HETG/E0102/Cal - Pollock-Shock
Back to E0102 for Calibration

Discrete lines (Pollock) and Shock models - 15 October 2006

The E0102 spectrum as observed with the Chandra HETG (Flanagan et al. 2004) and the XMM-Newton RGS (Rasmussen et al. 2001) clearly show the bright lines from H-like and He-like ions of elements O, Ne, Mg, Si and H-like C. Some hints of Fe ion lines were indicated in the RGS spectrum. It should be noted that neither of these papers undertook to create a model to fit the complete spectrum of E0102.

For calibration purposes a continuum-plus-lines model has been created by Andy Pollock based on re-analysis of RGS data; that model expressed in XSPEC format (.xcm) and converted to ISIS format (which uses the XSPEC model library) as well (.par) is given here in these files:

An early approximation to the global E0102 spectrum was made using wabs times a simple shock model - the model and it's parameters are given by the ISIS .par file:

Plots of the Pollock model and the simple shock model (calculated using the XSPEC NEIVERS of 1.1) are given here:

e0102_pollock_shock_ICWG .pdf , .ps
The three plots on this page are made in roughly similar format to the plots on pages 6,7,8 in Paul Plucinky's (2nd) presentation to the "ICWG" in June 2006, "E0102 as a Standard Candle for X-Ray Astronomy". Specifically, the Pollock model is shown in Red and the Shock model in Green. To emphasise where Fe lines are in the shock model, the shock model without Fe included is shown as the Blue line. The y-axis shows counts per bin and the same ARF and RMF have been applied to both models. (For reference the ARF and RMF are appropriate to the LETG as it was during an SNR 1987A observation. This has the property of good low-E response and a resolution that is not too good but not too blurry either - similar to the velocity blur Pollock's model includes...)
e0102_pollock_shock_hires .pdf , .ps
The three plots on this page are shown at the model resolution - narrow lines. The Pollock model (Red) has its lines 0.15 times narrower than the xcm model specifies whereas the Shock model (Blue) has bin-narrow lines - this helps to distinquish them. The Grey lines are from the Fe in the shock model and clearly show the "forest" these ions produce.
The middle panel is zoomed in a bit and plotted in wavelength.
The bottom panel shows the low-Energy end in the same color coding as above - note the Blue (from Silicon, I believe) lines in the shock model at ~ 0.37 and 0.40 keV.
In addition, this bottom panel includes, for reference, Carbon (orange) and Nitrogen (green) lines.

Comparing the two models

"Why compare with some random shock model?"
The idea is that this shock model is based on a range of temp and ionization times and so gives a good idea of all the lines that might be present - it can also be recomputed using improved line databasess and shock model physics. Comparing the shock model with the Pollock model then gives us some guidance for what to look for in the real data, e.g., to decide if Fe is present, etc. That will be the subject of further work.

There are similarities and some clear differences between these two models:

Similarities:

Differences:

Fe emission:
  • Fe emission/lines are (claimed to be) not explicitly included in the Pollock model, however comparing these spectra it is clear that the main two places where Fe lines show up in the shock model is also where there are "extra" lines in the Pollock model. So, the Pollock model has the degrees of freedom to "cover" for the Fe emission lines.
    Specifically the regions: 0.69 to 0.75 keV and 0.80 to 0.89 keV contain 5 lines each in the Pollock model (red), whereas in the shock model these same regions show 4 and 7 peaks (green) --- of these, 3 and 4 peaks, respectively, are due to Fe emission (not seen in blue).

Other, easily corrected, differences:

Velocity broadening of the lines:


dd@space.mit.edu