DIPANKAR BHATTACHARYA
Articles written in Journal of Astrophysics and Astronomy
Volume 16 Issue 2 June 1995 pp 217-232
The evolution of the magnetic fields of neutron stars
Observational evidence, and theoretical models of the magnetic field evolution of neutron stars is discussed. Observational data indicates that the magnetic field of a neutron star decays significantly only if it has been a member of a close interacting binary. Theoretically, the magnetic field evolution has been related to the processing of a neutron star in a binary system through the spin evolution of the neutron star, and also through the accretion of matter on the neutron star surface. I describe two specific models, one in which magnetic flux is expelled from the superconducting core during spin-down, via a copuling between Abrikosov fluxoids and Onsager-Feynman vortices; and another in which the compression and heating of the stellar crust by the accreted mass drastically reduces the ohmic decay time scale of a magnetic field configuration confined entirely to the crust. General remarks about the behaviour of the crustal field under ohmic diffusion are also made.
Volume 23 Issue 1-2 March 2002 pp 67-72
Evolution of neutron star magnetic fields
This paper reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems. Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic screening of the field by accreted plasma, are reviewed.
Volume 37 Issue 4 December 2016 Article ID 0036 Review
Neutron Star Physics in the Square Kilometre Array Era: An Indian Perspective
Sushan Konar Manjari Bagchi Debades Bandyopadhyay Sarmistha Banik Dipankar Bhattacharya Sudip Bhattacharyya R. T. Gangadhara A. Gopakumar Yashwant Gupta B. C. Joshi Yogesh Maan Chandreyee Maitra Dipanjan Mukherjee Archana Pai Biswajit Paul Alak K. Ray Firoza K. Sutaria
It is an exceptionally opportune time for astrophysics when a number of next-generation mega-instruments are poised to observe the Universe across the entire electromagnetic spectrum with unprecedented data quality. The Square Kilometre Array (SKA) is undoubtedly one of the major components of this scenario. In particular, the SKA is expected to discover tens of thousands of new neutron stars giving a major fillip to a wide range of scientific investigations. India has a sizeable community of scientists working on different aspects of neutron star physics with immediate access to both the uGMRT (an SKA pathfinder) and the recently launched X-ray observatory Astrosat. The current interests of the community largely centre around studies of (a) the generation of neutron stars and the SNe connection, (b) the neutron star population and evolutionary pathways, (c) the evolution of neutron stars in binaries and the magnetic fields, (d) the neutron star equation of state, (e) the radio pulsar emission mechanism, and (f) the radio pulsars as probes of gravitational physics. Most of these studies are the main goals of the SKA first phase, which is likely to be operational in the next four years. This article summarizes the science goals of the Indian neutron star community in the SKA era, with significant focus on coordinated efforts among the SKA and other existing/upcoming instruments.
Volume 38 Issue 2 June 2017 Article ID 0032 Review Article
Early In-orbit Performance of Scanning Sky Monitor Onboard AstroSat
M. C. Ramadevi B. T. Ravishankar N. Sitaramamurthy G. Meena Brajpal Singh Anand Jain Reena Yadav Anil Agarwal V. Chandra Babu Kumar Ankur Kushwaha S. Vaishali Nirmal Kumar Iyer Anuj Nandi Girish V. Vivek Kumar Agarwal S. Seetha Dipankar Bhattacharya K. Balaji Manoj Kumar Prashanth Kulshresta
We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ × 2.5∘ and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.
Volume 38 Issue 3 September 2017 Article ID 0036 Editorial
Dipankar Bhattacharya K. S. Dwarakanath Sushan Konar
Volume 38 Issue 3 September 2017 Article ID 0051 Review Article
Observing Compact Stars with AstroSat
This article presents a brief description of India’s AstroSat mission which is a powerful space based observatory for compact star research. An account is given of observational constraints and spectral and timing capabilities as realised post-launch. Some preliminary results of observations of the Crab pulsar and an X-ray binary system GX 301-2 are presented to illustrate some of the capabilities of the mission.
