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The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a novel transit radio telescope operating across the 400–800 MHz band. CHIME is composed of four 20 m × 100 m semicylindrical paraboloid reflectors, each of which has 256 dual-polarization feeds suspended along its axis, giving it a ≳200 deg² field of view. This, combined with wide bandwidth, high sensitivity, and a powerful correlator, makes CHIME an excellent instrument for the detection of fast radio bursts (FRBs). The CHIME Fast Radio Burst Project (CHIME/FRB) will search beam-formed, high time and frequency resolution data in real time for FRBs in the CHIME field of view. Here we describe the CHIME/FRB back end, including the real-time FRB search and detection software pipeline, as well as the planned offline analyses. We estimate a CHIME/FRB detection rate of 2–42 FRBs sky⁻¹ day⁻¹ normalizing to the rate estimated at 1.4 GHz by Vander Wiel et al. Likely science outcomes of CHIME/FRB are also discussed. CHIME/FRB is currently operational in a commissioning phase, with science operations expected to commence in the latter half of 2018.

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way1,2. This phenomenon was discovered at radio frequencies near 1.4 gigahertz and so far has been observed in one case3 at as high as 8 gigahertz, but not at below 700 megahertz in spite of substantial searches at low frequencies4,5,6,7. Here we report detections of 13 FRBs at radio frequencies as low as 400 megahertz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument8. They were detected during a telescope pre-commissioning phase, when the sensitivity and field of view were not yet at design specifications. Emission in multiple events is seen down to 400 megahertz, the lowest radio frequency to which the telescope is sensitive. The FRBs show various temporal scattering behaviours, with the majority detectably scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper9. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than in the diffuse interstellar medium in the Milky Way.

Measurement of the brightness temperature of extended radio emission demands knowledge of the gain (or aperture efficiency) of the telescope and measurement of the polarized component of the emission requires correction for the conversion of unpolarized emission from sky and ground to apparently polarized signal. Radiation properties of the John A. Galt Telescope at the Dominion Radio Astrophysical Observatory were studied through analysis and measurement in order to provide absolute calibration of a survey of polarized emission from the entire northern sky from 1280 to 1750 MHz, and to understand the polarization performance of the telescope. Electromagnetic simulation packages CST and GRASP-10 were used to compute complete radiation patterns of the telescope in all Stokes parameters, and thereby to establish gain and aperture efficiency. Aperture efficiency was also evaluated using geometrical optics and ray tracing analysis and was measured based on the known flux density of Cyg A. Measured aperture efficiency varied smoothly with frequency between values of 0.49 and 0.54; GRASP-10 yielded values 6.5% higher but with closely similar variation with frequency. Overall error across the frequency band is 3%, but values at any two frequencies are relatively correct to ∼1%. Dominant influences on aperture efficiency are the illumination taper of the feed radiation pattern and the shadowing of the reflector from the feed by the feed-support struts. A model of emission from the ground was developed based on measurements and on empirical data obtained from remote sensing of the Earth from satellite-borne telescopes. This model was convolved with the computed antenna response to estimate conversion of ground emission into spurious polarized signal. The computed spurious signal is comparable to measured values, but is not accurate enough to be used to correct observations. A simpler model, in which the ground is considered as an unpolarized emitter with a brightness temperature of ∼240 K, is shown to have useful accuracy when compared to measurements.

NRC publication: Yes

Synchrotron radiation is generated throughout the Milky Way. It fills the sky, and carries with it the imprint of the magnetic field at the point of origin and along the propagation path. Observations of the diffuse polarized radio emission should be able to provide information on Galactic magnetic fields with detail matching the angular resolution of the telescope. I review what has been learned from existing data, but the full potential cannot be realized from current observations because they do not adequately sample the frequency structure of the polarized emission, or they lack information on large-scale structure. I discuss three surveys, each overcoming one of these limitations, and show how use of complementary data on other ISM tracers can help elucidate the role of magnetic fields in interstellar processes. The focus of this review is on the small-scale field, on sizes comparable with the various forms of interaction of stars with their surroundings. The future is bright for this field of research as new telescopes are being built, designed for the survey mode of observation, equipped for wideband, multichannel polarization observations.

