground characterization and removal from reionization data from radio interferometers using machine learning techniques like neural networks. This group is also working on using the state-of-the-art radio imaging/calibration algorithms to achieve high dynamic range imaging with low frequency radio data-sets.
Dr. Datta is also collaborator in the international DARE (Dark Ages Radio Explorer) experiment which is currently a concept mission being proposed to NASA for flight. This involves probing cosmic reionization using the global 21cm signal. Currently, three PhD students are working in this area.
Cosmic Dawn and Epoch of Reionization with the redshifted 21-cm line
PI: Suman Majumdar
Cosmology is the study of the evolutionary history of our Universe. One of the most important missing pictures in this history is the Cosmic Dawn (CD) and the Epoch of Reionization (EoR), the period during which the very first sources of light were formed and thus marked the end of the dark ages. The radiation emitted by these sources gradually heated and “re”-ionized the neutral and cold hydrogen (HI) in their surrounding inter-galactic medium (IGM). Many fundamental issues regarding this era, such as its timing, duration, and the properties of the sources driving it, are still unresolved. Observations of the redshifted 21-cm signal, emitted by the HI from this era, hold a great promise to resolve many of these puzzles. Several radio telescopes around the world are currently in a race to detect this signal in great detail (for example -- GMRT, LOFAR, MWA, PAPER, 21CMA). Very recently, scientists may have got the very first glimpses of this signal through the EDGES experiment. The upcoming enormous Square Kilometre Array (SKA), an international radio telescope of which India is also a member, is expected to be able to image the HI distribution at different cosmic times from the beginning to the end of this era, owing to its great sensitivity. Once the redshifted 21-cm signal from the CD and the EoR is detected, one would require a robust data analysis and interpretation pipeline to answer the unresolved questions regarding this epoch.
My main research interest is focused on the development of such interpretation pipelines. As the actual signal is yet to be detected, such pipelines need to be trained and tested on simulated signal data sets. A major part of my past research focused on the development of detailed but fast computer simulations of the signal, to study different models of reionizations at a relatively low computational cost. Additionally, in the recent past and present, I have been studying different statistical estimators (such as the power spectrum, bispectrum, etc.) of the signal to identify its various unique characteristics, which can be used for the confirmative detection as well as for constraining the different reionization model parameters. As a member of the international Science Working Group for the CD and EoR with the SKA, I am involved in the development of such interpretation tools and pipelines along with my international collaborators. As soon as the SKA becomes operational and starts observing this epoch, it will open up a new exciting phase of cosmological exploration, which will enable us to better understand the Epoch of Reionization. Cosmologists around the world are eagerly waiting for this upcoming new era of “21-cm cosmology” that promises to revolutionize our understanding of the history of the universe.
Galaxy clusters: Mergers and Interaction with CMB
PI: Siddharth Malu and Abhirup Datta
The group led by Dr. Datta and Dr. Malu studies mergers or collisions between clusters of galaxies, which leads to copious amounts of radio emission, with a characteristic power law spectrum. Cluster-wide radio emission, which is found in central regions of the cluster, is known as a radio halo, and when found in peripheral regions of clusters/mergers, is known as a radio relic. There are several models that may explain the spectrum of this diffuse radio emission; however, the physical mechanisms that accelerate particles in these cluster mergers, and cause enhancements of the magnetic fields in the clusters, are not entirely understood. The group studies this diffuse radio emission at frequencies ranging from a few hundred MHz to ~ 20 GHz, to characterize its spectrum across a wide a range of frequencies, in order to gain insight into particle acceleration.
We also study inverse Compton scattering of cosmic microwave background photons from galaxy cluster electrons - known as the Sunyaev-Zeldovich Effect (SZ effect), as a way to characterize pressure structures. With X-ray observations of thermal plasma, and radio observations of non-thermal plasma in clusters, it is possible to characterize the energy distribution of the galaxy cluster plasma. This is the aim of SZ effect observations at cm-wavelengths - these are the lowest frequencies at which SZ effect can be measured. Currently, 2 PhD students are working in this area.
Radio astronomy Instrumentation
PI: Siddharth Malu and Abhirup Datta
Having set up a Radio Frequency (RF) laboratory, the discipline has received funds from DST-SERB to make a 4-element radio interferometer at 1.4 and 5 GHz. Other than constructing this pathfinder, the RF lab also helps characterize RF properties of novel materials (made by one of the Associate members, Dr. Somaditya Sen). Four dishes, of 2.5 metre diameter, are being readied for the interferometer. Currently, 1 PhD student and 1 JRF are working in this area.
