# Open Group Seminar: Jens Mahlmann (Princeton University)

11:00 am–12:00 pm ERC 583

Host: Siddhartha Gupta

### Jens Mahlmann (Princeton University) "3D dynamics of strongly twisted relativistic magnetospheres: Kinking flux tubes and global eruptions"

The origin of the various outbursts of hard X-rays from magnetars, highly magnetized neutron stars, is still unknown. We identify instabilities in relativistic magnetospheres that explain a range of X-ray flares. Crustal surface motions can twist the magnetar magnetosphere by shifting the frozen-in footpoints of magnetic field lines in current-carrying flux bundles. Axisymmetric (2D) magnetospheres show catastrophic lateral instabilities triggered by a critical footpoint displacement of $\psi_{\rm crit}\approx\pi$. Our new 3D localized twist models capture important non-axisymmetric dynamics of twisted force-free flux bundles in dipolar magnetospheres. Besides the well-established lateral eruption (global eruption), such 3D structures can develop helical, kink-like dynamics and dissipate energy locally (confined eruptions). Up to $25\%$ of the induced twist energy is dissipated and available to power X-ray flares, with most of our models showing an energy release in the range of the most common X-ray outbursts, $\lesssim 10^{43}$erg. Powerful eruptions occur when significant energy builds up deeply buried in the dipole magnetosphere. Less energetic outbursts likely accompany powerful flares due to intermittent instabilities of a continuously twisting flux tube. Upon reaching a critical state, global eruptions produce the necessary Poynting-flux-dominated outflows required by far-away fast radio burst models to produce coherent radio emission via magnetic reconnection or shocks.

Seminars

Dec 16