High Spectral Resolution Observation of Decimetric Radio Spikes Emitted by Solar Flares - First Results of the Phoenix-3 Spectrometer |
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Arnold O. Benz Submitted: 2009-09-23 01:27
A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1 - 5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1 - 5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350 - 850 MHz. Spike bandwidths are found to have a power-law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential.
Authors: Benz, A.O., Monstein, C., Beverland, M., Meyer, H., Stuber, B.
Projects: None
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Publication Status: Solar Physics, in press
Last Modified: 2009-09-23 06:36
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Subject will be restored when possible |
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Arnold O. Benz Submitted: 2008-02-26 11:45
Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays at 100 MeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, and SOHO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections (CMEs), electrons and ions may be accelerated at different sites, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and
particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting reconnection of magnetic
field lines as the basic cause. While this process has become generally accepted as the trigger, it does not explain the huge energy involved, nor the impulsive acceleration of charged particles. Flare-like processes may
be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's lower ionosphere. While flare scenarios have slowly converged over the past decades, every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain an unexplained problem of astrophysics.
Authors: Arnold O. Benz
Projects: None
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Publication Status: published in Living Reviews in Solar Physics (2008)
Last Modified: 2008-09-23 21:22
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Subject will be restored when possible |
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Arnold O. Benz Submitted: 2008-02-14 03:55
Radio spectrometers of the CALLISTO type to observe solar flares have been distributed to 9 locations around the globe. The instruments observe automatically. Their data is collected every day via internet and stored in a central data base. A public web-interface exists through which data can be browsed and retrieved. The 9 instruments form a network called e-CALLISTO. It is still growing in the number of stations, as redundancy is desirable for full 24 hour coverage of the solar radio emission in the meter and low decimeter band. The e-CALLISTO system has already proven to be a valuable new tool for monitoring solar activity and for space weather research.
Authors: A. O. Benz , C. Monstein, H. Meyer, P. K. Manoharan, R. Ramesh, A. Altyntsev, A. Lara, J. Paez, and K.-S. Cho
Projects: None
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Publication Status: in press at Earth, Moon, and Planets (2008)
Last Modified: 2008-02-14 09:53
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CALLISTO - A New Concept for Solar Radio Spectrometers |
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Arnold O. Benz Submitted: 2004-10-19 06:44
A new radio spectrometer, CALLISTO, is presented. It is a dual-channel frequency-agile receiver based on commercially available consumer electronics. Its major characteristic is the low price for hardware and software, and the short assembly time, both two or more orders of magnitude below existing spectrometers. The instrument is sensitive at the physical limit and extremely stable. The total bandwidth is 825 MHz, and the width of individual channels is 300 kHz. A total of 1000 measurements can be made per second. The spectrometer is well suited for solar low-frequency radio observations pertinent to space weather research. Five instruments of the type were constructed until now and put into operation at several sites, including Bleien (Zurich) and NRAO (USA). First results in the 45 - 870 MHz range are presented. Some of them were recorded in a preliminary setup during the time of high solar activity in October and November 2003.
Authors: Benz, A.O., Monstein, C., and Meyer, H.
Projects:
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Publication Status: Solar Physics, 226, 143 - 151 (2005)
Last Modified: 2005-11-21 03:23
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Survey on solar X-ray flares and associated coherent radio emissions |
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Arnold O. Benz Submitted: 2004-10-19 06:40
The radio emission during 201 X-ray selected solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% they are the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines.
Authors: Benz, A.O., Grigis, P.C., Csillaghy, A. and Saint-Hilaire, P.
Projects: RHESSI
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Publication Status: Solar Physics,226, 121 - 142 (2005)
Last Modified: 2005-11-21 03:24
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