Instrumentation and signal processing
PI: Avinash Deshpande
Development of optimal instrumentation and of novel techniques in image and signal processing, assessed at times with detailed simulations, facilitates incisive investigation, in the presence of inherent random noise and the consequent uncertainties.
Space weather and ionospheric studies
PI: Abhirup Datta
This group is involved in studying effect of ionosphere in low frequency radio astronomy. The group has recently acquired a GNSS receiver to study the ionosphere above Indore. The group is in talks to acquire IRNSS receiver from ISRO-SAC. The group is working on studying and characterizing the ionosphere. There is already a dense grid of GNSS receivers in Northern India. Our proposal will complement that in Central and Western India. This will allow us to predict the ionospheric conditions and model them with better precision. In turn, this will help in satellite and aerospace communication as well as making it possible to observe at low radio frequencies. This study will help us to establish leadership in ionospheric research mainly in context of astronomical observations. India’s role in SKA (Square Kilometer Array) can be used to share this information with the upcoming state-of-the-art largest radio telescope in the world. Currently, 3 PhD students are working in this area.
PI: Bhargav Vaidya
Computational astrophysics opens new windows in the way we perceive and study the heavens. This rapidly growing new discipline in astronomy combines modern computational methods and algorithms to simulate and analyse data so as to discover new phenomena, and to make predictions in astronomy, cosmology and planetary sciences.
Research in area of Computational Astrophysics is led by Dr. Bhargav Vaidya whose research interests cover a wide range of topics closely associated with Computational and theoretical aspects of Astrophysics. In particular, the main aim of his research is to develop synthetic observatory for multiple astrophysical sources to bridge results from state-of-the-art simulations with observations and develop templates that can predict and or verify various features observed using existing and up-coming observatories like ALMA, Lofar, SKA, TMT and CTA.
At present, the focus is on astrophysical jets that are an ubiquitous phenomenon seen in wide variety of astrophysical sources like young stellar objects, Active galactic nuclei, Pulsar wind nebulae etc. The current goal is to study the interplay of different processes that are responsible to accelerate particles to very high energies in these jets. Additionally, the goal is to combine these acceleration mechanisms with various processes that contribute to radiative losses via synchrotron and Inverse Compton to produce non-thermal emission commonly observed in jets. The condition for stability and the physics of magnetic energy dissipation in large scale collimated jets are also the major research interest of this group.
The synthetic observatory that will primarily be developed for Astrophysical jets will pave a new and versatile pathway to expand research capabilities in the area of space weather modelling, simulating radio haloes, triggered star formation, accretion disk physics and microscopic behaviour of astrophysical plasma.
Dr. Vaidya is one of the integral developer of a widely popular astrophysical code called PLUTO (http://plutocode.ph.unito.it) and has a strong collaborations with the developers in University of Torino, Italy.
PI: Avinash Deshpande
Pulsars, often described as Cosmic Light-houses, are believed to be strongly magnetized, fast rotating neutron stars, with over 2000 discovered in our Galaxy so far.
In the long march towards the elucidation of the mysterious ways of pulsars, we strive to decipher their intriguing pulse-to-pulse variations, seeking clues on the yet poorly-understood mechanism of coherent radio emission. This necessitates high time resolution multi-frequency observations of individual pulses, using some of the most sensitive radio telescopes in the world, and employing novel hardware and software techniques, to extract and interpret the underlying key messages. Apart from using pulsars as a probe of the intervening interstellar medium, we also exploit the imprint of the some of the propagation effects to in turn search for the illusive unpulsed component of their radiation, and also study the spectacular nebulae, resulting from the interaction of the collimated particle and radiation beams with the surroundings.
