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Indrajit V. Barve

Publications and source records attributed to Indrajit V. Barve.

8 recordsLinked to original sources
arXiv2026

Augmentation of the Gauribidanur radioheliograph for observations of circularly polarized emission from the solar corona at low radio frequencies

The magnetic field strengths (B) in the solar photosphere are routinely measured using the Zeeman effect. However, such measurements are not available in the solar chromosphere and corona. The Gauribidanur RAdioheliograPH (GRAPH), near Bangalore in India, has been successfully carrying out total intensity (Stokes I) observations of the solar corona at low frequencies ($\lesssim$ 100 MHz) for several years now. Radio emission from the Sun in the above frequency range originates typically in the heliocentric distance r $\gtrsim$ 1.2 $R_\odot$ . We recently augmented GRAPH with the aim to observe circularly polarized radio emission (Stokes V) from solar corona, in particular, from the 'quiet' corona. Combining the low frequency Stokes I & V radio images, and modeling techniques, it is possible to calculate the magnetic field strengths in the solar corona on regular basis. This work details the procedures undertaken to augment the GRAPH for simultaneous observations of both Stokes I & V radio emission from the solar corona, and the calibration procedure. Preliminary results indicate that the augmented GRAPH can effectively detect Stokes V emission associated with thermal emission from the 'quiet' Sun at frequencies $\lesssim$ 100 MHz, in addition to Stokes V emission associated with the non-thermal radio bursts from the 'active' Sun.

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arXiv2024

1-bit raw voltage recording system for dedicated observations of transients at low radio frequencies

Recently we had reported commissioning of a prototype for pulsar observations at low radio frequencies (<100 MHz) using log-periodic dipole antennas (LPDAs) in the Gauribidanur Radio Observatory near Bangalore in India. The aforementioned system (GAuribidanur Pulsar System, GAPS) is currently being augmented to directly digitize the radio frequency signals from the individual antennas in the array. Our initial results using 1-bit raw voltage recording system indicates that such a back-end receiver offers distinct advantages like, (i) simultaneous observations of any set of desired directions in the sky with multiple offline beams and smaller data rate/volume, (ii) archival of the observed data with minimal resources for re-analysis in the future, either in the same or different set of directions in the sky.

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arXiv2021

Radio Interferometric Observations of the Sun Using Commercial Dish TV Antennas

The radio astronomy group in the Indian Institute of Astrophysics (IIA) has been carrying out routine observations of radio emission from the solar corona at low frequencies (${\approx}$40-440MHz) at the Gauribidanur observatory, about 100km north of Bangalore. Since IIA has been performing regular observations of the solar photosphere and chromosphere using different optical telescopes in its Kodaikanal Solar Observatory (KSO) also, the possibilities of obtaining two-dimensional radio images of the solar chromosphere using low-cost instrumentation to supplement the optical observations are being explored. As a part of the exercise, recently the group had developed prototype instrumentation for interferometric observations of radio emission from the solar chromosphere at high frequencies (${\approx}$11.2GHz) using two commercial dish TV antennas. The hardware set-up and initial observations are presented.

astro-ph.SR↗
arXiv2021

Solar Radio Spectro-polarimetry (50-500 MHz) : Design and Development of Cross-Polarized Log-Periodic Dipole antenna and configuration of receiver system

