Fast radio bursts

Abstract

The discovery of radio pulsars over a half century ago was a seminal moment in astronomy. It demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. More recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the Milky Way and hence are many orders-of-magnitude more luminous. While most FRBs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. Beyond understanding how they are created, there is also the prospect of using FRBs-as with pulsars-to probe the extremes of the Universe as well as the otherwise invisible intervening medium. Such studies will be aided by the high-implied all-sky event rate: there is a detectable FRB roughly once every minute occurring somewhere on the sky. The fact that less than a hundred FRB sources have been discovered in the last decade is largely due to the small fields-of-view of current radio telescopes. A new generation of wide-field instruments is now coming online, however, and these will be capable of detecting multiple FRBs per day. We are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of FRBs. In this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field.

Keywords: Fast radio burst; Pulsar; Radio astronomy; Transient.

Fig. 1

The Lorimer burst ( Lorimer et al. , now also known as FRB 010724), as seen in the beam of the Parkes multi-beam receiver where it appeared brightest. These data have been one-bit digitized and contain 96 frequency channels sampled every millisecond. The burst has a DM of 375 ${\text{cm}}^{-3}$ pc. The pulse was so bright that it saturated the detector, causing a dip below the nominal baseline of the noise right after the pulse occurred. This signal was also detected in 3 other beams of the receiver. The top panel shows the burst as summed across all recorded frequencies. The bottom panel is the burst as a function of frequency and time (a ‘dynamic spectrum’). The red horizontal lines are frequency channels that have been excised because they are corrupted by RFI

Fig. 2

The dispersion measures (DMs) of Galactic radio pulsars, Galactic rotating radio transients (RRATs), radio pulsars in the Small and Large Magellanic Clouds (SMC & LMC), and published FRBs, relative to the modeled maximum Galactic DM along the line of sight from the NE2001 model (Cordes and Lazio 2002). Sources with $\mathrm{DM}/{\mathrm{DM}}_{\max }>1$ are thought to originate at extragalactic distances and accrue additional DM from the intergalactic medium and their host galaxy. This figure is based on an earlier version presented in Spitler et al. (2014)

Fig. 3

Compilation showing the first twenty-eight FRBs discovered using the Parkes telescope. The detections are arranged in order of date. Each light curve shows a 2-s window around the pulse. Following gamma-ray burst notation, the FRBs are named in YYMMDD format to indicate the year (YY) month (MM) and day (DD) on which the burst was detected. Also listed to the right of each pulse are the observed dispersion measures (DMs) in units of ${\text{cm}}^{-3}$ pc

Fig. 4

Apparent scintillation seen in FRB 150807. c A dedispersed dynamic spectrum of the burst at 390-kHz spectral resolution. The inferred scintillation bandwidth is $100\pm 50$ kHz. b The frequency-averaged burst profile with total intensity (black), linearly polarized signal (red), and circularly polarized signal (blue). a The polarization angle across the burst, and d a smoothed version of the burst spectrum. Image from Ravi et al. (2016), reproduced with permission from AAAS

Fig. 5

Scattering seen in FRB 110220. The main panel shows the dynamic spectrum of the burst and its dispersive sweep. The inset shows how the burst becomes asymmetrically broadened towards lower radio frequencies. Image from Thornton et al. (2013), reproduced with permission from AAAS

Fig. 6

Faraday rotation seen in FRB 121102. a, b The values of the Stokes Q and U parameters across the measured frequency range, normalized to the total linear intensity. c The residuals compared to a best-fit Faraday rotation model. The various colors represent measurements from separate bursts detected in the same observing session Image reproduced with permission from Michilli et al. (2018a), copyright by Macmillan

Fig. 7

A block diagram summarizing the analysis procedure discussed in Sect. 4.1

Fig. 8

Examples of single-dish radio telescopes used to search for FRBs (from left to right): the 64 m Parkes telescope in New South Wales, Australia, the 305 m Arecibo telescope in Puerto Rico, USA, and the 110 m Green Bank Telescope in West Virgina, USA

