69 research outputs found
Diagnostics of electron beam properties from the simultaneous hard X-ray and microwave emission in the 10 March 2001 flare
Simultaneous simulation of HXR and MW emission with the same populations of
electrons is still a great challenge for interpretation of observations in real
events. In this paper we apply the FP kinetic model of precipitation of
electron beam with energy range from 12 keV to 1.2 MeV to the interpretation of
X-ray and microwave emissions observed in the flare of 10 March 2001. Methods.
The theoretical HXR and MW emissions were calculated by using the distribution
functions of electron beams found by solving time-dependent Fokker-Planck
approach in a converging magnetic field (Zharkova at al., 2010; Kuznetsov and
Zharkova, 2010) for anisotropic scattering of beam electrons on the ambient
particles in Coloumb collisions and Ohmic losses. The simultaneous observed HXR
photon spectra and frequency distribution of MW emission and polarization were
fit by those simulated from FP models which include the effects of electric
field induced by beam electrons and precipitation into a converging magnetic
loop. Magnetic field strengths in the footpoints on the photosphere were
updated with newly calibrated SOHO/MDI data. The observed HXR energy spectrum
above 10 keV is shown to be a double power law which was fit precisely by the
photon HXR spectrum simulated for the model including the self-induced electric
field but without magnetic convergence. The MW emission simulated for different
models of electron precipitation revealed a better fit to the observed
distribution at higher frequencies for the models combining collisions and
electric field effects with a moderate magnetic field convergence of 2. The MW
simulations were able to reproduce closely the main features of the MW emission
observed at higher frequencies.Comment: 17 pages, 10 figures in press; A&A 201
Spectral and spatial observations of microwave spikes and zebra structure in the short radio burst of May 29, 2003
The unusual radio burst of May 29, 2003 connected with the M1.5 flare in AR
10368 has been analyzed. It was observed by the Solar Broadband Radio
Spectrometer (SBRS/Huairou station, Beijing) in the 5.2-7.6 GHz range. It
proved to be only the third case of a neat zebra structure appearing among all
observations at such high frequencies. Despite the short duration of the burst
(25 s), it provided a wealth of data for studying the superfine structure with
millisecond resolution (5 ms). We localize the site of emission sources in the
flare region, estimate plasma parameters in the generation sites, and suggest
applicable mechanisms for interpretating spikes and zebra-structure generation.
Positions of radio bursts were obtained by the Siberian Solar Radio Telescope
(SSRT) (5.7 GHz) and Nobeyama radioheliograph (NoRH) (17 GHz). The sources in
intensity gravitated to tops of short loops at 17 GHz, and to long loops at 5.7
GHz. Short pulses at 17 GHz (with a temporal resolution of 100 ms) are
registered in the R-polarized source over the N-magnetic polarity
(extraordinary mode). Dynamic spectra show that all the emission comprised
millisecond pulses (spikes) of 5-10 ms duration in the instantaneous band of 70
to 100 MHz, forming the superfine structure of different bursts, essentially in
the form of fast or slow-drift fibers and various zebra-structure stripes. Five
scales of zebra structures have been singled out. As the main mechanism for
generating spikes (as the initial emission) we suggest the coalescence of
plasma waves with whistlers in the pulse regime of interaction between
whistlers and ion-sound waves. In this case one can explain the appearance of
fibers and sporadic zebra-structure stripes exhibiting the frequency splitting.Comment: 11 pages, 5 figures, in press; A&A 201
Study of flare energy release using events with numerous type III-like bursts in microwaves
The analysis of narrowband drifting of type III-like structures in radio
bursts dynamic spectra allows to obtain unique information about primary energy
release mechanisms in solar flares. The SSRT spatially resolved images and a
high spectral and temporal resolution allow direct determination not only the
positions of its sources but also the exciter velocities along the flare loop.
Practically, such measurements are possible during some special time intervals
when the SSRT (about 5.7 GHz) is observing the flare region in two high-order
fringes; thus, two 1D scans are recorded simultaneously at two frequency bands.
The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is
presented. Using-muliwavelength radio observations recorded by SSRT, SBRS,
NoRP, RSTN we study an event with series of several tens of drifting microwave
pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the
fast-drifting bursts were located near the top of the flare loop in a volume of
a few Mm in size. The slow drift of the exciters along the flare loop suggests
a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201
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