astro-legacy-archive/cosb-photon-events

COS-B photon events

python -m venv .venv && .venv/bin/pip install datasets huggingface_hub pyarrow

[image]

This dataset contains the archive-natural event products for all 65 COS-B pointings served by HEASARC. Each configuration is one source event file; pointing 37, targeted on M31, is used in the examples below. Cite H. A. Meyer-Hasselwander et al. (1986), Explanatory Supplement to the COS-B Final Database, Proc. Cosmic Ray Conf., La Jolla, ESA Publication. No explicit dataset licence was found.

COS-B's long operational life included long-term sensitivity degradation and short-term performance disturbances. The archive incorporates instrumental background variation and sensitivity, but its statistical and systematic uncertainties must be considered in analysis.

The 65 configurations contain 208,750 served EVENTS rows in total. The source FITS HISTORY states, “During the mission, 208751 photons were retained.” These totals differ by one event; the source material does not resolve the discrepancy. Pointing 37 contains 1,685 rows. Nine angular 1I columns use TSCAL=0.1, and the three barycentric 1J columns use TSCAL=1e-6: the served values are TSCAL-applied physical float64, while the original TFORM/TSCAL cards remain embedded for exact reconstruction. ALLGTI and TSI are source-named companion tables embedded as JSON values in the Parquet event_list.auxiliary_tables metadata, rather than separate Hugging Face rows or configurations. Their START and STOP arrays are equal, as the source states. tools/event_list.py provides read_meta() access and to_fits() reconstruction.

RA and DEC are FK4 B1950 coordinates (EQUINOX=1950). X and Y are HEASARC archive-generated TAN pseudo-image pixels derived from sky position; DETX and DETY are corrected detector coordinates. The pointing-37 artifact preserves the measured X range -273--588 and Y range -88--583, including values outside the source header's nominal TLMIN/TLMAX=1/512; it never clips them.

The pointing-37 event energy range is 44--8,072 MeV. HEASARC's database account uses 50 MeV--5 GeV, the current mission page gives approximately 30 MeV--5 GeV, and the archive README gives 50--7,800 MeV for the derived map bands. PAIRCLAS classifies electron-positron pairs in the two spark-chamber views, ECLASSPH is photon edit class 1--3, and FOVCLASS is the Earth-horizon field-of-view class. The supplement documents PAIRCLAS 2, 22 and 3; pointing 37 also contains class 4, one of the extra archive classes HEASARC retained when energy and coordinates passed its integrity checks; the source does not define code 4. These mission-era quality fields must be interpreted with the changing response, sensitivity, and instrumental background described above.

TIME is absolute MJD with TIMEREF=LOCAL and CLOCKAPP=T. In pointing 37, the 106 source-named ALLGTI intervals are distributed across a 37.0536-day observation window and sum to 21.4756 days of accepted time.

Source pin

Observed 2026-09-06: the HEASARC raw directory serves 65 .evt files totalling 14,535,360 bytes. Each artifact embeds its source filename, URL, byte size and SHA-256. Pointing 37 is `cb_0023n42p37.evt`, 141,120 bytes, SHA-256 a4f53833abd76b1b7bda63840310a3e5f316ee585db66ef68d60db7e8a5cd8e4.

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/cosb-photon-events", "cb_0023n42p37__EVENTS", split="train[:1]")
print(dataset[0]["TIME"])

43853.52268210428

import json, pyarrow.parquet as pq
from huggingface_hub import hf_hub_download
path = hf_hub_download("astro-legacy-archive/cosb-photon-events", "cb_0023n42p37__EVENTS.parquet", repo_type="dataset")
metadata = json.loads(pq.read_metadata(path).metadata[b"event_list"])
print(metadata["schema"], [(table["extname"], table["representation"], table["row_count"]) for table in metadata["auxiliary_tables"]])

astro-legacy-archive/event-list [('ALLGTI', 'metadata-embedded-fits-bintable', 106), ('TSI', 'metadata-embedded-fits-bintable', 106)]

HEASARC states that its materials are freely available for use and requests the acknowledgement below.

This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC.

Citation

Please cite this dataset:

@misc{https://doi.org/10.57967/hf/10406,
  doi = {10.57967/hf/10406},
  url = {https://huggingface.co/datasets/astro-legacy-archive/cosb-photon-events},
  author = {{Astro Legacy Archive}},
  title = {cosb-photon-events},
  publisher = {Hugging Face},
  year = {2026}
}

The initial public release is Hub revision `dac4c5b11e4c73b5a6f1c9e73b96721e4aa5bb32`.

Errata and requests

Report corrections or dataset requests in the dataset's Community tab.