A mega-electron volt emission line in the spectrum of a gamma-ray burst.

A long gamma-ray burst (GRB) is observed when the collapse of a massive star produces an ultrarelativistic outflow pointed toward Earth. Gamma-ray spectra of long GRBs are smooth, typically modeled by joint power-law segments describing a continuum, with no detected spectral lines. We report a significant (>6σ) narrow emission feature at ~10 mega-electron volts (MeV) in the spectrum of the bright GRB 221009A.

Black hole spin-orbit misalignment in the x-ray binary MAXI J1820+070.

The observational signatures of black holes in x-ray binary systems depend on their masses, spins, accretion rate, and the misalignment angle between the black hole spin and the orbital angular momentum. We present optical polarimetric observations of the black hole x-ray binary MAXI J1820+070, from which we constrain the position angle of the binary orbital. Combining this with previous determinations of the relativistic jet orientation, which traces the black hole spin, and the inclination of the orbit, we determine a lower limit of 40° on the spin-orbit misalignment angle.

Electromagnetic counterparts of gravitational wave sources at the Very Large Telescope.

Andrew J. Levan and Peter G. Jonker discuss, on behalf of the Electromagnetic counterparts of gravitational wave sources at the Very Large Telescope (ENGRAVE), how the collaboration was formed and what its goals are in the era of multi-messenger astronomy.

A rapidly changing jet orientation in the stellar-mass black-hole system V404 Cygni.

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow, although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood.