78 research outputs found
Microwave Quasi-periodic Pulsation with Millisecond Bursts in A Solar Flare on 2011 August 9
An peculiar microwave quasi-periodic pulsation (QPP) accompanying with a hard
X-ray (HXR) QPP of about 20 s duration occurred just before the maximum of an
X6.9 solar flare on 2011 August 9. The most interesting is that the microwave
QPP is consisting of millisecond timescale superfine structures. Each microwave
QPP pulse is made up of clusters of millisecond spike bursts or narrow band
type III bursts. There are three different frequency drift rates: global
frequency drift rate of microwave QPP pulse group, frequency drift rate of
microwave QPP pulse, and frequency drift rate of individual millisecond spikes
or type III bursts. The physical analysis indicates that the energetic
electrons accelerating from a large-scale highly dynamic magnetic reconnecting
current sheet above the flaring loop propagate downwards, impact on the flaring
plasma loop, and produce HXR bursts. The tearing-mode (TM) oscillations in the
current sheet modulate HXR emission and generate HXR QPP; the energetic
electrons propagating downwards produce Langmuir turbulence and plasma waves,
result in plasma emission. The modulation of TM oscillation on the plasma
emission in the current-carrying plasma loop may generate microwave QPP. The TM
instability produces magnetic islands in the loop. Each X-point will be a small
reconnection site and accelerate the ambient electrons. These accelerated
electrons impact on the ambient plasma and trigger the millisecond spike
clusters or the group of type III bursts. Possibly each millisecond spike burst
or type III burst is one of the elementary burst (EB). Large numbers of such EB
clusters form an intense flaring microwave burst.Comment: 14 pages, 6 figures, accepted by Ap
Solar Radio Bursts with Spectral Fine Structures in Preflares
A good observation of preflare activities is important for us to understand
the origin and triggering mechanism of solar flares, and to predict the
occurrence of solar flares. This work presents the characteristics of microwave
spectral fine structures as preflare activities of four solar flares observed
by Ond\v{r}ejov radio spectrograph in the frequency range of 0.8--2.0 GHz. We
found that these microwave bursts which occurred 1--4 minutes before the onset
of flares have spectral fine structures with relatively weak intensities and
very short timescales. They include microwave quasi-periodic pulsations (QPP)
with very short period of 0.1-0.3 s and dot bursts with millisecond timescales
and narrow frequency bandwidths. Accompanying these microwave bursts, there are
filament motions, plasma ejection or loop brightening on the EUV imaging
observations and non-thermal hard X-ray emission enhancements observed by
RHESSI. These facts may reveal certain independent non-thermal energy releasing
processes and particle acceleration before the onset of solar flares. They may
be conducive to understand the nature of solar flares and predict their
occurrence
Microwave Zebra Pattern Structures in the X2.2 Solar Flare on Feb 15, 2011
Zebra pattern structure (ZP) is the most intriguing fine structure on the
dynamic spectrograph of solar microwave burst. On 15 February 2011, there
erupts an X2.2 flare event on the solar disk, it is the first X-class flare
since the solar Schwabe cycle 24. It is interesting that there are several
microwave ZPs observed by the Chinese Solar Broadband Radiospectrometer
(SBRS/Huairou) at frequency of 6.40 ~ 7.00 GHz (ZP1), 2.60 ~ 2.75 GHz (ZP2),
and the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at frequency of
1.04 ~ 1.13 GHz (ZP3). The most important phenomena is the unusual
high-frequency ZP structure (ZP1, up to 7.00 GHz) occurred in the early rising
phase of the flare, and there are two ZP structure (ZP2, ZP3) with relative low
frequencies occurred in the decay phase of the flare. By scrutinizing the
current prevalent theoretical models of ZP structure generations, and comparing
their estimated magnetic field strengths in the corresponding source regions,
we suggest that the double plasma resonance model should be the most possible
one for explaining the formation of microwave ZPs, which may derive the
magnetic field strengths as about 230 - 345 G, 126 - 147 G, and 23 - 26 G in
the source regions of ZP1, ZP2, and ZP3, respectively.Comment: 18 pages, 6 figures, submitted to ApJ, 201
Reversed Drifting Quasi-periodic Pulsating Structure in an X1.3 Solar Flare on 2005 July 30
Based on the analysis of the microwave observations at frequency of 2.60 --
3.80 GHz in a solar X1.3 flare event observed at Solar Broadband
RadioSpectrometer in Huairou (SBRS/Huairou) on 2005 July 30, an interesting
reversed drifting quasi-periodic pulsating structure (R-DPS) is confirmed. The
R-DPS is mainly composed of two drifting pulsating components: one is a
relatively slow very short-period pulsation (VSP) with period of about 130 --
170 ms, the other is a relatively fast VSP with period of about 70 -- 80 ms.
The R-DPS has a weak left-handed circular polarization. Based on the synthetic
investigations of Reuven Ramaty High Energy Solar Spectroscopic Imaging
(RHESSI) hard X-ray, Geostationary Operational Environmental Satellite (GOES)
soft X-ray observation, and magnetic field extrapolation, we suggest the R-DPS
possibly reflects flaring dynamic processes of the emission source regions
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