astro-legacy-archive/swift-xrt-cleaned-events

Swift XRT cleaned events

This dataset contains the Swift XRT cleaned photon-counting-mode event file sw00020000001xpcw4po_cl.evt.gz for public observation 00020000001, target GRB041217. The source is sw00020000001xpcw4po_cl.evt.gz, checked 2026-08-30: 47,326 bytes, SHA-256 65c8bd98bd37a184ee584459a25c09e9c0af92b0cc8235eb5071d593a2d3e61c.

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

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/swift-xrt-cleaned-events", "sw00020000001xpcw4po_cl__EVENTS", split="train[:1]")
print(dataset.num_rows, dataset[0]["TIME"], dataset[0]["PI"])

1 125040675.21347176 47

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/swift-xrt-cleaned-events", "sw00020000001xpcw4po_cl__EVENTS.parquet", repo_type="dataset")
print(json.loads(pq.read_schema(path).metadata[b"event_list"])["event_count"])

35

Source structure and decoding

The published table is the source EVENTS binary table: 35 rows and these 11 columns in source order:

source column	FITS form	unit	meaning
TIME	1D	s	TT mission elapsed time, local to the satellite
X, Y	1I	pixel	FK5 J2000 TAN-projected sky pixels
RAWX, RAWY	1I	pixel	raw CCD pixels
DETX, DETY	1I	pixel	focal-plane detector coordinates
PHA	1J	chan	pulse-height channel
PI	1J	chan	pulse-invariant response channel
GRADE	1I	—	XRT event grade
STATUS	16X	—	source 16-bit status field, served as 16 Booleans in stored FITS order

TIME ranges from 125040675.21347176 to 125042131.90997171 s and has 29 distinct values. PHA ranges from 85 to 3319 chan; PI ranges from 21 to 859 chan. xrtcalcpi corrects PI for gain/CTI, temperature, time, position and charge traps using CALDB. Its nominal scale is 10 eV/channel, but its response interpretation remains calibration- and grade-dependent. The source history records xrtscreen grade selection 0--12. No science-band cut was applied: PI=21 corresponds nominally to 0.21 keV, below the common 0.3 keV analysis threshold.

Three complete source companion tables are embedded in the event_list metadata, in HDU order:

• GTI: 2 rows; START 1D s, STOP 1D s.
• BADPIX: 10,326 rows; RAWX 1I pixel, RAWY 1I pixel, Amp 1I, TYPE 1I, YEXTENT I, BADFLAG 16X.
• BIASDIFF: 165 rows; TIME 1D s, ORBIT 1I, SUBIMG 1I, DETXMIN 1I pixel, DETXMAX 1I pixel, DETYMIN 1I pixel, DETYMAX 1I pixel, BIASDIFF 1J chan, BIASDIFF2 1J chan, BIASDIFF4 1J chan, BIASDIFF7 1J chan, BIASDIFF9 1J chan, NEVENTS 1J.

The metadata document is the machine-readable resolver. fields, in source order, gives each event column's description, unit, source dtype, TTYPE, TFORM, TUNIT, scaling, null, display and dimension declarations, served encoding, repeat and bit mapping. auxiliary_tables gives every companion column definition and every value. fits_sources[0].fits_headers carries the complete ordered primary and extension headers. sources records the URL, size, hash and check date. load_dataset retains the served values and types but not this schema metadata; read it with PyArrow as above.

The event header records TIMESYS=TT, TIMEREF=LOCAL, MJDREFI=51910, MJDREFF=0.00074287037, TIMEZERO=0.0, RADECSYS=FK5, EQUINOX=2000.0, OBJECT=GRB041217, OBS_ID=00020000001, DATAMODE=PHOTON, TELESCOP=SWIFT and INSTRUME=XRT.

Scientific caveats

These 35 rows are cleaned events across the full photon-counting window and field. They may include source, background and unrelated field events; they are not 35 source photons. Scientific extraction requires explicit source and background regions.

CLOCKAPP=F means spacecraft clock-drift correction was not applied. Independently, TIMEREF=LOCAL and TASSIGN=SATELLITE mean times are local to the satellite rather than barycentric. TIMEDEL=2.5073 s is the PC frame interval; 35 rows occupy 29 shared frame timestamps. The two GTIs span 1466.725791782 s wall time, with ONTIME=155.452599987 s and EXPOSURE=LIVETIME=154.871121906 s. Current precision timing requires the current Swift clock-correction file for all absolute timing; source-frame timing additionally requires the orbit ephemeris and barycorr.

The file records PROCVER=3.18.01 and CALDBVER=b20171016_u20170922_x20171113_m20180305 (processed in 2018). Current UKSSDC guidance recommends rerunning xrtpipeline from Level 1 rather than treating archived cleaned events as current calibration. This December 2004 observation was within Swift/XRT's early commissioning period and is not representative of later detector calibration or performance. The archive directory also contains unfiltered photon-counting events, two additional cleaned photon-counting products and products for other XRT readout modes; HEASARC states no corpus-wide file or byte total on the archive pages checked.

Event-list 1.1.1 could not represent this source: it permitted at most one auxiliary table, while this file has GTI, BADPIX and BIASDIFF; it also lacked the 16X forms and most explicit-repeat numeric forms used here. Event-list 1.2.0 retains all four tables without dropping, repacking or normalising them. The Parquet artifact has 35 rows and 2,934,650 bytes, SHA-256 b57adba26e44861ea1ef891971ba5374c2832353ef3d2b7eba67a566bb82ba2a.

Rights, credit and citations

No explicit data licence was found. 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.

Archive and reduction guidance: Swift archive and UKSSDC XRT analysis. Please cite Gehrels, N. et al. (2004), “The Swift Gamma-Ray Burst Mission,” The Astrophysical Journal 611, 1005--1020, DOI 10.1086/422091, and Burrows, D. N. et al. (2005), “The Swift X-Ray Telescope,” Space Science Reviews 120, 165--195, DOI 10.1007/s11214-005-5097-2.