Synchrotron radiation is generated throughout the Milky Way. It fills the sky, and carries with it the imprint of the magnetic field at the point of origin and along the propagation path. Observations of the diffuse polarized radio emission should be able to provide information on Galactic magnetic fields with detail matching the angular resolution of the telescope. I review what has been learned from existing data, but the full potential cannot be realized from current observations because they do not adequately sample the frequency structure of the polarized emission, or they lack information on large-scale structure. I discuss three surveys, each overcoming one of these limitations, and show how use of complementary data on other ISM tracers can help elucidate the role of magnetic fields in interstellar processes. The focus of this review is on the small-scale field, on sizes comparable with the various forms of interaction of stars with their surroundings. The future is bright for this field of research as new telescopes are being built, designed for the survey mode of observation, equipped for wideband, multichannel polarization observations.

NRC publication: Yes

Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes (1,2). Their physical origin remains unknown, but dozens of possible models have been postulated³. Some FRB sources exhibit repeat bursts⁴⁻⁷. Although over a hundred FRB sources have been discovered⁸, only four have been localized and associated with a host galaxy⁹⁻¹², and just one of these four is known to emit repeating FRBs⁹. The properties of the host galaxies, and the local environments of FRBs, could provide important clues about their physical origins. The first known repeating FRB, however, was localized to a low-metallicity, irregular dwarf galaxy, and the apparently non-repeating sources were localized to higher-metallicity, massive elliptical or star-forming galaxies, suggesting that perhaps the repeating and apparently non-repeating sources could have distinct physical origins. Here we report the precise localization of a second repeating FRB source⁶, FRB 180916.J0158+65, to a star-forming region in a nearby (redshift 0.0337 ± 0.0002) massive spiral galaxy, whose properties and proximity distinguish it from all known hosts. The lack of both a comparably luminous persistent radio counterpart and a high Faraday rotation measure⁶ further distinguish the local environment of FRB 180916.J0158+65 from that of the single previously localized repeating FRB source, FRB 121102. This suggests that repeating FRBs may have a wide range of luminosities, and originate from diverse host galaxies and local environments.

The disk of the Milky Way contains free electrons and magnetic fields which contribute significantly to the energetics of the interstellar medium 1 . The concentrations of electrons and magnetic fields are too low to be detected by direct methods, but may be investigated using Faraday rotation, a wavelength-dependent shift in linear polarization angle induced by a magneto-ionic medium 2 . Structures in polarization angle arising from Faraday rotation have been detected recently at long radio wavelengths 3 . These structures are disorganized and filamentary, probably arising from interstellar gas in the vicinity of the Sun. Here we report a more distant, highly ordered Faraday-rotation structure of elliptical shape, with its long axis parallel to the plane of the Galaxy. The feature appears to be located in an inter-arm region of the Milky Way, between the spiral arm containing the Sun and the next outer (Perseus) spiral arm. Within the elliptical region, small-scale structure which characterizes the turbulence seen in adjacent regions of the interstellar medium is absent. The origin of this magneto-ionic feature is uncertain, but it must arise from an organization of the magnetic-field and electron-density distributions on a scale of the order of 50 parsecs (165 light years).

The Global Magneto-Ionic Medium Survey (GMIMS) is a project to map the diffuse polarized emission over the entire sky, Northern and Southern hemispheres, from 300 MHz to 1.8 GHz. With an angular resolution of 30–60 arcmin and a frequency resolution of 1 MHz or better, GMIMS will provide the first spectro-polarimetric data set of the large-scale polarized emission over the entire sky, observed with single-dish telescopes. GMIMS will provide an invaluable resource for studies of the magneto-ionic medium of the Galaxy in the local disk, halo, and its transition.