Fast radio bursts in the discs of active galactic nuclei

Abstract

ABSTRACT Fast radio bursts (FRBs) are luminous millisecond-duration radio pulses with extragalactic origin, which were discovered more than a decade ago. Despite the numerous samples, the physical origin of FRBs remains poorly understood. FRBs have been thought to originate from young magnetars or accreting compact objects (COs). Massive stars or COs are predicted to be embedded in the accretion discs of active galactic nuclei (AGNs). The dense disc absorbs FRBs severely, making them difficult to observe. However, progenitors’ ejecta or outflow feedback from the accreting COs interact with the disc material to form a cavity. The existence of the cavity can reduce the absorption by the dense disc materials, making FRBs escape. Here, we investigate the production and propagation of FRBs in AGN discs and find that the AGN environments lead to the following unique observational properties, which can be verified in future observation. First, the dense material in the disc can cause large dispersion measure (DM) and rotation measure (RM). Secondly, the toroidal magnetic field in the AGN disc can cause Faraday conversion. Thirdly, during the shock breakout, DM and RM show non-power-law evolution patterns over time. Fourthly, for accreting-powered models, higher accretion rates lead to more bright bursts in AGN discs, accounting for up to 1 per cent of total bright repeating FRBs.