The oxygen-rich supernova remnant (SNR) 1E0102-72.3, the brightest SNR in the SMC, has been continually observed throughout the Chandra X-ray Observatory's mission as a calibration source for ACIS. We have used the strong O, Ne, and Mg lines in the spectrum of 1E0102-72.3 to characterize the ACIS spectral response below 1.5 keV, compensating for the lack of strong lines in this energy range in the on-board calibration source. We have used the well-characterized spectrum of 1E0102-72.3 to evaluate the quality of our time-dependent gain, and CTI correction software under development at the CXC. To facilitate the upcoming meeting of the International Astronomical Consortium for High Energy Calibration, we provide here links to the latest calibration model provided by Andy Pollock (with some modifications) and our source spectra and related calibration data. (source spectra and data to be available soon).

E0102 Spectral Model

Figure 1: An XSPEC plot of the E0102 calibration model.

The E0102 model is an empirical model used for calibration, it is NOT an astrophysical model. For example, the ratio of the OVII triplet to the OVIII Ly-alpha line has been shown by Flanagan et al. 2004 to vary as a function of position within the remnant. We ignore this effect and simply take the total emission within our extraction region and fit the total emission in the lines. The model we have prepared for the upcoming IACHEC meeting was provided in its original form from Andy Pollock and consists of these components:

  • interstellar absorption (which modifies only the Bremsstralung)
  • Bremsstrahlung component
  • 36 Gaussians to model the line emission from C, O, Ne, Mg, Si, and some Fe L lines (NOTE, none of these are modified by the absorption)
  • 6 Radiative recombination edges
Andy deleloped this version (2007-04-28) of the model from 7 RGS observations with position angles between 7 and 20 degrees with cross-dispersion source selection regions covering the whole remnant and backgrounds estimated from suitable off-axis cross-dispersion regions rather than the synthetic background models used in the past. We have made some modifications to the model to be used for fitting CCD spectra which have lower resolution than the gratings spectra:
  • replace wabs with phabs
  • set phabs to 8.0e20 to account for SMC absorption in addition to the galactic absorption.
  • we have linked the normalizations of all lines to the ratio of the strongest line in the group as derived from Andy's model.
  • we have added these lines to the model: Si 14 Ly a (2.006 keV), Si 14 Ly B (2.375 keV) and a line at 2.445 keV to account for the S 15 triplet which is not resolved in the Chandra data.
The XSPEC xcm file for this model can be found here. [use right-click->save as]
The XSPEC xcm for the unmodified version of Andy's model can be found here.

Figure 2: A plot of the fit to obsid 1311 showing the individual contributions of the model components to the fit.

Joseph DePasquale - Harvard-Smithsonian Center for Astrophysics