Chandra Grating Spectroscopy Database for
Active Galactic Nuclei
Home of the Grating Archive Spectra
Download Reduced Spectra and Other Products Now:
HETG: Ordered Sequence Number List
HETG: Ordered Right Ascension (RA) List
Archive currently contains HETG+ACIS observations public as of July 2004
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.
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
If you haven't done so already, familiarize yourself
further with the instruments before
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,
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,
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.