The Repeating Fast Radio Burst FRB 121102 as Seen on Milliarcsecond Angular Scales

Abstract

The millisecond-duration radio flashes known as fast radio bursts (FRBs) represent an enigmatic astrophysical phenomenon. Recently, the sub-arcsecond localization (∼100 mas precision) of FRB121102 using the Very Large Array has led to its unambiguous association with persistent radio and optical counterparts, and to the identification of its host galaxy. However, an even more precise localization is needed in order to probe the direct physical relationship between the millisecond bursts themselves and the associated persistent emission. Here, we report very-long-baseline radio interferometric observations using the European VLBI Network and the 305 m Arecibo telescope, which simultaneously detect both the bursts and the persistent radio emission at milliarcsecond angular scales and show that they are co-located to within a projected linear separation of 40 pc (12 mas angular separation, at 95% confidence). We detect consistent angular broadening of the bursts and persistent radio source (∼2-4 mas at 1.7 GHz), which are both similar to the expected Milky Way scattering contribution. The persistent radio source has a projected size constrained to be  0.7 pc (0.2 mas angular extent at 5.0 GHz) and a lower limit for the brightness temperature of T 5 10 K b 7´. Together, these observations provide strong evidence for a direct physical link between FRB121102 and the compact persistent radio source. We argue that a burst source associated with a low-luminosity active galactic nucleus or a young neutron star energizing a supernova remnant are the two scenarios for FRB121102 that best match the observed data.

The Host Galaxy and Redshift of the Repeating Fast Radio Burst FRB 121102

“…The Gaia frame is tied to the ICRF defined via radio VLBI to a ∼1 mas precision (Mignard et al 2016), much smaller than the centroid uncertainty. We find that the position of the persistent radio source seen with the EVN at an observing frequency of 5 GHz with a 1 mas precision (Marcote et al 2017) is offset from the galaxy centroids by 186±68 and 163±32 mas in the linedominated r′ and i′ images, and 286±64 mas in the continuum-dominated z′ image. Though offset from the centroids, the persistent radio source is located within the effective radii of the different bands.…”

“…Chatterjee et al (2017) reported the locations of the radio bursts, the optical and variable radio counterparts, and the absence of millimeter-wave and X-ray emission. Marcote et al (2017) have shown that the bursts and the persistent radio source are co-located to within a linear projected separation of 40 pc, suggesting that the two emission sources should be physically related, though not necessarily the same source. The radio source properties are consistent with a low-luminosity AGN or a young (<1000 year) supernova remnant (SNR) powered by an energetic neutron star (e.g., Murase et al 2016).…”

“…Chatterjee et al (2017) used the Karl G. Jansky Very Large Array (VLA) to directly localize the repeated bursts from FRB 121102 with 100 mas precision and reported an unresolved, persistent radio source and an extended optical counterpart at the location with a chance coincidence probability of ≈3×10 −4 -the first unambiguous identification of multi-wavelength counterparts to FRBs. Independently, Marcote et al (2017) used the European VLBI Network (EVN) to localize the bursts and the persistent source and showed that both are co-located within ∼12 mas.…”

A “Cosmic Comb” Model of Fast Radio Bursts

“…(3) DeLaunay et al (2016) discovered a sub-threshold long GRB that was spatially and temporally associated with FRB 131104 (Ravi et al 2015). (4) The repeating bursts from the FRB 121102 source are not associated with bright transient counterparts in other wavelengths, but the repeater is rather associated with a steady bright radio source (Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017).…”

“…The distance scale of FRBs is finally settled to the cosmological range (∼Gpc) thanks to multi-wavelength follow-up observations that nail down the host galaxy of the repeating source that produced FRB 121102 (Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017).…”