juliensimon/fermi-3fhl-hard-gamma-ray
Fermi LAT Third Catalog of Hard Sources (3FHL) Credit: NASA/DOE/Fermi LAT Collaboration Part of a dataset collection on Hugging Face. Dataset description The 3FHL catalog (Ajello et al. 2017) contains sources detected by Fermi LAT in the 10 GeV - 2 TeV energy range using 7 years of Pass 8 data. This catalog bridges the gap between the GeV regime covered by the standard Fermi catalogs and the TeV regime covered by ground-based Cherenkov telescopes… See the full description on the dataset page: https://huggingface.co/datasets/juliensimon/fermi-3fhl-hard-gamma-ray.
Fermi LAT Third Catalog of Hard Sources (3FHL)
<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/astronomy-datasets-69c24caf2f17e36128946743) on Hugging Face.
Dataset description
The 3FHL catalog (Ajello et al. 2017) contains sources detected by Fermi LAT in the 10 GeV - 2 TeV energy range using 7 years of Pass 8 data. This catalog bridges the gap between the GeV regime covered by the standard Fermi catalogs and the TeV regime covered by ground-based Cherenkov telescopes (H.E.S.S., MAGIC, VERITAS).
Sources include blazars, pulsar wind nebulae, supernova remnants, and unidentified gamma-ray emitters. The catalog is essential for planning observations with current and future TeV observatories like CTA.
The 10 GeV - 2 TeV energy range probed by 3FHL occupies a critical frontier in high-energy astrophysics. Below ~10 GeV, the Fermi LAT standard catalogs (3FGL, 4FGL) provide comprehensive coverage with large photon statistics. Above ~100 GeV, imaging atmospheric Cherenkov telescopes (IACTs) like H.E.S.S., MAGIC, and VERITAS achieve superior sensitivity but with limited fields of view and duty cycles. The 3FHL catalog bridges this gap using Fermi LAT's Pass 8 event reconstruction, which dramatically improved the instrument's effective area and point-spread function at high energies, enabling detection of hard-spectrum sources that were previously buried in background.
The source population in 3FHL is dominated by blazars — active galactic nuclei whose relativistic jets point close to our line of sight, producing Doppler-boosted emission that peaks in the GeV-TeV band. The catalog also contains Galactic sources such as pulsar wind nebulae (where ultra-relativistic electron-positron winds from young pulsars produce inverse-Compton emission), supernova remnants (candidate sites of cosmic-ray acceleration up to PeV energies), and a significant fraction of unidentified sources that may represent entirely new source classes. For extragalactic sources, the interaction of TeV photons with the extragalactic background light (EBL) via pair production imprints a redshift-dependent spectral cutoff, making this catalog a powerful probe of the EBL intensity and its evolution.
The 3FHL is the primary seed catalog for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory. Nearly every 3FHL source above the CTA sensitivity threshold is expected to be detected, and the catalog's uniform sky coverage helps define CTA's key science programs including surveys of the Galactic plane and extragalactic deep fields.
This dataset is suitable for tabular classification tasks.
Schema
Quick stats
- 1,558 gamma-ray sources above 10 GeV
- 1,212 blazar-type sources (BL Lac, FSRQ, BCU)
- 548 with measured redshift
- Median detection significance: 7.0 sigma
Usage
from datasets import load_dataset
ds = load_dataset("juliensimon/fermi-3fhl-hard-gamma-ray", split="train")
df = ds.to_pandas()from datasets import load_dataset
import matplotlib.pyplot as plt
ds = load_dataset("juliensimon/fermi-3fhl-hard-gamma-ray", split="train")
df = ds.to_pandas()
# Highest significance sources
print(df.sort_values("significance", ascending=False).head(10)[["name", "ra", "dec", "significance"]])
# Sky map in Galactic coordinates
fig, ax = plt.subplots(figsize=(12, 6), subplot_kw={"projection": "aitoff"})
import numpy as np
l = np.radians(df["lii"] - 180) # center on Galactic center
b = np.radians(df["bii"])
ax.scatter(l, b, s=df["significance"] * 0.5, alpha=0.5, c=df["energy_flux"],
cmap="inferno", norm=plt.matplotlib.colors.LogNorm())
ax.set_title("Fermi 3FHL Sources (>10 GeV) — Galactic Coordinates")
ax.grid(True)
plt.tight_layout()
plt.show()
# Spectral index distribution
plt.figure(figsize=(8, 5))
plt.hist(df["spectral_index"].dropna(), bins=40, edgecolor="black", alpha=0.7)
plt.xlabel("Photon Spectral Index")
plt.ylabel("Number of Sources")
plt.title("3FHL Spectral Index Distribution")
plt.tight_layout()
plt.show()Data source
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermi3fhl.html
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About the author
Created by Julien Simon — AI Operating Partner at Fortino Capital. Part of the Space Datasets collection.
Citation
@dataset{fermi_3fhl_hard_gamma_ray,
title = {Fermi LAT Third Catalog of Hard Sources (3FHL)},
author = {Simon, Julien},
year = {2026},
url = {https://huggingface.co/datasets/juliensimon/fermi-3fhl-hard-gamma-ray},
publisher = {Hugging Face},
note = {Derived from NASA HEASARC (High Energy Astrophysics Science Archive Research Center), https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermi3fhl.html}
}