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Register a new userBurst timescales and luminosities link young pulsars and fast radio bursts
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Fast radio bursts (FRBs) are extragalactic radio flashes of unknown physical origin (Petroff et al. 2019; Cordes & Chatterjee 2019). Their high luminosities and short durations require extreme energy densities, like those found in the vicinity of neutron stars and black holes. Studying the burst intensities and polarimetric properties on a wide range of timescales, from milliseconds down to nanoseconds, is key to understanding the emission mechanism. However, high-time-resolution studies of FRBs are limited by their unpredictable activity levels, available instrumentation and temporal broadening in the intervening ionised medium. Here we show that the repeating FRB 20200120E (Bhardwaj et al. 2021) can produce isolated shots of emission as short as about 60 nanoseconds in duration, with brightness temperatures as high as 3x10$^{41}$ K (excluding relativistic effects), comparable to nano-shots from the Crab pulsar. Comparing both the range of timescales and luminosities, we find that FRB 20200120E bridges the gap between known Galactic young pulsars and magnetars, and the much more distant extragalactic FRBs. This suggests a common emission mechanism spanning many orders of magnitude in timescale and luminosity. While the burst timescales and luminosities can be explained by magnetic reconnection in the vicinity of an isolated, young, highly magnetised neutron star, the localisation of FRB 20200120E to a globular cluster (Kirsten et al. submitted) also opens the possibility of magnetic reconnection in an older binary system featuring compact stars or a black hole.
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We present a newly implemented single-pulse pipeline for the PALFA survey to efficiently identify single radio pulses from pulsars, Rotating Radio Transients (RRATs) and Fast Radio Bursts (FRBs). We have conducted a sensitivity analysis of this new pipeline in which multiple single pulses with a wide range of parameters were injected into PALFA data sets and run through the pipeline. Based on the recovered pulses, we find that for pulse widths $rm < 5 ms$ the sensitivity of the PALFA pipeline is at most a factor of $rm sim 2$ less sensitive to single pulses than our theoretical predictions. For pulse widths $rm > 10 ms$, as the $rm DM$ decreases, the degradation in sensitivity gets worse and can increase up to a factor of $rm sim 4.5$. Using this pipeline, we have thus far discovered 7 pulsars and 2 RRATs and identified 3 candidate RRATs and 1 candidate FRB. The confirmed pulsars and RRATs have DMs ranging from 133 to 386 pc cm$^{-3}$ and flux densities ranging from 20 to 160 mJy. The pulsar periods range from 0.4 to 2.1 s. We report on candidate FRB 141113, which we argue is likely astrophysical and extragalactic, having $rm DM simeq 400 pc~cm^{-3}$, which represents an excess over the Galactic maximum along this line of sight of $rm sim$ 100 - 200 pc cm$^{-3}$. We consider implications for the FRB population and show via simulations that if FRB 141113 is real and extragalactic, the slope $alpha$ of the distribution of integral source counts as a function of flux density ($N (>S) propto S^{-alpha}$) is $1.4 pm 0.5$ (95% confidence range). However this conclusion is dependent on several assumptions that require verification.
We report on radio and X-ray observations of the only known repeating Fast Radio Burst (FRB) source, FRB 121102. We have detected six additional radio bursts from this source: five with the Green Bank Telescope at 2 GHz, and one at 1.4 GHz at the Arecibo Observatory for a total of 17 bursts from this source. All have dispersion measures consistent with a single value ($sim559$ pc cm$^{-3}$) that is three times the predicted maximum Galactic value. The 2-GHz bursts have highly variable spectra like those at 1.4 GHz, indicating that the frequency structure seen across the individual 1.4 and 2-GHz bandpasses is part of a wideband process. X-ray observations of the FRB 121102 field with the Swift and Chandra observatories show at least one possible counterpart; however, the probability of chance superposition is high. A radio imaging observation of the field with the Jansky Very Large Array at 1.6 GHz yields a 5$sigma$ upper limit of 0.3 mJy on any point-source continuum emission. This upper limit, combined with archival WISE 22-$mu$m and IPHAS H$alpha$ surveys, rules out the presence of an intervening Galactic HII region. We update our estimate of the FRB detection rate in the PALFA survey to be 1.1$^{+3.7}_{-1.0} times 10^4$ FRBs sky$^{-1}$ day$^{-1}$ (95% confidence) for peak flux density at 1.4 GHz above 300 mJy. We find that the intrinsic widths of the 12 FRB 121102 bursts from Arecibo are, on average, significantly longer than the intrinsic widths of the 13 single-component FRBs detected with the Parkes telescope.
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 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.
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.
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