Variance Models

Over the past few years my students and I have developed several models for fitting variance spectra of active galactic nuclei and X-ray binaries (e.g. Parker et al., 2020; Haerer et al., 2021). 

These models, accounting for variability caused by absorption, reflection, outflows and so on, are available as standard XSPEC tables. For more information please see the variance models page:

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The SPEX spectral fitting package (Kaastra et al., 1996) has very precise models for photoionised emission and absorption that are not available natively for XSPEC. I have generated XSPEC tables for some of the XABS photoionised absorption model, and the emitted spectrum from the PION photoionised emission/absorption model.

These models are evaluated at grid points and interpolated, so they are by definition less accurate than the native SPEX  versions. Use at your own risk!

If you do use these models, please cite:

Kaastra, Mewe and Nieuwenhuijzen, 1996 (SPEX)
Miller et al., 2015 and Mehdipour et al., 2016 (PION)
Steenbrugge et al., 2003 (XABS)
Parker et al., 2019 (XSPEC table implementation)


Note that, depending on your needs, Jeremy Sanders' more sophisticated implementation may be a better tool: github link


I have generated some custom reflection models using the Reflionx code (Ross & Fabian, 2005). This code is relatively fast, so custom models can be developed within a week or so. If you would like such a model, please contact me


reflionx_hc: reflionx with a high energy cutoff, ideal for use with NuSTAR data (Tomsick et al., 2014).

reflionx_bb: uses an input black body spectrum, rather than the standard powerlaw (King et al. 2016).

reflionx_nthcomp: uses a Comptonised input spectrum, using the NTHComp model (Zdziarski, Johnson & Magdziarz 1996, Zycki, Done & Smith 1999).