Objective: The primary aim of this workshop is to introduce students and early-career researchers to the theory and X-ray properties of compact objects — i.e., black holes, neutron stars, white dwarfs, and exotic singularities — and to train them in practical X-ray spectral analysis using HEASoft and XSPEC. Although motivated by AstroSat ’s capabilities, the workshop will place these tools and methods in a broader multi-mission context, including NICER , NuSTAR , XMM-Newton , and Chandra.
Motivation and Theme: Compact objects remain central to several crucial open problems in modern astrophysics, spanning strong-gravity accretion physics, dense-matter equations of state, and jet or outflow formation. Their extreme gravitational and magnetic fields create natural laboratories where fundamental physics, i.e., general relativity, plasma physics, radiative transfer, and nuclear matter interactions can be tested under conditions unattainable on Earth. Observations across the electromagnetic spectrum, especially in X-rays, reveal how matter behaves near event horizons, how neutron-star surfaces and magnetospheres emit radiation, and how compact-object (X-ray) binaries evolve and exchange mass.
Understanding compact objects is also becoming increasingly multi-messenger. Neutron-star mergers and compact binary inspirals, for instance, directly connect X-ray emission to gravitational-wave signals. As India prepares for major next-generation facilities such as LIGO-India and the Square Kilometre Array ( SKA), the study of compact objects becomes even more nationally relevant. LIGO-India will enable precision measurements of binary neutron star and black hole mergers, while SKA will significantly advance pulsar timing, magnetar studies, and the detection of exotic compact systems. Training researchers to interpret signals from compact objects using X-ray missions such as AstroSat , NICER , XpoSat , NuSTAR, etc. and placing these results in a broader theoretical and multi-mission context will therefore play a crucial role in maximising the scientific return of India’s future observatories.
The AstroSat mission has provided Indian and global researchers with high time-resolution and broadband spectral capabilities through its suite of instruments, including SXT, LAXPC, CZTI, and UVIT. These instruments have enabled detailed studies of timing and spectral properties of compact objects, making AstroSat one of the most versatile multi-band space observatories currently in operation. Importantly, the mission has fostered a truly nationwide participation in X-ray astronomy: AstroSat data are actively used by research groups throughout India, reflecting the broad geographical and institutional diversity of India’s scientific community.
The accessibility of AstroSat data, combined with targeted training programs and student-led research initiatives, has helped cultivate a rapidly growing cohort of young researchers working in high-energy astrophysics. Many students now conduct thesis projects based on AstroSat observations, and several institutions have incorporated X-ray astronomy into their research activities. As a result, AstroSat has not only produced high-impact scientific results but has also played a transformative
role in strengthening India’s human resource base in astronomy and enabling the next generation of scientists to contribute to the global high-energy astrophysics community.
With an increasingly growing Indian community working in high-energy astrophysics, there is a strong need for training that bridges theory, data analysis, and physical interpretation. This workshop aims to address this gap by offering both conceptual lectures and practical exercises that highlight how the spectral and timing properties of compact objects convey physical information about strong gravity, dense matter, accretion flows, magnetic fields, and the overall geometry.
Target participants: M.Sc. students, PhD students, postdocs, faculty, and researchers interested in compact objects, X-ray astronomy and/or AstroSat , including beginners who want to enter the field of high-energy astrophysics with hands-on experience. We expect a total of 50 or fewer participants, including organisers.
Technical Details: The sessions will be divided broadly into the following three subcategories. (1) Theoretical aspects [singularities and compact objects, accretion physics, radiative processes, and spectral/timing/polarisation properties] (~3 hrs). (2) AstroSat instrument overview and observational perspectives (~ 2 hrs). (3) Hands-on session for X-ray spectral analysis. (~2 hrs). We expect this to span from 9 am to 6 pm, including registration, welcome address, lunch/tea breaks, and closing remarks.
Requirements: Participants should bring laptops with Linux/MacOS (Windows with WSL acceptable). Pre-installation of HEASoft/XSPEC will be recommended (installation guide will be shared). Pre-installation of SXT Julia Merger tool will be recommended. (link: Astrosat data analysis ). Sample datasets ( AstroSat , NICER , NuSTAR ) will be provided ahead of the workshop.
Deliverables: A complete hands-on analysis notebook or tutorial PDF, example scripts and spectral-fitting templates, data sets and model files with comments for independent follow-up.
Organisers: Prof. Sudip Bhattacharyya (Main Organiser; PI, Soft X-ray Telescope (SXT), AstroSat, Tata Institute of Fundamental Research [TIFR], Mumbai), Prof. Pankaj Joshi (Ahmedabad University), Dr. Sayantan Bhattacharya (Postdoctoral Fellow, TIFR, Mumbai), Mr. Parag Shah ( AstroSat -LAXPC team member, TIFR, Mumbai), Dr. Tilak Katoch ( AstroSat -LAXPC & SXT team member, TIFR, Mumbai), Mrs. Nilima Kamble ( AstroSat -SXT team member, TIFR, Mumbai), Mr. Sandeep Vishwakarma ( AstroSat -SXT team member, TIFR, Mumbai), Mr. Aman Kaushik (Research Scholar, TIFR, Mumbai), Ms. Vishva Patel (Research Scholar, Charotar University of Science and Technology)