A study of two FRBs with low polarization fractions localized with the MeerTRAP transient buffer system

TL;DR

This paper reports the precise localization of two FRBs using MeerTRAP, identifying their host galaxies, analyzing their polarization, and discussing implications for their environments and origins.

Contribution

It presents the first localization of two FRBs with sub-arcsecond accuracy using MeerTRAP, enabling host galaxy identification and polarization analysis.

Findings

FRB 20220717A localized to a specific host galaxy with high confidence.

FRB 20220905A's host galaxy remains tentative due to observational challenges.

Both FRBs exhibit low polarization fractions consistent with other non-repeating FRBs.

Abstract

Localisation of fast radio bursts (FRBs) to arcsecond and sub-arcsecond precision maximizes their potential as cosmological probes. To that end, FRB detection instruments are deploying triggered complex-voltage capture systems to localize FRBs, identify their host galaxy and measure a redshift. Here, we report the discovery and localisation of two FRBs (20220717A and 20220905A) that were captured by the transient buffer system deployed by the MeerTRAP instrument at the MeerKAT telescope in South Africa. We were able to localize the FRBs to a precision of $\sim$1 arc-second that allowed us to unambiguously identify the host galaxy for FRB 20220717A (posterior probability$\sim$0.97). FRB 20220905A lies in a crowded region of the sky with a tentative identification of a host galaxy but the faintness and the difficulty in obtaining an optical spectrum preclude a conclusive association. The bursts show low linear polarization fractions (10--17$\%$) that conform to the large diversity in the polarization fraction observed in apparently non-repeating FRBs akin to single pulses from neutron stars. We also show that the host galaxy of FRB 20220717A contributes roughly 15$\%$ of the total dispersion measure (DM), indicating that it is located in a plasma-rich part of the host galaxy which can explain the large rotation measure. The scattering in FRB 20220717A can be mostly attributed to the host galaxy and the intervening medium and is consistent with what is seen in the wider FRB population.