Zeroth-order 1D FWHM vs Time, 5 February 2008

Back to HETG TechNotes


The FWHM of the 1D projection of the zeroth-order "trailed image" (streak) for HETGS observations has been monitored for eight years. The FWHM has remained stable.

Note: The FWHM value plotted here is for ACIS data with spatial-pixel "randomization" turned ON.
The recent EX Hy data was also analyzed with randomization OFF and gave a value of FWHM = 34.5 um; this change is about as expected.

The width of the PSF can be broader for sources with harder spectra, so filtering on E<2keV or E<3keV has been applied in these cases in more recent analyses.

The 1D FWHM was measured using the "streak" events as described in Measured and Modelled zeroth-order 1D projections.

[ also available as postscript or pdf versions. ]

Software and Data File
See earlier focus trends updates for info on software; the latest focus_trends.rdb file is available here.