Volume 39 Issue 1 February 2018 Article ID 0011 Review
Study of X-ray transients with Scanning Sky Monitor (SSM) onboard AstroSat
M. C. RAMADEVI B. T. RAVISHANKAR ABHILASH R. SARWADE S. VAISHALI NIRMAL KUMAR IYER ANUJ NANDI V. GIRISH VIVEK KUMAR AGARWAL BLESSY ELIZABETH BABY MOHAMMED HASAN S. SEETHA DIPANKAR BHATTACHARYA
Scanning Sky Monitor (SSM) onboard AstroSat is an X-ray sky monitor in the energy range 2.5–10 keV. SSM scans the sky for X-ray transient sources in this energy range of interest. If an X-ray transient source is detected in outburst by SSM, the information will be provided to the astronomical community for follow-up observations to do a detailed study of the source in various other bands. SSM instrument, since its power-ON in orbit, has observed a number of X-ray sources. This paper discusses observations of few X-ray transients by SSM. The flux reported by SSM for few sources during its Performance Verification phase (PV phase) is studied and the results are discussed.
Volume 42 All articles Published: 31 May 2021 Article ID 0027 MISSION
AstroSat proposal processing system
C. BALAMURUGAN SACHIN NARANG PRADNYA BHOYE MANDAR HULSURKAR GULAB DEWANGAN DIPANKAR BHATTACHARYA B. N. RAMAKRISHNA
AstroSat Proposal Processing System (APPS) is a mission critical software solution designed and developed by the joint efforts of Indian Space Research Organization and the Inter-University Centre for Astronomy and Astrophysics. It facilitates the participation of global scientific community to submit scientificproposals for observations with India’s first multi-wavelength space observatory. The software systematizes the proposal submission and review process before the successful proposed observations are scheduled to carryout scientific observations. This paper describes the overall architecture of the system,implementation stratagems, administrative aspects and security aspects of the software. The paper also describes the techniques adopted for seamless day-to-day operations in meeting the mission requirements. As a future direction, the paper summarizes the roadmap for development of a generic multi-mission proposal handling model from the experiences gained through APPS.
Volume 42 All articles Published: 28 June 2021 Article ID 0058 SCIENCE RESULTS
PARISEE SHIRKE SUMAN BALA JAYASHREE ROY DIPANKAR BHATTACHARYA
We present the timing results of out-of-eclipse observations of Centaurus X-3 spanning half a binary orbit, performed on 12–13 December, 2016 with the Large Area X-ray Proportional Counter (LAXPC) on-board AstroSat. The pulse profile was confirmed to exhibit a prominent pulse peak with a secondary inter-pulse. The systemic spin period of the pulsar was found to be $4.80188 \pm 0.000085$ s in agreement with its spin up trend. The spin up timescale seems to have increased to $7709\pm 58$ yr that points to negative torque effects in the inner accretion disk. We also report the derived values of projected semi-major axis and orbital velocity of the neutron star.
Volume 42 All articles Published: 29 June 2021 Article ID 0061 PAYLOAD CALIBRATION
Absolute time calibration of LAXPC aboard AstroSat
AVISHEK BASU DIPANKAR BHATTACHARYA BHAL CHANDRA JOSHI
The AstroSat mission carries several high-energy detectors meant for fast timing studies of cosmic sources. In order to carry out high precision multi-wavelength timing studies, it is essential to calibrate the absolute time stamps of these instruments to the best possible accuracy. We present here theabsolute time calibration of the AstroSat LAXPC instrument, utilising the broad-band electromagnetic emission from the Crab Pulsar to cross calibrate against Fermi-LAT and ground based radio observatories Giant Metrewave Radio Telescope (GMRT) and the Ooty Radio Telescope (ORT). Using the techniques of pulsar timing, we determine the fixed timing offsets of LAXPC with respect to these different instruments and also compare the offsets with those of another AstroSat instrument, CZTI.
