Bayesian inference-based spectral fitting for high-energy astrophysical data.

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BaySpec is a Python library for Bayesian inference on high-energy astrophysical spectra. It pairs MCMC and nested-sampling backends with multi-spectrum, multi-model fitting machinery, reads OGIP FITS data out of the box, and bridges to local, astromodels, and Xspec model libraries.

Features

• Inference backends. Posterior sampling via MCMC (emcee) or nested sampling (MultiNest via pymultinest); maximum-likelihood fits via lmfit or iminuit for quick checks.
• OGIP Type I & II FITS. Source and background PHA/PHA2 spectra, plus RMF, RSP/RSP2, and ARF/ARF2 responses — multi-extension archives are row-indexed so individual spectra plug in directly.
• Multi-dimensional. Time-evolving spectra fit with time-involved physical models.
• Multi-wavelength. Joint fitting across spectra at different wavelengths.
• Multi-spectrum, multi-model. Simultaneously fit any number of (data, model) pairs; combine, freeze, or link parameters across pairs.
• Pluggable model libraries. A local set plus optional astromodels and Xspec bridges. Register your own Python functions as new components.
• Browser workbench (optional). BaySpec App is a FastAPI + HTMX front-end that exposes the same fitting machinery through a web UI.

Installation

BaySpec is available on PyPI:

pip install bayspec

Optional: MultiNest sampler

To enable MultiNest for nested sampling, follow the pymultinest install guide.

Optional: astromodels components

To pull components from astromodels, install astromodels in your Python environment.

Optional: Xspec components

To pull components from Xspec:

1. Install HEASoft and Xspec v12.12.1+.
2. After initialising the HEASoft environment, install xspec-models-cxc.

Note: bayspec currently supports only Additive and Multiplicative Xspec models.

BaySpec App

BaySpec App is the browser front-end for bayspec — a FastAPI + HTMX workbench that loads OGIP spectra, composes models, and runs inference without notebook glue. A public, hosted deployment runs on Hugging Face Spaces:

Documentation

Read the full documentation or browse the examples for typical workflows end to end.

License

BaySpec is distributed under the GPL-3.0 license.