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Recalculating SXT Temperature Response Functions

(April, 2010 by Aki Takeda)
(October, 2010, revised: uncertainty analysis added.)
(February, 2011, revised: photospheric abundance added.)
(March, 2011, revised: made into a simplified version.)

1. Introduction.

What is the SXT temperature response functions?
As of 30-Apr-2010, our official SXT response function was the one made in 1995 April. It is based on the spectral model calculated by Mewe (1985, 1986). Since early 2000s, however, the new atomic data and the spectral models became available from the Chianti atomic database for the plasma in the X-ray range. Through a few upgrades, they are now considerably matured at the current latest version, 6.0.1. It is therefore a timely effort to update the SXT response functions based on the most recent database and made them available for the general users of the SXT data.

Details are described in Takeda (2011).

2. New response functions.

The response functions are influenced by the following three factors.

We provides three types of response functions according to the three elemental abundances available in the Chianti database, version 6.0.1, so that users can select from them as desired. The new response files and the software to utilize them are downloaded from here.

The former official responses and those calculated by Shimojo et al. (2002) correspond to the following pairs. For the purpose of making clear the source of difference, the following response functions are also plotted as references.

3. Comparison of New/Old response files.

New and old response curves for each analysis filter(filter B, in our convention), in linear and logarithmic scales.

No BackAl.1AlMg BeAl12Mg

Line ratios of the all filter pairs. For simplicity, only curves, (a) to (e) are plotted.

AlMg/Al.1Mg/Al.1Al12/Al.1 Be/Al.1Mg/AlMg
Al12/AlMgBe/AlMgAl12/Mg Be/MgBe/Al12

4. Information summary of the files used for our calculation.

4.1. Elemental abundances

We compared the following abundance files. Plot of comparison among these three files is here. The text version is here.

4.2. Ionization equilibrium

We will compare the following 3 abundance files. Plots of comparison among these three files for Fe ions. Chianti and Mazzotta_etal and Chianti and Arnaud_Rothenflug.

4.3. Continuum intensity from the isothermal plasma

The temperature dependance of the three atomic processes contributing to the continuum intensities (free-free, free-bound, and two photon) is here. The total continuum intensity (the sum of the three processes) from the 5MK, 2MK, and 1MK isothermal plasma is shown here, and these are the comparison with Mewe's results.

4.4. Line intensities from the isothermal plasma

The Chianti line intensities calculated with coronal_ and hybrid_ abundances are compared with Mewe's calculation in here. The dependance on the electoron density checked using coronal abundance and chianti.ioeq are here.

5. Examples of the temperature and emission measure analysis

The trend of temperatures derived from the Be/Al12 filter pair : For AR9026 flare kernal, the latest response functions give higher value (30 to 45%) than the traditional response file by Mewe. However, the AR6916 has the opposite trend. This difference comes from that two region uses different range of Be/Al12 filter ratio curve, as show in here.

For a given filter pair, the different versions of filter ratio can yield very close temperatures to each other (e.g., at around the intersection of the ratio curves). However, the emission measures derived from them differ substantially in most cases, because of the significantly different intensity of the response functions. As seen in the above figures, the data points appear as quite differnt from those from other versions of ratio curve. The differences are, in most cases, significantly larger than the amount of the calculated uncertainty that includes both statistical and systematic errors.

Even with more reliability on the latest Chianti emission model than older versions, the variation resulting from different abundance remains as a dominant source of uncertainty associated with the current analysis method. Proper choice of abundance (if at all possible!) is desirable for narrowing the range of uncertainty.


Mewe, R., Gronenschild, E. H. B. M., and van den Oord, G. H. J.: 1985, Astron. Astrophys. Suppl. Series 62, 197.

Mewe, R., Lemen, J. R., and van den Oord, G. H. J.: 1986, Astron. Astrophys. Suppl. Series 63, 511.

Shimojo, M., Hara, H., and Kano, R.: 2002, COSPAR Colloq. Ser., 13, Multi-Wavelength Observations of Coronal Structure and Dynamics, ed. P.C.H. Martens and D.P. Cauffman (Oxford Pergamon), 419.

Takeda, A. : 2011, Sol. Phys., 273, 295.