Vacuum ultraviolet coherent undulator radiation from attosecond electron bunches

Attosecond duration relativistic electron bunches travelling through an undulator can generate brilliant coherent radiation in the visible to vacuum ultraviolet spectral range. We present comprehensive numerical simulations to study the properties of coherent emission for a wide range of electron energies and bunch durations, including space-charge effects. These demonstrate that electron bunches with r.m.s. duration of 50 as, nominal charge of 0.1 pC and energy range of 100–250 MeV produce $$10^9$$ 10 9 coherent photons per pulse in the 100–600 nm wavelength range. We show that this can be enhanced substantially by self-compressing negatively chirped 100 pC bunches in the undulator to produce $$10^{14}$$ 10 14 coherent photons with pulse duration of 0.5–3 fs.

Emission Mechanisms of Fast Radio Bursts

Fast radio bursts (FRBs) are recently discovered mysterious single pulses of radio emission, mostly coming from cosmological distances (∼1 Gpc). Their short duration, ∼1 ms, and large luminosity demonstrate coherent emission. I review the basic physics of coherent emission mechanisms proposed for FRBs. In particular, I discuss the curvature emission of bunches, the synchrotron maser, and the emission of radio waves by variable currents during magnetic reconnection. Special attention is paid to magnetar flares as the most promising sources of FRBs. Non-linear effects are outlined that could place bounds on the power of the outgoing radiation.

Quark-Novae in the outskirts of galaxies: an explanation of the fast radio burst phenomenon

ABSTRACT We show that old isolated neutron stars in groups and clusters of galaxies experiencing a Quark-Nova phase (QN: an explosive transition to a quark star) may be the source of fast radio bursts (FRBs). Each of the millions of fragments of the ultrarelativistic QN ejecta provides a collisionless plasma for which the ambient medium (galactic/halo, the intragroup/intracluster medium) acts as a relativistic plasma beam. The Buneman and the Weibel instabilities, successively induced by the beam in the fragment, generate particle bunching and observed coherent emission at GHz frequency with a corresponding fluence in the Jy ms range. The duration, frequency drift, and the rate are in agreement with observed properties of FRBs. Repeats (on time-scales of minutes to months) are due to seeing multiple fragments each beaming at a different direction and coming in at different times. Single (non-repeating) FRBs occur when only emission from the primary fragment is within the detector’s sensitivity. Key properties of FRB 121102 (its years of activity) and of FRB 180916.J0158+65 (its ∼16 d period) are recovered. The spatial and temporal coincidence between SGR 1935+2154 and FRB 200428 finds an explanation in our model. We give testable predictions.