July 13th 2012 Leicester XSPEC, Fitting, and Atomic Data Keith Arnaud.

July 13th 2012 Leicester

XSPEC, Fitting, and Atomic Data

Keith Arnaud

July 13th 2012 Leicester

XSPEC

XSPEC is an interactive program widely used to fit parameterized models to energy spectra, primarily in the X-ray and gamma-ray bands.

It has been used for over 6000 refereed papers.

XSPEC includes a library of over 150 physical models. This library is available independently for use by other programs.

An individual researcher can easily add their own models. This can be done within an XSPEC run by loading an external subroutine, or reading a FITS file containing a grid of theoretical spectra.

July 13th 2012 Leicester

Latest version is XSPEC v12.7.1d. V12.7.1 was released as part of HEAsoft 6.12 which also included PyXspec v1.0, our XSPEC Python module.

HEAsoft 6.12 also included HEASP 1.0, a new C++/C/Python library for manipulating spectra, responses, table model files.

I recently had to overhaul WebSpec for security reasons and took the opportunity to add the ability to make confidence contours.

Current status

July 13th 2012 Leicester

Craig Gordon Bryan Irby

July 13th 2012 Leicester

Equilibrium ionization collisional models

apec based on AtomDB mekal an older version of SPEX raymond the original raymond-smith

A number of models build on these with multiple temperature components including power-law, gaussian, and Chebyshev polynomial differential emission distributions as well as physically-motivated examples such as cooling flows.

All these models run through a single routine so it is easy to build new multi-temperature models.

Almost all these models can also be run using alternative atomic physics data provided they are presented through apec coco and line FITS files.

July 13th 2012 Leicester

Non-equilibrium ionization collisional models

These models from Kazik Borkowski range from the simple, a single temperature and an ionization parameter, to plane parallel shocks and Sedov models. There is an option to use AtomDB to calculate the spectra though the current version does not include many of the lines produced by out of equilibrium plasma. Further, the ionization fractions are based on pre-AtomDB data so also need to be updated.

July 13th 2012 Leicester

Photoionized plasmas

Photoionized plasma codes are generally too CPU intensive to run inside XSPEC so instead they are run externally to generate grids of models which can be stored in table model FITS files and used in fitting. Both XSTAR and CLOUDY have been used in this way. XSPEC also includes models for ionized absorbers and Compton “reflection”. Some of these models use older atomic physics data however getting the physical model correct may be a larger source of uncertainty.

Leicester

Some useful XSPEC commands

addline – adds a gaussian or lorentzian line at the position of largest residual between current model and data

identify – list possible lines in a given energy range. Uses either the Bearden compilation of fluourescence lines, the mekal line list or the apec line list. If the latter then can also specify a temperature plasma and a minimum emissivity.

modid – runs identify on all the gaussian lines in the current model.

setplot id – add line IDs to plots. Uses the apec line list for a given temperature and minimum emissivity.

July 13th 2012 Leicester

A few things I’m working on / worrying about.

Models

Statistics

Computational issues

User support

Multi-wavelength support

July 13th 2012 Leicester

Rationalized the models involving Compton reflection – sharing the code.

Trying to sort out eqpair.

Need an XMM pileup model - Prashin Jethwa

What else ?

Models

July 13th 2012 Leicester

Separate statistics for parameter estimation and goodness-of-fit.

More goodness-of-fit options.

Poisson data with background.

More support for Bayesian methods - priors.

Statistics

July 13th 2012 Leicester

Parallelization of parts of code. - starting on derivatives wrt parameters

Improvement to Levenberg-Marquardt (standard fit algorithm).

Better error algorithm. - parallel ?

Use Goodman-Weare version of MCMC (emcee).

Computing in cloud.

Computational Issues

July 13th 2012 Leicester

July 13th 2012 Leicester

Spitzer IRS spectrum of NGC 4395

Riley et al., 2012

July 13th 2012 Leicester

July 13th 2012 Leicester

Multi-wavelength support

Allow spectra, responses and table models in other units. Convert when reading into xspec.

Allow models written in other units. Specify units in the model.dat entry.

Build up model libraries for other wavebands.

Spitzer IRS, SDSS, ???