A radio spectro-polarimeter was developed at the Gauribidanur radio observatory to study the characteristics of the polarized radio waves that are emitted by the impetuous solar corona in the 50 - 500 MHz frequency range. The instrument has three major components : a Cross-polarized Log-Periodic Dipole Antenna (CLPDA), an analog receiver, and a digital receiver (spectrum analyzer). This article elaborates the design and developmental aspects of the CLPDA, its characteristics and briefs about the configurations of the analog and digital receivers, setting up of the spectro-polarimeter, stage-wise tests performed to characterize it, etc. To demonstrate the instrumental capability, the estimation of the solar coronal magnetic field strength (B {\it Vs} heliocentric height), using the spectral data obtained with it, is exemplified. Throughout the above band, the CLPDA has a gain, return loss and polarization cross-talk of $\approx$ 6.6 dBi, $\lesssim$ -10 dB, and $\lesssim$ -27 dB, respectively. The design constraints, the procedure to tune its impedance and to minimize its dimension, etc. are elaborated. The analog receiver has a noise figure of $\approx 3$ dB and a receiver-noise-temperature ($T_{rcvr}$) of about 290 K. The receiver-flux-density ($S_{rcvr}$) is $\approx 5.3 \times 10^3 $, and $\approx 5.3 \times 10^5$ Jy at 50 and 500 MHz, respectively. The observed spectral data shows a Signal-to-Noise Ratio and Dynamic range of about 30 dB and 40 dB, respectively, at 50 MHz. The average polarization isolation / cross-talk of the CLPD varies from -30 dB to -24 dB over an azimuthal angle of $\pm 45^\circ$ with respect to the reference position angle ($0^\circ$). The average degree of circular polarization (DCP) is $\approx 100\%$ at the reference position and found to decrease gradually and reaches $\approx 80\%$ at an azimuthal angle of $\pm 45^\circ$.

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arXiv2016

Design and performance of a low frequency cross-polarized log-periodic dipole antenna

We report the design and performance of a cross-polarized log-periodic dipole (CLPD) antenna for observations of polarized radio emission from the solar corona at low frequencies. The measured isolation between the two mutually orthogonal log periodic dipole antennas was as low as $\approx$ -43 dBm in the 65-95 MHz range. We carried out observations of the solar corona at 80 MHz with the above CLPD and successfully recorded circularly polarized emission.

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arXiv2016

In-orbit Performance of UVIT on ASTROSAT

We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. The FUV and NUV channels have filters and gratings, whereas the VIS channel has filters. The ASTROSAT was launched on 28th September 2015. The performance verification of UVIT was carried out after the opening of the UVIT doors on 30th November 2015, till the end of March 2016 within the allotted time of 50 days for calibration. All the on-board systems were found to be working satisfactorily. During the PV phase, the UVIT observed several calibration sources to characterise the instrument and a few objects to demonstrate the capability of the UVIT. The resolution of the UVIT was found to be about 1.4 - 1.7 $arcsec$ in the FUV and NUV. The sensitivity in various filters were calibrated using standard stars (white dwarfs), to estimate the zero-point magnitudes as well as the flux conversion factor. The gratings were also calibrated to estimate their resolution as well as effective area. The sensitivity of the filters were found to be reduced up to 15\% with respect to the ground calibrations. The sensitivity variation is monitored on a monthly basis. UVIT is all set to roll out science results with its imaging capability with good resolution and large field of view, capability to sample the UV spectral region using different filters and capability to perform variability studies in the UV.

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arXiv2012

RRI-GBT Multi-Band Receiver: Motivation, Design & Development

We report the design and development of a self-contained multi-band receiver (MBR) system, intended for use with a single large aperture to facilitate sensitive & high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span (100-1500 MHz) in a nearly log-periodic fashion. The development of this system was primarily motivated by need for tomographic studies of pulsar polar emission regions. Although the system design is optimized for the primary goal, it is also suited for several other interesting astronomical investigations. The system consists of a dual-polarization multi-band feed (with discrete responses corresponding to the 10 bands pre-selected as relatively RFI-free), a common wide-band RF front-end, and independent back-end receiver chains for the 10 individual sub-bands. The raw voltage time-sequences corresponding to 16 MHz bandwidth each for the two linear polarization channels and the 10 bands, are recorded at the Nyquist rate simultaneously. We present the preliminary results from the tests and pulsar observations carried out with the Green Bank Telescope using this receiver. The system performance implied by these results, and possible improvements are also briefly discussed.

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