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Register a new userCoherent curvature radiation and Fast Radio Bursts
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Added by
Gabriele Ghisellini
Publication date
2017
fields
Physics
and research's language is
English
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Fast radio bursts are extragalactic radio transient events lasting a few milliseconds with a ~Jy flux at ~1 GHz. We propose that these properties suggest a neutron star progenitor, and focus on coherent curvature radiation as the radiation mechanism. We study for which sets of parameters the emission can fulfil the observational constraints. Even if the emission is coherent, we find that self-absorption can limit the produced luminosities at low radio frequencies and that an efficient re-acceleration process is needed to balance the dramatic energy losses of the emitting particles. Self-absorption limits the luminosities at low radio frequency, while coherence favours steep optically thin spectra. Furthermore, the magnetic geometry must have a high degree of order to obtain coherent curvature emission. Particles emit photons along their velocity vectors, thereby greatly reducing the inverse Compton mechanism. In this case we predict that fast radio bursts emit most of their luminosities in the radio band and have no strong counterpart in any other frequency bands.
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In this paper we develop a model for fast radio bursts (FRBs) based on triggered superradiance (SR) and apply it to previously published data of FRB 110220 and FRB 121102. We show how a young pulsar located at ~100 pc or more from an SR/FRB system could initiate the onset of a powerful burst of radiation detectable over cosmological distances. Our models using the OH$^2Pi_{3/2}$ $left(J=3/2right)$ 1612 MHz and $^2Pi_{3/2}$ $left(J=5/2right)$ 6030 MHz spectral lines match the light curves well and suggest the entanglement of more than $10^{30}$ initially inverted molecules over lengths of approximately 300 au for a single SR sample. SR also accounts for the observed temporal narrowing of FRB pulses with increasing frequency for FRB 121102, and predicts a scaling of the FRB spectral bandwidth with the frequency of observation, which we found to be consistent with the existing data.
We develop a model of the generation of coherent radio emission in the Crab pulsar, magnetars and Fast Radio Bursts (FRBs). Emission is produced by a reconnection-generated beam of particles via a variant of Free Electron Laser (FEL) mechanism, operating in a weakly-turbulent, guide-field dominated plasma. We first consider nonlinear Thomson scattering in a guide-field dominated regime, and apply to model to explain emission bands observed in Crab pulsar and in Fast Radio Bursts. We consider particle motion in a combined fields of the electromagnetic wave and thee lectromagnetic (Alfvenic) wiggler. Charge bunches, created via a ponderomotive force, Compton/Raman scatter the wiggler field coherently. The model is both robust to the underlying plasma parameters and succeeds in reproducing a number of subtle observed features: (i) emission frequencies depend mostly on the length $lambda_t$ of turbulence and the Lorentz factor of the reconnection generated beam, $omega sim gamma_b^2 ( c/lambda_t) $ - it is independent of the absolute value of the underlying magnetic field. (ii) The model explains both broadband emission and the presence of emission stripes, including multiple stripes observed in the High Frequency Interpulse of the Crab pulsar. (iii) The model reproduces correlated polarization properties: presence of narrow emission bands in the spectrum favors linear polarization, while broadband emission can have arbitrary polarization. (iv) The mechanism is robust to the momentum spread of the particle in the beam. We also discuss a model of wigglers as non-linear force-free Alfven solitons (light darts).
In this paper we identify some sub-optimal performance in algorithms that search for Fast Radio Bursts (FRBs), which can reduce the cosmological volume probed by over 20%, and result in missed discoveries and incorrect flux density and sky rate determinations. Re-calculating parameters for all of the FRBs discovered with the Parkes telescope (i.e. all of the reported FRBs bar one), we find some inconsistencies with previously determined values, e.g. FRB 010125 was approximately twice as bright as previously reported. We describe some incompleteness factors not previously considered which are important in determining accurate population statistics, e.g. accounting for fluence incompleteness the Thornton et al. all-sky rate can be re-phrased as ~2500 FRBs per sky per day above a 1.4-GHz fluence of ~2 Jy ms. Finally we make data for the FRBs easily available, along with software to analyse these.
We summarize our understanding of millisecond radio bursts from an extragalactic population of sources. FRBs occur at an extraordinary rate, thousands per day over the entire sky with radiation energy densities at the source about ten billion times larger than those from Galactic pulsars. We survey FRB phenomenology, source models and host galaxies, coherent radiation models, and the role of plasma propagation effects in burst detection. The FRB field is guaranteed to be exciting: new telescopes will expand the sample from the current ~80 unique burst sources (and a few secure localizations and redshifts) to thousands, with burst localizations that enable host-galaxy redshifts emerging directly from interferometric surveys. * FRBs are now established as an extragalactic phenomenon. * Only a few sources are known to repeat. Despite the failure to redetect other FRBs, they are not inconsistent with all being repeaters. * FRB sources may be new, exotic kinds of objects or known types in extreme circumstances. Many inventive models exist, ranging from alien spacecraft to cosmic strings but those concerning compact objects and supermassive black holes have gained the most attention. A rapidly rotating magnetar is a promising explanation for FRB 121102 along with the persistent source associated with it, but alternative source models are not ruled out for it or other FRBs. * FRBs are powerful tracers of circumsource environments, `missing baryons in the IGM, and dark matter. * The relative contributions of host galaxies and the IGM to propagation effects have yet to be disentangled, so dispersion measure distances have large uncertainties.
Fast radio bursts (FRBs) are bright, unresolved, millisecond-duration flashes of radio emission originating from outside of the Milky Way. The source of these mysterious outbursts is unknown, but their high luminosity, high dispersion measure and short duration requires an extreme, high-energy, astrophysical process. The majority of FRBs have been discovered as single events which would require a chance coincidence for contemporaneous multiwavelength observations. However, two have been observed to repeat: FRB 121102 and the recently detected FRB 180814.J0422+73. These repeating FRBs have allowed for targeted observations by a number of different instruments, including VERITAS. We present the VERITAS FRB observing program and the results of these observations.
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