A Population of Fast Radio Bursts at Cosmological Distances

Abstract: Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients we have uncovered four millisecond-duration radio transients all more than 40{\deg} from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1, and distances of up to 3 gigaparsecs. No temporally coincident x- or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the Universe.

• The paper reveals four extragalactic FRBs with high dispersion measures, establishing their cosmological distances up to 3 gigaparsecs.
• Advanced spectral analysis of Parkes radio telescope data confirmed FRB propagation through the intergalactic medium with precise dispersion and scattering parameters.
• Results emphasize the potential of FRBs as probes for the ionized intergalactic medium and to constrain the universe's baryonic content.

A Population of Fast Radio Bursts at Cosmological Distances

The investigation of transient astrophysical phenomena can yield significant insights into the workings of the universe, especially in regions beyond our immediate cosmic neighborhood. In Thornton et al.'s paper, the authors explore the discovery and analysis of four Fast Radio Bursts (FRBs) located far from the Galactic plane, providing strong evidence for their extragalactic origins. Their high dispersion measures (DMs) and substantial estimated distances suggest these FRBs are located at cosmological scales, potentially up to 3 gigaparsecs away.

Observations and Data Analysis

Detected during the High Time Resolution Universe (HTRU) survey utilizing the Parkes radio telescope, these FRBs display characteristics indicating they are not of terrestrial origin. The minimum fluence of these FRBs ranges from 0.6 to 8.0 Jy ms, suggesting they are more luminous than any known radio transients when accounting for their inferred cosmological distances. Importantly, no repeat bursts were detected, supporting a cataclysmic interpretation of their nature.

Despite the presence of previously reported candidate extragalactic bursts, the FRBs in this study featured properties affirming a celestial origin, as evidenced by consistent dispersive delays and frequency-dependent pulse widths. The spectral analysis performed at several radio frequencies further constrained dispersion and scattering parameters ($\alpha$ and $\beta$), solidifying their propagation through a cold plasma, likely the intergalactic medium (IGM).

Implications and Theoretical Context

Addressing the dispersion measures, the paper highlights the limited Galactic DM contribution relative to the overall DM observed, which strongly supports an extragalactic provenance. The likelihood of alternative sources such as neutron star mergers, gamma-ray bursts, and solar interferences was methodically excluded based on empirical observations and theoretical considerations.

Given the estimated redshifts ($z = 0.45-0.96$), these FRBs represent powerful probes into the ionized IGM, useful for constraining universal baryonic content. The paper posits that a real-time detection and follow-up process could result in identification of host galaxies, enabling redshift determination and further illuminating IGM characteristics. Moreover, the non-association with other known transient astrophysical phenomena underscores the need for additional research into potential progenitors of FRBs beyond extant theoretical models.

Future Directions

The primary conclusion drawn from the analysis is the potential of FRBs as cosmological probes, offering insights into the magneto-ionic composition of intergalactic space. Further studies that increase the detection of high-redshift FRBs may expand our understanding of the universe's baryonic distribution, as well as the nature of these brief but intense radio sources. Additionally, further refinement of detection techniques and real-time multi-wavelength observations could pave the way for a new class of astrophysical investigations, potentially informing models of cosmological structure formation and evolution.

This paper lays the groundwork for subsequent observational campaigns and theoretical developments aimed at unraveling the mystery of FRBs and fully uncovering the wealth of information they offer about the universe.