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:

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...

Software

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.