license: cc-by-4.0
pretty_name: Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog
language:
- en
description: >-
The 14-year all-sky gamma-ray source catalog from the Fermi Large Area
Telescope — the deepest survey of the gamma-ray sky.
task_categories:
- tabular-classification
- tabular-regression
tags:
- space
- gamma-ray
- fermi
- lat
- nasa
- astronomy
- high-energy
- open-data
size_categories:
- 1K<n<10K
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)}
}