The Impact of the Environment of White Dwarf Mergers on Fast Radio Bursts

TL;DR

This paper explores how the environment around white dwarf mergers influences fast radio bursts, proposing that shock interactions in the merger ejecta can explain observed DM and RM variations over time.

Contribution

It introduces a model linking white dwarf merger environments to FRB properties, highlighting how shock interactions affect dispersion and rotation measures differently from core-collapse scenarios.

Findings

DM increases with time during free expansion phase

RM varies depending on ejecta density profile, decreasing in later phases

Model explains observed DM and RM trends in some FRBs

Abstract

Fast radio bursts (FRBs) are transient intense radio pulses with duration of milliseconds. Although the first FRB was detected more than a decade ago, the progenitors of these energetic events are not yet known. The currently preferred formation channel involves the formation of a neutron star (NS)/magnetar. While these objects are often the end product of the core-collapse (CC) explosion of massive stars, they could also be the outcome of the merging of two massive white dwarfs. In the merger scenario the ejected material interacts with a constant-density circumbinary medium and creates supersonic shocks. We found that when a radio pulse passes through these shocks the dispersion measure (DM) increases with time during the free expansion phase. The rotation measure (RM) displays a similar trend if the power-law index, $n$, of the outer part of the ejecta is $>6$. For $n = 6$ the RM remains constant during this phase. Later, when the ejecta move into the Sedov-Taylor phase while the DM still increases, however, with a different rate, the RM reduces. This behaviour is somewhat similar to that of FRB 121102 for which a marginal increase of DM and a 10% decrease of RM have been observed over time. These features are in contrast to the CC scenario, where the DM and RM contributions to the radio signal always diminish with time.