fl129.hudson12 Posted: 31-Jul-93 Updated: 08-Mar-94, 20-Nov-94, 24-Feb-96 Events specified: flare at 20:23 on 7-Jan-92
Proposers:
A. S. Silva, R. P. Lin, I. de Pater, J. McTiernan UC Berkeley S. M. White, M. R. Kundu U. Maryland H. S. Hudson U. Hawaii N. Nitta, K. T. Strong Lockheed D. E. Gary Caltech J. G. Doyle Armagh T. Kosugi, T. Sakao NAOJThesis note: this study may form a part of A. Silva's thesis at UC Berkeley
Description:
The flare occurred at 20:20 on 1992 Jan 7 in the active region complex AR 6993/6994, two regions extended considerably east-west, and stacked on top of one another north-south in close proximity. This complex produced numerous flares from several locations. This particular flare was a C9 which occurred close to the geometric center of the complex, and was well-observed by SXT, HXT, BCS (with a data gap in the decay due to SAA), the Very Large Array (at 5 GHz in the impulsive phase and at 1.5 GHz later), the Owens Valley Frequency-Agile Interferometer and the Berkely-Illinois-Maryland millimeter interferometer.
There are a number of interesting features which make this flare worth close study:
- Yohkoh triggers on SXR brightening in locations distinct from the main flare loop: an arcade of very compact loops lying along a neutral line, and another very compact loop about 10 arcseconds away. These structures, which were heated in the preflare phase and are visible for some time in the preflare SXT images, have vanished completely when the flare ends.
- there is an additional SXR brightening 100" away from the main loop, at the end of loops connecting the main flare site to a sunspot in the other active region. Radio emission is also seen at that location before any SXR emission is seen, and the whole long loop brightens as the flare proceeds.
- at low radio features a very large structure appears to propagate away from the flare region, but towards disk center.
The scientific objectives in studying this event are: to relate the timing of the nonthermal emission seen in radio and HXT to the SXT emission at various locations, and thus to work out where primary energy release occurred; to try to deduce the magnetic connectivity of various features using a combination of timing from SXT data and magnetogram features; to try to understand how connectivity changed as a result of the flare; to understand the relation of the different radio emissions to the main flare; to identify the sources of the superhot and blue-shift emissions and to place all of this into a consistent theoretical framework.
Update 24-Feb-96
Below is the abstract of a paper that was submitted to the Astrophysical Journal Supplement Series on February 12th, 1996, about the flare on January 7, 1992.
COMPREHENSIVE MULTI-WAVELENGTH OBSERVATIONS OF THE 1992 JANUARY 7 SOLAR FLARE
Adriana V. R. Silva, et al.
Observations of a solar flare which occurred at 2022 UT on 1992 January 7, during the December 91/January 92 Max'91 Campaign, are presented here. This flare was observed simultaneously in \ha, radio (at microwave and millimeter wavelengths), and soft and hard X-rays (by the {\it Yohkoh} spacecraft) with high spatial and moderate spectral resolution. A comparison of magnetograms before and after the flare shows evidence of the emergence of new magnetic flux of opposite polarity at the flare site. Although this flare was only of moderate size (GOES classification C8.9 and \ha\ importance SF) it exhibited several distinct bursts and at least ten spatially distinct hard/soft X-ray sources. Co-spatial \ha\ brightenings suggest that most of the X-ray sources are located at footpoints of magnetic loops. Two of the hard X--ray sources have no \ha\ counterpart and are thus believed to be located at loop tops. The flare consisted of three bursts of particle acceleration followed by a purely thermal phase. High spectral resolution Ca XIX line profiles indicate up-flows shortly after the second acceleration phase. Analysis of the microwave/hard X-ray/soft X-ray emission from individual sources provides information on the radio emission mechanisms, the energetic electron population, the magnetic field strength, and plasma density. These parameters were estimated for the two microwave sources observed during the third acceleration burst, these sources were simultaneously detected in soft X-rays and one of the sources is also seen in hard X--ray maps. Although the microwave emission is consistent with the gyrosynchrotron mechanism, the millimeter emission, which peaks during the thermal phase when all nonthermal activity has ceased, is likely due to thermal bremsstrahlung from the hot soft X--ray emitting plasma. The energy lost to collisions by the energetic ($>15$ keV) electrons and the energy contained in the thermal plasma are calculated for each source. The energy injected by the nonthermal electrons from all sources is estimated to be $\sim 10^{30}$ erg. Only the soft X-ray sources with gradual time profiles seem to show the Neupert effect.
