UNSPECIFIED. (2005) Spatially resolved microwave pulsations of a flare loop. ASTRONOMY & ASTROPHYSICS, 439 (2). pp. 727-736. ISSN 0004-6361

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Abstract

A microwave burst with quasi-periodic pulsations was studied with high spatial resolution using observations with the Nobeyama Radioheliograph (NoRH). We found that the time profiles of the microwave emission at 17 and 34 GHz exhibit quasi-periodic ( with two well defined periods P-1 = 14-17 s and P-2 = 8-11 s) variations of the intensity at different parts of an observed flaring loop. Detailed Fourier analysis shows the P1 spectral component to be dominant at the top, while the P2 one near the feet of the loop. The 14-17 s pulsations are synchronous at the top and in both legs of the loop. The 8-11 s pulsations at the legs are well correlated with each other but the correlation is not so obvious with the pulsations at the loop top. For this P2 spectral component, a definite phase shift, P-2/4 approximate to 2.2 s, between pulsations in the northern leg and loop top parts of the loop have been found. The length of the flaring loop is estimated as L = 25 Mm (approximate to 34") and its average width at half intensity at 34 GHz as about 6 Mm (approximate to 8"). Microwave diagnostics shows the loop to be filled with a dense plasma with the number density n(0) approximate to 10(11) cm(-3), penetrated by the magnetic field changing from B-0 approximate to 100 G near the loop top up to B-0 approximate to 200 G near the north footpoint. A comparative analysis of different MHD modes of the loop demonstrates the possibility of the simultaneous existence of two modes of oscillations in the loop: the global sausage mode, with the period P1 = 14-17 s and the nodes at the footpoints, and a higher harmonics mode ( possibly with the radial wave number l > 1), with P2 = 8-11 s.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Journal or Publication Title:	ASTRONOMY & ASTROPHYSICS
Publisher:	EDP SCIENCES S A
ISSN:	0004-6361
Date:	August 2005
Volume:	439
Number:	2
Number of Pages:	10
Page Range:	pp. 727-736
Identification Number:	10.1051/0004-6361:20052774
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/6779

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