RESIK & Diogeness NEWS

Data gaps due to missing telemetry: ~ 10 h.

Note, that the link to the catalogue page  is now: http://www.cbk.pan.wroc.pl/resik_catalogue.htm.

RESIK Effective Areas – First Order Reflection

For quantitative analysis of the observed spectra it is of basic importance to know the response function of the spectrometer. This response function is conveniently represented as so-called effective area S, expressed in [cm²].

Known effective areas allow to convert the rates [cts/s/bin] observed in each RESIK spectral bin into „absolute” fluxes [photons/cm²/s]. Determination of wavelength (energy) dependence of effective area is a primary objective of the instrument ground and in-flight calibration and involves detailed knowledge of the instrument construction details.

We present below version_1.0 of  effective area dependence on the wavelength S(λ) calculated according to the following formula (based on Jim Lang’s RAL notice, 1995):

In this formula, parameters have the following meaning:

Dependence of individual factors on wavelength has been calculated according to the following equations:

where κ (λ), p, d,  are mass absorption coefficient, density and effective width of Kapton (index k) and aluminium layers of the thermal filter.

Similar quantities for detector’s  beryllium window: 

Probability of absorption in the detector gas mixture of Ar, Xe and CO₂, d_d - is the detector depth for absorption:

In the calculations, we have used κ(λ) from Tabulations from webpage http://www-cxro.lbl.gov/optical_constants/. The values of other parameters used are given in the Table.

Values of the total reflection coefficient R_C have been taken from interpolation of theoretical „ideal”, single crystal calculations performed using Cowan & Brennan Code (Brennan S. and Cowan P.L.: 1992, Rev. Sci. Instr., 63, 850). Uncertainties have been estimated based on comparison with respective data for double crystal reflectivities from Figures 26 and 27 given by Anthony Burek (Space Sci. Instrumentation, 2, 53 – 104, 1976)

Table 1. Values of parameters used in calculations of RESIK effective areas.

In the plot below we present calculated dependence of S(λ) for all channels. It should be noted that the values calculated represent the FIRST ORDER approach only as we have made a number of assumptions, which will be relaxed one by one as further progress in laboratory calibration is reached. The assumptions to be relaxed are:

Figure 1. Wavelength dependence of the RESIK effective area for the first order reflection.