Polarization and brightness temperature observations of Venus with the GMRT

Mohan, Nithin; Pillai, Suresh; Swarup, G.; Oberoi, D.

doi:10.1093/mnras/stz1556

Cited by 3 publications

(6 citation statements)

References 30 publications

(48 reference statements)

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“…In order to minimize the observation time, we chose to observe 3C 48, which is unpolarized at these frequencies (Perley & Butler 2013;Farnes et al 2014), allowing us to determine the leakage terms. For calibrating the polarization position angle, we used 3C 286 following Mohan et al (2019). However, we obtained a polarization fraction of ∼3.5% for 3C 286 at 650 MHz, which agrees with the value of 2.7% at 610 MHz by Farnes (2012) but is in tension with the value of 7.6% at 607 MHz given by Mohan et al (2019).…”

Section: Polarizationsupporting

confidence: 74%

Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the pilot study

Dokara,

Roy,

Menten

et al. 2023

A&A

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Context. The advent of wide-band receiver systems on interferometer arrays has enabled the undertaking of high-sensitivity and highresolution radio continuum surveys of the Galactic plane in a reasonable amount of telescope time. Yet, to date, there have been only a few such studies of the first quadrant of the Milky Way carried out at frequencies below 1 GHz. The Giant Metrewave Radio Telescope (GMRT) has recently upgraded its receivers with wide-band capabilities (now called the uGMRT), offering a prime opportunity to conduct high resolution surveys, while also demonstrating sensitivity to the extended structures. Aims. We wish to assess the feasibility of conducting a large-scale snapshot survey, the Metrewave Galactic Plane with the uGMRT Survey (MeGaPluG), to simultaneously map extended sources and compact objects at an angular resolution lower than 10″ and a point source sensitivity of 0.15 mJy beam−1. Methods. We performed an unbiased survey of a small portion of the Galactic plane, covering the W43/W44 regions (l = 29° – 35° and |b| < 1°) in two frequency bands: 300–500 MHz and 550–750 MHz. The 200 MHz wide-band receivers on the uGMRT were employed to observe the target field in several pointings, spending nearly 14 min on each pointing in two separate scans. We developed an automated pipeline for the calibration and a semi-automated self-calibration procedure was used to image each pointing using multi-scale CLEAN and outlier fields. Results. We produced continuum mosaics of the surveyed region at a final common resolution of 25″ in the two bands that have central frequencies of 400 MHz and 650 MHz, with a point source sensitivity better than 5 mJy beam−1. A spectral index map was also obtained, which is helpful to distinguish between thermal and nonthermal emission. By cross-matching with other surveys, we validated the positions and flux densities obtained from our data. We plan to cover a larger footprint of the Galactic plane in the near future based on the lessons drawn from this study.

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Section: Polarizationsupporting

confidence: 74%

Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the pilot study

Dokara,

Roy,

Menten

et al. 2023

A&A

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“…(2001) are given in filled black circle, and the GMRT observations reported by Mohan et al. (2017, 2019) are given in filled red circles. The vertical lines in the measurements indicate the standard deviation in the observed T b .…”

Section: Radiative Transfer Simulation For Surface Thermal Emissionmentioning

confidence: 99%

“…(2001) also arrived at similar results. Figure 1 shows the comparison of the simulated T b with various radiometric observations, including the VLA observations (Butler et al., 2001) and GMRT observations (Mohan et al., 2017, 2019). The RT simulations (thick black line in Figure 1) with a single layer of infinite depth with uniform dielectric constant fails to capture the observed decrease in T b with increase in wavelength.…”

Section: Radiative Transfer Simulation For Surface Thermal Emissionmentioning

confidence: 99%

“…In this work, we investigate the decrease of Venus' surface thermal emission in dm‐wavelength by using radiative transfer (RT) simulations without volume scattering, to an assumed Venusian two‐layer subsurface having contrasting dielectric properties. The simulated T b values are compared with the T b data derived from the Giant Metrewave Radio Telescope (GMRT) observations, carried out in 2015 when Venus was closest to its inferior conjunction (Mohan et al., 2019) and the GMRT archived data of Venus observation in 2004 (Mohan et al., 2017). GMRT is an interferometric radio telescope operating at five channels centred at 150, 235, 333, 610, and 1,280 MHz and comprises 30 dish antennas of 45 m diameter distributed in a Y‐shaped array of ∼26 km in length, located in Pune, India.…”

