The 35th annual conference on Astronomical Data Analysis Software & Systems 2025 in Görlitz, Germany

PySE (Python Source Extractor) was developed by Spreeuw & Swinbank between 2005 and 2010, as part of the LOFAR Transients Key Project. It has been in continuous use since 2017 within the Amsterdam–ASTRON Radio Transients Facility and Analysis Center (AARTFAAC) pipeline. More recently (2023), major performance enhancements reduced runtime dramatically: offline processing of typical 2300²-pixel AARTFAAC images with ~2000 sources improved from ~20 seconds to 0.9 seconds. Over the past two years, we have benchmarked PySE against a representative Square Kilometre Array (SKA) artificial test image of 4096² pixels, measuring all 167,000 inserted sources, within 0.9 seconds on a high-end consumer CPU. This was made possible by vectorizing the source extraction and measurement stages with Numba’s guvectorize decorator.

This talk will focus on the usability of the new PySE, in particular its “sky-eater” mode for rapid processing of very large images. We will briefly compare its advantages and limitations with other astronomical source extractors. We will then demonstrate PySE’s straightforward installation via pip and show how images can be processed from an IPython shell with just a few commands. Selected source parameters are collected in a Pandas dataframe, which can conveniently be stored as an HDF5 file.

Real-time performance is scientifically crucial: transient surveys typically generate a new sky image every second. If source extraction lags behind acquisition, detections are lost and follow-up becomes impossible. PySE’s ability to keep pace ensures that astronomical “alerts” can be issued within seconds, allowing other telescopes worldwide to repoint rapidly—an essential capability for catching rare events such as the merger of two neutron stars.

PySE is not limited to radio astronomy: it is a versatile package that takes astronomical images as input and delivers robust source-parameter measurements as output, making it suitable for integration as a library into pipelines across other wavelength domains.