Automated Detection of Transient, Solar X-ray Sources with NuSTAR

The Nuclear Spectroscopic Telescope ARray (NuSTAR) is a focusing high-energy x-ray telescope orbiting the Earth. NuSTAR detectors consist of arrays of pixels and are capable of measuring the time, energy, and position of each measured photon. Each photon is recorded as an individual event, providing high flexibility in the analysis process. While designed as an astrophysical instrument, the increased sensitivity of NuSTAR offers a unique view of the solar disk, particularly during "quiet Sun" conditions, through direct imaging of hard x-rays greater than 3 keV. However, observing the Sun renders one of the telescope's tracking cameras unusable, resulting in varying positional uncertainty in the measured data that can change mid-observation and presents a unique challenge for the analysis. This presentation introduces a method with user-customizable parameters for automatically detecting solar flares and other transient brightenings observed by NuSTAR. The flare detection methodology begins by binning the individual pixels into larger regions that we term "macropixels," which are then scanned using an algorithm adapted from Berghmans and Clette (1999) to identify areas of heightened photon count rates on a macropixel-by-macropixel basis. Bright macropixels are then grouped based on spatial and temporal connectivity to reconstruct the observed events. Identified events are further categorized through consideration of their physical extent, time evolution, and NuSTAR-specific measurements such as instrument live time and active tracking cameras. These categories organize the observed events and separates flare-like events from artificial "brightenings" which result from mid-observation changes in the positional uncertainty. Preliminary results have been verified against observations made by the Atmospheric Imaging Assembly from the Solar Dynamics Observatory, showing that flares and other transient brightenings can be confidently identified with NuSTAR.