The Square Kilometre Array

(Yashwant Gupta, Tirthankar Roy Choudhury, Yogesh Wadadekar, Niruj Mohan Ramanujam, Dharam Vir Lal, Ruta Kale)

The Square Kilometre Array (SKA), the next generation radio telescope, is now entering the design stage for SKA phase-I, that has started in November 2013 and will run for three years, after which SKA-I construction will start towards the end of 2017. Early science is expected to be possible from around 2020 or so. The capabilities of SKA-I will be phenomenal, for a variety of science goals and applications, and will far surpass that of any existing or planned radio astronomy facility. The SKA is a truly international telescope, with India being one of the member countries in the SKA Organisation and hence involved in the design and operation of SKA-I.

SKA has already formed a number of science working groups which are working towards achieving their long-term science programs. This is an opportune moment for astronomers in India to start working on a long-term strategy towards the use of the SKA in the country.

The SKA will be roughly contemporaneous with other International facilities like Large Synoptic Survey Telescope (LSST), Thirty Meter Telescope (TMT) etc. in optical/IR bands and next-generation successors of Swift, Chandra and XMM-Newton in the gamma-ray and X-ray bands such as Space Variable Objects Monitor (SVOM), Square Meter Arcsecond-Resolution Telescope for X-rays (SMART-X) and ATHENAmissions. Therefore, multi-waveband observational efforts with wide fields of view will be the key to the progress of transients astronomy from the middle 2020s offering unprecedented deep images and high spatial and spectral resolutions. Indian astronomers with wide-ranging experience of low-frequency radio astronomy in a variety of astronomical phenomena and targets would be particularly well-placed to pursue time critical transient objects with SKA and observatories at other bands.

Recent Results
Preparing for solar and heliospheric science with the SKAO: An Indian perspective
The Square Kilometre Array Observatory (SKAO) is perhaps the most ambitious radio observatory envisaged yet. It will enable unprecedented studies of the Sun, the corona and the heliosphere and help to answer many of the outstanding questions in these areas. Additionally, its ability to make a vast previously unexplored phase space accessible promises a large discovery potential. The Indian solar and heliospheric physics community has been preparing for this science opportunity. Over the last many years, this effort has taken the form of leading the solar science enterprise with a SKA-Low precursor, the Murchison Widefield Array (MWA). This long term sustained effort has included the development of the necessary tools, including dedicated solar radio imaging pipelines, and has lead to many interesting discoveries, insights and realizations. These pipelines now represent the state-of-the-art and the science they have enabled spans the range from coronal heating to space weather, and coronal magnetography to discovering novel features in emissions from well known solar radio bursts. This article briefly summarises this journey, highlighting the major milestones on the way (till early 2022), and shares our future plans and long term objectives. The authors also discuss the novel heliospheric science which will be enabled by the future SKA-Low, primarily by the unprecedentedly detailed and sensitive studies of propagation effects suffered by the low frequency radio waves from distant cosmic sources as they traverse the magnetised heliospheric plasma.
Solar physics with the Square Kilometre Array
Although solar physics is one of the most mature branches of astrophysics, the Sun confronts us with many long standing problems that are fundamental in nature. Some of these problems, like the physics of shocks, are common across many astrophysical contexts and some others, like developing the ability to predict space weather, are of enormous societal relevance for the present technologically reliant society. Nindos et al. discuss how the Square Kilometre Array, the upcoming most ambitious radio telescope designed yet, can potentially lead to transformative advances in our understanding of the Sun and address some of these fundamental problems. In its first incarnation, SKA1 will comprise two instruments, the SKA1-Low aperture array (top panel) to be built in the Murchison region of Western Australia, and the SKA1-Mid dishes (bottom panel) to be build in the Karoo region of South Africa (image credit: SKA Organization). Nindos et al. summarise our current understanding of the key open problems in solar physics, based on work done across a large swathe of the electromagnetic spectrum. It then articulate the reasons why SKA observations can play an important role in answering some of these questions. These questions include: (1) the location and magnetic configuration of the electron acceleration site; (2) the mechanism(s) responsible for particle acceleration; (3) the flare-coronal mass ejection (CME) relationship; (4) the timing and evolution of CMEs from the early stages of development all the way to the outer corona; (5) the drivers of coronal shocks as well as the locations and efficiency of electron acceleration by shocks; and (6) the origin of solar energetic particles. This paper also showcases the recent work from the SKA precursors and pathfinders, namely the Murchison Widefield Array in Australia and the Low Frequency Array in Europe, which are already revealing previously unknown details of solar emissions and enabling more detailed and realistic modelling of solar phenomena. In addition, as is always the case with new instruments that outperform their predecessors in significant ways, it also emphasises the high probability of new discoveries that cannot yet be predicted.