Update Fermi 3FHL catalog: 1,558 hard gamma-ray sources

README.md

@@ -3,7 +3,7 @@ license: cc-by-4.0
 pretty_name: "Fermi LAT Third Catalog of Hard Sources (3FHL)"
 language:
   - en
-description: "1,556 gamma-ray sources detected above 10 GeV by Fermi LAT over 7 years, bridging the GeV-TeV energy gap."
+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 covere"
 task_categories:
   - tabular-classification
 tags:
@@ -16,6 +16,7 @@ tags:
   - astronomy
   - open-data
   - tabular-data
+  - parquet
 size_categories:
   - 1K<n<10K
 configs:
@@ -28,74 +29,156 @@ configs:
 
 # Fermi LAT Third Catalog of Hard Sources (3FHL)
 
-*Part of the [Astronomy Datasets](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) collection on Hugging Face.*
 
-Gamma-ray sources detected above 10 GeV by the Fermi Large Area Telescope (LAT)
-over 7 years of observation. Currently **1,558** sources with 67 attributes each.
+<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>
 
-## 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).
+*Part of a [dataset collection](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) on Hugging Face.*
+
+## Dataset description
 
-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 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.
+
+
+## Schema
+
+| Column | Type | Description | Sample | Null % |
+|--------|------|-------------|--------|--------|
+| `name` | object | Official 3FHL source designation, e.g. '3FHL J0001.2-0748'; encodes the catalog prefix and J2000 coordinates of the source centroid; uniquely identifies each entry in the catalog | 3FHL J0534.5+2201 | 0.1% |
+| `ra` | float64 | Right ascension of the source in degrees (J2000, ICRS); range 0-360; derived from a maximum-likelihood fit to the >10 GeV photon distribution | 83.6348 | 0.1% |
+| `dec` | float64 | Declination of the source in degrees (J2000, ICRS); range -90 to +90; derived from a maximum-likelihood fit to the >10 GeV photon distribution | 22.0192 | 0.1% |
+| `lii` | float64 | Galactic longitude in degrees; range 0-360; derived from ra and dec via the standard IAU coordinate transformation; useful for studying Galactic plane sources | 184.5543 | 0.1% |
+| `bii` | float64 | Galactic latitude in degrees; range -90 to +90; sources near bii=0 lie in the Galactic plane where diffuse emission complicates detection | -5.7805 | 0.1% |
+| `error_radius` | float64 | 95% confidence radius on the source position in degrees; smaller values indicate better localization; typically 0.01-0.1 deg for bright sources | 0.008 | 3.2% |
+| `roi` | float64 | Region of interest number used in the analysis; the sky was divided into overlapping ROIs for the maximum-likelihood source detection | 430.0 | 0.1% |
+| `significance` | float64 | Detection significance in the 10 GeV - 2 TeV band expressed as the square root of the test statistic (sqrt(TS)); higher values indicate more confident detections; catalog threshold is sqrt(TS) >= 4 | 168.641 | 0.1% |
+| `pivot_energy` | float64 | Pivot (decorrelation) energy in MeV at which the flux uncertainty is minimized; chosen to reduce correlation between spectral index and flux normalization | 22.73 | 0.1% |
+| `flux_density` | float64 | Differential photon flux at the pivot energy in units of ph/cm2/s/MeV; the spectral normalization parameter used in the likelihood fit | 1.7132e-10 | 0.1% |
+| `flux_density_error` | float64 | 1-sigma statistical uncertainty on flux_density in ph/cm2/s/MeV | 3.3886e-12 | 0.1% |
+| `flux` | float64 | Integrated photon flux in the 10 GeV - 2 TeV band in ph/cm2/s; obtained by integrating the best-fit spectral model over the full energy range | 8.6589e-09 | 0.1% |
+| `flux_error` | float64 | 1-sigma statistical uncertainty on the integrated photon flux in ph/cm2/s | 1.7127e-10 | 0.1% |
+| `energy_flux` | float64 | Integrated energy flux in the 10 GeV - 2 TeV band in erg/cm2/s; accounts for the energy weighting of the spectrum; more physically meaningful than photon flux for comparing source luminosities | 4.9149e-10 | 0.1% |
+| `energy_flux_error` | float64 | 1-sigma statistical uncertainty on the energy flux in erg/cm2/s | 1.6631e-11 | 0.1% |
