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Title: What mechanism produces coherent pulsar radio emission?
Plain: Pulsar radio waves are so bright that huge numbers of electrons must radiate in step (coherently), and the process that synchronizes them is not established.
Precise: Pulsar radio brightness temperatures exceed $1e25\,\mathrm{K}$. Identify the mechanism (plasma instabilities in the outflow, coherent curvature radiation from charge bunches, direct emission from nonstationary pair discharges) that reproduces the mean spectrum (flux ~ nu^-1.6), radius-to-frequency mapping, polarization and the population of luminosities. Answer: a first-principles kinetic model reproducing these observables.
Settled by: A kinetic model that predicts spectra, polarization and luminosity versus spin-down power matching population data from FAST and MeerKAT surveys.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: 2020: kinetic simulations showed that nonstationary pair discharges at the polar cap emit coherent electromagnetic waves, a candidate mechanism now being tested against observed spectra.
Posed since: 1968