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Fast radio bursts (FRBs) are microsecond-to-millisecond-duration radio transients 1 that originate mostly from extragalactic distances. The FRB emission mechanism remains debated, with two main competing classes of models: physical processes that occur within close proximity to a central engine 2 , 3 – 4 ; and relativistic shocks that propagate out to large radial distances 5 , 6 , 7 – 8 . The expected emission-region sizes are notably different between these two types of models 9 . Here we present the measurement of two mutually coherent scintillation scales in the frequency spectrum of FRB 20221022A 10 : one originating from a scattering screen located within the Milky Way, and the second originating from its host galaxy or local environment. We use the scattering media as an astrophysical lens to constrain the size of the observed FRB lateral emission region 9 to ≲3 × 10 4  kilometres. This emission size is inconsistent with the expectation for the large-radial-distance models 5 , 6 , 7 – 8 , and is more naturally explained by an emission process that operates within or just beyond the magnetosphere of a central compact object. Recently, FRB 20221022A was found to exhibit an S-shaped polarization angle swing 10 , most likely originating from a magnetospheric emission process. The scintillation results presented in this work independently support this conclusion, while highlighting scintillation as a useful tool in our understanding of FRB emission physics and progenitors. The detection of scintillation caused by inhomogeneous plasma near a fast radio burst indicates an emission process that occurs within or just beyond the magnetosphere of a compact object.

Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that are visible at distances of billions of light years. The nature of their progenitors and their emission mechanism remain open astrophysical questions. Here we report the detection of the multicomponent FRB 20191221A and the identification of a periodic separation of 216.8(1) ms between its components, with a significance of 6.5σ. The long (roughly 3 s) duration and nine or more components forming the pulse profile make this source an outlier in the FRB population. Such short periodicity provides strong evidence for a neutron-star origin of the event. Moreover, our detection favours emission arising from the neutron-star magnetosphere, as opposed to emission regions located further away from the star, as predicted by some models.

Fast radio bursts (FRBs) last for milliseconds and arrive at Earth from cosmological distances. Although their origins and emission mechanisms are unknown, their signals bear similarities with the much less luminous radio emission generated by pulsars within our Miky Way Galaxy 1 , with properties suggesting neutron star origins 2 , 3 . However, unlike pulsars, FRBs typically show minimal variability in their linear polarization position angle (PA) curves 4 . Even when marked PA evolution is present, their curves deviate significantly from the canonical shape predicted by the rotating vector model (RVM) of pulsars 5 . Here we report on FRB 20221022A, detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst project (CHIME/FRB) and localized to a nearby host galaxy (about 65 Mpc), MCG+14-02-011. This FRB shows a notable approximately 130° PA rotation over its about 2.5 ms burst duration, resembling the characteristic S-shaped evolution seen in many pulsars and some radio magnetars. The observed PA evolution supports magnetospheric origins 6 , 7 – 8 over models involving distant shocks 9 , 10 – 11 , echoing similar conclusions drawn from tempo-polarimetric studies of some repeating FRBs 12 , 13 . The PA evolution is well described by the RVM and, although we cannot determine the inclination and magnetic obliquity because of the unknown period or duty cycle of the source, we exclude very short-period pulsars (for example, recycled millisecond pulsars) as the progenitor. FRB 20221022A, detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst project, shows a pronounced change in polarization during the burst, providing important clues into the nature of the source.

NRC publication: Yes

We present the first results from an extended survey of the Andromeda galaxy (M31) using 41.1 h of observations by Spitzer-IRAC at 3.6 and 4.5\\(\\,\\mu\\)m. This survey extends previous observations to the outer disc and halo, covering total lengths of 4\\(.\\!\\!^\\circ\\)4 and 6\\(.\\!\\!^\\circ\\)6 along the minor and major axes, respectively. We have produced surface brightness profiles by combining the integrated light from background-corrected maps with stellar counts from a new catalogue of point sources. Using auxiliary catalogues we have carried out a statistical analysis in colour-magnitude space to discriminate M31 objects from foreground Milky Way stars and background galaxies. The catalogue includes 426,529 sources, of which 66 per cent have been assigned probability values to identify M31 objects with magnitude depths of [3.6]\\(\\,=\\,\\)19.0\\(\\,\\pm\\,\\)0.2, [4.5]\\(\\,=\\,\\)18.7\\(\\,\\pm\\,\\)0.2. We discuss applications of our data for constraining the stellar mass and characterising point sources in the outer radii.

Extragalactic fast radio bursts (FRBs) are a new class of astrophysical transients with unknown origins that have become a main focus of radio observatories worldwide. FRBs are highly energetic (\\(\\sim 10^{36}\\)-\\(10^{42}\\) ergs) flashes that last for about a millisecond. Thanks to its broad bandwidth (400-800 MHz), large field of view (\\(\\sim\\)200 sq. deg.), and massive data rate (1500 TB of coherently beamformed data per day), the Canadian Hydrogen Intensity Mapping Experiment / Fast Radio Burst (CHIME/FRB) project has increased the total number of discovered FRBs by over a factor 10 in 3 years of operation. CHIME/FRB observations are hampered by the constant exposure to radio frequency interference (RFI) from artificial devices (e.g., cellular phones, aircraft), resulting in \\(\\sim\\)20% loss of bandwidth. In this work, we describe our novel technique for mitigating RFI in CHIME/FRB real-time intensity data. We mitigate RFI through a sequence of iterative operations, which mask out statistical outliers from frequency-channelized intensity data that have been effectively high-pass filtered. Keeping false positive and false negative rates at very low levels, our approach is useful for any high-performance surveys of radio transients in the future.