+| `curve_significance` | float64 | Significance of spectral curvature with respect to a simple power-law model; high values (>3) indicate that a curved spectrum (log-parabola or exponential cutoff) is preferred over a power law | 1.43 | 0.1% |
+| `spectrum_type` | object | Best-fit spectral model type: 'PowerLaw', 'LogParabola', or 'PLExpCutoff'; selected based on the curve_significance test | PowerLaw | 0.1% |
+| `spectral_index` | float64 | Photon spectral index of the best-fit model; for a power law dN/dE ~ E^(-index), typical values are 1.5-4; harder (lower index) sources emit relatively more high-energy photons | 2.2853 | 0.1% |
+| `spectral_index_error` | float64 | 1-sigma statistical uncertainty on the spectral index | 0.0378 | 0.1% |
+| `beta` | float64 | Curvature parameter for LogParabola spectra: dN/dE ~ (E/E0)^(-(alpha + beta*ln(E/E0))); zero for pure power-law sources; larger beta indicates stronger curvature | -0.0469 | 0.1% |
+| `beta_error` | float64 | 1-sigma statistical uncertainty on the beta curvature parameter; null for sources fit with a simple power law | 0.0181 | 0.1% |
+| `powerlaw_index` | float64 | Photon index when the source is fit with a simple power law regardless of whether curvature is significant; useful for uniform comparisons across all sources | 2.2202 | 0.1% |
+| `powerlaw_index_error` | float64 | 1-sigma uncertainty on the power-law photon index | 0.025 | 0.1% |
+| `flux_10_20_gev` | float64 | Photon flux in the 10-20 GeV sub-band in ph/cm2/s; first of five logarithmically spaced energy bins used to construct the broadband spectral energy distribution | 5.1699e-09 | 0.1% |
+| `flux_10_20_gev_neg_err` | float64 | Lower (negative) 1-sigma error on the 10-20 GeV photon flux in ph/cm2/s; asymmetric errors reflect the Poisson nature of photon counting | -1.3339e-10 | 1.3% |
+| `flux_10_20_gev_pos_err` | float64 | Upper (positive) 1-sigma error on the 10-20 GeV photon flux in ph/cm2/s | 1.3339e-10 | 0.1% |
+| `nufnu_10_20_gev` | float64 | Energy flux (nu*F_nu) in the 10-20 GeV band in erg/cm2/s; represents the spectral energy distribution value at the geometric mean energy of the bin | 1.642e-10 | 0.1% |
+| `sqrt_ts_10_20_gev` | float64 | Detection significance (sqrt of test statistic) in the 10-20 GeV band; values below ~2 indicate the source is not significantly detected in this sub-band | 125.1574 | 0.1% |
+| `flux_20_50_gev` | float64 | Photon flux in the 20-50 GeV sub-band in ph/cm2/s | 2.245e-09 | 0.1% |
+| `flux_20_50_gev_neg_err` | float64 | Lower 1-sigma error on the 20-50 GeV photon flux in ph/cm2/s | -8.6719e-11 | 7.2% |
+| `flux_20_50_gev_pos_err` | float64 | Upper 1-sigma error on the 20-50 GeV photon flux in ph/cm2/s | 8.6719e-11 | 0.1% |
+| `nufnu_20_50_gev` | float64 | Energy flux (nu*F_nu) in the 20-50 GeV band in erg/cm2/s | 1.1808e-10 | 0.1% |
+| `sqrt_ts_20_50_gev` | float64 | Detection significance (sqrt(TS)) in the 20-50 GeV band | 88.7153 | 0.1% |
+| `flux_50_150_gev` | float64 | Photon flux in the 50-150 GeV sub-band in ph/cm2/s | 9.2432e-10 | 0.1% |
+| `flux_50_150_gev_neg_err` | float64 | Lower 1-sigma error on the 50-150 GeV photon flux in ph/cm2/s | -5.4975e-11 | 36.3% |
+| `flux_50_150_gev_pos_err` | float64 | Upper 1-sigma error on the 50-150 GeV photon flux in ph/cm2/s | 5.4975e-11 | 0.1% |
+| `nufnu_50_150_gev` | float64 | Energy flux (nu*F_nu) in the 50-150 GeV band in erg/cm2/s | 1.0869e-10 | 0.1% |
+| `sqrt_ts_50_150_gev` | float64 | Detection significance (sqrt(TS)) in the 50-150 GeV band | 59.0875 | 0.1% |
+| `flux_150_500_gev` | float64 | Photon flux in the 150-500 GeV sub-band in ph/cm2/s | 2.759e-10 | 0.1% |
+| `flux_150_500_gev_neg_err` | float64 | Lower 1-sigma error on the 150-500 GeV photon flux in ph/cm2/s | -2.9165e-11 | 77.8% |
+| `flux_150_500_gev_pos_err` | float64 | Upper 1-sigma error on the 150-500 GeV photon flux in ph/cm2/s | 3.136e-11 | 0.1% |
+| `nufnu_150_500_gev` | float64 | Energy flux (nu*F_nu) in the 150-500 GeV band in erg/cm2/s | 9.2302e-11 | 0.1% |
+| `sqrt_ts_150_500_gev` | float64 | Detection significance (sqrt(TS)) in the 150-500 GeV band | 33.0762 | 0.1% |
