fl125.kucera01 Posted: 06-Jun-93 Updated: 15-Jan-94, 23-Sep-94, 03-Apr-95, 22-Aug-95 Events specified: Flares of 17-Feb-92 15:38 UT, 13-Jan-92 17:27 UT and 25-Jun-92 17:55 UT
T. Kucera, J. Lemen, B. Dennis, N. Nitta, H. Wang
This proposal was originally posted as fl125.lemen01,
We will investigate specific solar flares using data from the CGRO/BATSE Spectral Detectors (SDs), images from the Yohkoh SXT and HXT, and microwave data from the Owens Valley Radio Observatory (OVRO). It is estimated that there may be 10-15 events which have good coverage at all three sites. We are particularly interested in studying a thermal/nonthermal hybrid model of flare acceleration (Holman 1985 ApJ, 293, p.584).
Specific questions to be addressed:
We will analyze maps and spectra to determine the sites of emission, energies of the emitting populations, and the geometry of the magnetic field. The radio and X-ray data for simple flares will be fit with the thermal/nonthermal model. We wish to discover whether the physical parameters calculated by modeling the data from different wavelength regimes are compatible.
Update 22-Aug-95
The following is the abstract for a paper we have submitted to the Astrophysical Journal. It is a part of proposal fl125.kucera01.
A Study of the Thermal/Nonthermal Electric Field Model Using Spectral and Spatial X-ray Data from CGRO and Yohkoh T.A. Kucera, P.J. Love, B.R. Dennis, G.D. Holman, R.A. Schwartz, D.M. Zarro
We have analyzed a solar flare in terms of a model in which electric fields produce both thermal emission from Joule heated electrons and nonthermal emission from runaway electrons. The flare was observed by the Compton Gamma Ray Observatory Burst and Transient Source Experiment (BATSE), the Yohkoh satellite, and GOES. The measured BATSE hard X-ray spectra were fit with functions derived from the electric field model, thus allowing values for the temperature ($4-5\times 10^7$ K) and emission measure ($1\times10^{26}-2\times10^{27}$ cm$^{-3}$) of the thermal source to be determined. These are qualitatively consistent with the characteristics of the looptop emission observed with Yohkoh/HXT. Furthermore, the hard X-ray footpoint emission observed by Yohkoh had flatter spectra than the looptop emission, as predicted by the model. We found that the effects on the model spectra of changes in the nonthermal parameters are not unique, and it is possible to establish two of the three nonthermal parameters only if the third is determined by other means. Using Yohkoh images in conjunction with the fits to BATSE spectra, we calculated upper limits to the length of the region in which the electric field causes runaway electron acceleration. We find that this distance must be shorter than the length of the flaring loop (i.e.\ $<3\times10^9$ cm).
Update 03-Apr-95
We are currently preparing a journal paper and presentations for meetings this spring.
Electric Field Model of Electron Acceleration Applied to Solar Flare Data from CGRO/BATSE and Yohkoh
T.A. Kucera, P.J. Love, B.R. Dennis, G.D. Holman, R.A. Schwartz, D.M. Zarro
We analyze a solar flare which occurred on 17 Feb 1992 in terms of an electric field model in which current sheets aligned with electric fields produce both thermal emission from Joule heated electrons, and nonthermal emission from runaway electrons. The flare was observed by the Compton Gamma Ray Observatory Burst and Transient Source Experiment (BATSE), the Yohkoh satellite, and GOES. We perform, for the first time, a spectral analysis on BATSE data using this electric field model. The measured spectra can be fit with spectra derived from the model, but we are unable to determine a unique set of physical parameters for given spectra. We can calculate values for the temperature and emission measure of the thermal source and limits for values of other parameters, including the electric field strength, and find that these values are consistent with ones found for an earlier flare analyzed with this method. We compare rates of heating determined from the spectral fits themselves and also from a model of the energy budget in the flaring loop. The two methods for calculating the heating rate do not give the same results, suggesting that a more complex model is needed to describe this flare. This work was supported by the NRC and the NASA CGRO Guest Investigator Program.
Update 23-Sep-94
We are analyzing the flare of 17-Feb-92 at 15:38 UT with respect to the thermal/nonthermal (T/NT) model. The parameters for the model can be obtained both with data from Yohkoh SXT and HXT using simple power-law spectral models and with more rigorous fits to CGRO/BATSE data using the full T/NT formalism ofBenka & Holman. We wish to use these different approaches to obtain a model of the flare which is consistent with all the data.
Update 15-Jan-94
We are investigating particular flares to determine the characteristics and relationships between the different particle populations. One goal in particular is to compare the data with predictions and calculations made using a thermal/nonthermal hybrid model of flare acceleration. We are using data from the CGRO/BATSE Spectral Detectors (SDs), images from the Yohkoh SXT and HXT, microwave data from the Owens Valley Radio Observatory (OVRO), and BBSO vector magnetograms and H-alpha images. At this time we are concentrating on two events: 13-Jan-92 17:27 UT 25-Jun-92 17:55 UT