Fast Radio Bursts: An Extragalactic Enigma (1906.05878v2)

Abstract: We summarize our understanding of millisecond radio bursts from an extragalactic population of sources. FRBs occur at an extraordinary rate, thousands per day over the entire sky with radiation energy densities at the source about ten billion times larger than those from Galactic pulsars. We survey FRB phenomenology, source models and host galaxies, coherent radiation models, and the role of plasma propagation effects in burst detection. The FRB field is guaranteed to be exciting: new telescopes will expand the sample from the current ~80 unique burst sources (and a few secure localizations and redshifts) to thousands, with burst localizations that enable host-galaxy redshifts emerging directly from interferometric surveys. * FRBs are now established as an extragalactic phenomenon. * Only a few sources are known to repeat. Despite the failure to redetect other FRBs, they are not inconsistent with all being repeaters. * FRB sources may be new, exotic kinds of objects or known types in extreme circumstances. Many inventive models exist, ranging from alien spacecraft to cosmic strings but those concerning compact objects and supermassive black holes have gained the most attention. A rapidly rotating magnetar is a promising explanation for FRB 121102 along with the persistent source associated with it, but alternative source models are not ruled out for it or other FRBs. * FRBs are powerful tracers of circumsource environments, `missing baryons' in the IGM, and dark matter. * The relative contributions of host galaxies and the IGM to propagation effects have yet to be disentangled, so dispersion measure distances have large uncertainties.

• The paper provides a comprehensive review of Fast Radio Bursts, detailing their extragalactic characteristics, current observational data, and the enigmatic nature of their origins.
• Source hypotheses discussed include cataclysmic neutron star events like magnetar activity, with repeating FRBs providing key insights into potential progenitor models.
• FRBs hold significant potential as cosmological probes, offering insights into the distribution of baryons in the universe and complementing large-scale structure studies.

Fast Radio Bursts: An Extragalactic Enigma

The paper by James M. Cordes and Shami Chatterjee offers an extensive examination of Fast Radio Bursts (FRBs), transient astrophysical phenomena characterized by brief millisecond-duration radio emissions. The nature and origin of FRBs are still enigmatic, chiefly due to their unpredictable occurrences and extragalactic origins suggested by their dispersion measures. This work gathers current data and hypotheses, aiming to consolidate the shared understanding within the community and highlight unresolved questions about these phenomena.

Summary of Findings

The document systematically addresses several core aspects of FRB research:

1. Characterization of FRBs: The authors emphasize the distinction of FRBs from other transient radio signals, detailing their high dispersion measures relative to typical Galactic sources which imply extragalactic distances.
2. Source Hypotheses: A prevailing hypothesis ties FRBs to cataclysmic events involving neutron stars, particularly magnetars. The possibility of a significant subset of FRBs being repeaters, as exemplified by FRB 121102, is also considered. The paper discusses potential progenitor models without committing to any single explanation.
3. Astrophysical Tools: The potential of FRBs as cosmological probes is scrutinized. Through dispersion measure analysis, FRBs could offer insights into the baryon distribution in the cosmos, which complements studies focused on the cosmic microwave background and large-scale structure.
4. Data and Observational Techniques: Recent advances in data collection, notably through instruments like CHIME, have expanded the catalog of observed FRBs. These advances improve statistical analysis of FRB populations, thereby refining our understanding of their properties and distributions.
5. Scattering and Host Galaxies: The paper examines the impact of propagation effects such as scattering, which can modify observed pulse profiles. Understanding the environment of host galaxies and the morphological classification thereof (e.g., spiral vs. elliptical) is crucial for understanding intrinsic FRB characteristics.

Numerical Results and Claims

The authors present quantitative analyses regarding the dispersion measures and their implied distances, strengthening the case for an extragalactic origin. The role of magnetars is particularly underscored due to the association of repeating FRBs with environments conducive to high-energy magnetar activity.

Implications and Future Research Directions

Practically, the identification of FRBs as extragalactic facilitates new methods for probing the intergalactic medium and calculating cosmological parameters. The potential for FRBs to illuminate dark matter distributions is noted, contingent upon resolving prevailing uncertainties about their origins and emission mechanisms.

Theoretically, this synthesis of current knowledge necessitates further observational campaigns and theoretical work to resolve outstanding questions about the physics that generate FRBs. Future instruments with wider fields of view or greater sensitivities are expected to enhance the detection rate, thereby supporting a more complete characterization of the FRB population.

Conclusion

This paper serves as a valuable compendium for FRB researchers, establishing a comprehensive baseline for subsequent discoveries and theoretical developments in the field. The premise that FRBs may serve both as astrophysical tools and subjects of paper remains at the forefront of this discourse, and the collective pursuit of these questions promises to contribute significantly to both astronomy and astrophysics at large.