Discovery of unusual large group delay in microwave
millisecond oscillating events

Fleishman, G. D.; Fu, Qiang; Huang, Guojun; Melnikov, V. F.; Wang, M

doi:10.1051/0004-6361:20020172

Cited by 31 publications

(31 citation statements)

References 15 publications

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“…They found a delay of approximately 100 μs between different spike polarities. The group delay for pulsations was studied by Fleishman et al (2002) who reported a delay of up to 20 ms in an exceptional event at 2.8 GHz.…”

Section: Origin Of Delaysmentioning

confidence: 99%

Correlation between decimetric radio emission and hard X-rays in solar flares

Dąbrowski

Benz²

2009

A&A

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Aims. The emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate in accelerated, non-thermal particles. On the other hand, non-thermal hard X-rays are also understood to be products of this acceleration. Do radio emission and hard X-ray signatures originate from the same acceleration process? A strong correlation between the light curves in the radio and HXR ranges may help answer this question. Methods. The delay between the radio and hard X-ray emission was determined by cross-correlation. The time profiles of X-ray and radio emission include a wide range of energies and frequencies. Thus, correlation is not simply a yes/no question, but must be systematically searched for in various ranges. The high spectral resolution of RHESSI ensured that it was possible to carefully choose the energy range, excluding thermal emission. The broad bandwidth of Phoenix-2 allowed the selection of any emission in the full decimetre range. The energy range and duration in hard X-rays, and the frequency range in radio spectrograms were chosen to optimize the correlation. The cross-correlation coefficient was then analyzed by a Gaussian fitting method. Results. The measured delays have a distribution of FWHM 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from such a Gaussian fitting method. The mean delay for pulsations was found to be −1.4 ± 0.9 s (minus indicates that hard X-ray emission comes first), and for narrowband spikes to −2.5 ± 2.5 s. There are broad wings in the distribution, which we interpret as chance coincidences. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence, and position on the disk. However, we find an increase in the delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux. This was not the case for pulsations. Conclusions. In contrast to previous reports, the average delays for all pulsations and all spike groups are consistent with zero. Thus, correlated decimetric pulsations and spikes are, on average, concomitant with non-thermal X-rays.

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Section: Origin Of Delaysmentioning

confidence: 99%

Correlation between decimetric radio emission and hard X-rays in solar flares

Dąbrowski

Benz²

2009

A&A

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“…For completeness, we mention that the presence of a magnetic field renders a plasma birefringent and causes radiation at a fixed frequency to show a differential delay between the ordinary and extraordinary modes, which corresponds to a delay between RCP and LCP emissions. At frequencies where 3 pe and Be , the differential group delay between RCP and LCP over a path from the region of source emission to observation is (Benz & Pianezzi 1997;Fleishman et al 2002aFleishman et al , 2002b)…”

Section: Propagation Effectsmentioning

confidence: 99%

Ultrahigh Time Resolution Observations of Radio Bursts on AD Leonis

Osten

Bastian

2008

ApJ

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We report observations of a radio burst that occurred on the flare star AD Leonis over a frequency range of 1120Y 1620 MHz (k % 18Y27 cm). These observations, made by the 305 m telescope of the Arecibo Observatory, are unique in providing the highest time resolution (1 ms) and broadest spectral coverage (Á / ¼ 0:36) of a stellar radio burst yet obtained. The burst was observed on 2005 April 9. It produced a peak flux density of $500 mJy, and it was essentially 100% right-circularly polarized. The dynamic spectrum shows a rich variety of structure: patchy emission, diffuse bands, and narrowband, fast-drift striae. Focusing our attention on the fast-drift striae, we consider the possible role of dispersion, and find that it requires rather special conditions in the source to be a significant factor. We suggest that the emission may be due to the cyclotron maser instability, a mechanism known to occur in planetary magnetospheres. We briefly explore possible implications of this possibility.

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“…Solar microwave bursts often display quasi-periodical pulsations with periods from ≈40 ms in narrowband bursts (Fleishman et al 2002) up to 20 s in broadband bursts (Nakajima 1983;Stepanov et al 1992;Qin et al 1996;Asai et al 2001). Broadband microwave bursts are generated by the gyrosynchrotron emission mechanism which is very sensitive to the magnetic field in the radio source.…”

Section: An Observational Examplementioning

confidence: 99%

Global sausage modes of coronal loops

Nakariakov¹,

Melnikov

Reznikova³

2003

A&A

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216

196

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Abstract. Sufficiently thick and dense coronal loops can support global sausage magnetoacoustic modes. We demonstrate that the oscillation period of this mode, calculated in the straight cylinder approximation, is determined by the length of the loop, not by its diameter, as it was previously assumed. The existence condition for this mode is the ratio of the loop length to its diameter to be less than about a half of the square root of the density contrast ratio. This mode has a maximum of the magnetic field perturbation at the loop apex and nodes at the footpoints. We demonstrate that the 14−17 s quasi-periodic pulsations, oscillating in phase at a loop apex and at its legs, observed with the Nobeyama Radioheliograph, are interpreted in terms of the global sausage mode.

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Discovery of unusual large group delay in microwave millisecond oscillating events

Cited by 31 publications

References 15 publications

Correlation between decimetric radio emission and hard X-rays in solar flares

Correlation between decimetric radio emission and hard X-rays in solar flares

Ultrahigh Time Resolution Observations of Radio Bursts on AD Leonis

Global sausage modes of coronal loops

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