Status and Version History

• New or updated stacks in CSC 2.2 were adjusted in stack astrometry with a slightly more accurate weighting formula in the weighted least squares calculation. The fixes includes changing \(weight = \frac{1}{x_{\mathrm{err}} y_{\mathrm{err}}}\) which was previously calculated as \(weight = \frac{y_{\mathrm{err}}}{x_{\mathrm{err}}}\). Another fix is in the summation of the weights, \(\sum_{i}{w_{i} r_{i}^{2}}\) which was previously calculated as \(\sum_{i}{w_{i} r_{i}}\). Both changes have little impact on stack astrometry and only improve the calculation for current runs.
• Region event lists (regevt3) and exposure maps (regexp3) are now provided for highly extended (convex hull) detections at the per-observation detection and stack detection levels.
• For all regimg3 files, recomputed the size of the data product represents to be the area of the background region. This is now consistent with the spatial area represented with the regevt3 files.
• For all fov3 and sens3 files, fixed the RA/DEC_STK keywords to be correctly calculated with the corrected stack astrometry.
• A new photdraws3 data product is provided at the Master Source, stack, and per-observation levels, containing aperture photometry draws for photon flux, source counts, source rate, and energy flux.

Release 2.1.1 of the Chandra Source Catalog resolves four issues detected in release 2.1.

1. Source names in the Master Sources Table for 400 sources that had been previously identified and published in CSC 2.0 were incorrect in CSC 2.1. These source names are corrected in CSC 2.1.1. Most of the affected sources were located in the vicinity of SNR E0102-72.3. For a list of corrected source names see here.
2. Some properties (primarily aperture photometry properties and properties derived from them, such as hardness ratios and temporal variability) for approximately 7,000 sources in the Master Sources Table and detections in the Stacked Observation Detections Table may be incorrectly set to NULL in some energy bands in CSC 2.1. This occurs for master sources and stacked observation detections for which one or more ACIS observations has energy bands truncated by onboard PHA filters. These source properties are correctly populated in CSC 2.1.1. Most of the affected sources were located in the vicinity of Sgr A*.
3. For highly extended (convex hull) detections listed in the Per-Observation Detections Table, the relative astrometry offsets deltax and deltay were incorrectly reported in pixels rather than arcseconds. These properties are correctly reported in arcseconds in CSC 2.1.1.
4. The individual observation manual astrometry flag listed in the Per-Observation Detections Table may have been incorrectly set to FALSE if the detection was originally identified in CSC 2.0. These flag is correctly set in CSC 2.1.1.

The release of the Chandra Source Catalog (CSC release 2.1) includes data for 407,806 unique sources and 1,304,376 individual observation detections of ACIS and HRC public imaging observations through the end of 2021. There are approximately 1700 columns of tabular data with pertinent information about each source across 5 bands (broad, hard, medium, soft, and ultra-soft) for ACIS and 1 band (wide) for HRC (see the energy-bands page for the definition of these bands), and 40 data products per source. The total size of the archive is close to 44 TB.