[Paper Review] A repeating FRB in a dense environment with a compact persistent radio source

Chenhui Niu, K.K. Aggarwal+33 more|arXiv (Cornell University)|Oct 14, 2021

Pulsars and Gravitational Waves Research4 citations

TL;DR

This paper reports the discovery of FRB 190520B, a repeating fast radio burst localized to a dense, compact host galaxy with a high specific star formation rate at z=0.241, and identifies a persistent radio source (PRS) co-located with the burst. The host DM of ~902 pc cm⁻³ is significantly higher than typical FRB hosts, challenging standard redshift inference methods and suggesting a unique or early evolutionary stage for active repeating FRBs in dense environments.

ABSTRACT

Fast radio bursts (FRBs) are the most energetic radio transients in the Universe, the central engines of which remain unknown and could be diverse. The dispersion sweeps of FRBs provide a unique probe of the ionized baryon content of the intergalactic medium as well as FRBs natal environments. Here we report the discovery and localization of a new active repeater, FRB 190520B, which is co-located with a compact, persistent radio source (PRS) and identified with a dwarf host galaxy of high specific star formation rate at a redshift $z=0.241$. The estimated host galaxy dispersion measure (DM) $ m DM_{ m host} \approx 902^{+88}_{-128}$~pc~cm$^{-3}$ is nearly an order of magnitude higher than the average of FRB host galaxies and much larger than those of the intergalactic medium, suggesting caution in inferring redshifts for FRBs without accurate host galaxy identifications. This represents the second source after FRB 121102 with a confirmed association between a FRB and a compact PRS. The dense, complex host galaxy environment and the associated persistent radio source may point to a distinctive origin or an earlier evolutionary stage for active repeating FRBs.

Motivation & Objective

• To identify the host galaxy and environmental context of the repeating FRB 190520B.
• To investigate the origin and implications of a compact persistent radio source (PRS) associated with a repeating FRB.
• To assess the impact of high host dispersion measure (DM) on redshift estimation for FRBs.
• To explore whether dense, star-forming environments and PRS associations indicate a distinct evolutionary stage or origin for active repeating FRBs.
• To compare FRB 190520B with FRB 121102 to evaluate similarities in persistent radio emission and host environments.

Proposed method

• Used deep radio and optical follow-up observations to localize FRB 190520B to a dwarf galaxy at redshift z=0.241.
• Measured the host galaxy dispersion measure (DM_host) from the burst's dispersion sweep, yielding DM_host ≈ 902⁺⁸⁸₋₁₂⁸ pc cm⁻³.
• Identified a compact, persistent radio source (PRS) co-located with the FRB using high-resolution radio imaging.
• Analyzed the host galaxy's star formation rate and environment using multi-wavelength data to assess its density and complexity.
• Compared the DM and environmental properties of FRB 190520B with those of FRB 121102 and other FRB hosts to identify patterns.
• Evaluated the implications of high DM_host for redshift inference, emphasizing the need for accurate host galaxy identification.

Experimental results

Research questions

• RQ1 What is the host galaxy environment of FRB 190520B, and how does its high DM compare to typical FRB hosts?
• RQ2 Is there a physical association between the repeating FRB and a compact persistent radio source (PRS)?
• RQ3 How does the high host DM (~902 pc cm⁻³) affect the reliability of redshift estimation for FRBs?
• RQ4 What does the co-location of a PRS and a repeating FRB imply about the progenitor system or its evolutionary state?
• RQ5 How do the properties of FRB 190520B compare to those of FRB 121102, the only other FRB with a confirmed PRS association?

Key findings

• FRB 190520B is localized to a dwarf host galaxy with a high specific star formation rate at redshift z=0.241.
• The host galaxy dispersion measure (DM_host) is estimated at ~902⁺⁸⁸₋₁²⁸ pc cm⁻³, which is nearly an order of magnitude higher than the average for FRB hosts.
• A compact, persistent radio source (PRS) is co-located with FRB 190520B, marking the second such association after FRB 121102.
• The high DM_host is significantly larger than expected from the intergalactic medium, indicating that host galaxy contributions must be carefully accounted for in redshift estimation.
• The dense, complex environment and PRS association suggest FRB 190520B may represent a distinct origin or earlier evolutionary stage for active repeating FRBs.
• The findings underscore the importance of accurate host galaxy identification when inferring cosmological distances from FRB dispersion measures.