X-ray binaries and magnetars
PI: Manoneeta Chakraborty
The research in this group encompasses a variety of high energy astrophysics topics with particular emphasis on compact object physics. Neutron stars and black holes exhibit the most extreme physical conditions in the universe. They offer the ideal laboratories to probe strong gravity, the properties of supranuclear matter and the most intense magnetic field conditions. The group is actively involved in the timing and spectroscopic studies of stellar and super-massive black holes, neutron star, pulsars and magnetars. The research here focuses deeply on the study of accretion in X-ray binary systems and its radiative properties and variabilities. The spectral evolution of such compact objects in both isolated and binary systems is studied to understand the behavior of the accretion disk and the corona during the outburst state of the X-ray binary. A multi-wavelength monitoring of these objects can reveal intricacies of the disk-jet connection and the hard X-ray component. Thermonuclear bursts and burst oscillations can be used to probe the surface properties of neutron star and thus are the most promising candidates to constrain the equation of state of ultra-degenerate supra-nuclear neutron star matter. Research is also carried out on pulsars - rotation powered, accretion powered and magnetically powered - and how blurring of classes among the different categories of pulsars can lead to understanding about the evolution and lifecycle of pulsars. The timing and spectral variability are also studied across different scales - from stellar mass black holes in X-ray binaries to supermassive black holes in active galactic nuclei. The group is also interested in investigating the connection of more recently discovered class of objects like Ultra-luminous X-ray sources (ULXs) and fast radio bursts (FRBs) with current understanding of the compact objects.
For pursuing the above science problems data from multiple instruments across multiple wavelengths are analyzed. The research involves extensive analysis of data from missions like RXTE, Chandra, Swift, XMM-Newton, NuStar, Astrosat, GMRT, VLA, SALT and many others. Apart from the electromagnetic window the group is also interested in the observation of these objects in the gravitational wave window as these compact objects are the primary origins of gravitational waves either through mergers or through steady spin-down decay of pulsars.
Navigation, Spacecraft and Payload Control
PI: Hari Hablani
Satellite-Based Navigation of Flight Vehicles
ISRO has invested significant resources in establishing and providing navigation signals to users from national satellites system NavIC (Navigation with Indian Constellation). Our research is concerned with developing algorithms to use these signals for precise navigation of land vehicles, airplanes, satellites, launch vehicles, and missiles.
Control of Satellites and Payloads and Minimization of Mutual Interference
Remote sensing, communication and navigation satellites have payloads with mirrors, radars and infrared sensors that scan the earth, ocean and space with satellite platforms as their base. But this motion causes the platforms to reorient, which interferes with the operation of the payloads. Additionally, due to environmental perturbing forces, the satellites deviate from their intended ideal position and velocity, which interferes with spatial registration of images acquired with remote sensing. The objective of this research is to understand the mechanics of these interferences and minimize them.
Agile Maneuvers of Reconnaissance and Surveillance Spacecraft with Control Moment Gyros
As spacecraft become heavy with their imaging payloads, the high-torque control moment gyros (CMGs) become the actuators of choice so that the spacecraft can be reoriented rapidly to acquire and track successive objects or areas of interest on the ground. But CMGs have spinning wheels and their momentum is turned around to produce the desired spacecraft control torque. But this occasionally results in alignment of the CMGs momentums, and the CMGs then cannot produce the desired torque, a state known as singularity. The objective of this research is to develop control algorithms for CMGs so that they steer away from singularity while acquiring and tracking the targets of interest. An additional objective is to demonstrate these controllers on a CMG testbed at ISRO Inertial Systems Unit.
Navigation of Precision Munition with Infrared and Millimeter-Wave Radar Sensors Homing in on Moving Ground Targets
The objective of this research is to develop navigation and guidance algorithms for dual-sensor air-to-surface precision munition to neutralize moving tanks in mountainous areas covered with snow and trees or in deserts in inclement weather. The infrared and millimeter-wave radar dual-sensor is particularly apt for targets with electronic countermeasures, suppressed radar signature, and small temperature difference with cluttered surroundings. Navigation algorithms and Kalman filters are developed to meet or exceed the specified performance metrics of probability of detection, probability of false alarm and circular error probable radius of miss distance.
Dynamics and Guidance of Reentry Spacecraft
The objective of this research is to develop an understanding and a simulation of reentry dynamics under classic guidance laws, namely, the constant drag deceleration, and the constant descent rate to land at a specific site. Furthermore, the objectives are to overcome the limitations of these guidance laws by treating reentry as a two-point boundary value problem with initial conditions at the interface of the final orbit or approaching interplanetary trajectory and the reentry trajectory ending at the desired landing latitude and longitude on the land or ocean with a desired touchdown velocity.
Entry and Descent Navigation of Lunar Lander
The objective of this research is to develop a high-accuracy inertial navigation system aided with a radar altimeter for entry and descent on the Moon's surface.