TG_FINDZO: Finding the Zeroth Order Centroid


TG_FINDZO: An algorithm for finding zeroth order position

TG_FINDZO is an algorithm for detecting a centroid position of a zeroth order image of Chandra HETGS and LETGS by finding an intersection between grating arms and a data transfer streak.

The new routine is designed to handle the following cases:

  • the source is bright and its image is piled up, causing distortion or even ``cratering'';

  • the source is blocked out entirely.

It is often ideal to use this algorithm for detecting the position of a extremely bright source (e.g., X-ray binaries) in the HETGS (or LETGS) + ACIS-S configuration. When the source is faint and/or the HRC-S is used as a detector (hence the pile-up is not an issue), tgdetect is recommended for the zeroth order detection.

For more information, see this detailed description of the tg_findzo algorithm.

Next: Usage: TG_FINDZO

This page was last updated Oct 9, 2020 by David P. Huenemoerder. To comment on it or the material presented here, send email to
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