Frequency and time profiles of metric wave isolated Type I solar noise storm bursts at high spectral and temporal resolution

Sundaram, G. A. Shanmugha; Subramanian, K. R.

doi:10.1111/j.1365-2966.2005.08924.x

Cited by 7 publications

(3 citation statements)

References 43 publications

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“…Solar absolute flux density calibration usually relies on the use of the few very bright sources whose flux density is large enough for them to be observed using the same attenuation setting as solar observations. This approach is followed at the Nançay Radio Heliograph (NRH; e.g., Bonmartin et al 1983;Avignon et al 1989), the Gauribidanur Radio Heliograph (GRH; e.g., Sundaram & Subramanian 2004, 2005, and the Low Frequency Array (LOFAR; e.g., Breitling et al 2015;Kontar et al 2017). Conventionally, calibrator observations are scheduled to be observed adjacent to and/or interspersed with observations of the target source(s).…”

Section: Introductionmentioning

confidence: 99%

Robust Absolute Solar Flux Density Calibration for the Murchison Widefield Array

Kansabanik

Mondal

Oberoi

et al. 2022

ApJ

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Sensitive radio instruments are optimized for observing faint astronomical sources, and usually need to attenuate the received signal when observing the Sun. There are only a handful of flux density calibrators that can comfortably be observed with the same attenuation setup as the Sun. Additionally, for wide field-of-view (FoV) instruments like the Murchison Widefield Array (MWA) calibrator observations are generally done when the Sun is below the horizon, to avoid the contamination from solar emissions. These considerations imply that the usual radio interferometric approach to flux density calibration is not applicable for solar imaging. A novel technique, relying on a good sky model and detailed characterization of the MWA hardware, was developed for solar flux density calibration for MWA. Though successful, this technique is not general enough to be extended to the data from the extended configuration of the MWA Phase II. Here, we present a robust flux density calibration method for solar observations with MWA independent of the array configuration. We use different approaches—the serendipitous presence of strong sources; detection of numerous background sources using high dynamic range images in the FoV along with the Sun; and observations of strong flux density calibrators with and without the additional attenuation used for solar observations—to obtain the flux scaling parameters required for the flux density calibration. Using the present method, we have achieved an absolute flux density uncertainty ∼10% for solar observations even in the absence of dedicated calibrator observations.

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Section: Introductionmentioning

confidence: 99%

Robust Absolute Solar Flux Density Calibration for the Murchison Widefield Array

Kansabanik

Mondal

Oberoi

et al. 2022

ApJ

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“…However, to study the source dynamics in tandem with its sub-second and sub-MHz scale flux variability (e.g. Wild 1957;Elgaroy & Ugland 1970;Guedel & Benz 1990;Sundaram & Subramanian 2005), high fidelity snapshot spectroscopic imag-ing at similar scales is essential. This remained a challenge until the advent of modern interferometric arrays like Murchison Widefield Array (MWA; Tingay et al 2013), LOw Frequency ARray (LOFAR; van Haarlem et al 2013) and the Long Wavelength Array (LWA; Ellingson et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Discovery of correlated evolution in solar noise storm source parameters: Insights on magnetic field dynamics during a microflare

Mohan

2021

Preprint

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A solar type-I noise storm is produced by accelerated particle beams generated at active regions undergoing magnetic field restructuring. Their intensity varies by orders of magnitude within subsecond and sub-MHz scales. But, the morphological evolution of these sources are not studied at these scales, due to the lack of required imaging cadence and fidelity in metrewave bands. Using data from the Murchison Widefield Array (MWA), this work explores the coevolution of size, sky-orientation and intensity of a noise storm source associated with a weak microflare. The work presents the discovery of two correlated modes of evolution in the source parameters: a sausage like 'S' mode where the source intensity and size shows an anti-correlated evolution; and a torsional like 'T' mode where the source size and sky-orientation shows a correlated evolution. A flare mediated mode conversion is observed from 'T' to 'S' for the first time in these sources. These results support the idea of build up of magnetic stress energy in braided active region loops, which later go unstable causing flares and particle acceleration until they relax to a minimally braided state. The discovered mode conversion can be a future diagnostic to such active region phenomena.

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“…Bonmartin et al 1983;Avignon et al 1989), the Gauribidanur Radio Heliograph (GRH; e.g. Sundaram & Subramanian 2004, 2005 and the Low Frequency Array (LOFAR; e.g. Breitling et al 2015;Kontar et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Robust absolute solar flux density calibration for the Murchison Widefield Array

Kansabanik,

Mondal,

Oberoi

et al. 2022

Preprint

View full text Add to dashboard Cite

Sensitive radio instruments are optimized for observing faint astronomical sources, and usually need to attenuate the received signal when observing the Sun. There are only a handful of flux density calibrators which can comfortably be observed with the same attenuation set up as the Sun. Additionally, for wide field-of-view (FoV) instruments like the Murchison Widefield Array (MWA) calibrator observations are generally done when the Sun is below the horizon to avoid the contamination from solar emissions. These considerations imply that the usual radio interferometric approach to flux density calibration is not applicable for solar imaging. A novel technique, relying on a good sky model and detailed characterization of the MWA hardware, was developed for solar flux density calibration for MWA (Oberoi et al. 2017;Mohan & Oberoi 2017). Though successful, this technique is not general enough to be extended to the data from the extended configuration of the MWA Phase II. Here we present a robust flux density calibration method for solar observations with MWA independent of the array configuration. We use different approaches -the serendipitous presence of strong sources; detection of numerous background sources using high dynamic range images in the FoV along with the Sun and observations of strong flux density calibrators with and without the additional attenuation used for solar observations; to obtain the flux scaling parameters required for the flux density calibration. Using the present method we have achieved an absolute flux density uncertainty ∼ 10% for solar observations even in absence of dedicated calibrator observations.

show abstract

Frequency and time profiles of metric wave isolated Type I solar noise storm bursts at high spectral and temporal resolution

Cited by 7 publications

References 43 publications

Robust Absolute Solar Flux Density Calibration for the Murchison Widefield Array

Robust Absolute Solar Flux Density Calibration for the Murchison Widefield Array

Discovery of correlated evolution in solar noise storm source parameters: Insights on magnetic field dynamics during a microflare

Robust absolute solar flux density calibration for the Murchison Widefield Array

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