juliensimon/fermi-4fgl-dr4

Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog

The Fourth Fermi Large Area Telescope Source Catalog, Data Release 4 (4FGL-DR4), based on 14 years of all-sky gamma-ray survey data. Currently 7,195 sources.

Dataset description

This dataset contains every gamma-ray source detected by the Fermi LAT instrument in its 14-year all-sky survey. The 4FGL-DR4 is the deepest catalog of the gamma-ray sky ever produced, with sources spanning blazars, pulsars, supernova remnants, globular clusters, starburst galaxies, and many unidentified sources.

Each record includes sky position, spectral properties, flux measurements, variability information, and source associations with counterparts at other wavelengths.

Schema

Column	Type	Description
source_name	string	4FGL source name (e.g. "4FGL J0001.2+3738")
ra_deg	float64	Right Ascension J2000 (degrees)
dec_deg	float64	Declination J2000 (degrees)
glon_deg	float64	Galactic longitude (degrees)
glat_deg	float64	Galactic latitude (degrees)
significance	float64	Detection significance (sigma)
flux_1000_mev	float64	Photon flux above 1 GeV (photons/cm2/s)
energy_flux_100_mev	float64	Energy flux above 100 MeV (erg/cm2/s)
spectrum_type	string	Spectral model type (PowerLaw, LogParabola, etc.)
variability_index	float64	Variability index (>18.48 = variable at 99%)
source_class	string	Source classification (e.g. "bll", "psr", "fsrq")
association	string	Associated source name at other wavelengths
redshift	float64	Redshift (where available)
flags	Int64	Analysis flags
pivot_energy_mev	float64	Pivot energy (MeV)
power_law_index	float64	Power-law spectral index
log_parabola_index	float64	Log-parabola spectral index
log_parabola_beta	float64	Log-parabola curvature parameter
is_variable	bool	Variability flag (variability_index > 18.48)

Quick stats

• 7,195 gamma-ray sources
• 3,051 variable sources (99% confidence)
• 0 sources with measured redshift
• Top source classes:
  • bcu: 1,622
  • bll: 1,468
  • fsrq: 776
  • MSP: 139
  • PSR: 137
  • unk: 137
  • spp: 126
  • rdg: 47
  • FSRQ: 44
  • glc: 41

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/fermi-4fgl-dr4", split="train")
df = ds.to_pandas()

# Brightest sources by significance
brightest = df.sort_values("significance", ascending=False).head(20)

# Variable blazars
variable_blazars = df[
    (df["is_variable"] == True) &
    (df["source_class"].isin(["bll", "fsrq", "BLL", "FSRQ"]))
]

# Sources with known redshift
with_z = df[df["redshift"].notna()].sort_values("redshift", ascending=False)

# Sky distribution
import matplotlib.pyplot as plt
fig, ax = plt.subplots(subplot_kw={"projection": "aitoff"})
import numpy as np
l = np.radians(df["glon_deg"].values)
l[l > np.pi] -= 2 * np.pi
b = np.radians(df["glat_deg"].values)
ax.scatter(l, b, s=0.1, alpha=0.3)

Data source

Fermi LAT collaboration, 4FGL-DR4 (Abdollahi et al. 2022, updated). Based on 14 years of Fermi LAT Pass 8 data.

Update schedule

Annual (January 1) via GitHub Actions.

Related datasets

• grb-catalog -- Gamma-ray burst catalog
• snr-catalog -- Supernova remnant catalog
• pulsar-catalog -- Pulsar catalog

Pipeline

Source code: juliensimon/space-datasets

Citation

@dataset{fermi_4fgl_dr4,
  author = {Simon, Julien},
  title = {Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/datasets/juliensimon/fermi-4fgl-dr4},
  note = {Based on Fermi LAT 4FGL-DR4 catalog (Abdollahi et al. 2022, updated)}
}

License

CC-BY-4.0