D..13 October, 2005 (AE Version 3.89)

• AE's spectral grouping algorithm now defines groups based on SNR in the background-subtracted (net) spectrum. Traditional grouping algorithms work with the source spectrum alone, sometimes leading to significant under-grouping where the background is high. New AE keyword parameters control the algorithm--see §5.7 and §7.18.

• The XSPEC scripts officially supplied by AE are now distributed in the AE package itself rather than via a separate web page. See §5.12.
  • The scripts/models currently available are wabs_apec.xcm and wabs_pow.xcm. Each supports both the $\chi^2$ and C statistics.
  • These scripts require XSPEC version 12.2.0bz or higher. Note that XSPEC 12 currently has some crashing problems under the OS-X Tiger operating system, as described at http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/xanadu/xspec/issues/issues.html
  • The default confidence intervals for model parameters and fluxes are now 90% rather than 1-$\sigma$.
  • Two plots showing the data and model are now produced: the traditional grouped spectrum plot (ldata.ps) and an ungrouped cumulative spectrum plot (icounts.ps). The latter is perhaps useful for visualizing fits to very weak sources. Note however that when the C-statistic (recommended for weak sources) is used one often sees what appear to be sub-optimal model normalizations in these cumulative plots, even though the minimum in the C-statistic seems to have been found.
  • A Tcl variable skip_errors can now be used to force the scripts to skip over the computation of model parameter errors when that computation causes problems, such as hanging XSPEC.

• For better file organization, the files produced by each fitting session are now stored in a sub-directory of the source directory and some file names have been changed (§7.18).

• The algorithm for estimating position errors has been improved (see footnote in §7.7).

• AE's timing analysis (e.g. light curves, variability) has been moved from the EXTRACT_SPECTRA stage to a new TIMING stage (§7.11).