Update 20-Nov-94
abstract of ApJ paper
Comprehensive Multi-Wavelength Observations of the 1992 January 7 Solar Flare
Adriana V.R. Silva, Imke de Pater, Robert P. Lin, James M. McTiernan, Stephen M. White, Mukul R. Kundu, Dale E. Gary, Hugh S. Hudson, Mona J. Hagyard, J. Gerry Doyle
During the December 91/January 92 Max'91 Campaign a solar flare occurring at 2022 UT on 7 January 1992 was observed simultaneously in soft and hard X-rays (by the Yohkoh} spacecraft), H-alpha, and radio (microwave and millimeter) with high spatial and moderate spectral resolution. Although this flare was only of moderate size (GOES classification C8.9 and H-alpha importance SF) it exhibited several distinct bursts and at least eight spatially distinct hard/soft X-ray sources. Co-spatial H-alpha brightenings indicate that most of the X-ray sources are located at footpoints of magnetic loops, and at least one source shows evidence for a 3.7 x 10^7 K superhot plasma at a looptop. In addition, there were several microwave sources, only one of them coincident with a X-ray source. High spectral resolution CaXIX line profiles also indicate up-flows early in the flare. Analysis of the microwave/hard X-rays/soft X-rays on an individual source basis provides information on the radio emission mechanisms and estimates of the energetic electron population, the magnetic field strength, plasma density, etc. Although the microwave emission is consistent with the gyrosynchrotron mechanism, the millimeter emission appears more likely to be due to thermal bremsstrahlung. The energy contained in the thermal plasma and energetic >15 keV) electrons is calculated for each source. The flare totals are ~10^{30} ergs, and there is approximately equipartition of energy in energetic electrons and in the thermal plasma. The gradual X-ray sources seem to follow well the Neupert effect. Finally, a comparison of magnetograms before and after the flare shows evidence of emergence of new magnetic polarity at the flare site.
Update 8-Mar-94
Following is the SPD/AGU abstract.
Multiwavelength Coverage of the 7 January 1992 Flare
Adriana V. Silva et al.
The flare studied here, probably with the best wavelength coverage so far, occurred on 7 January 1992 at around 2022 UT, in the large target region complex AR 6693/6694. A pre-flare vector magnetogram (MSFC) and a post-flare magnetogram from KPNO show the complexity of the magnetic field connectivity and the emergence of new positive polarity at the flare site. The flare was simultaneously observed in X-rays by Yohkoh (SXT, HXT and BCS) and GOES (listed as C8.9); in \ha\ by MSFC; in microwaves in total power with high temporal resolution by RSTN, by the VLA with high spatial resoltuion at 0.33, 1.5 and 5.0 GHz, and by OVRO with high spectral resolution from 2 to 14 GHz; and by BIMA at millimeter wavelength (86 GHz). A four channel photon spectra is also obtained from hard X-ray observations (HXT). Time profiles of the hard X-ray and microwave emission indicate that the flare was actually composed of two bursts, the first peak at 20:22:30 UT and a second burst at 20:25 UT. Data from Yohkoh BCS show evidence of up-flowing plasma between the two bursts. The millimeter emission was delayed by almost a minute from the microwave emission. The 7 January flare was highly complex, with several locations brightening at different times, as X-ray, \ha\ and microwave images show. Comparison of the hard X-rays with the microwave and \ha\ observation resulted in estimates of the physical parameters for two common sources. The X-ray data also seem to imply the presence of a superhot component. The probable emission mechanism of the microwave and millimeter radiation is discussed, and whether the hard X-rays are produced by the thick or thin target model. Moreover, the energetics of the flare is determined.