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A Living Theory Catalogue for Fast Radio Bursts

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A Living Theory Catalogue for Fast Radio Bursts A Living Theory Catalogue for Fast Radio Bursts E. Plattsa,∗, A. Weltmana, A. Waltersb,c, S. P. Tendulkard, J.E.B. Gordina, S. Kandhaia aHigh Energy Physics, Cosmology & Astrophysics Theory (HEPCAT) group, Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch, 7700, South Africa bAstrophysics & Cosmology Research Unit, School of Chemistry and Physics, University of KwaZulu-Natal, Durban, 4000, South Africa cNAOC-UKZN Computational Astrophysics Centre (NUCAC), University of KwaZulu-Natal, Durban, 4000, South Africa dDepartment of Physics & McGill Space Institute, McGill University, 3600 University Street, Montreal QC, H3A 2T8, Canada Abstract At present, we have almost as many theories to explain Fast Radio Bursts as we have Fast Radio Bursts observed. This landscape will be changing rapidly with CHIME/FRB, recently commis- sioned in Canada, and HIRAX, under construction in South Africa. This is an opportune time to review existing theories and their observational consequences, allowing us to efficiently curtail viable astrophysical models as more data becomes available. In this article we provide a currently up to date catalogue of the numerous and varied theories proposed for Fast Radio Bursts so far. We also launched an online evolving repository for the use and benefit of the community to dynamically update our theoretical knowledge and discuss constraints and uses of Fast Radio Bursts. Keywords: Fast Radio Bursts, transients, neutron stars, black holes arXiv:1810.05836v5 [astro-ph.HE] 7 Jun 2019 ∗Corresponding author Email addresses: [email protected] (E. Platts), [email protected] (A. Weltman), [email protected] (A. Walters), [email protected] (S. P. Tendulkar), [email protected] (J.E.B. Gordin), [email protected] (S. Kandhai) Preprint submitted to Elsevier June 10, 2019 Contents 1 Introduction 4 2 Basic Observational Constraints 6 2.1 DispersionMeasures ................................. ... 6 2.2 Polarization and Rotation Measures . ..... 6 2.3 Observed Counterparts / Possible Counterparts . ........... 7 2.3.1 FRB150418..................................... 7 2.3.2 FRB131104..................................... 7 2.3.3 FRB121102..................................... 8 2.4 TheCuriousCaseofFRB121102. .... 8 3 Model Ingredients 8 3.1 EmissionMechanisms .................................. 9 3.1.1 Bremsstrahlung Radiation . 9 3.1.2 Atomic Electron Transition . 9 3.1.3 SynchrotronRadiation.............................. 9 3.1.4 CurvatureRadiation................................ 9 3.1.5 Undulator Radiation . 9 3.1.6 InverseComptonScattering. ... 9 3.2 GeneratingCoherence ............................... .... 10 3.2.1 BunchedParticles ................................. 10 3.2.2 Masers........................................ 10 3.2.3 Dicke’s Superradiance . 11 4 Progenitor Theories 11 4.1 CompactObjectMergers/Interactions . ........ 11 4.1.1 Neutron Star–Neutron Star Mergers / Interactions . ......... 11 4.1.2 NeutronStar–SupernovaInteractions. ....... 12 4.1.3 NeutronStar–WhiteDwarfMergers . ... 12 4.1.4 BinaryWhiteDwarfMerger. .. .. .. .. .. .. .. .. .. .. .. .. 13 4.1.5 White Dwarf–Black Hole Mergers . 13 4.1.6 NeutronStar–BlackHoleMergers . .. 13 4.1.7 Pulsar–Black Hole Interactions . .. 14 4.1.8 Kerr-Newman–Black Hole Interactions . .... 14 4.2 CollapseofCompactObjects . .. .. .. .. .. .. .. .. .. .. .. .... 15 4.2.1 Supramassive Neutron Star to Kerr-Newman Black Hole . ...... 15 4.2.2 NeutronStartoQuarkStar. .. 15 4.2.3 DarkMatterInducedNeutronStarCollapse . .... 15 4.2.4 CollapseofStrangeStarCrust . .. 16 4.3 SupernovaeRemnants ............................... .... 16 4.3.1 GiantPulses .................................... 16 4.3.2 Giant Flares in Magnetars . 18 4.3.3 EjectaPenetration ................................ 19 4.4 Active Galactic Nuclei . .. 20 4.4.1 AGN Jet Interacting with Cavitons . .. 20 2 4.4.2 Kerr Black Hole Interacting with AGN . 20 4.4.3 StrangeStarInteractingwithAGN. ... 21 4.4.4 AGN-like Wandering Beams . 21 4.5 Collisions and Close Encounters . .... 21 4.5.1 NeutronStarsandSmallBodies . 21 4.5.2 Collisions Between Neutron Stars and Primordial Black Holes . ..... 22 4.5.3 Interactions Between Axions and Compact Bodies . ..... 22 4.6 OtherModels....................................... 24 4.6.1 Starquake-InducedRepeaters . ..... 24 4.6.2 VariableStars.................................... 24 4.6.3 Lightning in Pulsars . 24 4.6.4 WanderingPulsarBeam.............................. 24 4.6.5 Tiny Electromagnetic Explosions . 25 4.6.6 White Hole Explosions . 25 4.6.7 NeutronStarCombing............................... 25 4.6.8 NeutralStrings................................... 26 4.6.9 SuperconductingStrings. .. 