Long-Term Datasets for the Understanding of Solar and Stellar Magnetic Cycles Proceedings IAU Symposium No. 340, 2018 D. Banerjee, J. Jiang, K. Kusano & S. Solanki, eds. c  International Astronomical Union 2018 doi:10.1017/S1743921318002004 Quantifying weak non-thermal meterwave solar emission using non-imaging techniques Rohit Sharma 1 , Divya Oberoi 1 , Akshay Suresh 2 and Mihir Arjunwadkar 3 1 National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India email: rohit@ncra.tifr.res.in 2 Cornell Centre for Astrophysics and Planetary Science, Ithlaca, New York, USA 3 Centre for Modeling and Simulation, Savitribai Phule Pune University, Ganeshkhind, Pune, India An improved understanding of the solar corona is crucial for making progress on long- standing problems like coronal heating and the origin of the solar wind. Metrewave radio emissions arise in the coronal regions and form a unique diagnostic probe of this, otherwise hard to study region. The background radio emission at these wavelengths comes from the slowly varying thermal free-free emission and on it are superposed a variety of nonthermal emissions arising from a range of plasma emission processes. The latter are coherent in nature and hence lead to a much larger observational contrast, as compared to that in EUV or X-ray, for emissions involving similar energetics. One of the prevalent hypotheses for explaining coronal heating is based on the presence of an energetically weak population of ‘nanoflares’ (Parker 1988). A necessary requirement for nanoflares based coronal heating to be effective is that their occurrence rate slopes must be <-2 (Hudson 1991). There is hence a lot of interest in studies of weak nonthermal emissions. Existing studies in EUV and X-ray bands have detected ‘microflares’ with slopes >-2 (e.g. Hannah et al. 2011). Some of the weak meterwave emissions detected are, however, believed to correspond to energies in the ‘picoflare’ range (Ramesh et al. 2013). It is hence, very interesting to study weak nonthermal emissions at metric wavelengths. Though the importance of metric solar observations has been known for a long time, the Sun is a challenging radio source to study. The metric solar emissions show structures at small spectral (order MHz) and temporal (sub-second) scales, which are accompanied by corresponding changes in the solar images. To follow the details of these emissions in their full glory, one needs a high-fidelity spectroscopic snapshot imaging capability, which had till recently simply not been available. The new generation of interferometers, like the Murchison Widefield Array (MWA), represents a significant step forward in meeting the needs of solar imaging (Tingay et al. 2013). MWA observations have already demonstrated the presence of numerous weak, narrow-band and short-lived impulsive emission features, even during quiet times (Oberoi et al. 2011). Here we briefly describe our non-imaging investigations of these weak emission features. A complete overview of solar science efforts with MWA data is described in Oberoi et al. (this volume). The new generation arrays produce very large data volumes (∼1 TB/hr) and traditional interferometric analysis is very human effort and computation intensive. An automated imaging pipeline for harnessing these science-rich data is described by Mondal et al. (this volume). The first requirement for characterising these weak features is a robust flux calibration. The highly variable solar emission and the Sun being much brighter than typical cali- brator sources make this a non-trivial task. We have devised a computationally lean flux 181 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921318002004 Downloaded from https://www.cambridge.org/core. IP address: 35.175.113.235, on 03 Dec 2021 at 08:18:38, subject to the Cambridge Core terms of use, available at