Searching for Persistent Gamma-ray Emission from Galactic Magnetars with 16 Years of Fermi-LAT Data

Magnetars are young, highly magnetized neutron stars whose persistent spectral energy distribution peaks in the X-ray band and shows an upturn above 10 keV observed up to several tens of keV. A notable example is 1RXS J170849-400910, which shows a spectrum consisting of blackbody radiation, resonant up-scattering, and an additional component above 10 keV whose origin and cut-off remain uncertain. Their strong magnetic fields are expected to produce quantum electrodynamics (QED) effects such as photon splitting, quantum synchrotron and resonant Compton scattering, and single photon magnetic electron-positron production. Determining the cut-off of magnetars' persistent emission is crucial for informing neutron star emission models and constraining QED processes in magnetospheres. In 2017, Li et al. analyzed 6 years of Fermi-LAT data from 20 magnetars, deriving upper limits of 10^-12 to 10^-11 erg s^-1 cm^-2 in the 0.1-10 GeV energy band. We present preliminary results on an updated search of magnetar emission above 100 MeV using 16 years of Fermi-LAT data to investigate gamma-ray emission from magnetars. This expanded dataset allows us to place tighter constraints on persistent magnetar emission and provide insights on detectability for future MeV gamma-ray missions, like COSI.