Magnetic-Induced Force Noise in LISA Pathfinder Free-Falling Test Masses

LISA Pathfinder was a mission designed to test key technologies required for gravitational wave detection in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime, which corresponds to the measurement band of interest for future space-borne gravitational wave observatories. Magnetically induced forces couple to the test mass motion, introducing a contribution to the relative acceleration noise between the free-falling test masses. In this Letter we present the first complete estimate of this term of the instrument performance model. Our results set the magnetic-induced acceleration noise during the February 2017 noise run of 0.25_{-0.08}^{+0.15}  fm s^{-2}/sqrt[Hz] at 1 mHz and 1.01_{-0.24}^{+0.73}  fm s^{-2}/sqrt[Hz] at 0.1 mHz. We also discuss how the nonstationarities of the interplanetary magnetic field can affect these values during extreme space weather conditions.