Pulsar radio emission and magnetar origin

6 problems

• What mechanism produces coherent pulsar radio emission?

  Contested

  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.

• What triggers magnetar bursts and giant flares?

  Open

  Magnetars sometimes release up to about $10^{46}\,\mathrm{erg}$ in a fraction of a second, possibly when their solid crust cracks under magnetic stress or when twisted magnetic field outside the star suddenly reconnects.

• What are the long-period radio transients?

  Partially resolved

  Radio telescopes have found, mostly since 2022, sources that pulse once every few minutes to hours, far slower than any known pulsar should still emit radio waves.

• How do magnetars acquire fields of $1\mathrm{e}14\ \text{to}\ 1\mathrm{e}15\,\mathrm{G}$?

  Contested

  The field could be inherited from a strongly magnetic parent star or amplified by a dynamo (stirring motions that regenerate magnetic field) during the collapse.

• Do polar-cap pair discharges reproduce observed pulsar radio spectra?

  Open

  Bursts of electron-positron pair creation above the magnetic poles may generate the radio waves directly; whether they produce the right brightness and spectrum is untested.

• How does a pulsar wind turn magnetic energy into fast particles?

  Partially resolved

  Close to the pulsar the outflowing wind carries its energy almost entirely as magnetic field, yet nebulae such as the Crab require that most of it be in fast particles by the time the wind reaches them.