FermiPhased: A tool for phase-resolved likelihood analysis of Fermi-LAT data

TL;DR

The paper tackles the high computational cost of phase-resolved likelihood analyses for Fermi-LAT data by introducing FermiPhased, a GUI-driven, open-source pipeline built on Fermipy that automatically generates and executes phase-binned analyses. It offers three modes—Standard, Adaptive Fixed Counts, and Joint Phase-Resolved analysis—along with Slurm-based parallelization to run many phase bins or epochs concurrently, either locally or on a cluster. The tool outputs per-phase products (phase bins, fluxes, spectra, and test statistics) and supports configuration management via JSON/YAML, enabling reproducibility and scalable exploration of pulsars, binaries, and other periodic sources. This approach significantly enhances efficiency and consistency in phase-resolved gamma-ray studies, reducing manual scripting and enabling robust multi-epoch analyses with Fermi-LAT data using $ ext{phase} \, \phi = ((START\,\text{MJD} - T_0)/P) \bmod 1 $ and bin widths $ \delta\phi = 1/n$. The open-source release, documentation, and tutorials further democratize access to advanced phase-resolved analyses for the high-energy astrophysics community.

Abstract

The Fermi Large Area Telescope has enabled detailed studies of high-energy astrophysical sources. To support analysis, we present FermiPhased, a flexible, open-source tool for phase-resolved studies of pulsars, binaries, and other periodically variable sources. Built on the Fermipy framework, FermiPhased offers three modes: standard, adaptive (fixed counts), and joint phase-resolved analysis, enabling users to flexibly bin data based on phase, count statistics, or jointly fit different epochs of interest. FermiPhased is optimized for parallel execution and use on computing clusters. It enables parallelized extraction of phase-resolved fluxes, spectra, and intermediary data products, with tutorials and documentation available on GitHub.

Figures (7)

• Figure 1: Graphical user interface (GUI) for FermiPhased, a script generator for phase-resolved analysis of Fermi-LAT data. The user can specify key parameters such as source position, energy and time ranges, binning configuration, and file paths. FermiPhased supports multiple modes of phase binning (e.g., Standard Phase-Resolved Analysis, Adaptive (Fixed Counts) Phase-Resolved Analysis, Joint Phase-Resolved Analysis) and allows script export with optional automatic cluster submission for batch processing. Parameters and settings can be saved and loaded here.
• Figure 2: Phase-folded light curve and polar histogram generated by FermiPhased for a selected region of interest in phase space. The blue-shaded region indicates a user-defined phase interval selected for data filtering and analysis based on user inputs. Top: A visualization of the phaseogram along with a schematic of an example binary. Bottom: The same phaseogram highlighting modulation features and selected phase cuts. Two orbital cycles are given for clarity.
• Figure 3: Phase-resolved analysis of LS 5039 from nearly 17 years of Fermi-LAT data. The 0.1--100 GeV integrated flux is shown in the top panel, spectral parameters $\alpha$ and $\beta$ are shown in the middle two panels. The TS for LS 5039 is shown in the bottom panel. Two orbital cycles are shown for clarity.
• Figure 4: Zoomed-in image of FermiPhased interface in “Adaptive (Fixed Counts)” mode, where the user specifies the desired number of counts per phase bin.
• Figure 5: Widths of phase bins as a function of pulse phase in “Adaptive (Fixed Counts)” mode for the Vela pulsar. The bin widths (blue) vary inversely with count rate (grey).