An Introduction to Tartarus (Version 3.1)
This ASCA AGN products database contains source and background events
files, spectra, ancillary response files and response matrices, images
and assorted light curves for a large number of ASCA AGN observations.
This AGN database is composed of the products of a detailed but
systematic analysis, with results of publishable quality (we have
published several papers based upon this analysis ourselves). This
database has been created by the Tartarus Team, and they, rather than
Imperial College London or the HEASARC, are responsible for the
contents.
Tartarus (Version 3.1) has been created by analysing all ASCA
observing sequences with targets designated as AGN, as indicated by a
leading "7" in the observing sequence number. Version 3.1 contains
products for 611 observing sequences out of a total of 661 sequences
designated as AGN observations. Tartarus (Version 3.1) is a
significant improvement over Versions 1 and 2. Version 3.1 contains
products for more observing sequences than were available in Version
2. Moreover, the 611 sequences for which products are available are
complete in the sense that either: the target object was not detected,
in which case an upper limit on GIS2 source counts is given; or the
intended AGN target was detected and the data were fully
analysed. Version 3.1 will itself be replaced when the final ASCA
calibration is completed.
Note that Version 3.1 and Version 3.0 were created using the same set of
processing scripts and are thus very nearly identical. Negligible
differences are present only in the exposure maps that were generated using an assumed photon index.
We hope that this database will allow easy access to reduced AGN data
for the whole community, allowing the maximum scientific return from
the data. Availability of publishable spectra, light curves and images
for immediate model-fitting will be particularly valuable to
astronomers with little direct experience in the reduction of X-ray data.
The HEASARC has released an online ASCA products database for
"quick-look" analysis, with the intention that users re-analyse
interesting datasets themselves from scratch. Our intention is to
allow users to bypass this step, by providing more detailed products
tailored specifically to the scientific requirements of the AGN
community. The data reduction software for the nominal mission
archive must be designed to produce products for all classes of X-ray
source, and will not be optimised for the analysis of AGN
data. Specifically, our experience with ASCA data has indicated a need
for careful consideration of instrument and sky background, and of
extraction regions, in order to obtain the most accurate background
subtraction and minimise contamination from any nearby sources.
Version 3.0 and 3.1, in particular, make more use of "custom regions" than
does Version 2.
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