fastropop

fastropop is the package that generates your SMBHB populations at lightning speed. It is designed to be a fast, flexible, and user-friendly tool for simulating the cosmic population of supermassive black hole binaries (SMBHBs) and their gravitational wave signatures in the nanohertz regime.

The package is centered on the semi analytic population from arXiv:0804.4476, which is implemented in the SemiAnalyticPopulation class. It also includes a suite of utilities for computing characteristic-strain quantities, sampling population realizations, binning into PTA-style spectra

Documentation: fastropop.readthedocs.io

This repository is maintained by Jonas El Gammal and reflects scientific work carried out with Chiara Cecchini, Gabriele Franciolini, and Mauro Pieroni. The package was used for the analysis in arXiv:2605.05157, but of course you can use it for whatever you want!

What It Does

• defines a semi-analytic SMBHB population model
• computes characteristic-strain quantities and expected binary counts
• samples population realizations with JAX-backed randomness
• bins sampled realizations into PTA-style spectra
• generates HEALPix skymaps with either jax-healpy or healpy

Installation

git clone git@github.com:jonaselgammal/fastropop.git
cd fastropop
pip install -e .

Notes:

• jax and jaxlib are core dependencies
• skymap generation requires a HEALPix backend
• jax-healpy is preferred when installed
• standard healpy is supported as a fallback backend

Quick Start

import fastropop

pop = fastropop.SemiAnalyticPopulation()

distM, distz, distlog10f = pop.sample_dist(Nbinaries=1000, key=0)
spec = fastropop.binning(distM, distz, distlog10f, do_plot=False)

For reproducible stochastic methods, pass a JAX key or integer seed:

params = fastropop.draw_parameters(key=0)
Nbinaries = pop.generate_poisson_realization(1, key=1)

If key=None, the package creates a fresh nondeterministic JAX key internally.

Notebooks

The main examples currently live in:

• examples/semi-analytic.ipynb
• examples/population-spectra.ipynb
• examples/skymaps.ipynb

Repository Layout

src/fastropop/        Package source
tests/                Unit and regression tests
examples/             Example scripts and notebooks
.github/workflows/    CI and release automation