astro-legacy-archive/asca-gis2-screened-events

ASCA GIS2 screened events

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

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This dataset contains one ASCA GIS2 revision-2 screened PH-mode, medium-telemetry-rate event file for GX5-1. It is the index-002 GIS2 medium-rate sibling under archive sequence path 10001000, named ad10001000g200270m.evt.gz. The sequence number comes from the archive path and filename; the FITS headers contain no OBS_ID keyword. The sequence's screened directory contains nine siblings: two GIS2, two GIS3, three SIS0 and two SIS1 files across instrument, telemetry-rate, mode and index combinations. This dataset serves only this one archive-natural file.

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/asca-gis2-screened-events", "ad10001000g200270m__EVENTS", split="train", streaming=True)
print(next(iter(dataset))["TIME"])

9901

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/asca-gis2-screened-events", "ad10001000g200270m__EVENTS.parquet", repo_type="dataset")
print(json.loads(pq.read_metadata(path).metadata[b"event_list"])["schema"])

astro-legacy-archive/event-list

Source and structure

Canonical source, checked 2026-08-30:

https://heasarc.gsfc.nasa.gov/FTP/asca/data/rev2/10001000/screened/ad10001000g200270m.evt.gz

Size: 153223 bytes

SHA-256: b17e665038281bd48c55a9f92bd5a613f8d9e05f104097e3886bd79b3f255f04

The artifact mirrors all 9901 EVENTS rows and the source-named two-row STDGTI companion. EVENTS has these 12 source columns in source order:

TIME ranges from 24291977.61419783 to 24336073.554726087 s and every TIME is distinct. PHA ranges from 20 to 1005 channel and PI from 18 to

1. 1.STDGTI contains START and STOP, both 1D seconds, in two rows. The intervals sum to 640.1510407142341 s within TSTART=24291977.60916975 and TSTOP=24336073.60916975, an elapsed span of 44096 s. Header ONTIME, LIVETIME and EXPOSURE are all 640.1510407142341 s; DEADC is absent. The retained event rate is 15.466662350424647 events/s, close to the official 16 events/s/sensor GIS PH medium-rate telemetry limit and above the regime where the official guide says GIS deadtime matters (much greater than 10 events/s). Counts and rates derived directly from this event table are neither electronic-deadtime nor telemetry-loss corrected.

Every Parquet file embeds an event-list 1.2.0 JSON document under the event_list metadata key. fields records every source TTYPE, TFORM, TUNIT, scaling, null declaration, served encoding and bit mapping; auxiliary_tables carries every STDGTI row; and fits_sources carries the complete source headers. This is the precise machine-readable route for reconstructing the source structure. event-list 1.1.1 did not fit because the source names its companion STDGTI and retains explicit 1D/1I TFORM spellings. event-list 1.2.0 preserves those identifiers, forms, rows and the scalar MJDREF verbatim.

Interpretation and caveats

This is a standard-screened full GIS2 field, not a source-region extraction or background subtraction. RADECSYS=FK5 and EQUINOX=2000. Spectroscopy requires source and background regions, the appropriate GIS RMF, a region-specific ARF, and deadtime/telemetry treatment. Raw PHA is not a calibrated energy measurement, and PI is not energy by itself. See the GIS issues and telemetry limits and spectral-response guidance.

Time uses the source's TIMESYS='1993.0' epoch, TIMEREF=LOCAL, scalar MJDREF=48988.0, TIMEZERO=0.0, and TIMEDEL=0.5 s. The artifact carries the scalar epoch without inventing MJDREFI/MJDREFF. 1993.0 is ASCA's mission epoch label, not a modern TT or TDB declaration, and TIMEDEL alone does not determine absolute arrival time. ASCA time is defined as ASCATIME = TAI - 27 s; UTC diverged from it as leap seconds were introduced after launch. Precision absolute, geocentric, or barycentric work requires the ASCA timeconv path with orbit and Earth-ephemeris inputs and leap-second handling. Use timeconv v1.53 or later; it corrected the earlier omission of post-launch leap seconds. These table times remain local and non-barycentric. See the ASCA temporal-analysis guide and the timeconv v1.53 correction notice.

Citation, licence and credit

Cite Tanaka, Y., Inoue, H. and Holt, S. S. 1994, Publications of the Astronomical Society of Japan 46, L37--L41.

No explicit data licence was found. HEASARC states:

HEASARC materials are all available freely for your use.

This is a free-use statement, not a named or formal licence. 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.

Errata and requests

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