THE RELATIONSHIP BETWEEN PEAK ELECTRON TEMPERATURE AND THE SOFT X-RAY MAGNITUDE OF SOLAR FLARES

fl186.feldman05
Posted:  28-Aug-94
Updated: 27-Dec-94, 13-Feb-95, 13-May-95, 24-Feb-96
Events specified: N/A

U. FELDMAN, J. T. MARISKA, G. A. DOSCHEK, AND C. M. BROWN Naval Research Laboratory

Abstract: We intend to analyze a large sample of Yohkoh flares in order to determine the relationship between temperature at flare maximum and the X-ray magnitude as recorded by GOES. It is a well documented fact that a flare's maximum temperature is reached during or shortly before the flare attains its maximum intensity. Flare temperatures will be determine from spectra recorded by the Bent Crystal Spectrometer (BCS) Fe XXV channel. Once the analysis is completed we will investigate possibility for predicting from temperatures during the first few minutes after onset which of the flares are expected to become major X-ray events.

Update 24-Feb-96

We have finished working on proposal fl186.feldman.05. Attached is a list of five papers that resulted from our study.

RELATIONSHIPS BETWEEN TEMPERATURE AND EMISSION MEASURE IN SOLAR FLARES DETERMINED FROM HIGHLY IONIZED IRON SPECTRA AND FROM BROADBAND X-RAY DETECTORS U. FELDMAN, G. A. DOSCHEK, J. T. MARISKA, AND C. M. BROWN Astrophysical Journal 450, 441 (1995)

PROPERTIES OF COOL FLARES WITH GOES CLASS B5 TO C2 K.J.H. PHILLIPS and U. FELDMAN Astronomy and Astrophysics 304, 563 (1995)

ELECTRON TEMPERATURE AND EMISSION MEASURE DETERMINATIONS OF VERY FAINT SOLAR FLARES

  U. FELDMAN, G.A. DOSCHEK, and W.E. BEHRING
                Astrophysical Journal to be published 
                in the April 10 1996 issue

ELECTRON TEMPERATURE, EMISSION MEASURE AND X-RAY FLUX IN A2 TO X2 X-RAY CLASS SOLAR FLARES

  U. FELDMAN, G.A. DOSCHEK, W.E. BEHRING and K.J.H. PHILLIPS
                Astrophysical Journal to be published
                in the April 1 1996 issue

THE CORRELATION OF SOLAR FLARE TEMPERATURE AND EMISSION MEASURE EXTRAPOLATED TO THE CASE OF STELLAR FLARES U. Feldman, J.M. Laming and G.A. Doschek Astrophysical Journal Letters 451, L79 (1995)

Update 13-May-95

THE RELATIONSHIP BETWEEN ELECTRON TEMPERATURE, EMISSION MEASURE AND

                 X-RAY MAGNITUDES IN SOLAR FLARES
                                by
                    U. FELDMAN and G.A. DOSCHEK
        Code 7674, E. O. Hulburt Center for Space Research
     Naval Research Laboratory, Washington DC 20375-5352, USA

                           W.E. BEHRING
               Code 682 Goddard Space Flight Center
                     Greenbelt, Maryland 20771
                                and
                          K.J.H. Phillips
       Astrophysics Division, Rutherford Appleton Laboratory
                Chilton, Didcot, Oxon OX11 OQX, UK

To be submitted to the Astrophysical Journal

ABSTRACT In this paper we present a statistical analysis of soft X-ray flare class and emission measure as a function of electron temperature determined for the time of maximum flare brightness. The study includes 868 flares of X-ray class A2 to X2. Our work shows that their properties are very different, although large and small flares as seen by the 1-8 ^O detector aboard the Geostationary Operational Environmental Satellite (GOES) records have similar appearances. The peak temperature of intense (major) flares is much higher than the peak temperature of weak (minor) flares. This finding has important implications on the nature of the flare heating mechanism. For example, if a flare is a collection of elementary bursts, the plasma properties of the elementary-bursts occurring during peak emission of large flares and small flares must be different.

Using the relationship between electron temperature and emission measure in solar flares, we provide an estimate of the electron temperature during the peak emission of large stellar flares.

Update 13-Feb-95

Title and abstract of a paper to be sent to ApJ

ELECTRON TEMPERATURE AND EMISSION MEASURE DETERMINATIONS OF VERY FAINT SOLAR FLARES

                   U. FELDMAN and G.A. DOSCHEK
       Code 7674, E. O. Hulburt Center for Space Research
    Naval Research Laboratory, Washington DC 20375-5352, USA
                               and
                          W.E. BEHRING
              Code 682 Goddard Space Flight Center
                    Greenbelt, Maryland 20771

February 1995

To be submitted to the Astrophysical Journal

ABSTRACT

We have studied 28 flares in the X-ray magnitude range of A2 to A9 using a high resolution Bragg crystal spectrometer data obtained from instrumentation flown on the Yohkoh spacecraft. Flares in the A class category can be detected in spectral lines of He-like ions formed at low temperatures. From our study we have found that the A type flares are similar in their appearance to the much brighter flares. Their average temperature is approximately 5 MK and their emission measure as determined from the S XV resonance line near 5 varies between 2x10**46 and 1x10**48 cm-3.

Update 27-Dec-94

The Abstract of a paper to be send to ApJ.

     RELATIONSHIPS BETWEEN TEMPERATURE AND EMISSION MEASURE
      DETERMINED FROM HIGHLY IONIZED IRON SPECTRA AND FROM
                    BROADBAND X-RAY DETECTORS
    U. FELDMAN, G. A. DOSCHEK, J. T. MARISKA, AND C. M. BROWN
       Code 7670, E. O. Hulburt Center for Space Research
    Naval Research Laboratory, Washington DC 20375-5352, USA
                            ABSTRACT
     We compare the electron temperature and emission measure of
flares at the time of maximum soft X-ray intensity derived using

two different techniques: (1) from the ratio of a dielectronic Fe XXIV line to the resonance line of Fe XXV, combined with the absolute intensity of the Fe XXV line, and, (2) from the ratio of the 0.5 - 4.0 and 1 - 8 broadband X-ray fluxes, combined with the absolute flux in one of the broadband spectral regions. The high resolution Fe spectra are obtained with the Bragg crystal spectrometer experiment flown on the Japanese Yohkoh spacecraft. The broadband fluxes are obtained from Geostationary Operational Environmental Satellites (GOES). A data set of 540 X-ray magnitude C2 or brighter flares, observed by both spacecraft, is used for the analysis. Both techniques assume an isothermal plasma. The broadband temperatures are a factor of 1.6 lower than the Fe XXV temperatures. We find that the maximum temperature of flares brighter than M5 exceeds 20 MK and that the maximum temperature of flares fainter than C4 is substantially lower than 20 MK. We also find that the Fe XXV emission measure is linearly proportional to the GOES flux in the 0.5 - 4.0 detector. From this work we develop a method for selecting a subset of flares that may produce very large peak X-ray fluxes. The method is based on the flare onset Fe XXV temperature.