+| `flux_0p5_2_tev` | float64 | Photon flux in the 0.5-2 TeV sub-band in ph/cm2/s; the highest energy bin, probing the TeV regime where ground-based Cherenkov telescopes provide complementary coverage | 6.684e-11 | 0.1% |
+| `flux_0p5_2_tev_neg_err` | float64 | Lower 1-sigma error on the 0.5-2 TeV photon flux in ph/cm2/s | -1.463e-11 | 93.8% |
+| `flux_0p5_2_tev_pos_err` | float64 | Upper 1-sigma error on the 0.5-2 TeV photon flux in ph/cm2/s | 1.6916e-11 | 0.1% |
+| `nufnu_0p5_2_tev` | float64 | Energy flux (nu*F_nu) in the 0.5-2 TeV band in erg/cm2/s | 6.9012e-11 | 0.1% |
+| `sqrt_ts_0p5_2_tev` | float64 | Detection significance (sqrt(TS)) in the 0.5-2 TeV band | 15.5731 | 0.1% |
+| `npred` | float64 | Total number of predicted photons from this source in the model; a measure of signal strength that accounts for exposure and PSF; higher npred means more photons attributed to this source | 2602.9 | 0.1% |
+| `hep_energy` | float64 | Energy of the highest-energy photon associated with the source in GeV; constrained by the LAT effective area and source spectrum; can exceed 1 TeV for the hardest sources | 1463.3 | 0.1% |
+| `hep_prob` | float64 | Probability that the highest-energy photon truly belongs to this source rather than a neighboring source or diffuse background; values near 1.0 give high confidence in the association | 1.0 | 0.1% |
+| `num_bayesian_blocks` | float64 | Number of Bayesian blocks in the source light curve; a value of 1 indicates no significant variability detected; higher values suggest flux changes over the 7-year observation period | 1.0 | 0.1% |
+| `extended_source_name` | object | Name of the spatial template if the source is modeled as spatially extended (e.g. supernova remnants, pulsar wind nebulae); null for point sources which are the majority of the catalog | IC 443 | 96.9% |
+| `alt_gammaray_name` | object | Alternative gamma-ray catalog designation from earlier Fermi catalogs (e.g. 3FGL, 2FHL) or other experiments; useful for cross-matching with the broader gamma-ray literature | 3FGL J0534.5+2201i | 13.5% |
+| `tev_assoc_flag` | object | Flag indicating association with a known TeV source from ground-based observations; non-null values indicate overlap with sources detected by H.E.S.S., MAGIC, or VERITAS | P | 0.1% |
+| `assoc_tevcat` | object | Name of the associated TeV source in TeVCat; provides the link between Fermi LAT and ground-based Cherenkov telescope detections of the same astrophysical object | Crab Nebula | 91.5% |
+| `source_class` | object | Astrophysical classification of the source (e.g. 'bll' = BL Lac blazar, 'fsrq' = flat-spectrum radio quasar, 'psr' = pulsar, 'snr' = supernova remnant, 'pwn' = pulsar wind nebula, '' = unassociated) | PWN | 11.5% |
+| `assoc_name_1` | object | Primary counterpart name at other wavelengths from automated association methods; typically a radio or X-ray catalog designation used to identify the gamma-ray source | Crab Nebula | 11.5% |
+| `assoc_name_2` | object | Secondary counterpart name at other wavelengths; provides an alternative identification when multiple association methods yield different but plausible counterparts | Vela X field | 98.3% |
+| `assoc_prob_bay` | float64 | Bayesian association probability for the primary counterpart; range 0-1; values above 0.8 indicate a highly confident multi-wavelength association | 1.0 | 3.2% |
+| `assoc_prob_lr` | float64 | Likelihood-ratio association probability for the primary counterpart; range 0-1; an independent association metric complementing the Bayesian probability | 0.9999 | 3.2% |
+| `redshift` | float64 | Spectroscopic redshift of the associated extragalactic counterpart; null for Galactic sources and unassociated sources; used to compute intrinsic luminosity and EBL absorption corrections | 0.03 | 64.8% |
+| `nupeak_obs` | float64 | Observed synchrotron peak frequency in Hz (log10 scale) for blazar-type sources; classifies blazars as low-synchrotron-peaked (LSP, <10^14 Hz), intermediate (ISP), or high-synchrotron-peaked (HSP, >10^15 Hz); null for non-blazar sources | 1.1482e+17 | 29.6% |
 
