The TGCat web tool is designed to be easily navigable and straightforward. Because this catalog is designed to be user friendly, we encourage the user to comment on its content and navigability. This can be done by sending comments/questions/suggestion to the TGCat administrator at On every page there are links that will bring you to a particular topic on this page for in-depth help, please consult these help pages for questions before contacting the administrator.

TGCat video demos: Video Demo 1 -- Video Demo 2 -- Video Demo 3 --

TGCat tutorial on plotting combined observations, and then identifying lines with WebGUIDE.

This catalog is an interface to an archive of X-ray spectra taken with the diffraction grating spectrometers on the Chandra X-ray Observatory. Here you can
  • search for observations by source,instrument, or other criteria
  • browse selections
  • review pre-computed summary products
  • generate custom plots
  • download data for detailed analysis
Chandra has two diffraction grating instruments, the High Energy Transmission Grating (HETG), and the Low Energy Transmission Grating (LETG). When used with their primary readout arrays, they are known as the HETG and LETG spectrometers (HETGS and LETGS, respectively). The readout arrays are a CCD array (ACIS), or a microchannel plate detector (HRC). The LETG is also often paired with ACIS. The instruments have different sensitivities, resolving powers, and wavelength coverages. The HETGS itself has two channels, the Medium Energy Grating and the High Energy Grating (MEG and HEG). The Chandra grating spectrometers are fully described in the Proposers' Observatory Guide (POG;

In particular, see: which describe the wavelength coverage, efficiency, and resolving power of these instruments.

Note for non-X-ray spectroscopists:
On the summary pages, you will see spectra in counts units which includes the strong signature of the instrumental response. Quantitative analysis of X-ray spectra --- even at high resolution --- is most often done using the counts in conjunction with the response files via forward-folding. In addition, some instruments do not allow direct inversion - the LETG/HRC configuration does not allow separation of overlapping orders, so we cannot provide an accurate flux corrected spectrum (it is source-model dependent). On these pages, you will find flux-corrected spectra, and you can plot in spectra in flux units (for data taken with ACIS), and download an ASCII table of the plot. But be aware that these are still approximations and that robust results are available through detailed analysis.
You are currently browsing guide: help/tgcat_help_intro.html