---
license: cc-by-4.0
pretty_name: "Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog"
language:
  - en
description: "The Fourth Fermi Large Area Telescope Source Catalog, Data Release 4 (4FGL-DR4), based on 14 years of all-sky gamma-ray survey data. The deepest catalog of the gamma-ray sky ever produced, with source"
task_categories:
  - tabular-classification
  - tabular-regression
tags:
  - space
  - gamma-ray
  - fermi
  - lat
  - nasa
  - astronomy
  - high-energy
  - open-data
  - tabular-data
  - parquet
size_categories:
  - 1K<n<10K
configs:
  - config_name: default
    data_files:
      - split: train
        path: data/fermi_4fgl_dr4.parquet
    default: true
---

# Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog


<div align="center">
  <img src="banner.jpg" alt="The gamma-ray sky as seen by NASA's Fermi telescope" width="400">
  <p><em>Credit: NASA/DOE/Fermi LAT Collaboration</em></p>
</div>


*Part of a [dataset collection](https://huggingface.co/collections/juliensimon/physics-datasets-69c2d4682d37dfdb77447bd7) on Hugging Face.*

## Dataset description

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

The Fermi LAT is a pair-conversion telescope sensitive to gamma rays from roughly 20 MeV to more than 1 TeV. With Pass 8 event reconstruction and 14 years of exposure, the catalog reaches a point-source sensitivity of approximately 2 x 10^-12 erg/cm2/s in energy flux -- deep enough to detect faint pulsars, distant blazars, and diffuse emission from star-forming regions.

The source population is remarkably diverse. Blazars dominate the extragalactic sky, their relativistic jets producing variable gamma-ray emission through inverse-Compton scattering. Pulsars are the most numerous Galactic source class, emitting pulsed gamma rays from magnetospheric particle acceleration. Over a thousand sources remain unassociated with known counterparts, representing active classification targets for machine learning and multi-wavelength follow-up.


This dataset is suitable for **tabular classification, tabular regression** tasks.

## Schema

| Column | Type | Description | Sample | Null % |
|--------|------|-------------|--------|--------|
| `source_name` | str | 4FGL catalog designation encoding position (e.g. '4FGL J0001.2+3738' = J2000 RA 00h01m, Dec +37d38'); the '4FGL' prefix identifies this as the Fourth Fermi LAT catalog | 4FGL J0000.3-7355 | 0.0% |
| `ra_deg` | float32 | Right ascension of source centroid (ICRS J2000.0, degrees, 0-360); LAT angular resolution is ~0.1 deg at 10 GeV, ~1 deg at 1 GeV | 0.0983 | 0.0% |
| `dec_deg` | float32 | Declination of source centroid (ICRS J2000.0, degrees, -90 to +90) | -73.922 | 0.0% |
| `glon_deg` | float32 | Galactic longitude (degrees, 0-360); sources at low \|b\| sit in the Galactic plane where diffuse emission and source confusion are highest | 307.70898 | 0.0% |
| `glat_deg` | float32 | Galactic latitude (degrees, -90 to +90); \|b\| < 10 deg indicates Galactic plane sources; extragalactic sources (blazars, radio galaxies) populate high latitudes | -42.729538 | 0.0% |
| `significance` | float32 | Detection significance averaged over the full energy range (sigma); threshold for catalog inclusion is ~4 sigma; bright sources exceed 100 sigma | 8.492646 | 0.0% |
| `flux_1000_mev` | float32 | Integral photon flux above 1 GeV (photons/cm2/s); chosen to minimize dependence on the poorly constrained low-energy spectral shape; null for very soft sources | 1.479606e-10 | 0.0% |
| `energy_flux_100_mev` | float32 | Integral energy flux from 100 MeV to 100 GeV (erg/cm2/s); the most physically meaningful flux measure capturing the bolometric gamma-ray output over the LAT band | 1.7352088e-12 | 0.0% |
| `spectrum_type` | str | Best-fit spectral model: 'PowerLaw' (single power law, typical for young pulsars), 'LogParabola' (curved spectrum, typical for BL Lacs), 'PLSuperExpCutoff' (power law with exponential cutoff, characteristic of pulsars) | PowerLaw | 0.0% |
| `variability_index` | float32 | Sum of log-likelihood ratio test statistics from monthly light curve fits; values above 18.48 indicate flux variability at >99% confidence; blazars typically show values of 20-1000 | 12.834996 | 0.0% |
| `source_class` | str | Astrophysical classification: 'bll' (BL Lac object), 'fsrq' (Flat Spectrum Radio Quasar), 'psr' (pulsar), 'snr' (supernova remnant), 'pwn' (pulsar wind nebula), '' / null (unassociated); uppercase indicates high-confidence association | bcu | 33.7% |
| `association` | str | Name of the counterpart source at other wavelengths (e.g. radio, X-ray, optical); null for unassociated sources (~26% of catalog) | B3 2358+474 | 33.7% |
| `flags` | Int64 | Bitmask of analysis quality and caution flags (see 4FGL paper Table 3); bit 0 = source is in a region of bright diffuse emission; non-zero flags indicate results should be used with caution | 0 | 0.0% |
| `pivot_energy_mev` | float32 | Reference energy at which the spectral normalization and index are decorrelated (MeV); chosen to minimize the covariance between flux normalization and spectral index; typically 500-5000 MeV | 1917.7155 | 0.0% |
| `power_law_index` | float32 | Photon spectral index Gamma for sources fit with a power law (flux proportional to E^-Gamma); typical values: 1.5-2.0 for hard blazars, 2.0-3.0 for soft sources and pulsars; null for other spectral models | 2.2473958 | 0.0% |
| `log_parabola_index` | float32 | Spectral index alpha at the pivot energy for sources fit with a log-parabola; null for sources using a different spectral model | 2.1280127 | 0.0% |
| `log_parabola_beta` | float32 | Spectral curvature parameter beta for log-parabola sources; beta > 0 means the spectrum curves downward (softer at higher energies); null for other spectral models | 0.10999863 | 0.0% |
| `is_variable` | bool | True when variability_index exceeds 18.48 (99% confidence variability threshold); predominantly blazars; False includes both truly steady sources and sources with insufficient statistics | False | 0.0% |

## 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

```python
from datasets import load_dataset

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

```python
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"]))
]

# Sky distribution
import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots(subplot_kw={"projection": "aitoff"})
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)
plt.title("Fermi 4FGL-DR4 Gamma-Ray Sky")
plt.show()
```

## Data source

https://fermi.gsfc.nasa.gov/ssc/data/access/lat/14yr_catalog/

## Related datasets

- [juliensimon/gamma-ray-bursts](https://huggingface.co/datasets/juliensimon/gamma-ray-bursts)

- [juliensimon/supernova-remnants](https://huggingface.co/datasets/juliensimon/supernova-remnants)

- [juliensimon/pulsar-catalog](https://huggingface.co/datasets/juliensimon/pulsar-catalog)

> If you find this dataset useful, please consider [giving it a like](https://huggingface.co/datasets/juliensimon/fermi-4fgl-dr4) on Hugging Face. It helps others discover it.

## About the author

Created by [Julien Simon](https://julien.org) — AI Operating Partner at Fortino Capital. Part of the [Space Datasets](https://julien.org/datasets) collection.

## Citation

```bibtex
@dataset{fermi_4fgl_dr4,
  title = {Fermi LAT 4FGL-DR4 Gamma-Ray Source Catalog},
  author = {juliensimon},
  year = {2026},
  url = {https://huggingface.co/datasets/juliensimon/fermi-4fgl-dr4},
  publisher = {Hugging Face}
}
```

## License

[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)