Gamma-ray burst central engines and jets

7 problems

• Millisecond magnetar or accreting black hole as GRB engine?

  Contested

  The engine could be a fast-spinning, highly magnetized neutron star or a newborn black hole swallowing a disk; each leaves different marks in the X-ray afterglow.

• What are the fast X-ray transients found by Einstein Probe?

  Open

  Since 2024 the Einstein Probe satellite has found many short X-ray flashes from distant galaxies, some with no gamma rays; they may be gamma-ray bursts seen from the side, weaker jets, or something new.

• Nature of the repeating gamma-ray burst GRB 250702B

  Open

  In July 2025 a gamma-ray source in a distant galaxy, seen as it was roughly 8 billion years ago, flared three times over several hours, unlike any known burst.

• Are GRB jets dominated by magnetic energy or hot matter?

  Contested

  The jet may carry its energy mainly as magnetic field or as hot gas and light; the two pictures predict different signals.

• Why do some compact-binary mergers produce long gamma-ray bursts?

  Open

  Long bursts are usually linked to collapsing massive stars, but GRB 060614 in 2006 showed no supernova, and two long bursts in 2021 and 2023 were followed by kilonovae, the glow of radioactive debris from neutron-star mergers.

• What radiation mechanism produces GRB prompt gamma-ray spectra?

  Contested

  The first seconds of gamma rays have a spectral shape that neither the glow of hot gas nor electrons spiraling in magnetic fields (synchrotron radiation) reproduces cleanly.

• What emits the TeV photons in gamma-ray burst afterglows?

  Contested

  Some bursts emit photons above $1e12\,\mathrm{eV}$ for hours after the explosion, more energetic than electrons spiraling in the shock's magnetic field are thought able to make.