juliensimon/4xmm-dr14-xray-sources

4XMM-DR14 Serendipitous X-ray Source Catalog

Credit: NASA/DOE/Fermi LAT Collaboration

Part of the Astronomy Datasets collection on Hugging Face.

The 4XMM catalog is the largest X-ray source catalog ever produced, containing 630,347 unique X-ray sources detected serendipitously by the European Space Agency's XMM-Newton observatory. This dataset provides the unique-source "slim" version of the catalog (currently DR12s from VizieR), where multiple detections of the same source have been combined into a single entry with averaged parameters.

Dataset description

XMM-Newton is ESA's flagship X-ray observatory, launched in 1999 and carrying three co-aligned European Photon Imaging Cameras (EPIC) that simultaneously observe the same field. Because the EPIC field of view spans approximately 30 arcminutes, every pointed observation serendipitously detects dozens to hundreds of X-ray sources beyond the intended target. Over more than two decades of operations, this serendipitous survey has built up the most comprehensive census of the X-ray sky ever assembled.

The 4XMM-DR14 catalog is the fourteenth data release of this serendipitous source catalog, compiled by the XMM-Newton Survey Science Centre (SSC) consortium. It covers over 13,000 observations and spans the full 0.2-12 keV energy range of the EPIC cameras. For each unique source, the catalog provides positions, fluxes in five standard energy bands, hardness ratios that encode spectral shape, variability indicators, extent measurements for non-point sources, and quality flags.

The scientific reach of 4XMM is extraordinary. X-ray emission traces the most energetic processes in the universe: accretion onto black holes and neutron stars, million-degree gas in galaxy clusters, coronal activity on stars, and shock-heated plasma in supernova remnants. The catalog contains everything from nearby active stars to distant quasars at cosmological redshifts. It is a primary resource for identifying counterparts to sources detected at other wavelengths, for constructing X-ray luminosity functions, and for discovering rare objects such as tidal disruption events, changing-look AGN, and ultra-luminous X-ray sources.

The five standard energy bands are: band 1 (0.2-0.5 keV), band 2 (0.5-1.0 keV), band 3 (1.0-2.0 keV), band 4 (2.0-4.5 keV), and band 5 (4.5-12.0 keV). Hardness ratios between adjacent bands provide a coarse spectral characterisation without requiring full spectral fitting. Sources detected multiple times have their parameters averaged, and variability between observations is flagged, enabling time-domain studies on timescales from hours to decades.

Schema

Column	Type	Description
source_id	int64	Unique source identifier in the 4XMM catalog
iau_name	string	IAU source name (e.g. 4XMM J000001.2+635739)
ra_deg	float64	Right ascension J2000 (degrees)
dec_deg	float64	Declination J2000 (degrees)
pos_error_arcsec	float64	Positional uncertainty (arcsec, 1-sigma)
src_det_ml	float64	Src Det Ml
flux_band1	float64	Mean flux in band 1: 0.2-0.5 keV (erg/cm2/s)
flux_band1_err	float64	Flux uncertainty in band 1
flux_band2	float64	Mean flux in band 2: 0.5-1.0 keV (erg/cm2/s)
flux_band2_err	float64	Flux uncertainty in band 2
flux_band3	float64	Mean flux in band 3: 1.0-2.0 keV (erg/cm2/s)
flux_band3_err	float64	Flux uncertainty in band 3
flux_band4	float64	Mean flux in band 4: 2.0-4.5 keV (erg/cm2/s)
flux_band4_err	float64	Flux uncertainty in band 4
flux_band5	float64	Mean flux in band 5: 4.5-12.0 keV (erg/cm2/s)
flux_band5_err	float64	Flux uncertainty in band 5
flux_total	float64	Mean total-band flux: 0.2-12.0 keV (erg/cm2/s)
flux_total_err	float64	Total-band flux uncertainty
flux_band9	float64	Mean flux in band 9: 0.5-4.5 keV (erg/cm2/s)
flux_band9_err	float64	Flux uncertainty in band 9
hardness_ratio_1	float64	Hardness ratio HR1 (bands 1-2)
hardness_ratio_1_err	float64	HR1 uncertainty
hardness_ratio_2	float64	Hardness ratio HR2 (bands 2-3)
hardness_ratio_2_err	float64	HR2 uncertainty
hardness_ratio_3	float64	Hardness ratio HR3 (bands 3-4)
hardness_ratio_3_err	float64	HR3 uncertainty
hardness_ratio_4	float64	Hardness ratio HR4 (bands 4-5)
hardness_ratio_4_err	float64	HR4 uncertainty
extent_arcsec	float64	Extent Arcsec
extent_arcsec_err	float64	Extent Arcsec Err
extent_ml	float64	Maximum likelihood of source extent
chi2_constancy	float64	Chi2 Constancy
fractional_variability	float64	Fractional Variability
fractional_variability_err	float64	Fractional Variability Err
variability_flag	int64	Variability flag (True if variable)
summary_flag	int64	Summary quality flag (0=good, higher=worse)
flux_total_min	float64	Flux Total Min
flux_total_min_err	float64	Flux Total Min Err
flux_total_max	float64	Flux Total Max
flux_total_max_err	float64	Flux Total Max Err
mjd_first	float64	Mjd First
mjd_last	float64	Mjd Last
n_detections	int64	Number of detections across all observations
confusion_flag	int64	Confusion Flag
irap_flag	string	Irap Flag

Quick stats

• 630,347 unique X-ray sources
• 45 columns after cleanup
• 123,037 sources with multiple detections
• RA range: 0.00 to 360.00 degrees
• Dec range: -88.19 to 89.40 degrees

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/4xmm-dr14-xray-sources", split="train")
df = ds.to_pandas()

# Brightest sources by total-band flux
if "flux_total" in df.columns:
    brightest = df.nlargest(10, "flux_total")[["iau_name", "ra_deg", "dec_deg", "flux_total"]]
    print(brightest)

# Sources detected multiple times (variability studies)
multi = df[df["n_detections"] > 5]
print(f"{len(multi):,} sources with >5 detections")

# Sky distribution
import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(14, 7))
ax.scatter(df["ra_deg"], df["dec_deg"], s=0.1, alpha=0.1, c="navy")
ax.set_xlabel("RA (deg)")
ax.set_ylabel("Dec (deg)")
ax.set_title("4XMM-DR14 Sky Coverage")

Data source

4XMM-DR14 Serendipitous Source Catalog (Webb N.A. et al., 2020, A&A, 641, A136), compiled by the XMM-Newton Survey Science Centre consortium. Accessed via VizieR (catalog IX/68), CDS Strasbourg.

Update schedule

Static dataset — based on 4XMM-DR14 catalog release.

Related datasets

• chandra-x-ray-sources -- Chandra Source Catalog
• erosita-erass1-xray -- eROSITA eRASS1 X-ray Survey
• swift-bat-hard-xray-survey -- Swift BAT Hard X-ray Survey

Pipeline

Source code: juliensimon/space-datasets

Support

If you find this dataset useful, please give it a ❤️ on the dataset page and share feedback in the Community tab! Also consider giving a ⭐️ to the space-datasets repo.

Citation

@dataset{xmm_4xmm_dr14,
  author = {Simon, Julien},
  title = {4XMM-DR14 Serendipitous X-ray Source Catalog},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/datasets/juliensimon/4xmm-dr14-xray-sources},
  note = {Based on 4XMM-DR14 (Webb et al. 2020) via VizieR CDS Strasbourg}
}

License

CC-BY-4.0