**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.*