A model for fitting power spectra in xspec

A model from Adam Ingram and Chris Done for the power spectra from black hole binaries is now available from the new models page.

I've added a note based on their paper to the XSPEC wiki which explains how to read power spectra into XSPEC.

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.

Patch to replace AtomDB 2.0 with 2.0.1 in xspec

We have updated the current HEAsoft release downloads to replace AtomDB 2.0 with AtomDB 2.0.1 following the discovery of an error in the 2.0 RRC data. If you have already downloaded HEAsoft 6.11 (containing XSPEC 12.7.0) you can either get the fix from the HEAsoft issues page (http://heasarcdev.gsfc.nasa.gov/lheasoft/issues.html) or patch 12.7.0e from the XSPEC bugs page (http://xspec.gsfc.nasa.gov/docs/xanadu/xspec/bugs.html).

AtomDB v2.0 support added to xspec in v12.7

The new release of xspec uses AtomDB 2.0 for the various apec models. Since AtomDB 2.0 includes all elements to Zn there are a couple of issues to note.

1. New models vvapec and bvvapec allow all AtomDB 2.o elements to be varied independently.

2. By default the apec, bapec, vapec and bvapec models set to Solar the abundances of the elements included in AtomDB 2.0 but not in earlier versions (we refer to these as the trace elements). To set these abundances to zero use "xset APEC_TRACE_ABUND 0.0". The trace element abundances can be set to any value or linked to the abundance of one of the more common elements e.g. "xset APEC_TRACE_ABUND Fe".

xspec v12.7 released

The latest xspec release is now available through the HEAsoft download page.

The major new feature is the beta release of the Python xspec module. This is built and installed automatically on most platforms if the source code distribution is downloaded. PyXspec is not intended as a replacement for the current user interface but provides an alternative method for scripting xspec.

To learn more see the PyXspec users' manual.

pexmon model

Paul Nandra's pexmon model has been added to the more models page. This is a modification of Paul's original code to work with recent versions of xspec.

eqpair model and redshift convolution models

The next xspec release (due April-ish) will include eqpair as a standard model. At the prompting of Andrzej Zdziarski, I have added the ability to write out the temperature of the thermal electron distribution if chatter is set to 15. Andrzej notes that this provides an important self-consistency check.

Also at Andrzej's suggestion the new version will include zashift and zmshift convolution models to redshift additive and multiplicative components, respectively.

patch update

A couple of minor patches can be found at the usual place.

12.6.0y	Both the writefits tcl script and the tclout error command fail when dealing with a scale or switch parameter. Our thanks to Juan Luna for pointing this out. Report added on Jan 31, 2011.
12.6.0z	If a spectral data file has both quality and grouping columns, and all of the channel qualities are marked as bad, it will crash upon loading on Linux platforms. Our thanks to Fabio Pintore for pointing this out. Report added on Feb 09, 2011.

Minor enhancement of fakeit and fix to model weighting

New patches for xspec which can be found in the usual place.

12.6.0w

This adds a new option for the fakeit command. When prompted for the exposure time and correction norm, you may now enter a 3rd argument to change the fake background exposure time. Previously this parameter was fixed by the exposure time in the original background file upon which the fake background was based. For backwards compatibility, fakeit will produce the same behavior as before if this argument is not entered. Our thanks to Francois Dufor for making this suggestion. Report added on Jan 11, 2011.

12.6.0x

When the model weighting option of the weight command is selected and applied to a spectrum with a background file, the variance ought to include the background in addition to the model. Our thanks to Giacomo Vianello for bringing this to our attention. Report added on Jan 11, 2011.

xspec in python testers wanted

We have an alpha release of xspec for python available. This only supports a subset of commands as yet but we would like some volunteers to try it out and provide feedback on what they like and don't like as well as priorities for what to add next. Please e-mail us at the usual xspec12 address.

Minor fixes for MCMC code and new tclout version option

12.6.0t

Various improvements made to the chain (MCMC) command: Removed misleading multiple chain output from the chain stat command when only 1 chain is loaded. Clarification added to the 1-D plot margin label. If chains are loaded, tclout simpar may now be used without a valid fit and even if no spectra are loaded. Bug fix to the definition of the Rubin-Gelman convergence measure. Our thanks to Simon Vaughan for pointing these issues out. This patch also fixes a bug wherein a "Chain IO" error may appear due to the selection of row 0 when internally accessing random rows in chains. Report added on Oct 22, 2010.

12.6.0u

This adds a new tclout version option, making it easier to access the XSPEC version string from inside of Tcl scripts. Our thanks to Stefano Bianchi for this suggestion. Report added on Oct 22, 2010.

HEAsoft 6.10 available

The latest version of HEAsoft is available from the usual place. The only change to xspec is to include bug patches up to 12.6.0q. However, this release includes an update to QDP/PLT which fixes a problem when saving xspec plots to qdp files.

TBnew

I've added a link on the xspec additional models page to Jörn Wilms' high-resolution ISM absorption model. This should be used by anyone analyzing grating spectra.

A note on the pileup model

It is easy to misinterpret the "PSF fraction" parameter in the pileup model. A natural reading is to suppose that this means the fraction of the PSF which is included in the source extraction region. This is not correct. For the pileup model to work well the extraction region should be large enough to include essentially all the PSF. The "PSF fraction" parameter is actually the fraction of counts detected which should not be included in the pileup calculation. The manual will be modified to make this clearer. My thanks to Pat Broos for pointing out this potential confusion.

cplinear model

I have added Pat Broos' cplinear model to the additional models page. This is a non-physical model developed within the AE package to handle background in the low count case.

Yaqoob & Murphy toroidal reprocessor model

I've added a link to the additional models page for the Yaqoob & Murphy model for X-ray obscuration and reflection by a toroidal reprocessor, valid in the Compton-thick regime.

new local models

I have added two new local model pages to the collection. Maurice Leutenegger has supplied his models for hot star winds and David Ballantyne has provided table model files for the reflection of a blackbody from a constant density ionized accretion disk.