Dispersion and Rotation Measures from the Ejecta of Compact Binary Mergers: Clue to the Progenitors of Fast Radio Bursts

Abstract

Magnetars are promising central engines of fast radio bursts (FRBs), since the discovery of FRB 200428 from the Galactic SGR 1935+2154. It is widely believed that magnetars could form by core-collapse (CC) explosions and compact binary mergers, such as binary neutron star (BNS), binary white dwarfs (BWD) and neutron star-white dwarf (NSWD) mergers. Therefore, it is particularly important to distinguish the various progenitors of FRBs. The expansion of the merger ejecta produces a time-evolving dispersion measure (DM) and rotation measure (RM) that can probe the local environments of FRBs. In this paper, we derive the scaling laws for the DM and RM from ejecta with different dynamical structures (the mass and energy distribution) in the uniform ambient medium (merger scenario) and wind environment (CC scenario). We find that the DM and RM will increase in early phase, while DM will continue to grow slowly but RM will decrease in later phase in merger scenario. We also fit the DM and RM evolution of FRB 121102 simultaneously in BNS merger scenario, and find that the source age is ∼ 10 yr when it was first detected in 2012, and the ambient medium density is ∼ 2.3 cm −3 . The large offsets of some FRBs are consistent with BNS/NSWD channel. The population synthesis method is used to estimate the rate of compact binary mergers. The rate of BWD mergers is close to the observed FRB rate. Therefore, the progenitors of FRBs may not be unique.

Possible periodic activity in the short bursts of SGR 1806-20: connection to fast radio bursts

“…Considering the association between FRBs and X-ray bursts, if the precession explanation is correct, we predict that the periods of FRBs evolve with time. Some works suggested the ages of central magnetars of FRB 121102 and FRB 180916 are young (Metzger et al 2017;Cao et al 2017;Marcote et al 2020;Wu et al 2020;Zhao et al 2020). Future long-term monitoring is required to test this prediction.…”

The Environment of FRB 121102 and Possible Relation to SGR/PSR J1745-2900

“…The expansion of a SNR generally produces a decreasing DM (Margalit & Metzger 2018; Piro & Gaensler 2018), in contradiction to the observed (Hilmarsson et al 2020;Oostrum et al 2020) increase, although increasing ionization could increase DM. More complex models (Zhao et al 2020) may have more complex behavior. A spherically symmetric remnant cannot have a magnetic field at all, but a remnant might be approximately symmetric on large scales while being asymmetric (turbulent or otherwise structured) on smaller scales.…”

The physics of fast radio bursts

“…Still, significant absorption could possibly happen in the vicinity of the FRB source, where the plasma is dense enough. For instance, the FRB progenitor may locate in pulsar wind nebulae where there are numerous electrons [59,[70][71][72]. In this case, synchrotron self-absorption (SSA) 000000-6 may also play an important role [73,74].…”