MEG -1
MEG +1
HEG -1
HEG +1
2D residual images of E0102 data (obsid 3828) with respect to a simple 2T continuum model. Red regions indicated Data-Model is greater than 1 sigma (Chi > 1), clearly highlighting the line emission. Yellow, Black and Green pixels indicate Chi values between 1.0 and -1.0 and Blue pixels show Chi < -1. The MEG and HEG images are shown at the same wavelength range, from 3 A (left) to 23 A (right).

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 !

Rough 1-D Fitting

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:

  • The data: noticed continuum regions in Blue
  • The data: ignored line regions in Grey
  • Best joint-fit 2T APEC continuum model in Purple
  • Low-T model component in Red.
  • High-T model component in Green.
  • The 2T model with lines in Yellow.

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.

Adjustment and Comparisons

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:

 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 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: and