Radio imaging-spectroscopy observations of the Sun in decimetric and centimetric wavelengths

Yan, Yihua; Wang, Wei; Liu, Fei; Geng, Lihong; Chen, Zhijun; Zhang, Jian

doi:10.1017/s1743921313003001

Cited by 16 publications

(14 citation statements)

References 16 publications

(11 reference statements)

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“…In addition, with the increase in the number of ground-based and space-based instruments for solar observations that have characteristics of high time resolution, high space resolution, and high frequency resolution, massive amounts of scientific observation data is produced every day (e.g., Lemen et al 2011;Yan et al 2012;Wang et al 2013;van Haarlem et al 2013). The high quality and quantity of data is helpful in order to improve the reliability of the results from statistical analysis, to study the fine structures of solar activities, and to distinguish different theoretic models, etc.…”

Section: Introductionmentioning

confidence: 99%

A type III radio burst automatic analysis system and statistic results for a half solar cycle with Nançay Decameter Array data

Zhang

Wang

2018

A&A

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Aims. We design an event recognition-analysis system that can automatically detect solar type III radio burst and can mine information of the burst from the dynamic spectra observed by Nançay Decameter Array (NDA). We investigate the frequency drift rate of type III bursts and the speed of electron beams responsible for the generation of the bursts.Methods. Several computer vision methods are used in this automatic analysis system. The Hough transform is performed to recognize the line segment associated with type III bursts in the dynamic spectra. A modified active contour model is used to track the backbone of the burst and estimate the frequency drift rate at different frequency channels. We run this system on the NDA data from 2012 to 2017, and give a statistical survey of the event number distribution, the starting and stopping frequencies of bursts, the frequency dependence of the drift rate, and the exciter speed using three corona density models.Results. The median value of the average frequency drift rates is about 6.94MHz/s for 1389 simple well-isolated type III bursts detected in the frequency range 10-80 MHz of NDA observation.The frequency drift rate changes with frequency as d f /dt = −0.0672 f 1.23 from a least-squares fitting. The average exciter speed is about 0.2c based the density models. We do not find any significant dependence of the drift rate and the exciter speed on the solar activity cycle.Article number, page 1 of 20 P. J. Zhang et al.: A type III radio burst automatic analysis system and statistic results for a half solar cycle with Nançay Decameter Array data Use \titlerunning to supply a shorter title and/or \authorrunning to supply a shorter list of authors.

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Section: Introductionmentioning

confidence: 99%

A type III radio burst automatic analysis system and statistic results for a half solar cycle with Nançay Decameter Array data

Zhang

Wang

2018

A&A

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“…The spatially resolved data of the Stokes I and V components are available from a number of solar radio instruments at different microwave frequencies, such as the Nobeyama Radioheliograph (NoRH, Nakajima et al, 1994), the Siberian Solar Radio Telescope (SSRT, Grechnev et al, 2003), and Owens Valley Solar Arrays (OVSA, Gary and Hurford, 1994). A new generation of microwave multi'wavelength radioheliographs is now under various stages of development: the expanded OVSA (Gary et al, 2012), the Frequency Agile Solar Radiotelescope (FASR, Bastian, 2004), the Mingantu Ultrawide Spectral Radioheliograph (MUSER, Yan et al, 2013) and the Siberian Radio Heliograph (SRH, Lesovoi et al, 2014;.…”

Section: Introductionmentioning

confidence: 99%

Flare SOL2012-07-06: On the Origin of the Circular Polarization Reversal Between 17 GHz and 34 GHz

et al. 2017

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The new generations of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz. It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes. The flare occurred in the central part of the solar disk, which allows reconstructing the magnetic field in the flare region using vector magnetogram data. We have investigated the three possible known reasons of the circular polarization sense reversal -mode coupling, positron contribution, and the effect of beamed angular distribution. We excluded polarization reversal due to contribution of positrons because there was no relevant response in the X-ray emission. We find that a beam-like electron distribution can produce the observed polarization behavior, but the source thermal density must be much higher than the estimate from to the X-ray data. We conclude that the apparent ordinary wave emission in the optically thin mode is due to radio wave propagation across the quasi-transverse (QT) layer. The abnormally high transition frequency (above 35 GHz) can be achieved reasonably low in the corona where the magnetic field value is high and transverse to the line of sight. This places the microwave source below this QT layer, i.e. very low in the corona.

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“…The CSRH-II array is comprised of 60 reflector antennas with 2-m dishes and covers a frequency range from 2-15 GHz (Li et al 2015b). All 100 antennas (Yan et al 2012) are placed along 3 spiral arms with a maximum baseline of 3 km and surrounded by small hills . The CSRH will make full solar disk radio images at multiple frequency channels with a time resolution down to 3 ms (Takano 1996).…”

Section: Introductionmentioning

confidence: 99%

A New Impedance Matching Method for an Ultra-Wide Band and Dual Circularly Polarised Feed

Yan

Wang

et al. 2016

Publ. Astron. Soc. Aust.

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N. (2016) A new impedance matching method for an ultra-wide band and dual circularly polarised feed. Publications of the Astronomical Society of Australia, 33, e061. (doi:10.1017Australia, 33, e061. (doi:10. /pasa.2016 This is the author's final accepted version.There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it. AbstractIn traditional antenna design, metal components are not placed in the central part of the antenna as they change the characteristics of near field radiation. However, we show that placing a metal ring in the center of the strip lines, which connect the ends of folded high frequency dipoles, does not damage the performance of the feed. Instead it significantly improves the voltage standing wave ratio (VSWR) of the feed while other performance indicators are not compromised. Thus, our findings show an excellent way of improving the wide band feed. Based on this foundation, a new circularly polarized feed for operation between 0.4 to 2 GHz is introduced for the Chinese Spectral Radioheliograph (CSRH) in this paper. The issue of a feed impedance matching network is investigated. By optimizing the impedance matching, the performance of the feed is enhanced with respect to the previous realizations of the Eleven feed. The simulation and experimental results show that the gain of the feed is about 10 dB, and the VSWR is less than 2:1. In addition, the feed has a low axial ratio, fixed phase center location, and constant beam width in the range of 0.4 to 2 GHz.

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Radio imaging-spectroscopy observations of the Sun in decimetric and centimetric wavelengths

Cited by 16 publications

References 16 publications

A type III radio burst automatic analysis system and statistic results for a half solar cycle with Nançay Decameter Array data

A type III radio burst automatic analysis system and statistic results for a half solar cycle with Nançay Decameter Array data

Flare SOL2012-07-06: On the Origin of the Circular Polarization Reversal Between 17 GHz and 34 GHz

A New Impedance Matching Method for an Ultra-Wide Band and Dual Circularly Polarised Feed

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