# # Program information file # PROGRAM_ID 2021A019 PROGRAM_TITLE Disentangling radiating particle properties and jet physics from M87 multi-wavelength variability PROGRAM_INV1 Steven Willner PROGRAM_INV2 Mark Gurwell PROGRAM_INV3 Joseph Hora PROGRAM_INV4 Sera Markoff PROGRAM_INV5 Joseph Neilsen PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG Jets from active galactic nuclei play a key role in galactic evolution. While some of the basic dynamical properties of jets are understood, the location and mechanism of particle acceleration are unknown. As one consequence, the ~10% error in the M87 black hole mass determination by the Event Horizon Telescope is dominated by such uncertainties. We propose novel observations exploiting jet variability at millimeter and infrared wavelengths to discriminate between the three primary scenarios: 1] thermal particles dominating the inner jets, 2] nonthermal particles dominating the inner jets, and 3] thermal particles at the base, then nonthermally accelerated perhaps 100 gravitational radii from the black hole. By monitoring the inner jet emission of M87 at 3.8 microns and the jet base emission with the SMA at 230 GHz, we will determine whether there is correlated variability, and if so, whether there is a time lag. Whatever mechanism we find for M87 likely applies to many AGN jets. This is a continuation of a project initially granted time in 2020B. PROGRAM_ABSTRACT_END