Volume 42 All articles Published: 1 July 2021 Article ID 0064 SCIENCE RESULTS
Using collimated CZTI as all-sky X-ray detector based on Earth occultation technique
AKSHAT SINGHAL RAHUL SRINIVASAN VARUN BHALERAO DIPANKAR BHATTACHARYA A. R. RAO SANTOSH VADAWALE
All-sky monitors can measure the fluxes of astrophysical sources by measuring the changes in observed counts as the source is occulted by the Earth. Such measurements have typically been carried out by all-sky monitors like
Volume 42 All articles Published: 3 July 2021 Article ID 0067 SCIENCE RESULTS
Exploring sub-MeV sensitivity of AstroSat–CZTI for ON-axis bright sources
ABHAY KUMAR TANMOY CHATTOPADHYAY SANTOSH V. VADAWALE A. R. RAO SOUMYA GUPTA N. P. S. MITHUN VARUN BHALERAO DIPANKAR BHATTACHARYA
The Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat is designed for hard X-ray imaging and spectroscopy in the energy range of 20–100 keV. The CZT detectors are of 5-mm thickness and hence have good efficiency for Compton interactions beyond 100 keV. The polarisation analysis using CZTIrelies on such Compton events and have been verified experimentally. The same Compton events can also be used to extend the spectroscopy up to 380 keV. Further, it has been observed that about 20% pixels of the CZTI detector plane have low gain, and they are excluded from the primary spectroscopy. If these pixels are included, then the spectroscopic capability of CZTI can be extended up to 500 keV and further up to 700 keV with a better gain calibration in the future. Here we explore the possibility of using the Compton events as well as the low gain pixels to extend the spectroscopic energy range of CZTI for ON-axis bright X-ray sources. We demonstrate this technique using Crab observations and explore its sensitivity.
Volume 42 All articles Published: 3 July 2021 Article ID 0070 PAYLOAD CALIBRATION
Calibration of Scanning Sky Monitor (SSM) onboard AstroSat
ABHILASH R. SARWADE M. C. RAMADEVI B. T. RAVISHANKAR BRAJPAL SINGH BLESSY ELIZABETH BABY DIPANKAR BHATTACHARYA S. SEETHA
SSM onboard AstroSat is designed to monitor X-ray sky in the energy range 2.5–10 keV to detect and locate X-ray sources in outburst. SSM with its three almost identical 1D-proportional counters mounted on a rotating platform, scans the sky in step and stare mode of operation. It observes the X-ray skyand generates light curves for X-ray sources detected. Here, we discuss the positional calibration to carry out imaging with SSM. Onboard calibration of SSM has been carried out with Crab, the standard X-ray source. SSM observations of Crab are compared with that of MAXI on ISS for cross calibration of the instrument.
Volume 42 All articles Published: 16 July 2021 Article ID 0076 PAYLOAD CALIBRATION
Imaging calibration of AstroSat Cadmium Zinc Telluride Imager (CZTI)
AJAY VIBHUTE DIPANKAR BHATTACHARYA N. P. S. MITHUN V. BHALERAO A. R. RAO S. V. VADAWALE
AstroSat is India’s first space-based astronomical observatory, launched on September 28, 2015. One of the payloads aboard AstroSat is the Cadmium Zinc Telluride Imager (CZTI), operating at hard X-rays. CZTI employs a two-dimensional coded aperture mask for the purpose of imaging. In this paper, we discuss various image reconstruction algorithms adopted for the test and calibration of the imaging capability of CZTI and present results from CZTI on-ground as well as in-orbit image calibration.
