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

Abstract

The precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability p3×10 −4 ) of an FRB with an optical and persistent radio counterpart. We report on optical imaging and spectroscopy of the counterpart and find that it is an extended (0 6-0 8) object displaying prominent Balmer and [O III] emission lines. Based on the spectrum and emission line ratios, we classify the counterpart as a low-metallicity, star-forming, m r′ = 25.1 AB mag dwarf galaxy at a redshift of z = 0.19273(8), corresponding to a luminosity distance of 972 Mpc. From the angular size, the redshift, and luminosity, we estimate the host galaxy to have a diameter 4 kpc and a stellar mass of M * ∼(4-7)×107 M e , assuming a mass-to-light ratio between 2 to 3 M e L e −1 . Based on the Hα flux, we estimate the star formation rate of the host to be 0.4 M e yr −1 and a substantial host dispersion measure (DM) depth 324 pc cm −3 . The net DM contribution of the host galaxy to FRB 121102 is likely to be lower than this value depending on geometrical factors. We show that the persistent radio source at FRB 121102's location reported by Marcote et al. is offset from the galaxy's center of light by ∼200 mas and the host galaxy does not show optical signatures for AGN activity. If FRB 121102 is typical of the wider FRB population and if future interferometric localizations preferentially find them in dwarf galaxies with low metallicities and prominent emission lines, they would share such a preference with long gamma-ray bursts and superluminous supernovae.

Large Host-galaxy Dispersion Measure of Fast Radio Bursts

“…For FRB 121102, optical imaging and spectroscopy indicate a dwarf galaxy with a mass of M ∼ (4 − 7) × 10 7 M ⊙ as the host galaxy. The H α flux of the host galaxy suggests a star formation rate of SFR ∼ 0.4M ⊙ yr −1 (Tendulkar et al 2017). No information about the host galaxies of other FRBs is available.…”

“…Recently, thanks to the precise localization and multi-wavelength follow-up observations of the repeating source FRB 121102 (Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017), the distance scale of FRBs has been finally settled to a cosmological scale at z = 0.19273 (Tendulkar et al 2017). The large DM excess of other FRBs with respect to the Galactic value and their high Galactic latitudes also suggest that most, if not all, FRBs should have an extragalactic (e.g.…”

CHIME FRB: An application of FFT beamforming for a radio telescope

“…Secondly, only one FRB has been observed to repeat [11]. It remains the only FRB that has been localized by subsequent interferometric observations, which allowed for the identification of a host galaxy [14]. For all other FRBs, the localization is only approximately as good as the full width at half-maximum (FWHM) of the beam of the initial single dish detection, typically of the order of a few square arcminutes.…”

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).…”