BXA

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Freedom report

Two barsScore 6.3

Free tierA free tier is on its own pricing page
Open codeNo open-source code on record
Runs widely1 of 6 device platforms
DocumentedPlans, terms and facts published

BXA is ranked #9 of 34 in astronomy apps on Freedom251. It runs on Linux. There is a free plan.

BXA plans and pricing

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BXA Free Free software under GNU GPL v3 or later github.com · 5 Oct 2026

Compared on astronomy apps

Platform coverage: desktop

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The record

Purpose: BXA connects Xspec and Sherpa X-ray spectral analysis environments to UltraNest for Bayesian parameter estimation and model comparison.
Parameter estimation: It estimates parameters in arbitrary dimensions, finds best fits, computes error bars and marginal probability distributions, and supports MPI parallelisation.
Model comparison: It computes model evidence for Bayes factors and supports comparing models that are not nested.
Model discovery: It provides Quantile-Quantile plots to visualize deviations between a model and data without binning.
Automated fitting: The fitting algorithm explores parameter spaces without requiring good starting points and runs until convergence.
Intended use: The documentation highlights systematic analysis of large datasets, comparing multiple models, and analyzing low-count datasets with realistic models.
Installation: BXA can be installed with pip or conda and requires either Sherpa or Xspec to be installed and configured.
Supported systems: BXA runs on operating systems supported by CIAO/Sherpa or HEASoft/Xspec, while release testing is stated to cover Ubuntu Linux only.
Parallel processing: MPI parallelisation can scale inference from laptops to computing clusters when mpi4py is installed.
Xspec compatibility: When run from pyxspec, BXA provides chain FITS files compatible with Xspec/pyxspec MCMC features and error propagation tools.
Support: The project directs users to file bug reports and feedback as GitHub issues and asks bug reports to include operating system, Sherpa or Xspec version, setup details, and reproduction steps.
Security and warranty: The repository publishes a GNU GPL license whose text disclaims warranties for the program.
Notable change: In version 5, Xspec priors use soft parameter limits instead of hard parameter limits, which the release notes flag as a potentially breaking change.
Price from: Free

Where it ranks on Freedom251

Best Astronomy Apps in 2026#9 of 34

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Sources

johannesbuchner.github.io/BXA/· checked 5 Oct 2026
johannesbuchner.github.io/BXA/convenience.html· checked 5 Oct 2026
johannesbuchner.github.io/BXA/contributing.html· checked 5 Oct 2026
github.com/JohannesBuchner/BXA/blob/master/LICENSE· checked 5 Oct 2026
johannesbuchner.github.io/BXA/history.html· checked 5 Oct 2026