Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: The Algorithm by Devojyoti Kansabanik et al

2022-08-23

The solar corona comprises hot magnetized plasma. Coronal magnetic fields are well known to be one of the crucial parameters determining the physics of the solar corona and are vital drivers of Space Weather. Despite the fact that the importance of coronal magnetic fields has been recognised for a long, in practice, they remain rather hard to measure. The polarization properties of coronal emission at low radio frequencies can, in […]

Discovery of correlated evolution in noise storm source parameters: Insights on $\vec{B}$ dynamics during a microflare by A. Mohan

2021-04-13

Solar noise storms are known to be related to small and large scale magnetic field enhancements at active regions (Elgaroy 1977, Li et al.,2017). However, the mechanism still remain unclear. Their high spectro-temporal variability and ubiquity of weak events demanded sub-second and sub-MHz scale imaging with high dynamic ranges (DRs) to reliably study emission from individual sources. Using high DR snapshot spectroscopic images from the Murchison Widefield Array, this work […]

Propagation Effects in Quiet Sun Observations at Meter Wavelengths by R. Sharma and D. Oberoi

2021-02-02

The quiet Sun coronal emission dominantly comes from thermal bremsstrahlung. As this radiation traverses the coronal medium on its way to the Earthbound observer, the coronal optical depth, τ, along typical ray paths is neither low enough to be approximated as optically thin, nor high enough to be treated as optically thick. On its way to the observer, it gets modified substantially due to propagation effects —primarily refraction and scattering—through the […]

First radio evidence of impulsive heating contribution to the quiet solar corona by Surajit Mondal et al

2020-06-30

The solar community has been trying to understand the mechanism responsible for coronal heating for several decades now. In the past decade, a number of studies have shown that the active regions and the coronal loops are heated impulsively. However, such a consensus is yet to be reached for the quiet sun. Past searches for impulsive events in the EUV and X-ray are yet to provide conclusive evidence in favour […]

A microflare associated with periodic particle acceleration by A. Mohan et al.*

2019-10-29

Microflares are weaker cousins of large flares with 103 to 106 times less energies. They are also much more ubiquitous and frequent than larger flares. A very common phenomena of the Extreme Ultra-Violet (EUV) corona, namely the Active Region Transient Brightening (ARTB; Shimizu, 1996) event is known to be associated with microflares. The ARTBs are associated with active coronal loops of length ranging from 5 – 40 Mm and often […]

Unsupervised Generation of High Dynamic Range Solar Images: A Novel Algorithm for Self-calibration of Interferometry Data by Surajit Mondal et al.*

2019-07-16

Imaging the sun at radio wavelengths with high fidelity is an intrinsically hard problem. This stems from: a) the large range of angular scales on which the emission is present; b) the huge difference in brightness temperature associated with the various emission mechanisms which are responsible for radio emission; and c) high variability of solar emission on small temporal (<1s) and spectral (~kHz) scales. These together imply that the uv […]

Coronal Densities Probed by Type III Radio Burst Imaging by P. McCauley et al.*

2018-11-13

Type III solar radio bursts are caused by electron beams accelerated to modest fractions of light speed by magnetic reconnection, the process that drives solar flares. The beams stimulate oscillations in the ambient plasma, which in turn produce short periods of intense radio emission. The standard theory predicts emission at either the fundamental electron plasma frequency (fp) or its harmonic (2fp). These values are proportional to the square root of […]

Wavelet-based characterization of small-scale solar emission features at low radio frequencies by A. Suresh et al.*

2017-08-15

The improved sensitivity provided by new-generation radio arrays has unveiled an enormous diversity of previously under-appreciated solar radio bursts. Observations in the 100-240 MHz band using the Murchison Widefield Array (MWA) have highlighted the presence of a myriad of weak, short-lived, narrow-band solar emission features (Fig. 1), even during calm solar periods. Their appearance in the MWA solar dynamic spectrum (DS) comes closest to miniature versions of type-III bursts with […]