MechE PhD Prospectus Defense: Anika Dujakovich

TITLE: CHARACTERIZING THE SOURCES OF MAGNETOSPHERIC SOFT X-RAY EMISSIONS OBSERVED WITH THE NEUTRON STAR INTERIOR COMPOSITION EXPLORER

ABSTRACT: The Neutron Star Interior Composition Explorer (NICER), an X-ray telescope aboard the International Space Station (ISS), is primarily designed to capture X-ray emissions from distant astrophysical targets. However, as its field-of-view passes through Earth's magnetosphere, NICER also detects local magnetospheric emissions. These emissions are proposed to originate from either low-altitude auroral emission, excitation and fluorescing of outflowing ions, or solar wind charge-exchange. Therefore, this research is valuable for understanding the complex interaction between the solar wind and Earth. To explore these X-ray emissions, three paths of investigation are being pursued. First, a case study was conducted, revealing a signal with distinct spectral lines near the K-alpha lines of oxygen (0.537 keV) and nitrogen (0.404 keV). Following thorough analysis of spatial, temporal, and energy signatures, findings suggest the possibility of both photoionization and auroral emissions, with evidence favoring auroral processes. Second, to further substantiate these initial results, a statistical study with a much larger, year-long dataset of NICER observations will explore correlations between magnetospheric activity and X-ray emissions. By grouping observations based on the presence or absence of these emissions, the study aims to discern NICER’s pointing locations—specifically through the cusp region and auroral oval—while simultaneously accounting for geomagnetic activity and substorm disturbances. Third, a directed measurement approach involving a northern cusp altitude variation observation will examine emissions resulting from local mechanisms in both high (8 Earth radii) and low (2 Earth radii) altitude northern cusp regions. This opportunity to customize NICER observations to specific magnetospheric regions will provide an unprecedented dataset, enabling a more direct and conclusive investigation into the origins and characteristics of these non-astrophysical X-ray emissions. Additional avenues being explored for future work include a storm-time analysis using NICER and a study of region-specific data from the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission.

COMMITTEE: ADVISOR/CHAIR Professor Brian Walsh, ME/ECE; Professor J. Gregory McDaniel, ME/MSE; Professor John Semeter, ECE; Gonzalo Cucho-Padin (Catholic University of America, NASA Goddard Space Flight Center)