---
license: cc-by-4.0
pretty_name: "Chandra X-Ray Source Catalog"
language:
  - en
description: "The Chandra Source Catalog (CSC 2.1) is the definitive catalog of X-ray sources detected by NASA's Chandra X-Ray Observatory, the most powerful X-ray telescope ever built.  The Chandra X-Ray Observato"
task_categories:
  - tabular-classification
  - tabular-regression
tags:
  - space
  - x-ray
  - chandra
  - nasa
  - astronomy
  - open-data
  - tabular-data
  - parquet
size_categories:
  - 10K<n<100K
configs:
  - config_name: default
    data_files:
      - split: train
        path: data/chandra_x_ray_sources.parquet
    default: true
---

# Chandra 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 a [dataset collection](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) on Hugging Face.*

## Dataset description

The Chandra Source Catalog (CSC 2.1) is the definitive catalog of X-ray sources detected by NASA's Chandra X-Ray Observatory, the most powerful X-ray telescope ever built.

The Chandra X-Ray Observatory, launched in 1999, provides the sharpest X-ray images ever achieved, with sub-arcsecond angular resolution. The Chandra Source Catalog is a comprehensive catalog of all X-ray sources detected in Chandra observations, including positions, multi-band photometry (soft, medium, hard, broad, wide bands), hardness ratios for spectral characterization, variability flags, and source extent measurements.

CSC 2.1 covers roughly 560 square degrees of sky and includes sources from over 15,000 individual Chandra observations. The catalog is essential for multi-wavelength studies of active galactic nuclei, X-ray binaries, supernova remnants, galaxy clusters, and stellar coronae.

Chandra's angular resolution of approximately 0.5 arcseconds is achieved by its four nested pairs of grazing-incidence Wolter Type-I mirrors. This resolution makes the Chandra Source Catalog uniquely powerful: it resolves individual X-ray sources in crowded fields such as the Galactic center, globular clusters, and nearby galaxies where other X-ray telescopes would see only confused blends.

## Schema

| Column | Type | Description | Sample | Null % |
|--------|------|-------------|--------|--------|
| `row` | int64 | HEASARC internal row identifier | 7978 | 0.0% |
| `obsid` | int64 | Chandra observation identifier (unique per pointing) | 31425 | 0.0% |
| `status` | string | Observation status: archived, observed, or scheduled | untriggered | 0.0% |
| `name` | string | Chandra observation target name or source designation | IGR J17480-2446 | 0.0% |
| `ra` | float64 | ICRS right ascension in degrees; sub-arcsecond accuracy from Chandra's 0.5" resolution | 267.02013 | 0.2% |
| `dec` | float64 | ICRS declination in degrees | -24.78024 | 0.2% |
| `lii` | float64 | Galactic longitude in degrees | 3.83841844 | 0.2% |
| `bii` | float64 | Galactic latitude in degrees | 1.68626595 | 0.2% |
| `time` | float64 | Observation start time | 56190.3067361111 | 1.8% |
| `detector` | string | Instrument detector used: ACIS-I, ACIS-S, HRC-I, or HRC-S | ACIS-S | 0.0% |
| `grating` | string | Grating configuration: NONE, LETG, or HETG | HETG | 0.0% |
| `exposure` | float64 | Exposure time in kiloseconds | 200000.0 | 0.0% |
| `type` | string | Observation type: GO (guest observer), GTO (guaranteed time), DDT (director's discretionary), CAL (calibration) | TOO | 0.0% |
| `pi` | string | Principal investigator last name | Marshall | 0.0% |
| `cycle` | int64 | Chandra observing cycle number (proposal cycle) | 27 | 0.0% |
| `proposal` | int64 | Proposal title for the observation | 27400375 | 0.0% |
| `public_date` | float64 | Date when the observation data became publicly available | 56576.0 | 4.4% |
| `sequence_number` | int64 | Chandra sequence number for the observation | 402653 | 0.0% |
| `data_mode` | string | Telemetry mode used (e.g., FAINT, VFAINT, CC33_FAINT) | CC_0012C | 0.7% |
| `category` | string | Science category assigned to the observation (e.g., AGN, SNR, STARS) | BH AND NS BINARIES | 0.0% |
| `x_ra_dec` | float64 | Unit vector X component of the pointing direction | -0.90669444668946 | 0.2% |
| `y_ra_dec` | float64 | Unit vector Y component of the pointing direction | -0.0471984200843957 | 0.2% |
| `z_ra_dec` | float64 | Unit vector Z component of the pointing direction | -0.419138985879422 | 0.2% |

## Quick stats

- **28,176** Chandra observations in the master catalog
- Median exposure: **15040.0** ks
- Instruments: **4** detector configurations

## Usage

```python
from datasets import load_dataset

ds = load_dataset("juliensimon/chandra-x-ray-sources", split="train")
df = ds.to_pandas()

# Longest observations
top = df.nlargest(10, "exposure")[["name", "ra", "dec", "exposure", "detector"]]
print(top.to_string())

# Sky coverage map
import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(12, 6))
ax.scatter(df["ra"], df["dec"], s=0.1, alpha=0.2)
ax.set_xlabel("RA (deg)")
ax.set_ylabel("Dec (deg)")
ax.invert_xaxis()
ax.set_title("Chandra Observation Pointings")
plt.tight_layout()
plt.show()

# Detector usage breakdown
df["detector"].value_counts().plot.bar()
plt.title("Chandra Detector Usage")
plt.show()
```

## Data source

https://cxc.cfa.harvard.edu/csc/

## Related datasets

- [juliensimon/erosita-erass1-xray](https://huggingface.co/datasets/juliensimon/erosita-erass1-xray)

- [juliensimon/fermi-4fgl-dr4](https://huggingface.co/datasets/juliensimon/fermi-4fgl-dr4)

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

## Citation

```bibtex
@dataset{chandra_x_ray_sources,
  title = {Chandra X-Ray Source Catalog},
  author = {juliensimon},
  year = {2026},
  url = {https://huggingface.co/datasets/juliensimon/chandra-x-ray-sources},
  publisher = {Hugging Face}
}
```

## License

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