HETGS Line Profiles  

HETGS Line Profile Analysis


This is an analysis of HETGS line profile "features" via Monte-Carlo simulation in ISIS. A script loads Capella data and responses, fits a line, and then uses those fit parameters to "fakeit" a number of times. The resulting simulation, model, and residuals are plotted in a mosaic along with the observation.

The simulations are done in several different ways: parametrically, by folding of a single gaussian by the response on a region with one major contributing emission line; folding an APED model through the response; and folding an APED model with thermal broadening through the response. For all cases, the data are from default processing parameters (0.0025A HEG bins, randomization on), and the HEG first order RMF is from the CALDB.

The Gaussian fits have the center, flux, and dispersion as free parameters. The dispersion is for the intrinsic model; since the model is convolved by the instrumental response, the observed width is roughly the root-sum-squares of the model width and line spread function width.

The APED model fits have two free parameters: the radial velocity, and the normalization (related to the emission measure).

This work was prompted by reports of spurious looking features in HETGS line profiles, such as narrow gaps or spikes. Inspecting the plots, it appears that these features can all be explained by statistical fluctuations, and that a fit using the instrumental profile can be trusted.

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This page was last updated Jun 6, 2002 by David P. Huenemoerder. To comment on it or the material presented here, send email to dph@space.mit.edu.
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