Understanding the origin of fast radio bursts (FRB's) is a central unsolved problem in astrophysics that is severely hampered by their poorly determined distance scale. Determining the redshift distribution of FRB's appears to require arcsecond angular resolution, in order to associate FRB's with host galaxies. In this paper, we forecast prospects for determining the redshift distribution without host galaxy associations, by cross-correlating FRB's with a galaxy catalog such as the SDSS photometric sample. The forecasts are extremely promising: a survey such as CHIME/FRB that measures catalogs of \\(\\sim 10^3\\) FRB's with few-arcminute angular resolution can place strong constraints on the FRB redshift distribution, by measuring the cross-correlation as a function of galaxy redshift \\(z\\) and FRB dispersion measure \\(D\\). In addition, propagation effects from free electron inhomogeneities modulate the observed FRB number density, either by shifting FRB's between dispersion measure (DM) bins or through DM-dependent selection effects. We show that these propagation effects, coupled with the spatial clustering between galaxies and free electrons, can produce FRB-galaxy correlations which are comparable to the intrinsic clustering signal. Such effects can be disentangled based on their angular and \\((z, D)\\) dependence, providing an opportunity to study not only FRB's but the clustering of free electrons.

We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for eight weeks immediately following the source's detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on \\(0.5-10.0\\) keV X-ray fluence of \\((1.5-14.5)\\times 10^{-10}\\) erg cm\\(^{-2}\\) (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio \\(\\eta_{\\text{ x/r}} = F_{\\text{X-ray}}/F_{\\text{radio}}\\), this corresponds to \\({\\eta}_{\\text{ x/r}} < 7\\times10^{6}\\). For persistent emission from the location of FRB 20220912A, we derive a 99.7% \\(0.5-10.0\\) keV isotropic flux limit of \\(8.8\\times 10^{-15}\\) erg cm\\(^{-2}\\) s\\(^{-1}\\) (unabsorbed) or an isotropic luminosity limit of 1.4\\(\\times10^{41}\\) erg s\\(^{-1}\\) at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB \\({\\eta}_{\\text{ x/r}}\\) to date, \\({\\eta}_{\\text{ x/r}} < 2\\times10^6\\), assuming that all thirty detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on \\({\\eta}_{\\text{ x/r}}\\) of \\(8\\times10^5\\), which is only 3 times the observed value of \\({\\eta}_{\\text{ x/r}}\\) for SGR 1935+2154.

Fast Radio Bursts (FRBs) are a class of highly energetic, mostly extragalactic radio transients lasting for a few milliseconds. While over 600 FRBs have been published so far, their origins are presently unclear, with some theories for extragalactic FRBs predicting accompanying high-energy emission. In this work, we use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst (CHIME/FRB) Project to explore whether any FRB-like radio emission coincides in space and time with 81 gamma-ray bursts (GRBs) detected between 2018 July 17 and 2019 July 8 by Swift/BAT and Fermi/GBM. We do not find any statistically significant, coincident pairs within 3sigma of each other's spatial localization regions and within a time difference of up to one week. In addition to searching for spatial matches between known FRBs and known GRBs, we use CHIME/FRB to constrain FRB-like radio emission before, at the time of, or after the reported high-energy emission at the position of 39 GRBs. Our most constraining radio flux limits in the 400- to 800-MHz band for short gamma-ray bursts (SGRBs) are <50 Jy at 18.6 ks pre-high-energy emission, and <5 Jy at 28.4 ks post-high-energy emission, assuming a 10-ms radio burst width with each limit valid for 60 seconds. We use these limits to constrain models that predict FRB-like prompt radio emission before and after SGRBs. We also place limits as low as 2 Jy for long gamma-ray bursts (LGRBs), but there are no strong theoretical predictions for coincident FRB-like radio emission for LGRBs.

Fast radio bursts (FRBs) are millisecond-duration, luminous radio transients of extragalactic origin. These events have been used to trace the baryonic structure of the Universe using their dispersion measure (DM) assuming that the contribution from host galaxies can be reliably estimated. However, contributions from the immediate environment of an FRB may dominate the observed DM, thus making redshift estimates challenging without a robust host galaxy association. Furthermore, while at least one Galactic burst has been associated with a magnetar, other localized FRBs argue against magnetars as the sole progenitor model. Precise localization within the host galaxy can discriminate between progenitor models, a major goal of the field. Until now, localizations on this spatial scale have only been carried out in follow-up observations of repeating sources. Here we demonstrate the localization of FRB 20210603A with very long baseline interferometry (VLBI) on two baselines, using data collected only at the time of detection. We localize the burst to SDSS J004105.82+211331.9, an edge-on galaxy at \\(z\\approx 0.177\\), and detect recent star formation in the kiloparsec-scale vicinity of the burst. The edge-on inclination of the host galaxy allows for a unique comparison between the line of sight towards the FRB and lines of sight towards known Galactic pulsars. The DM, Faraday rotation measure (RM), and scattering suggest a progenitor coincident with the host galactic plane, strengthening the link between the environment of FRB 20210603A and the disk of its host galaxy. Single-pulse VLBI localizations of FRBs to within their host galaxies, following the one presented here, will further constrain the origins and host environments of one-off FRBs.