2-Gaussian Zeroth-order streak fit, Nov.'08

Summary

The 1D projection of the zeroth-order image of HETGS observations is used to monitor the FWHM of the core HRMA response. Here the streak events are fit by both a core Gaussian and an additional Gaussian. Because of background events this is about the limit of the PSF that the streak is able to sample.

Analysis and Results

The streak events from 14 obsids were combined and binned and fit first with a single Gaussian plus a constant in a narrow +/- 2 pixel range. Then with this Gaussian's center and FWHM fixed, a second Gaussian was added to improve the fit. The script, hlm_streak_extract.sl was used for this and builds on the TGCat-based Zeroth-order 1D FWHM monitoring and software, see, e.g, focus_trends.081020.html.

The folowing plots and parameter file give the results. Note that the X-axis label of "Wavelength [A]" is really cross-streak location in pixels (0.492" per pixel) with the nominal center at 15.0.

• - Data (black) and fits with a constant plus one (red) and two (blue) Gaussians.
  
  
• - Residual (ratio) plot of the streak data and the 2-Guassian model.
  
  
• Parameter file for the 2-Guassian-plus-constant fit.
  This gives Gaussian sigma values of 0.586 and 1.388 pixels (~ 33.0 and 78.3 um FWHM) with a ratio of areas of 0.825 : 0.175, respectively.

Please send any comments to Dan Dewey at dd@space.mit.edu.