Lorenzo Sironi

Plasmoids in relativistic reconnection, from birth to adulthood: first they grow, then they go

Blobs, or quasi-spherical emission regions containing relativistic particles and magnetic fields, are often assumed ad hoc in emission models of relativistic astrophysical jets, yet their physical origin is still not well understood. Here, we employ a suite of large-scale two-dimensional particle-in-cell simulations in electron-positron plasmas to demonstrate that relativistic magnetic reconnection can naturally account for the formation of quasi-spherical plasmoids filled with high-energy particles and magnetic fields. Our simulations extend to unprecedentedly long temporal and spatial scales, so we can capture the asymptotic physics independently of the initial setup. We characterize the properties of the plasmoids that are continuously generated as a self-consistent by-product of the reconnection process: they are in rough energy equipartition between particles and magnetic fields; the upper energy cutoff of the plasmoid particle spectrum is proportional to the plasmoid width w, corresponding to a Larmor radius ~0.2 w; the plasmoids grow in size at ~0.1 of the speed of light, with most of the growth happening while they are still non-relativistic (first they grow); their growth is suppressed once they get accelerated to relativistic speeds by the field line tension, up to the Alfven speed (then they go). The largest plasmoids, whose typical recurrence interval is ~2.5 L/c, reach a characteristic size w ~ 0.2 L independently of the system length L, they have nearly isotropic particle distributions and they contain the highest energy particles, whose Larmor radius is ~0.03 L. The latter can be regarded as the Hillas criterion for relativistic reconnection. We briefly discuss the implications of our results for the high-energy emission from relativistic jets and pulsar winds.

The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum

We report deep Chandra, HST and VLA observations of the binary neutron star event GW170817 at

Blazar flares powered by plasmoids in relativistic reconnection

t<160

A Decline in the X-ray through Radio Emission from GW170817 Continues to Support an Off-Axis Structured Jet

d after merger. These observations show that GW170817 has been steadily brightening with time and might have now reached its peak, and constrain the emission process as non-thermal synchrotron emission where the cooling frequency

Electron and Proton Acceleration in Trans-relativistic Magnetic Reconnection: Dependence on Plasma Beta and Magnetization

\nu_c

The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows

is above the X-ray band and the synchrotron frequency

Plasmoid statistics in relativistic magnetic reconnection

\nu_m

Electron Heating in Low-Mach-number Perpendicular Shocks. I. Heating Mechanism

is below the radio band. The very simple power-law spectrum extending for eight orders of magnitude in frequency enables the most precise measurement of the index

Probing dissipation mechanisms in BL Lac jets through X-ray polarimetry

p

Generalized, Energy-conserving Numerical Simulations of Particles in General Relativity. I. Time-like and Null Geodesics

of the distribution of non-thermal relativistic electrons