Electromagnetic Fireworks: Fast Radio Bursts from Rapid Reconnection in the Compressed Magnetar Wind

• Published in: Astrophysical journal. Letters 2022-06, Vol.932 (2), p.L20
• Main Authors: Mahlmann, J. F., Philippov, A. A., Levinson, A., Spitkovsky, A., Hakobyan, H.
• Format: Article
• Language: English
• Subjects: ASTRONOMY AND ASTROPHYSICS; Coalescence; Coherent radiation; Current sheets; Emission analysis; Fireworks; Frequency drift; Magnetars; Magnetic fields; Magnetic islands; Magnetic reconnection; Narrowband; Particle in cell technique; Plasma astrophysics; Plasma currents; Radiation; Radio bursts; Radio emission; Radio transient sources; Relativistic particles; Self-similarity; Wind
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/ac7156

One scenario for the generation of fast radio bursts (FRBs) is magnetic reconnection in a current sheet of the magnetar wind. Compressed by a strong magnetic pulse induced by a magnetar flare, the current sheet fragments into a self-similar chain of magnetic islands. Time-dependent plasma currents at their interfaces produce coherent radiation during their hierarchical coalescence. We investigate this scenario using 2D radiative relativistic particle-in-cell simulations to compute the efficiency of the coherent emission and to obtain frequency scalings. Consistent with expectations, a fraction of the reconnected magnetic field energy, f ∼ 0.002, is converted to packets of high-frequency fast magnetosonic waves, which can escape from the magnetar wind as radio emission. In agreement with analytical estimates, we find that magnetic pulses of 10 47 erg s −1 can trigger relatively narrowband GHz emission with luminosities of approximately 10 42 erg s −1 , sufficient to explain bright extragalactic FRBs. The mechanism provides a natural explanation for a downward frequency drift of burst signals, as well as the ∼100 ns substructure recently detected in FRB 20200120E .