X-ray Transient Candidate Database using a Custom Pipeline on the Chandra Data Archive

📄 Description of the file final_candidates_catalogue_2026_clean_with_suffixes.csv

This catalogue contains transient candidate detections identified in the Chandra X-ray archive using a custom pipeline (including the novel CuDiDi method). Each row corresponds to one candidate event. The candidates are named using the convention:

XT YYMMDD[a-z],
where YYMMDD represents the date of the observation, and the optional lowercase letter (a, b, c, …) distinguishes multiple candidates from the same observation.

The table includes the following columns:

🔢 General Columns

• CANDIDATE:
  Name of the candidate in the format XT YYMMDD, with an optional alphabetical suffix (e.g., XT 230615b) if multiple candidates were found in the same observation.

• OBSID:
  Chandra Observation ID in which the candidate was found.

• SOURCE:
  Internal source number within the observation (from source detection).

• RA / DEC:
  Right Ascension and Declination of the candidate (J2000 coordinates).

🚩 Diagnostic Flags (Boolean)

These flags help assess the reliability of each candidate and identify potential artefacts or known sources. A value of True indicates that the corresponding condition applies:

• non_unique:
  True if the transient is matched with a source detected at low significance in other Chandra observations (sources detected at >3σ in more than one observation are already excluded).

• snr_match:
  True if the candidate falls within an observation known to contain a Galactic supernova remnant (e.g., Cassiopeia A, Tycho), based on cross-matching with SNR catalogs.

• extended_fov:
  True if the source lies within or near an extended structure (e.g., diffuse Galactic emission) identified by manual inspection of the field of view.

• readout_streak:
  True if the source overlaps with a known instrumental readout streak, often caused by bright sources like Cyg X-1.

• edge_affected:
  True if the detected source region is only partially covered by the detector due to dithering, which may result in unreliable flux or light curve measurements.

• bkg_correlated:
  True if the source light curve is strongly correlated (Pearson coefficient > 0.15) with the background during the T90 interval, indicating likely background flaring.

• start_or_end:
  True if the start (T5) or end (T95) of the transient lies within the first or last 5% of the observation. Such events may be truncated by the observational window.

Of 1420 candidates, 765 have no flags set to true and are considered the 'golden sample'.