Section: Introductionmentioning

confidence: 99%

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Radiative Transfer Simulations for the Observed Decrease of Radio Brightness Temperature of Venus With Increasing Decimeter Wavelengths: Possible Existence of a Reflective or Quasi‐Conductive Subsurface

et al. 2022

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Radiometric observations of Venus have revealed a monotonic decrease of brightness temperature (Tb) in the decimeter wavelength regime. Such a decrease has also been independently reported by the observations using interferometric radio‐telescopes, like the Very Large Array (VLA) in the USA and the Giant Metrewave Radio Telescope (GMRT) in India. In this work, we have carried out microwave radiative transfer (RT) simulations of thermal emission from the Venusian surface at decimeter wavelengths to examine the role of subsurface properties of Venusian regolith in the continuous reduction of Tb at the microwave‐radiowave spectral domain. These simulations are compared against spectral microwave measurements by GMRT over a wide decimeter wavelength regime ranging from ∼23–128 cm. Good agreements are obtained for simulations that consider a two‐layer Venusian surface (a low‐loss medium overlaid over a reflecting/lossy medium) a situation that would arise if the subsurface layer has high dielectric properties due to the presence of semiconducting mineral assemblages such as pyrites, ferroelectric minerals, magnetite–hematite, magnetite–pyrite or magnetite–hematite–pyrite equilibrium assemblages. The thickness of the top layer, the possibilities of the formation of such layers and their geological and chemical evolutions are also discussed.

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“…Recently, Saxena et al (2018) have discovered the most distant radio galaxy identified to date at a redshift of z = 5.72. Mohan et al (2019) described polarizations and brightness temperature observations of Venus, placing constraints on its emission mechanism. Using the uGMRT, neutral hydrogen, Hi, has been detected at a redshift of 0.37 by stacking 445 16…”

Section: The Giant Metrewave Radio Telescopementioning

confidence: 99%

The Journey of a Radio Astronomer: Growth of Radio Astronomy in India

Swarup

2021

Annu. Rev. Astron. Astrophys.

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In this autobiographical account, I first describe my family, then childhood and education in India. During 1953–55, I worked in the new field of radio astronomy at the Division of Radiophysics of the Commonwealth Scientific and Industrial Research Organisation in Australia. During 1956–57, I worked at the Radio Astronomy Station of Harvard University at Fort Davis, Texas, where I made observations of solar radio bursts at decimeter wavelengths. I then joined Stanford University as a graduate student in 1957. I contributed to the successful operation of the Stanford Cross Antenna and then used it for studying microwave radio emission from the Sun. I was awarded the Ph.D. degree by Stanford University in 1960 and was then appointed as an Assistant Professor for three years. With an urge to contribute to evolving scientific endeavors in India, I joined the Tata Institute of Fundamental Research (TIFR) at Mumbai, India, in April 1963. In my stay of more than three decades at TIFR, I conceived of, and guided, construction of two of the world's largest radio telescopes, namely the Ooty Radio Telescope and the Giant Metrewave Radio Telescope. These instruments have led to several outstanding contributions and discoveries in the areas of radio galaxies, quasars, pulsars, and cosmology. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 59 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Polarization and brightness temperature observations of Venus with the GMRT

Cited by 3 publications

References 30 publications

Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the pilot study

Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the pilot study

Radiative Transfer Simulations for the Observed Decrease of Radio Brightness Temperature of Venus With Increasing Decimeter Wavelengths: Possible Existence of a Reflective or Quasi‐Conductive Subsurface

The Journey of a Radio Astronomer: Growth of Radio Astronomy in India

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