Editing X-ray astronomy (section)

===Extrasolar X-ray source astrometry===
{{main|Extrasolar X-ray source astrometry}}
With the initial detection of an extrasolar X-ray source, the first question usually asked is "What is the source?" An extensive search is often made in other wavelengths such as visible or radio for possible coincident objects. Many of the verified X-ray locations still do not have readily discernible sources. X-ray [[astrometry]] becomes a serious concern that results in ever greater demands for finer [[angular resolution]] and [[Radiance|spectral radiance]].

There are inherent difficulties in making X-ray/optical, X-ray/radio, and X-ray/X-ray identifications based solely on positional coincidents, especially with handicaps in making identifications, such as the large uncertainties in positional determinants made from balloons and rockets, poor source separation in the crowded region toward the galactic center, source variability, and the multiplicity of source nomenclature.<ref name=Thomas>{{Cite journal|author=Thomas RM|author2=Davison PJN |title=A comment on X-ray source identifications |journal=Proceedings of the Astronomical Society of Australia|date=1974 |volume=2 |issue=5 |page=290|doi=10.1017/S1323358000013953 |bibcode=1974PASA....2..290T|s2cid=116484669 }}</ref>

X‐ray source counterparts to stars can be identified by calculating the angular separation between source centroids and the position of the star. The maximum allowable separation is a compromise between a larger value to identify as many real matches as possible and a smaller value to minimize the probability of spurious matches. "An adopted matching criterion of 40" finds nearly all possible X‐ray source matches while keeping the probability of any spurious matches in the sample to 3%."<ref name=Gaidos>{{Cite journal|author=Gaidos EJ |title=Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics |date=Nov 1998 |volume=110 |issue=753 |pages=1259–76 |doi=10.1086/316251 |journal=Publ. Astron. Soc. Pac. |bibcode=1998PASP..110.1259G|doi-access=free }}</ref>