The Astronomy and Astrophysics Review (2019) 27:4 https://doi.org/10.1007/s00159-019-0116-6 REVIEW ARTICLE Fast radio bursts E. Petroff1,2 · J. W. T. Hessels1,2 · D. R. Lorimer3,4 Received: 30 November 2018 © The Author(s) 2019 Abstract The discovery of radio pulsars over a half century ago was a seminal moment in astron- omy. 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 inter- stellar 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 instru- ments 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 B E. Petroff [email protected] 1 Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands 2 ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands 3 Department of Physics and Astronomy, West Virginia University, PO Box 6315, Morgantown, WV, USA 4 Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV, USA 0123456789().: V,-vol 123 4 Page 2 of 75 E. Petroff et al. Contents 1 Introduction ............................................... 1.1 A brief history ............................................ 1.2 The FRB population ......................................... 1.3 Motivation for this review ...................................... 2 Properties of FRBs ............................................ 2.1 Observed properties ......................................... 2.2 Basic derived properties ....................................... 2.2.1 Distance constraints ..................................... 2.2.2 Source luminosity ...................................... 2.2.3 DM–flux relationship ..................................... 2.2.4 Brightness temperature .................................... 3 Propagation effects ............................................ 3.1 Dispersion .............................................. 3.2 Scintillation ............................................. 3.3 Scattering .............................................. 3.4 Faraday rotation ........................................... 3.5 Plasma lensing ............................................ 3.6 Hi absorption ............................................ 3.7 Free–free absorption ........................................ 4 Observational techniques ........................................ 4.1 Searching for FRBs ......................................... 4.1.1 Preliminary radio frequency interference excision ...................... 4.1.2 Dedispersion ......................................... 4.1.3 Extracting a time series .................................... 4.1.4 Baseline estimation or smoothing .............................. 4.1.5 Normalization ......................................... 4.1.6 Matched filtering ....................................... 4.1.7 Candidate grouping ...................................... 4.1.8 Post-processing RFI excision ................................. 4.2 FRB search pipelines ........................................ 4.3 FRB searches with radio telescopes ................................. 4.3.1 Single-dish methods ..................................... 4.3.2 Interferometric methods ................................... 5 Landmark FRB discoveries ....................................... 5.1 FRB 010724: the Lorimer burst ................................... 5.2 FRB 010621: the Keane burst .................................... 5.3 FRB 140514 ............................................. 5.4 FRB 121102 ............................................. 5.5 FRB 180814.J0422+73 ....................................... 6 Population properties .......................................... 6.1 FRB polarization and rotation measures .............................. 6.2 Multi-wavelength follow-up of FRBs ................................ 6.3 Properties of the FRB population .................................. 6.4 The sky distribution ......................................... 6.5 The DM distribution ......................................... 6.6 The pulse width distribution ..................................... 6.7 Repeating and non-repeating FRBs ................................. 6.8 Sub-population emerging? ..................................... 7 The intrinsic population distribution ................................... 7.1 The fluence–dispersion measure plane ............................... 7.2 The FRB luminosity function .................................... 7.3 FRB rates and source counts .................................... 7.4 Intrinsic pulse widths ........................................ 7.5 Intrinsic spectra ........................................... 8 Emission mechanisms for FRBs ..................................... 123 Fast radio bursts Page 3 of 75 4 9 Progenitor models ............................................ 9.1 Neutron star progenitors ....................................... 9.1.1 Isolated neutron star models ................................. 9.1.2 Interacting neutron star models ................................ 9.1.3 Colliding neutron star models ................................ 9.2 Black hole progenitors ....................................... 9.3 White dwarf progenitors ...................................... 9.4 Exotic progenitors .......................................... 9.5 Differentiating between progenitor models ............................. 10 Summary and conclusions ........................................ 11 Predictions for 2024 ........................................... 11.1EP .................................................. 11.2JWTH ................................................ 11.3DRL ................................................. Glossary ................................................... References .................................................. 1 Introduction Astrophysical transients are events that appear and disappear on human-observable timescales, and are produced in a wide variety of physical processes. Longer duration transients, on timescales of hours to decades, such as fading supernovae, can emit incoherently from thermal electrons. Short-duration transients, however, with emission on timescales of seconds or less, are necessarily coherent in nature since the emission is too bright to be explained by individual electrons emitting separately. Whereas variable sources are characterized by occasional brightening and fading, often superimposed on a stable flux source, transients are often one-off events that fade when the emission mechanism turns off. The processes that produce both fast and slow transients are some of the most energetic in the Universe. The collapse of a massive star (Smith 2014), or the collision of two neutron stars (Abbott et al. 2017a), injects massive amounts of energy and material into the surrounding environment, producing heavy elements and seeding further star formation in galaxies. These violent processes emit across the electromagnetic spectrum on various timescales—from a few seconds of coherent gamma-ray emission from gamma-ray bursts (GRBs; Gehrels et al. 2009)to the sometimes years-long incoherent thermal radio emission from expanding material after a supernova explosion or GRB (Chandra and Frail 2012). Binary neutron star mergers can now also be observed through gravitational radiation (Abbott et al. 2017b). The energetic remnants of stellar explosions such as neutron stars are also known to produce millisecond-duration radio pulses (Hewish et al. 1968). Studies of fast transients can provide new windows on the processes that fuel galaxy evolution (Abbott et al. 2017b), and the compact stellar remnants left behind (Hamilton et al. 1985; Lyne et al. 2001). Within this context, it is no surprise that the discovery of fast radio bursts (FRBs), bright and seemingly extragalactic radio pulses, in 2007 (Lorimer et al. 2007) presented a tantalizing opportunity to the astronomical community as a potential new window on energetic extragalactic processes. FRBs are one of the most exciting new mysteries of astrophysics. They are bright (50 mJy–100