Observations of Near-Simultaneous Split-Band Solar Type-II Radio Bursts at Low Frequencies

Hariharan, K.; Ramesh, R.; Kathiravan, C.

doi:10.1007/s11207-015-0761-5

Cited by 20 publications

(16 citation statements)

References 60 publications

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“…So, even when the Sun is at −23° decl., its elevation for GRAPH would be high (≈53°). For radio spectral data, we used observations with the Gauribidanur LOw‐frequency Solar Spectrograph (GLOSS; Ebenezer et al, 2001, 2007; Hariharan et al, 2016; Kishore et al, 2014), Gauribidanur RAdio Spectro‐Polarimeter (GRASP; Hariharan et al, 2015; Kishore et al, 2015; Sasikumar Raja et al, 2013), and e‐CALLISTO (Benz et al, 2009; Monstein et al, 2007). We also used data obtained with the Gauribidanur Radio Interferometric Polarimeter (GRIP; Ramesh et al, 2008).…”

Section: Observationsmentioning

confidence: 99%

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Ramesh

Kumari

Kathiravan

et al. 2020

Geophysical Research Letters

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We carried out a statistical study of the "quiet" solar corona during the descending phase of the Sunspot Cycle 24 (i.e., January 2015 to May 2019) using data obtained with the Gauribidanur RAdioheliograPH (GRAPH) at 53 and 80 MHz simultaneously. Our results show that the equatorial (east-west) diameters of the solar corona at the above two frequencies shrunk steadily. The decrease was found to be due to a gradual reduction in the coronal electron density (N e). Independent estimates of N e in the equatorial region of the "background" corona using white-light coronagraph observations indicate a decline consistent with our findings.

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Section: Observationsmentioning

confidence: 99%

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Ramesh

Kumari

Kathiravan

et al. 2020

Geophysical Research Letters

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“…The radio observations reported in the present work were carried out using the different facilities operated by the Indian Institute of Astrophysics (IIA) in the Gauribidanur observatory 1 (Ramesh 2011). The Gauribidanur RAdio Spectro-Polarimeter (GRASP; Kishore et al (2015); Hariharan et al (2015)) observed a split-band type II radio burst from the Sun on 2016 March 16 during the period ≈ 06:45 -07:00 UT. The frequency range of the burst was ≈ 90 -50 MHz.…”

Section: Radio Observationsmentioning

confidence: 99%

Direct Estimates of the Solar Coronal Magnetic Field Using Contemporaneous Extreme-ultraviolet, Radio, and White-light Observations

Kumari

Ramesh

Kathiravan

et al. 2019

ApJ

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We report a solar coronal split-band type II radio burst that was observed on 2016 March 16 with the Gauribidanur Radio Spectro-Polarimeter (GRASP) in the frequency range ≈ 90 -50 MHz, and the Gauribidanur RadioheliograPH (GRAPH) at two discrete frequencies, viz. 80 MHz and 53.3 MHz. Observations around the same epoch in extreme-ultraviolet (EUV) and white-light show that the above burst was associated with a flux rope structure and a coronal mass ejection (CME), respectively. The combined height-time plot generated using EUV, radio, and whitelight data suggest that the different observed features (i.e. the flux rope, type II burst and the CME) are all closely associated. We constructed an empirical model for the coronal electron density distribution (N e (r), where r is the heliocentric distance) from the above set of observations themselves and used it to estimate the coronal magnetic field strength (B) over the range of r values in which the respective events were observed. The B values are consistent with each other. They vary as B(r) = 2.61×r −2.21 G in the range r ≈ 1.1 -2.2R . As far as we know, similar 'direct' estimates of B in the near-Sun corona without assuming a model for N e (r), and by combining co-temporal set of observations in two different regions (radio and whitelight) of the electromagnetic spectrum, have rarely been reported. Further, the present work is a novel attempt where the characteristics of a propagating EUV flux rope structure, considered to be the signature of a CME close the Sun, have been used to estimate B(r) in the corresponding distance range.

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“…GRH imaging and simultaneous polarimeter observations have been used for studies of Type I noise storms (Ramesh, Kathiravan, and Narayanan, 2011;Ramesh et al, 2013;Mugundhan et al, 2018), Type II bursts (Hariharan et al, 2014;Hariharan, Ramesh, and Kathiravan, 2015;Kumari et al, 2017), Type III bursts Kishore et al, 2017), Type IV bursts (Hariharan et al, 2016), and gyrosynchrotron emission from CMEs (Sasikumar Raja et al, 2014). Most of these results include estimates of the associated magnetic field strength assuming a particular emission mechanism.…”

Section: Introductionmentioning

confidence: 99%

The Low-Frequency Solar Corona in Circular Polarization

et al. 2019

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We present spectropolarimetric imaging observations of the solar corona at low frequencies (80 -240 MHz) using the Murchison Widefield Array (MWA). These images are the first of their kind, and we introduce an algorithm to mitigate an instrumental artefact by which the total intensity signal contaminates the polarimetric images due to calibration errors. We then survey the range of circular polarization (Stokes V ) features detected in over 100 observing runs near solar maximum during quiescent periods. First, we detect around 700 compact polarized sources across our dataset with polarization fractions ranging from less than 0.5 % to nearly 100 %. These sources exhibit a positive correlation between polarization fraction and total intensity, and we interpret them as a continuum of plasma emission noise storm (Type I burst) continua sources associated with active regions. Second, we report a characteristic "bullseye" structure observed for many low-latitude coronal holes in which a central polarized component is surrounded by a ring of the opposite sense. The central component does not match the sign expected from thermal bremsstrahlung emission, and we speculate that propagation effects or an alternative emission mechanism may be responsible. Third, we show that the large-scale polarimetric structure at our lowest frequencies is reasonably well-correlated with the line-of-sight (LOS) magnetic field component inferred from a global potential field source surface (PFSS) model. The boundaries between opposite circular polarization signs are generally aligned with polarity inversion lines in the model at a height roughly corresponding to that of the radio limb. This is not true at our highest frequencies, however, where the LOS magnetic field direction and polarization sign are often not straightforwardly correlated.

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Observations of Near-Simultaneous Split-Band Solar Type-II Radio Bursts at Low Frequencies

Cited by 20 publications

References 60 publications

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Low‐Frequency Radio Observations of the “Quiet” Corona During the Descending Phase of Sunspot Cycle 24

Direct Estimates of the Solar Coronal Magnetic Field Using Contemporaneous Extreme-ultraviolet, Radio, and White-light Observations

The Low-Frequency Solar Corona in Circular Polarization

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