Fig. 9

Examples of radio interferometers used to search for FRBs (from left to right): the Jansky Very Large Array (JVLA) of 2725 m dishes in New Mexico, USA, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with four cylindrical paraboloids each 100 m long and 20 m in diameter in British Columbia, Canada, and the core of the Low-Frequency Array (LOFAR) of dipoles in the Netherlands

Fig. 10

Left: using the VLA, repeating bursts from FRB 121102 were localized to sub-arcsecond precision using interferometric techniques. Right: the localization allowed for the identification of the host galaxy at radio and optical (inset) wavelengths. Images reproduced with permission from Chatterjee et al. (2017), copyright by Macmillan

Fig. 11

Dedispersed spectra of individual bursts from a the repeating FRB 121102 at 1.4 GHz using Arecibo, and b the repeating FRB 180814.J0422+73 discovered with CHIME at 700 MHz. Both repeating sources have some bursts that show distinct sub-burst structure with descending center frequencies over time. Horizontal bands in both spectra are due to narrow-band RFI excision in the data. FRB 121102 data from Hessels et al. (2018). FRB 180814.J0422+73 data from CHIME/FRB Collaboration et al. (2019a)

Fig. 12

Polarization profiles for FRB 140514 (left), the first FRB with measured circular polarization (Petroff et al. 2015a), and FRB 110523 (right), the first FRB with measured linear polarization (Masui et al. 2015). The Stokes parameters for total intensity I (solid), Q (dashed), U (dot-dashed), and V(dotted) are plotted for each burst. FRB 140514 profile from Fig. 1 of Petroff et al. (2015a); FRB 110523 profile from Fig. 3 of Masui et al. (2015)

Fig. 13

The properties of the cataloged FRB population. a The pulse duration (width) versus DM. Solid lines represent temporal broadening from DM smearing in an individual frequency channel combined with the sampling time for different telescopes. In the case of FRBs from CHIME, plotted widths have been obtained through modeling and are not the observed FRB widths from the instrument. b Scattering timescale versus DM for all FRBs where scattering has been measured. The curve shows the DM-scattering relation for pulsars in the Galaxy derived by Bhat et al. (2004). FRBs are under-scattered relative to Galactic pulsars of similar DMs. c A histogram of the DM excess compared to the expected Galactic maximum along the line of sight. d A histogram of the pulse durations. For a, b colors correspond to the Parkes (black), ASKAP (blue), Arecibo (green), UTMOST (red), GBT (aqua) and CHIME (pink) telescopes

Fig. 14

An Aitoff projection map of the sky positions of all published FRBs as a function of Galactic longitude and latitude. As in Fig. 13, colors correspond to the Parkes (black), ASKAP (blue), Arecibo (green), UTMOST (red), GBT (aqua) and CHIME (pink) telescopes

Fig. 15

Dedispersed pulse profiles and dynamic spectra of several FRBs. FRB 170827 (top, left) from Farah et al. (2018) detected with UTMOST at 835 MHz, FRB 110220 (top, middle) from Thornton et al. (2013) detected with Parkes at 1.4 GHz, FRB 110523 (top, right) from Masui et al. (2015) detected with GBT at 800 MHz, FRB 180110 (bottom, left) from Shannon et al. (2018) detected with ASKAP at 1.3 GHz, a pulse from FRB 121102 (bottom, middle) from Michilli et al. (2018a) detected with Arecibo at 4.5 GHz, and a pulse from FRB 180814.J0422+73 (bottom, right) from CHIME/FRB Collaboration et al. (2019a) detected with CHIME at 600 MHz

Fig. 16

Fluence–dispersion measure distribution for the currently observed sample overlaid with lines of isotropic equivalent luminosity values assuming a contribution of ${\mathrm{DM}}_{\mathrm{Host}}=50$ ${\text{cm}}^{-3}$ pc. The recent detections from CHIME/FRB have been omitted (see text)