The NuSTAR Serendipitous Survey and Archival X-ray Data

The Nuclear Spectroscopic Telescope Array (NuSTAR) provides an improvement in sensitivity at energies above 10 keV by two orders of magnitude over non-focusing satellites, making it possible to probe deeper into the Galaxy and Universe. Lansbury and collaborators recently completed a catalog of 497 sources serendipitously detected in the 3-24 keV band using 13 square degrees of NuSTAR coverage. With NuSTAR alone, the "serendips" have error circles with radii of 14-22 arcseconds, which is not accurate enough to identify optical or near-IR counterparts that would allow the sources to be classified. Thus, X-ray data, including catalogs and archival data, have been used extensively to classify the NuSTAR serendips. In some cases, the catalogs provide immediate source classification, while in other cases, the improved positions allow for classification via follow-up ground-based optical spectroscopy. In this talk, we describe the procedures that have been used to classify a large percentage of the serendips, highlighting the use of the X-ray catalogs and archives. We also describe the scientific results, which include new information about populations of Active Galactic Nuclei as well as Galactic sources such as High-Mass X-ray Binaries.