E0102: Simple 2-Temp APEC Continuum | 10 March 2008 - dd |
W A R N I N G !!! This is a very approximate estimate of the
continuum !!! The material here is for exploration and demonstration only ! |
To roughly fit the continuum in E0102, the MEG minus and plus order spectra of obsid 3828 were used with only the most line-free regions "noticed". The plots at left (Click them for larger PDF version), although a little busy at first, show for MEG minus (upper plot) and MEG plus (lower plot) the following:
For reference the fit values are in: e0102_2Tcontinuum_meg.par; the low-T value is 0.376 keV and the high-T value was fixed at 2.0 keV (see kT-kT contour comments below.) |
The plot at left shows contours of Chi^2 for a one-T fit to the noticed continuum regions versus the N_H and the kT values. There seems to be correlation between the two variables and a very large N_H is preferred. The nominal N_H value of ~0.08, however, doesn't require going too far down the countours. This may be an indication that a 2T model is preferred? |
The plot at left shows Chi^2 contours for a 2T continuum model in kT-kT space; the model has N_H fixed at 0.0836. While the low-T value (Y-axis) is fairly well constrained, it appears that the high-T value can cover a large range (above 1.5 keV) and still have comparable fit quality. For this reason the high-T value was manually fixed at 2.0 keV for the 2T fit given above. |
The 2T model parameters from the fitting above were manually adjusted to give a better agreement with the data as seen using Event2D software, see the plots below. These plots use the parameters in e0102_2Tcontinuum_meg_adj.par with a T_low = 0.34 keV and T_high = 2.0 keV:
tbabs(1)*(apec(1)+apec(2)) idx param tie-to freeze value min max 1 tbabs(1).nH 0 1 0.0836 0 100000 10^22 2 apec(1).norm 0 0 0.0337 0.0001 10 3 apec(1).kT 0 0 0.34 0.2 0.5 keV 4 apec(1).Abundanc 0 1 1 0 5 5 apec(1).Redshift 0 1 0 0 2 6 apec(2).norm 0 0 0.001066 0.0001 10 7 apec(2).kT 0 1 2 0.5 4 keV 8 apec(2).Abundanc 0 1 1 0 5 9 apec(2).Redshift 0 1 0 0 2
Plots at left show MEG (top row) and HEG (bottom row), minus(left) and plus (right) -order spectra (Red) with the 2T continuum model (Blue). The 2-D residual images at the top of this page are based on these same data and models. |
This plot at left shows the ACIS spectrum of the zeroth-order events (Red) and the corresponding 2T continuum model (Blue). Looks good... |
The 1D PHA fits were carried out in ISIS using the commands in analysis_phacontB.sl with data files (pha2 and arfs) from nominal ciao processing of obsid 3828 with a large extraction region and fixed order-sorting limits of +/-0.20. To give the fewer-counts low-energy portion of the data a better weighting in the fitting, a term equivalent to the OGIP/XSPEC "SYS_ERR" value of 0.20 is used (the err_limit variable in the .sl file).
The 2-D residual images and 1-D HETG and Zeroth-order plots were made with commands in analysis_global.txt, with data and model defined in: e0102_data.sl and e0102_cal_model.sl.