StrayCats: A catalog of NuSTAR Stray Light Observations

In addition to being the first focusing hard X-ray space observatory, NuSTAR is also sensitive to sources from 1- to 3-degrees from the optical axis that pass through the telescope structure to shine on the detectors. When a bright source falls into this region of the sky, a characteristic stray light pattern is observed on the detectors and the instrument can be used as a classical collimated instrument. For bright (mostly Galactic) X-ray sources, this provides additional data suitable both for spectroscopy (including above the fiducial 78 keV cutoff caused by the NuSTAR optics) and timing/variability studies. We systematically analyzed the entire NuSTAR archive and identified over 1400 potential stray light observations. Of these we have identified 436 instances where at least one of the NuSTAR telescopes shows evidence for stray light from 78 different X-ray sources. Most of these sources have multiple epochs spanning a variety of source behaviors. We present an overview of the catalog and some of the science highlights, including work done by the Caltech Summer Undergraduate Research Fellows who participated in this work.