Chandra Grating Spectroscopy Database for Active Galactic Nuclei


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HETG: Ordered Sequence Number List

HETG: Ordered Right Ascension (RA) List

Archive currently contains HETG+ACIS observations public as of July 2004

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General Information

Welcome to the Chandra High Energy Grating Spectroscopy Archive for AGN. The purpose of this database is to make Chandra high-resolution grating spectra accessible to scientists who may be non-experts in X-ray astronomy, or X-ray astronomers who want to quickly examine spectra without having to go through the process of downloading the entire set of observation files, processing and reducing the data. The spectra in this archive are available in several useful formats. Additional products (e.g. lightcurves, cross-dispersion profiles, instrument effective areas, and associated plots) are also available to aid in quick-look analyses and/or assessments.

What is and What is Not in This Archive

This archive contains data from the High Energy Transmission Grating (HETG) aboard Chandra from observations of Type 1 and Type 2 Active Galactic Nuclei (AGN) (i.e. including quasars) which were public as of July 2004. It does not include BL Lac objects or Blazars, nor does the archive include any data obtained with the Low Energy Transmission Grating (LETG) aboard Chandra. Future expansion of HotGAS to include later HETG observations, BL Lacs/Blazars, and LETG data is contingent upon further funding.


  • The Instruments This archive so far contains data from the High Energy Transmission Grating (HETG) aboard Chandra, taken in conjunction with the ACIS CCDs as the X-ray detector. HETG constists of the Medium Energy Grating (MEG) and the High Energy Grating (HEG). The banpasses for the MEG and HEG are approximately ~0.4--8 keV and ~0.9-10 keV respectively. The spectral resolutions for the MEG and HEG are approximately 0.023 and 0.012 angstroms FWHM respectively. If you haven't done so already, familiarize yourself further with the instruments before proceeding (the MIT HETG website and the CXC website are good starting points).
  • The Processing and Calibration If you are interested in the details of the reprocessing and calibration applied to obtain the data products, go here.

  • The Data Products Familiarize yourself with the products which are available for each observation segment (specified by a sequence number and an Observation ID) by reading the Overview of Data Products. Further information on the data products is available from links on the individual web page for every sequence number and Observation ID. Many items on the web page for a particular sequence number and observation ID have a link on the item name pointing to an explanation of what the item is and any relevant details.
  • Find Your Observation(s) If you know only the name of the target and want to find all data relevant to that target, currently the best thing to do is to find the sequence number(s) and Observation ID(s) available for LETG and/or HETG using the Chandra Target Search Page. Then come back here and find the correct web page in this archive using the links to the sequence-ordered lists at the top of this page. If you already know the sequence number start there. If you know the Right Ascension of the target, you could use the links to the RA-ordered lists at the top of this page. Before proceeding further click on the link "Known Problems" on the web page for the particular sequence number and Obs ID to see if there are any known bugs, caveats, or problems with that data set.
  • Combined Data Sets Some AGN were observed several times, and in some cases different Obs IDs for multiple observations of the same source are not separated by a large amount of time. Combined spectra, lightcurves and other data products for such cases are not yet available from HotGAS but will be in the future.
  • Disclaimer, and Background Subtraction Whilst every effort has been made to ensure that the reduced data products are accurate and their method of derivation from the lower-level data documented, we do not take any responsibility for results published using the data products. Although the data products are of publishable quality, we insist that the user (or a collaborator) should verify results by producing their own reduced products before publishing such results. In particular, note that we do not include any background subtraction for any of the sequences and it is the responsibility of the user to assess the level of the background and account for it if necessary. Some background spectra are available in the so-called pha2 spectral file, or else the user could extract his/her own background spectra from the events file (which is available from HotGAS). In most cases, the background is negligible, but will be an issue at the extreme ends of the instrument bandpasses (especially at low energies if a source suffers from significant X-ray absorption), and for weak sources over more of the instrument bandpasses.
  • Citing the Database If your research has benefited from this database please include the following acknowledgment in your paper or article. This research has made use of the HotGAS database, created and maintained under the supervision of Tahir Yaqoob. HotGAS has been supported by a Chandra archival research grant, AR4-5009X, issued by the Chandra X-ray Observatory center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-39073.

    Atomic Data & Analysis Software It is beyond the scope of this database to provide detailed information on data analysis and atomic data for interpreting the Chandra grating data. However, a set of non-exhaustive links are given here to get you started, which are also useful for handy reference.

    Contact If you have any problems and/or questions, contact Tahir Yaqoob, at

    Acknowledgments Many thanks to Julie Ho, Jen Rolston, Beth Stewart, and Katie Battick for the hard their hard work and dedication which went into producing this database. Thanks also to Kip Kuntz for his help with reprocessing scripts.