[en] We report deep radio observations of nearby Type Ia supernovae (SNe Ia) with the electronic Multi-Element Radio Linked Interferometer Network and the Australia Telescope Compact Array. No detections were made. With standard assumptions for the energy densities of relativistic electrons going into a power-law energy distribution and the magnetic field strength (ϵ _e = ϵ _B = 0.1), we arrive at upper limits on mass-loss rate for the progenitor system of SN 2013dy (SN 2016coj, SN 2018gv, SN 2018pv, SN 2019np) of $\stackrel{\dot{}<!--\; ??\; -->}{M}\lesssim <!--\; ???\; -->12(2.8,1.3,2.1,1.7)\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->8}{M}_{\odot <!--\; ???\; -->}{\mathrm{y}\mathrm{r}}^{-<!--\; ???\; -->1}(v_w/100\mathrm{k}\mathrm{m}{\mathrm{s}}^{-<!--\; ???\; -->1})$, where v _w is the wind speed of the mass loss. To SN 2016coj, SN 2018gv, SN 2018pv, and SN 2019np we add radio data for 17 other nearby SNe Ia and model their nondetections. With the same model as described, all 21 SNe Ia have $\stackrel{\dot{}<!--\; ??\; -->}{M}\lesssim <!--\; ???\; -->4\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->8}{M}_{\odot <!--\; ???\; -->}{\mathrm{y}\mathrm{r}}^{-<!--\; ???\; -->1}(v_w/100\mathrm{k}\mathrm{m}{\mathrm{s}}^{-<!--\; ???\; -->1})$. We compare those limits with the expected mass-loss rates in different single-degenerate progenitor scenarios. We also discuss how information on ϵ _e and ϵ _B can be obtained from late observations of SNe Ia and the youngest SN Ia remnant detected in radio, G1.9+0.3, as well as stripped-envelope core-collapse SNe. We highlight SN 2011dh and argue for ϵ _e ≈ 0.1 and ϵ _B ≈ 0.0033. Finally, we discuss strategies to observe at radio frequencies to maximize the chance of detection, given the time since explosion, the distance to the SN, and the telescope sensitivity.

[en] Fast radio burst (FRB) 190608 was detected by the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to a spiral galaxy at $z_{\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}}=0.11778$ in the Sloan Digital Sky Survey (SDSS) footprint. The burst has a large dispersion measure (${\mathrm{D}\mathrm{M}}_{\mathrm{F}\mathrm{R}\mathrm{B}}=339.8\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$) compared to the expected cosmic average at its redshift. It also has a large rotation measure (${\mathrm{R}\mathrm{M}}_{\mathrm{F}\mathrm{R}\mathrm{B}}=353\mathrm{r}\mathrm{a}\mathrm{d}{\mathrm{m}}^{-<!--\; ???\; -->2}$) and scattering timescale (τ = 3.3 ms at 1.28 GHz). Chittidi et al. perform a detailed analysis of the ultraviolet and optical emission of the host galaxy and estimate the host DM contribution to be $110\pm <!--\; ??\; -->37\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$. This work complements theirs and reports the analysis of the optical data of galaxies in the foreground of FRB 190608 in order to explore their contributions to the FRB signal. Together, the two studies delineate an observationally driven, end-to-end study of matter distribution along an FRB sightline, the first study of its kind. Combining our Keck Cosmic Web Imager (KCWI) observations and public SDSS data, we estimate the expected cosmic dispersion measure ${\mathrm{D}\mathrm{M}}_{\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{m}\mathrm{i}\mathrm{c}}$ along the sightline to FRB 190608. We first estimate the contribution of hot, ionized gas in intervening virialized halos (${\mathrm{D}\mathrm{M}}_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}\mathrm{s}}\approx <!--\; ???\; -->7\text{--}28\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$). Then, using the Monte Carlo Physarum Machine methodology, we produce a 3D map of ionized gas in cosmic web filaments and compute the DM contribution from matter outside halos (${\mathrm{D}\mathrm{M}}_{\mathrm{I}\mathrm{G}\mathrm{M}}\approx <!--\; ???\; -->91\text{--}126\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$). This implies that a greater fraction of ionized gas along this sightline is extant outside virialized halos. We also investigate whether the intervening halos can account for the large FRB rotation measure and pulse width and conclude that it is implausible. Both the pulse broadening and the large Faraday rotation likely arise from the progenitor environment or the host galaxy.

[en] The Australian SKA Pathfinder (ASKAP) telescope has started to localize fast radio bursts (FRBs) to arcsecond accuracy from the detection of a single pulse, allowing their host galaxies to be reliably identified. We discuss the global properties of the host galaxies of the first four FRBs localized by ASKAP, which lie in the redshift range 0.11 < z < 0.48. All four are massive galaxies (log(M _*/M _⊙) ∼ 9.4–10.4) with modest star formation rates of up to 2 M _⊙ yr⁻¹—very different to the host galaxy of the first repeating FRB 121102, which is a dwarf galaxy with a high specific star formation rate. The FRBs localized by ASKAP typically lie in the outskirts of their host galaxies, which appears to rule out FRB progenitor models that invoke active galactic nuclei or free-floating cosmic strings. The stellar population seen in these host galaxies also disfavors models in which all FRBs arise from young magnetars produced by superluminous supernovae, as proposed for the progenitor of FRB 121102. A range of other progenitor models (including compact-object mergers and magnetars arising from normal core-collapse supernovae) remain plausible.

