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

TL;DR

This paper investigates the environment of FRB 121102, revealing magnetic fields and plasma characteristics, and explores its possible relation to SGR/PSR J1745-2900, suggesting a unique environment and formation process for this FRB.

Contribution

It provides detailed analysis of the plasma environment of FRB 121102 and proposes a possible connection to SGR/PSR J1745-2900 based on magnetic field and RM similarities.

Findings

Magnetic fields of 3-17 mG in the plasma environment.

Electron density around 10^4 cm^-3.

Large and variable RM indicating a unique environment.

Abstract

Variations of the dispersion (DM) and rotation (RM) measures of FRB 121102 indicate magnetic fields $\sim$ 3--17 mG in the dispersing plasma. The electron density may be $\sim 10^4\,$cm$^{-3}$. The observed time scales $\sim 1$ year constrain the size of the plasma cloud. Increasing DM excludes simple models involving an expanding supernova remnant, and the non-zero RM excludes spherical symmetry. The varying DM and RM may be attributable to the motion of plasma into or out of the line of sight or changing electron density within slower-moving plasma. The extraordinarily large RM of FRB 121102 implies an environment, and possibly also a formation process and source, qualitatively different from those of other FRB. The comparable and comparably varying RM of SGR/PSR J1745-2900 suggests it as an FRB candidate. An appendix discusses the age of FRB 121102 in the context of a "Copernican Principle".