26 4.6.10 Dicke’s Superradiance in Galaxies . 26 4.6.11 Alien Light Sails . 26 4.7 TheoriesThatHaveBeenRuledOut . .... 27 4.7.1 StellarCoronae................................... 27 4.7.2 Annihilating Mini Black Holes . 27 5 Conclusion 27 5.1 FutureObservationalConstraints . ........ 27 5.1.1 Astrophysical Formation Channels . ... 28 5.1.2 Emission Mechanisms . 28 6 Acknowledgements 28 7 Tabulated Summary 29 8 Acronyms 31 9 References 33 3 1. Introduction A little over a decade after their discovery (Lorimer et al., 2007), Fast Radio Bursts (FRBs) remain an enigmatic class of radio transients. FRBs are characterized by one or multiple very bright (∼ Jy) and very brief (∼ ms) bursts of radio photons, and have been detected at frequencies ranging between 400 MHz − 8 GHz by a number of ground-based radio telescopes. Importantly, the arrival time of the frequency components is dispersed, precisely going as ∆t ∼ ν−2, which is consistent with the propagation of a radio wave through cold plasma (Lorimer et al., 2007; Dennison, 2014; Caleb et al., 2016). While some early speculation considered FRBs to be of galactic origin (Keane et al., 2012; Burke-Spolaor and Bannister, 2014; Bannister and Madsen, 2014; Maoz et al., 2015), current consensus is that their excessively large dispersion measure (DM) (see Section 2.1), high galactic latitude, apparent isotropy over the sky (Champion et al., 2016), and lack of HII regions or other sources of excess DM indicate an extragalactic (Keane et al., 2012; Xu and Han, 2015; Xu and Han, 2015; Cordes and Wasserman, 2016; Connor et al., 2016) or cosmological (Dolag et al., 2015; Kulkarni et al., 2014; Katz, 2016d; Caleb et al., 2016; Vedantham et al., 2016a; Cao et al., 2017; Niino, 2018) origin. This consensus is supported by the identification of the host galaxy of FRB 121102 at redshift z=0.1932 (Chatterjee et al., 2017; Tendulkar et al., 2017). One of the central challenges facing theoretical model builders is finding a physical mechanism with which one can explain the vast amount of energy radiated over such short timescales. If one assumes isotropic emission, the extreme brightness indicates that some beamed, coherent emission process is required (Thornton et al., 2013), and the brevity of the signals suggests the source is extremely compact (Thornton et al., 2013). Compounding the model building challenges, the characteristic properties of FRBs appear to be heterogeneous. Where measurements have been possible, FRBs have been observed to have circular (Ravi et al., 2015; Petroff et al., 2015a; Caleb et al., 2018) and/or linear (Petroff et al., 2015b; Masui et al., 2015; Ravi et al., 2016; Michilli et al., 2018; Gajjar et al., 2018) polarizations, as well as some that seem unpolarized (although this may be due to extremely high Faraday rotation (Michilli et al., 2018)). The pulse profiles of FRBs also differ: two have double or triple peaks (Champion et al., 2016; Farah et al., 2018), while the rest have only single peaks. Many FRBs have now shown complex microstructure and features at timescales of 10s of microseconds (Farah et al., 2018) (and Hessels et al., in preparation). Even more baffling is that only two FRBs, FRB 121102 and FRB 180814.J0422+73 have been observed to repeat (Spitler et al., 2016; Scholz et al., 2017; Gajjar et al., 2018; Spitler et al., 2018; CHIME/FRB Collaboration et al., 2019), with modulating pulse shapes and no apparent periodicity (see Section 2.4). Some FRBs have been monitored for up to hundreds of hours with no indication of repetition (Lorimer et al., 2007; Petroff et al., 2015a; Ravi et al., 2016; Petroff et al., 2017; Bhandari et al., 2018; Shannon et al., 2010), and while this may imply there are two different classes of FRB (repeaters and non-repeaters) (Palaniswamy et al., 2018; Michilli et al., 2018), there may just be a large range in repetition rates (Caleb et al., 2019). Further, the observed repetition or lack thereof can be strongly affected by interstellar scintillations (Cordes and Rickett, 1998) or plasma lensing (Cordes et al., 2017; Main et al., 2018; Spitler et al., 2018). FRB 121102 was found to have a rotation measure (RM) 400 times larger than any other known FRB (Michilli et al., 2018; Gajjar et al., 2018), but previous FRBs may have had high RMs that were simply not detectable (Petroff et al., 2015a; Keane et al., 2016). There is currently no consensus on the matter. 4 There have only been 541 FRB detections subsequent to the Lorimer burst in 20072, but the non- detection of FRBs can provide some insight. For example, one can constrain event rates (Siemion et al., 2012; Wayth et al., 2012; Trott et al., 2013a,b; Tingay et al., 2015; Karastergiou et al., 2015; Burke-Spolaor et al., 2016; Rowlinson et al., 2016; Amiri et al., 2017; Surnis et al., 2017), spectral indices (Tingay
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