 ## 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
 
 ```python
 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.head(10)[["name", "ra", "dec"]])
-
-# Sky map
-import matplotlib.pyplot as plt
-plt.figure(figsize=(12, 6))
-plt.scatter(df["ra"], df["dec"], s=2, alpha=0.5)
-plt.xlabel("RA (deg)")
-plt.ylabel("Dec (deg)")
-plt.title("Fermi 3FHL Sources (>10 GeV)")
-plt.gca().invert_xaxis()
+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
 
-All data comes from the [Fermi 3FHL Catalog](https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermi3fhl.html)
-hosted by NASA's High Energy Astrophysics Science Archive Research Center (HEASARC),
-accessed via the TAP protocol.
-
-Reference: Ajello, M. et al. 2017, ApJS, 232, 18.
+https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermi3fhl.html
 
 ## Related datasets
 
-- [gamma-ray-bursts](https://huggingface.co/datasets/juliensimon/gamma-ray-bursts) — Fermi GBM Gamma-Ray Burst Catalog
-- [pulsar-catalog](https://huggingface.co/datasets/juliensimon/pulsar-catalog) — ATNF Pulsar Catalogue
-
-## Pipeline
+- [juliensimon/gamma-ray-bursts](https://huggingface.co/datasets/juliensimon/gamma-ray-bursts)
 
-Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)
+- [juliensimon/pulsar-catalog](https://huggingface.co/datasets/juliensimon/pulsar-catalog)
 
 ## Citation
 
 ```bibtex
-@dataset{fermi_3fhl,
-  author = {Simon, Julien},
+@dataset{fermi_3fhl_hard_gamma_ray,
   title = {Fermi LAT Third Catalog of Hard Sources (3FHL)},
+  author = {juliensimon},
   year = {2026},
-  publisher = {Hugging Face},
   url = {https://huggingface.co/datasets/juliensimon/fermi-3fhl-hard-gamma-ray},
-  note = {Based on Fermi 3FHL (Ajello et al. 2017) via NASA HEASARC}
+  publisher = {Hugging Face}
 }
 ```
 

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