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RHESSI and Microwave Imaging Observations of Two Solar Flares  

Edward Schmahl   Submitted: 2005-08-18 13:19

We describe two flares of GOES class M5.7 and 1.5 which were observed simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH (Nobeyama Radio Heliograph). Both of these flares exhibit slow motions suggestive of changing magnetic shear, loop expansion, or gradual reconnection.

Authors: M.R. Kundu, E.J. Schmahl, & V.I. Garaimov
Projects: RHESSI

Publication Status: Multi-Wavelength Investigations of Solar Activity, IAU Symposium 223 (2005)
Last Modified: 2005-08-18 13:58
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RHESSI AND RADIO IMAGING OBSERVATIONS OF MICROFLARES  

Edward Schmahl   Submitted: 2005-08-17 14:25

We present an analysis of five microflares, three observed simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz) and two observed by RHESSI and Nançay RadioHeliograph (NRH) at metric wavelengths (150-450 MHz). Since we have no radio imaging telescopes simultaneously operating at microwave and meter wavelengths in the same time zone, we are obliged to use a different set of metric events in contrast to that used for comparison with the two radio wavelengths. We are interested in using the locations and other imaging characteristics of the events from both RHESSI and radio observations instead of just temporal correlation. So we've used the Nançay (France) metric radioheliograph at 150-450 MHz for this purpose. Here we describe the properties of five events - three in microwaves and two at metric wavelengths. We discuss the brightness temperatures, emission measures and the hard X-ray spectral properties of these microevents. One sees small (mini) flaring loops clearly in NoRH and RHESSI images. The microwave emission often seems to come from the RHESSI foot points (for higher energies), and from the entire small (mini) flaring loop (for lower energies).The RHESSI microflares seem to be associated in position with metric type III bursts. Frequently, the hard X-ray spectrum of the microwave associated RHESSI microflares can be fit by a thermal component at low energies (sim 3-12 keV) and a nonthermal component at higher energies (sim 12-20 keV).

Authors: Kundu, Trottet, Grigis & Schmahl
Projects: RHESSI

Publication Status: Adv. Spa. Res. in press
Last Modified: 2005-08-18 13:12
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Observations of the failed eruption of a filament  

Edward Schmahl   Submitted: 2003-04-29 07:41

We have observed the fine temporal and spatial structure of a filament eruption on 2002 May 27 following an M2-class flare. Our observations at Big Bear Solar Observatory (BBSO) were made at the wavelength of Hα 1.3 A, with a cadence of 40 ms. The event was also observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at X-ray energies from 3 to 50 keV and by the Transition Region And Coronal Explorer (TRACE) in Fe XII 195 A. The event appears to be a ``failed eruption'', as the filament material, seen in absorption by TRACE, first accelerated, then decelerated as it approached its peak height of ~ 8 X 104 km while the filament threads drained back to the Sun. The fact that the eruption did not lead to a coronal mass ejection indicates that the coronal magnetic field near ~ 8 X 104 km did not open during the flare. The height-time curve obtained from the TRACE 195 A images during the deceleration phase shows that the deceleration of the filament exceeded the gravitational deceleration by more than a factor of 10, which suggests that the filament material was pulled back by magnetic tension. Also of importance are three sequential, but co-spatial, features-brightenings in EUV, a looptop hard X-ray emission, and `rupturing' of the Hα filament-which point to a release of energy (and probably magnetic reconnection) above the initial filament's location but well below its terminal height. Reconnection above a filament does not appear in most models, with the notable exception of quadrupolar and `breakout' models. These observations provide evidence that at least two conditions are required for a successful eruption: a reconnection very low in the corona (possibly above the filament), and open or opening fields above that point.

Authors: Ji,H. Wang,H., Schmahl, E.,Moon,Y.-J., and Jiang,Y.
Projects: RHESSI

Publication Status: Accepted by Ap.J.(Letters) April 28, 2003
Last Modified: 2003-04-29 07:41
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HARD X-RAY SOURCE PROFILES AS DETERMINED BY RHESSI  

Edward Schmahl   Submitted: 2002-12-19 15:09

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has been recording rotationally-modulated X-rays from solar flares since its launch on February 5, 2002. Its 9 grid pairs time-modulate the detected photon flux giving RHESSI spatial information on hard X-rays at 9 logarithmically spaced angular scales ranging from 2.3 to 183 arcsec. Using the calibrated modulation profiles for a variety of flares, we present new information on the spatial profiles of the hard X-ray structures in flares. We find that the FWHM of cores of single-component flares range from 3 to 11'' in size. Most of the flares in this set show extended emission out to 2 to 3 times the radii of the cores, and these `halos' contain up to 25% of the total flux.

Authors: E. J. Schmahl and G. J. Hurfordaddress
Projects:

Publication Status: Accepted for publication by COSPAR for ASR special section, 2003
Last Modified: 2002-12-19 15:09
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Abstracts by Author
RHESSI and Microwave Imaging Observations of Two Solar Flares
RHESSI AND RADIO IMAGING OBSERVATIONS OF MICROFLARES
Observations of the failed eruption of a filament
HARD X-RAY SOURCE PROFILES AS DETERMINED BY RHESSI

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