Dense magnetized plasma associated with a fast radio burst (1512.00529v1)

Abstract: Fast Radio Bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source. The inferred all-sky burst rate is comparable to the core-collapse supernova rate out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1. These parameters are consistent with a wide range of source models. One fast radio burst showed circular polarization [21(7)%] of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in a newly detected burst - FRB 110523. It has radio flux at least 0.6 Jy and dispersion measure 623.30(5) pc cm$^{-3}$. Using Galactic contribution 45 pc cm$^{-3}$ and a model of intergalactic electron density, we place the source at a maximum redshift of 0.5. The burst has rotation measure -186.1(1.4) rad m$^{-2}$, much higher than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. Keeping in mind that there may be more than one type of fast radio burst source, the detection in this instance of source-local magnetization and scattering favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low density regions of the host galaxy.

• The paper reveals that FRB 110523 exhibits a high rotation measure (-186.1 rad m²) and a dispersion measure of 623.30 pc cm⁻³, indicating a dense, magnetized plasma environment.
• The study employs a new dedispersion algorithm on archival Green Bank survey data to successfully isolate the fast radio burst from background noise.
• The findings support magnetar progenitor models and enhance the use of FRBs as probes for understanding intergalactic magnetic field structures.

Dense Magnetized Plasma Associated with a Fast Radio Burst

The research paper titled "Dense Magnetized Plasma Associated with a Fast Radio Burst" investigates the characteristics and implications of fast radio bursts (FRBs), focusing particularly on new findings from the detection of FRB 110523. The authors present an extensive analysis of this FRB, revealing insights into the nature of its source and the intervening media between the source and the observer.

Key Findings and Methodology

FRB 110523 was detected within archival data from the Green Bank Hydrogen Intensity Mapping survey operating in the frequency range of 700 to 900 MHz. The research utilized a new dedispersion algorithm to identify the FRB from a swath of data. The burst's significant linear polarization and high rotation measure (RM) suggest an environment of dense magnetized plasma near the source. The RM of -186.1(1.4) rad m$^2$ is far greater than what could be expected from the Milky Way or the intergalactic medium, indicating local magnetization around the source itself.

Numerical analysis displayed a dispersion measure (DM) of 623.30(6) pc cm$^-3$ for FRB 110523, situating it extragalactically with a redshift indicator (z) of up to 0.5. The presence of scattering by two distinct plasma screens and scintillation suggests the proximity of the scattering material to the FRB, with additional analysis indicating its likely location within the central regions of a host galaxy.

Implications

A critical theoretical implication of this analysis is the support it offers to models of FRBs originating from young stellar populations like magnetars, as opposed to mergers of older neutron stars, which are typically not found in dense, magnetized regions. This discovery provides a basis for distinguishing between different FRB progenitor models, potentially narrowing down the candidates for the sources of these cosmic phenomena.

From a practical perspective, the detection process substantiates FRBs as an astronomical, rather than anthropogenic, phenomenon due to their alignment with the expected pattern for dispersion and scattering when observed across multiple frequency bands. This has significant implications for astronomy, particularly in using FRBs as tools to probe the intergalactic medium and improve existing cosmological models.

Future Directions

The paper of FRB 110523 enhances our understanding of the cosmic environment surrounding FRB sources. As data from more FRBs becomes available, this can validate the hypothesis surrounding magnetar origins or potentially unveil new source classes through comprehensive analysis of RM, DM, and scattering measures. Further, understanding the magnetization and scattering properties in the vicinity of FRBs can provide insights into the magnetic field structure of the universe, contributing to broader astrophysical models.

In the field of astrophysical discovery, the methodological advancements and techniques applied in this paper set a precedent for future research, providing tools and frameworks necessary for the continued exploration of these enigmatic cosmic events. Continued cross-wavelength observations, particularly incorporating data from X-ray and optical counterparts, are likely necessary to further elucidate the nature of these bursts and their environments.