Constraints on the Persistent Radio Source Associated with FRB 20190520B Using the European VLBI Network

Abstract

We present very long baseline interferometry (VLBI) observations of a continuum radio source potentially associated with the fast radio burst source FRB 20190520B. Using the European VLBI network, we find the source to be compact on VLBI scales with an angular size of <2.3 mas (3σ). This corresponds to a transverse physical size of <9 pc (at the z = 0.241 redshift of the host galaxy), confirming it to be as fast radio burst (FRB) persistent radio source (PRS) like that associated with the first-known repeater FRB 20121102A. The PRS has a flux density of 201 ± 34 μJy at 1.7 GHz and a spectral radio luminosity of L 1.7 GHz = (3.0 ± 0.5) × 1029 erg s−1 Hz−1 (also similar to the FRB 20121102A PRS). Compared to previous lower-resolution observations, we find that no flux is resolved out on milliarcsecond scales. We have refined the PRS position, improving its precision by an order of magnitude compared to previous results. We also report the detection of the FRB 20190520B burst at 1.4 GHz and find the burst position to be consistent with the PRS position, at ≲20 mas. This strongly supports their direct physical association and the hypothesis that a single central engine powers both the bursts and the PRS. We discuss the model of a magnetar in a wind nebula and present an allowed parameter space for its age and the radius of the putative nebula powering the observed PRS emission. Alternatively, we find that an accretion-powered hypernebula model also fits our observational constraints.

A Generic Model for a Persistent Radio Source around Fast Radio Bursts

“…More importantly, radio interferometric localization of FRB 1211012A revealed a compact (size < 0.7 pc), luminous (νL ν ∼ 10 39 erg s −1 ) persistent radio source (PRS) coincident to within 40 pc of the FRB location (Marcote et al 2017;Chen et al 2023). The second PRS counterpart of FRB 190520B was confirmed later and located in a dwarf galaxy (20 mas) similar to that of FRB 121102A (Niu et al 2022;Bhandari et al 2023). Although the origin of the PRS remains unclear, these two PRSs show common spectral properties (Zhang et al 2023), and thus the comparison of bursts arises between FRB 121102A and FRB 190520B (Lyu & Liang 2023).…”

“…Dai et al (2017) and Margalit & Metzger (2018) under the assumption of isotropic radiation. Another limit on active time for the PRS is the size of ∼0.66 pc for PRS 121102 according to Marcote et al (2017) and the size of ∼4.5 pc for PRS 190520 according to Bhandari et al (2023). We use the velocity of the PWN as a constant, ∼1.18 × 10 16 cm yr −1 (Vink 2020) Note that the PWN could expand rapidly in its early epoch instead of expanding uniformly.…”

“…Since counterparts like PRSs can unveil insights into the FRB itself, a search for other counterparts in different wave bands (e.g., optical) was raised (Chibueze et al 2022;Li et al 2022;Vohl et al 2023aVohl et al , 2023b), yet no optical counterpart of FRB 190520B was confirmed (Niino et al 2022). With the discovery of an FRB in a clean environment (Feng et al 2023) and the suggestion that there is no obvious evidence for repeaters or nonrepeaters to be preferentially associated with PRSs (Law et al 2022), this may indicate that FRBs and PRSs are two aspects of the central engine rather than the same origin, as pointed out that the polarization of PRSs differs from that of FRBs in Bhandari et al (2023).…”

Mapping Obscured Star Formation in the Host Galaxy of FRB 20201124A

“…In the case of FRB 20191001A, we instead use the published spectral index of α = −0.8 (Bhandari et al 2020a). 30 We plot the upper limits on the radio-inferred SFR from measurements of compact persistent radio emission associated with FRB 20121102A (Marcote et al 2017) and FRB 20190520B (Bhandari et al 2023b). We also incorporate radio limit on star formation for FRB 20210117A, the only nonrepeating FRB in a dwarf host galaxy (Bhandari et al 2023a).…”

“…Unless otherwise specified, all luminosity measurements are from Law et al (2022Law et al ( , 2023, and all optical SFRs are from Heintz et al (2020). We add the the luminosities of PRS 20121102A and 20190520B as upper limits on star formation from Marcote et al (2017), Bhandari et al (2023b), respectively.…”