astro-legacy-archive/heao-1-a2-spectrum-backgrounds

HEAO-1 A2 Spectrum Backgrounds

The HEAO-1 A2 spec_back directory serves 1,506 .bck and 36 .alt pointed-phase files from the MED, HED-1 and HED-3 detectors.

Use

from datasets import load_dataset

ds = load_dataset("astro-legacy-archive/heao-1-a2-spectrum-backgrounds", "a2_h1l_1058s084_po.bck", split="train")
row = ds[0]
print(row["CHANNEL"], row["COUNTS"])

1 0

The example configuration is a2_h1l_1058s084_po.bck. Configuration names are the source filename stems. The complete configuration inventory is in the card metadata above.

import json, re, pyarrow.parquet as pq
from huggingface_hub import hf_hub_download; source = hf_hub_download("astro-legacy-archive/heao-1-a2-spectra", "a2_h1l_2a0343s532_p.pha.parquet", repo_type="dataset")
source_header = json.loads(pq.read_metadata(source).metadata[b"spectrum"])["fits"]["member_header"]; background = re.search(r"^BACKFILE\s*=\s*\'?([^\'/]+)", source_header, re.M).group(1).strip()
path = hf_hub_download("astro-legacy-archive/heao-1-a2-spectrum-backgrounds", f"{background}.parquet", repo_type="dataset"); header = json.loads(pq.read_metadata(path).metadata[b"spectrum"])["fits"]["member_header"]
print(background, {key: re.search(rf"^{key}\s*=\s*\'?([^\'/]+)", header, re.M).group(1).strip() for key in ("DETNAM", "EXPOSURE", "BACKFILE")})

a2_h1l_1058s084_po.bck {'DETNAM': 'HED-1l', 'EXPOSURE': '7529.299805', 'BACKFILE': 'NONE'}

Install the baseline readers with python -m venv .venv && .venv/bin/pip install datasets pyarrow huggingface_hub.

Records and fields

Every SPECTRUM table has 63 source rows and exactly the columns CHANNEL (FITS I, no unit) and COUNTS (FITS J, unit count).

There are 1,542 configurations and 97,146 Parquet rows. Source row order is retained. Units, dtypes, FITS declarations, complete logical primary/member headers, source URL, served byte size and SHA-256 are attached to each artifact. Coordinate or energy axes that exist only in FITS header metadata remain there.

These 1,542 files are byte-identical to the same-named .bck and .alt files also served under spectra/; this dataset preserves HEASARC's separate spec_back/ surface. The A2SPECTRA table records the background associated with each on-axis _p or wobbling/off-source _po source spectrum. Use that association rather than inferring a pairing from filename similarity; HEASARC warns that the automatically associated background was not always the best available and exposes additional files through the A2SPECBACK table. Not every associated source-spectrum set is complete, and _po spectra can contain background, nearby sources, or the target at low collimator response.

The source says these files were derived from blank-sky pointings, mostly observations made by A2 in the opposite sky direction while A1 was the primary pointing experiment. The six source detector identifiers are MEDs, MEDl, HED-1s, HED-1l, HED-3s and HED-3l; read DETNAM rather than decoding the filename. HEASARC documents no separate meaning for the .alt suffix, so select alternate files through A2SPECBACK rather than treating the suffix as a scientific classification.

Each table stores accumulated integer COUNTS by detector CHANNEL. The source declares CHANTYPE=UNKNOWN, DETCHANS=63, TLMIN1=1, TLMAX1=63, HDUCLAS3=COUNT and POISSERR=T; EXPOSURE, AREASCAL and BACKSCAL retain the source exposure and scaling values. The headers also say HDUCLAS2=NET and BACKFILE=NONE, despite HEASARC serving the files as background products. A background artifact alone therefore does not establish a valid source pairing or subtraction. The cited HEASARC product pages publish no background-systematic uncertainty.

A response matrix is required to map detector channel to energy. Use the source spectrum's A2SPECTRA association; the database documents 2--10 keV for MED and 8--15 keV for HED-1/HED-3 count-rate summaries. The matching source spectrum and response products are in `heao-1-a2-spectra`.

Source, rights, and rebuilding

Canonical A2 product documentation: https://heasarc.gsfc.nasa.gov/docs/heao1/archive/heao1_a2.html

HEASARC states: “HEASARC materials are all available freely for your use.”

HEASARC requests: “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.”

Rebuild this product with python tools/make_heao1_a2_spectra.py --out data --source <source-directory> --provenance-commit <commit> --product heao-1-a2-spectrum-backgrounds.

Errata and requests

Please report corrections through the Hugging Face Community tab. A free Hugging Face account is enough to participate.