juliensimon/4xmm-dr14-xray-sources

---
license: cc-by-4.0
pretty_name: "4XMM-DR14 Serendipitous X-ray Source Catalog"
language:
- en
description: "The largest X-ray source catalog: ~630K unique sources from ESA XMM-Newton serendipitous detections. Currently DR12s from VizieR CDS Strasbourg."
task_categories:
- tabular-classification
tags:
- space
- x-ray
- xmm-newton
- esa
- astronomy
- serendipitous-survey
- high-energy
- open-data
- tabular-data
- parquet
size_categories:
- 100K<n<1M
configs:
- config_name: default
data_files:
- split: train
path: data/4xmm_dr14_xray_sources.parquet
default: true
---

# 4XMM-DR14 Serendipitous X-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 the [Astronomy Datasets](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) 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

```python
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](https://www.cosmos.esa.int/web/xmm-newton/xsa#download)
(Webb N.A. et al., 2020, A&A, 641, A136), compiled by the XMM-Newton Survey Science Centre consortium.
Accessed via [VizieR](https://vizier.cds.unistra.fr/) (catalog IX/68), CDS Strasbourg.

## Update schedule

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

## Related datasets

- [chandra-x-ray-sources](https://huggingface.co/datasets/juliensimon/chandra-x-ray-sources) -- Chandra Source Catalog
- [erosita-erass1-xray](https://huggingface.co/datasets/juliensimon/erosita-erass1-xray) -- eROSITA eRASS1 X-ray Survey
- [swift-bat-hard-xray-survey](https://huggingface.co/datasets/juliensimon/swift-bat-hard-xray-survey) -- Swift BAT Hard X-ray Survey

## Pipeline

Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)

## Support

If you find this dataset useful, please give it a ❤️ on the [dataset page](https://huggingface.co/datasets/juliensimon/4xmm-dr14-xray-sources) and share feedback in the Community tab! Also consider giving a ⭐️ to the [space-datasets](https://github.com/juliensimon/space-datasets) repo.

## Citation

```bibtex
@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](https://creativecommons.org/licenses/by/4.0/)