Origin of fast radio bursts

6 problems

• Do all fast radio burst sources eventually repeat?

  Open

  A few sources flash again and again while most have been seen once; they may be two kinds of object or one kind seen at different activity levels.

• Do FRBs form inside neutron-star magnetospheres or in outer shocks?

  Partially resolved

  The radio flash could be made close to the neutron star, inside its cloud of magnetic field and plasma (the magnetosphere), or far out where an ejected shell hits surrounding gas.

• How do FRB sources arise in old stellar populations?

  Open

  Some bursts come from a globular cluster (a ball of stars about $10^{10}\,\mathrm{years}$ old) or from galaxies that stopped forming stars long ago, where newborn magnetars should be absent.

• Origin of periodic activity windows in repeating FRB sources

  Open

  Some repeating sources are active only in windows that recur every 16 or about 160 days, and the clock behind this is unknown.

• What powers the persistent radio sources around some repeating FRBs?

  Open

  A few repeating FRB sources lie inside a compact, steady radio glow and very strongly magnetized gas, which could be a nebula inflated by a young magnetar or the outflow of an accreting black hole.

• Which astrophysical objects produce fast radio bursts?

  Contested

  One magnetar in our own galaxy (a neutron star with a magnetic field of about $2 \times 10^{14}\ \mathrm{G}$) has emitted an FRB-like burst, but it is unknown whether magnetars make all FRBs. Bursts also come from an old star cluster and from dead galaxies, where young magnetars should be rare.