Volume 42 All articles Published: 21 July 2021 Article ID 0082 SCIENCE RESULTS
Sub-MeV spectroscopy with AstroSat-CZT imager for gamma ray bursts
TANMOY CHATTOPADHYAY SOUMYA GUPTA VIDUSHI SHARMA SHABNAM IYYANI AJAY RATHEESH N. P. S. MITHUN E. AARTHY SOURAV PALIT ABHAY KUMAR SANTOSH V. VADAWALE A. R. RAO VARUN BHALERAO DIPANKAR BHATTACHARYA
Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100–300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels ($\sim$20% of the detector plane) aftercareful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature also allows single-pixel spectroscopy of the GRBs to the sub-MeV range which is otherwise limited to 150 keV. We also introduced a new noise rejection algorithm in the analysis (‘Compton noise’). These new additionsnot only enhances the spectroscopic sensitivity of CZTI, but the sub-MeV spectroscopy will also allow proper characterization of the GRBs not detected by
Volume 42 All articles Published: 2 August 2021 Article ID 0093 SCIENCE RESULTS
The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI
SUJAY MATE TANMOY CHATTOPADHYAY VARUN BHALERAO E. AARTHY ARVIND BALASUBRAMANIAN DIPANKAR BHATTACHARYA SOUMYA GUPTA KRISHNAN KUTTY N. P. S. MITHUN SOURAV PALIT A. R. RAO DIVITA SARAOGI SANTOSH VADAWALE AJAY VIBHUTE
The Cadmium Zinc Telluride Imager (CZTI) on AstroSat is a hard X-ray coded-aperture mask instrument with a primary field-of-view of $4.6^{\circ} \times 4.6^{\circ}$ (FWHM).The instrument collimators become increasinglytransparent at energies above $\sim$100 keV, making CZTI sensitive to radiation from the entire sky. While this has enabled CZTI to detect a large number of off-axis transient sources, calculating the source flux or spectrum requires knowledge of the direction and energy dependent attenuation of the radiation incident upon the detector. Here, we present a GEANT4-based mass model of CZTI and AstroSat that can be used to simulate the satellite response to the incident radiation, and to calculate an effective ‘‘response file’’ for converting the source counts into fluxes and spectra. We provide details of the geometry and interaction physics, and validate the model by comparing the simulations of imaging and flux studies with observations. Spectroscopic validation of the massmodel is discussed in a companion paper, Chattopadhyay
Volume 43 All articles Published: 6 December 2022 Article ID 0091
K. G. ANUSREE DIPANKAR BHATTACHARYA VARUN BHALERAO AKASH ANUMARLAPUDI
The Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat, an open detector above $\sim$100 keV, is a promising tool for the investigation of hard X-ray characteristics of $\gamma$-ray pulsars. A custom algorithm has been developed to detect pulsars from long integration ($\sim$years) of archival data, as reported by us earlier. Here, we extend this method in the analysis to include additional $\sim$20% of the CZTI pixels that were earlier ignored due to their lower gain values. Recent efforts have provided better and more secure calibration of these pixels, demonstrating their higher thresholds and extended energy range up to $\sim$1 MeV. Here, we use the additional information provided by these pixels, enabling the construction of pulse profiles over a larger energy range. We compare the profiles of the Crab pulsar at different sub-bands and show that the behavior is consistent with theextended energy coverage. As detailed spectroscopy over this full band remains difficult due to the limited count rate, we construct hardness ratios which, together with AstroSat mass model simulations, are able to constrain the power-law index of the radiation spectrum. We present our results for the phase-resolved spectrum of PSRJ0534+2200 and for the total pulsed emission of PSR J1513$-$5908. The recovered photon indices are found to be accurate within $\sim$20%.
Volume 44 All articles Published: 3 February 2023 Article ID 0009 TECHNICAL REVIEW
Plans for building a prototype SKA regional centre in India
YOGESH WADADEKAR DIPANKAR BHATTACHARYA ABHIRUP DATTA SURAJIT PAUL DIVYA OBEROI
To deliver the full science potential of the square kilometer array (SKA) telescope, several SKA regional centres (SRCs) will be required to be constructed in different SKA member countries around the world. These SRCs will provide high performance compute and storage, for the generation, of advanced science data products from the basic data streams generated by the SKA science data handling and processing system, critically necessary to the success of the key science projects to be carried out by the SKA user community. They will also provide support to astronomers to enable them to carry out analysis on very large SKA datasets. Construction of such large data centre is a technical challenge for all SKA member nations. In such a situation,each country plans to construct a smaller SRC over the next few years (2022 onwards), known as a proto-SRC. In India, we propose to construct a proto-SRC, which will be used for the analysis of data from SKA pathfinders and precursors with strong Indian involvement, such as uGMRT, Meerkat and MWA.We describe our thinking on some aspects of the storage, compute and network of the proto-SRC and how it will be used for data analysis as well as for carrying out various simulations related to SKA key science projects led by Indian astronomers. We also present our thoughts on how the proto-SRC plans to evaluate emerging hardware and software technologies and to also begin software development in areas of relevance to SKA data processing and analysis, such as algorithm implementation, pipeline development and data visualisation software.
Volume 44, 2023
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