[en] We present a new fast radio burst (FRB) at 920 MHz discovered during commensal observations conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) as part of the Commensal Real-time ASKAP Fast Transients (CRAFT) survey. FRB 191001 was detected at a dispersion measure (DM) of 506.92(4) pc cm⁻³ and its measured fluence of 143(15) Jy ms is the highest of the bursts localized to host galaxies by ASKAP to date. The subarcsecond localization of the FRB provided by ASKAP reveals that the burst originated in the outskirts of a highly star-forming spiral in a galaxy pair at redshift z = 0.2340(1). Radio observations show no evidence for a compact persistent radio source associated with the FRB 191001 above a flux density of 15 μJy. However, we detect diffuse synchrotron radio emission from the disk of the host galaxy that we ascribe to ongoing star formation. FRB 191001 was also detected as an image-plane transient in a single 10 s snapshot with a flux density of 19.3 mJy in the low-time-resolution visibilities obtained simultaneously with CRAFT data. The commensal observation facilitated a search for repeating and slowly varying radio emissions 8 hr before and 1 hr after the burst. We found no variable radio emission on timescales ranging from 1 ms to 1.4 hr. We report our upper limits and briefly review FRB progenitor theories in the literature that predict radio afterglows. Our data are still only weakly constraining of any afterglows at the redshift of the FRB. Future commensal observations of more nearby and bright FRBs will potentially provide stronger constraints.

[en] We present Hubble Space Telescope ultraviolet and infrared observations of eight fast radio burst (FRB) host galaxies with subarcsecond localizations, including the hosts of three known repeating FRBs. We quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding that they occur at moderate host-normalized offsets of 1.4r _e ([0.6, 2.1]r _e; 68% interval) and on fainter regions of their hosts in terms of IR light but overall trace the radial distribution of IR light in their galaxies. The FRBs in our tested distribution do not clearly trace the distributions of any other transient population with known progenitors and are statistically distinct from the locations of LGRBs, H-poor SLSNe, SGRBs, and Ca-rich transients. We further find that most FRBs are not in regions of elevated local star formation rates and stellar mass surface densities in comparison to the mean global values of their hosts. We also place upper limits on the IR flux at the FRB positions of m _IR ≳ 24.8–27.6 AB mag, constraining both satellite and background galaxies to luminosities well below the host luminosity of FRB 121102. We find that 5/8 FRB hosts exhibit clear spiral arm features in IR light, and that the positions of all well-localized FRBs located in such hosts are consistent with their spiral arms, although not on their brightest regions. Our results do not strongly support the primary progenitor channel of FRBs being connected with either the most massive (stripped-envelope) stars or events that require kicks and long delay times (neutron star mergers).

[en] We present the Australian Square Kilometre Array Pathfinder localization and follow-up observations of the host galaxy of the repeating fast radio burst (FRB) source, FRB 20201124A, the fifth such extragalactic repeating FRB with an identified host. From spectroscopic observations using the 6.5 m MMT Observatory, we derive a redshift z = 0.0979 ± 0.0001, a star formation rate inferred from Hα emission SFR(Hα) ≈ 2.1 M _⊙ yr⁻¹, and a gas-phase metallicity of 12+log(O/H) ≈ 9.0. By jointly modeling the 12 filter optical−mid-infrared (MIR) photometry and spectroscopy of the host, we infer a median stellar mass of ∼2 × 10¹⁰ M _⊙, internal dust extinction A _V ≈ 1–1.5 mag, and a mass-weighted stellar population age of ∼5–6 Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broadband behavior with strong active galactic nucleus activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the MIR luminosity at a level of ∼10%–30%. We model the host galaxy’s star formation and mass assembly histories, finding that the host assembled >90% of its mass by 1 Gyr ago and exhibited a fairly constant SFR for most of its existence, with no clear evidence of past starburst activity.

[en] We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs) discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to ≲1″. Combining these galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a subsample of 10 highly confident associations (at z = 0.03–0.52), 3 of which correspond to known repeating FRBs. Overall, the FRB-host galaxies exhibit a broad, continuous range of color (M _u − M _r = 0.9–2.0), stellar mass (M _⋆ = 10⁸ − 6 × 10¹⁰ M _⊙), and star formation rate (SFR = 0.05–10 M _⊙ yr⁻¹) spanning the full parameter space occupied by z < 0.5 galaxies. However, they do not track the color–magnitude, SFR–M _⋆, nor BPT diagrams of field galaxies surveyed at similar redshifts. There is an excess of “green valley” galaxies and an excess of emission-line ratios indicative of a harder radiation field than that generated by star formation alone. From the observed stellar mass distribution, we rule out the hypothesis that FRBs strictly track stellar mass in galaxies (>99% c.l.). We measure a median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and SGRBs), core-collapse supernovae (CC-SNe), and SNe Ia. This analysis rules out galaxies hosting LGRBs (faint, star-forming galaxies) as common hosts for FRBs (>95% c.l.). Other transient channels (SGRBs, CC-, and SNe Ia) have host-galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities are made publicly available on a dedicated website and repository.