An Update on Chandra Target and Source Names
Acknowledgement: Arnold Rots & the Chandra Data Archive
Last year, as the culmination of a two year long project, over 5000 target names of Chandra archival observations taken through 2016 were replaced with alternative names that resolve into sky coordinates. Resolvable names optimize search and discovery through all Chandra public interfaces. This mass name migration occurred prior to the start of the fifth general reprocessing of the Chandra archive (Repro-V), which recently concluded. Repetition is the key to building good habits, so this year we took another step in the direction of a sustainable, incremental and unobtrusive improvement of the archive by selecting and changing bad target names among observations obtained during 2017 and among all Chandra Cool Targets (CCTs) observed so far.
This is the first occurrence of future annual migrations that will seek out and replace less than optimal target names of archival observations with the goal of making the Chandra Data Archive asymptotically fully transparent and resolvable. But we know that the key to a more open and usable archive as complex and rich as the Chandra archive lies with our community: for this reason, starting with Cycle 22, we have asked all observers of approved targets to weigh in on possible alternative names for their sources and to allow us to change them before the targets are observed. This continuous effort has already allowed us to significantly reduce the number of bad target names that will need to be substituted in future annual migrations. So, if you are an observer and took some time to review your target names, thank you! We at the Chandra Archive and the future cohorts of X-ray astronomers that will keep using your Chandra observations for great science are in debt to you! A multitude of small actions dramatically enhances the scientific legacy of the mission by making its data permanently easier to find and use.
The same need for rigor that inspired the clean-up of bad target names should also guide scientists when naming new X-ray sources discovered in their observations. In an agreement with the IAU Clearing House, the Chandra Data Archive defined at the beginning of the mission a set of rules to correctly name new Chandra sources. This convention requires the names of sources discovered in Chandra observations to be the result of the union of the common prefix CXOU which stands for Chandra X-ray Observatory Unregistered and a positional segment based on the sexagesimal representation of the J2000 coordinates of the source: Jhhmmss.s+ddmmss. Please keep in mind that the number of digits in the positional subsection of the source names is fixed and that the coordinates need to be truncated, not approximated or rounded, as per the universal rule that applies to all source acronyms registered with the IAU Clearing House. All users are, of course, also free to register their own source name acronym with the IAU Clearing House of Source Designations, especially if they are presenting a significant list or catalog of sources.