New models available

Two new sets of models are now available through the XSPEC extra models page (http://heasarc.gsfc.nasa.gov/docs/xanadu/xspec/newmodels.html)

logpar and eplogpar are power-laws whose indices have a log parabolic energy dependence. These models are widely used in blazar research.

optxagnf and optxagn are models for AGN which combine a colour temperature corrected disc and energetically coupled Comptonisation.

Update to PyXspec

A patch (12.7.0f) is available which adds the ability to set multiple parameters at the same time in PyXspec. This can be a significant speed-up since the current version evaluates the model after each individual parameter change.

XSPEC and Chandra grating spectra

I have recently become aware (thanks to Lijun Gou and Mike Nowak) that the Chandra HETG ARF files include an EXPOSURE keyword which may differ from that in the spectrum (PHA2) file. If you are using XSPEC to analyze these spectra you should check whether the EXPOSURE values differ and if so replace that in the PHA2 file with the value from the ARF. The difference should only be significant if CC-mode was used.

A note on the gabs model

Oleg Kargaltsev has pointed out that the gaussian absorption line (gabs) is badly documented. The third parameter is called Tau although it is not the optical depth. The on-line help page has been amended and the gabs entry in model.dat will be changed so that the third parameter is just called Strength. In practice, if the optical depth is small then the third parameter is the equivalent width of the line.