Articles written in Journal of Astrophysics and Astronomy

    • Detection of radio-AGN in dust-obscured galaxies using deep uGMRT radio continuum observations


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      Radio observations being insensitive to the dust-obscuration, have been exploited to unveil the population of active galactic nuclei residing in galaxies with large dust content. In this paper, we investigate the radio characteristics of 321 dust-obscured galaxies (DOGs; $S_{24 \ \mu{\rm m}}/S_{r\mbox{−}{\rm band}} \geq 1000$) by using mainly deep band-3 (250–550 MHz) observations from the upgraded giant metrewave radio telescope (uGMRT) and 1.5 GHz Jansky very large array (JVLA) observations. We find that for our sample of DOGs, deep (median noise-rms $=$ 30 $\mu$Jy beam$^{-1}$) 400 MHz band-3 uGMRT observations yield the highest detection rate (28%) among those obtained with the JVLA, and low frequency array (LOFAR) radio observations and XMM-N X-ray observations. The radio characteristics of our sample sources, i.e., linear extent (<40 kpc at $z$ < 1.2), bimodal spectral index ($\alpha^{1.5 \ {\rm GHz}}_{400 \ {\rm MHz}}$) distribution and the radio luminosities ($L_{1.5 \ {\rm GHz}}$ > $5.0 \times 10^{23}$ W Hz$^{-1}$), suggestthem to be mainly consist of compact-steep-spectrum (CSS) or peaked-spectrum (PS) sources representing an early phase of the AGN-jet activity in dust-obscured environments. With stacking, we find the existence of faint radio emission ($S_{400 \ {\rm MHz}} = 72.9$ $\mu$Jy beam$^{-1}$ and $S_{1.5 \ {\rm GHz}} = 29$ $\mu$Jy beam$^{-1}$ with signal-to-noise ratio $\sim$20) in otherwise radio-undetected DOGs. Our study reveals the faint emission at a few tens of $\mu$Jy level in high-$z$ DOGs, which can be used as a test-bed for the deeper radio continuum surveys planned with the square-kilometer array (SKA) and its pathfinders.

    • Characteristics of remnant radio galaxies detected in deep radio continuum observations from SKA pathfinders


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      The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The time-scale of the remnant phase and AGN duty cycle are vital to understand the evolution of radio galaxies. In this paper, we report newband-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of low-surface-brightness in all five remnants with 400 MHz surface brightness in the range of 36–201 mJy arcmin$^{-2}$. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150, 325, 400 MHz and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off (CI$_{\rm OFF}$) model, that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages ($t_{\rm s}$) in the range of 20.3–41.4 Myr with $t_{\rm OFF}/t_{\rm s}$ distributed in the range of 0.16–0.63, which in turn suggests that they belong to different evolutionary phases. We note that when compared to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobesin their less dense environments.

    • Plans for building a prototype SKA regional centre in India


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      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.

    • Telescope Manager for the SKA


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      India has been a significant contributor to the SKA project from 2009, with a special emphasis on the Telescope Manager, the central control system for the SKA Observatory. This paper describes the details of the design and early prototyping phases of the Telescope Manager work package, including the accompanying life cycle activities. It also traces the history of India’s involvement in the work on the Telescope Manager in various phases of the project, describing the contribution starting with the concept design to the currentlyongoing construction phase, and looks at the road ahead. The details of the design and the outcomes of the prototyping and development contributed by India in each phase, are also included.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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