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Abstract We propose a scenario that can describe a broad range of fast radio burst (FRB) phenomenology, from nonrepeating bursts to highly prolific repeaters. Coherent radio waves in these bursts are produced in the polar cap region of a magnetar, where magnetic field lines are open. The angle between the rotation and magnetic axes, relative to the angular size of the polar cap region, partially determines the repetition rate and polarization properties of FRBs. We discuss how many of the properties of repeating FRBs—such as their lack of periodicity, energetics, small polarization angle (PA) swing, spectro–temporal correlation, and inferred low source density— are explained by this scenario. The systematic PA swing and the periodic modulation of long-duration bursts from nonrepeaters are also natural outcomes. We derive a lower limit of about 400 on the Lorentz factor of FRB sources applying this scenario to bursts with a linear polarization degree greater than 95%. 

In precision agriculture, integrating advanced technologies is crucial for optimizing plant growth and health monitoring. Cyber-physical system (CPS) platforms tailored to specific agricultural environments have emerged, but the diversity of these environments poses challenges in developing adaptive CPS platforms. This paper explores rapid prototyping methods to address these challenges, focusing on non-destructive techniques for estimating plant growth. We present a CPS prototype that combines sensors, microcontrollers, digital image processing, and predictive modeling to measure leaf area and biomass accumulation in hydroponic environments. Our results show that the prototype effectively monitors and predicts plant growth, highlighting the potential of rapid CPS prototyping in promoting sustainability and improving crop yields at a moderate cost of hardware. 

ABSTRACT Most fast radio burst (FRB) models can be divided into two groups based on the distance of the radio emission region from the central engine. The first group of models, the so-called ‘nearby’ or magnetospheric models, invoke FRB emission at distances of 109 cm or less from the central engine, while the second ‘far-away’ models involve emission from distances of 1011 cm or greater. The lateral size for the emission region for the former class of models (≲107 cm) is much smaller than the second class of models (≳109 cm). We propose that an interstellar scattering screen in the host galaxy is well-suited to differentiate between the two classes of models, particularly based on the level of modulations in the observed intensity with frequency, in the regime of strong diffractive scintillation. This is because the diffractive length scale for the host galaxy’s interstellar medium scattering screen is expected to lie between the transverse emission-region sizes for the ‘nearby’ and the ‘far-away’ class of models. Determining the strength of flux modulation caused by scintillation (scintillation modulation index) across the scintillation bandwidth (∼1/2πδts) would provide a strong constraint on the FRB radiation mechanism when the scatter broadening (δts) is shown to be from the FRB host galaxy. The scaling of the scintillation bandwidth as ∼ν4.4 may make it easier to determine the modulation index at ≳ 1 GHz. 

ABSTRACT We describe how gravitational lensing of fast radio bursts (FRBs) is affected by a plasma screen in the vicinity of the lens or somewhere between the source and the observer. Wave passage through a turbulent medium affects gravitational image magnification, lensing probability (particularly for strong magnification events), and the time delay between images. The magnification is suppressed because of the broadening of the angular size of the source due to scattering by the plasma. The time delay between images is modified as the result of different dispersion measures (DM) along photon trajectories for different images. Each of the image light curves is also broadened due to wave scattering so that the images could have distinct temporal profiles. The first two effects are most severe for stellar and sub-stellar mass lens, and the last one (scatter broadening) for lenses and plasma screens at cosmological distances from the source/observer. This could limit the use of FRBs to measure their cosmic abundance. On the other hand, when the time delay between images is large, such that the light curve of a transient source has two or more well-separated peaks, the different DMs along the wave paths of different images can probe density fluctuations in the IGM on scales ≲10−6 rad and explore the patchy reionization history of the universe using lensed FRBs at high redshifts. Different rotation measures (RM) along two-image paths can convert linearly polarized radiation from a source to partial circular polarization. 

ABSTRACT We show that the 216.8 ± 0.1 ms periodicity reported for the fast radio burst (FRB) 20191221A is very constraining for burst models. The high accuracy of burst periodicity (better than one part in 103), and the 2 per cent duty cycle (ratio of burst duration and interburst interval), suggest a pulsar-like rotating beam model for the observed activity; the radio waves are produced along open field lines within ∼107 cm of the neutron star surface, and the beam periodically sweeps across the observer as the star spins. According to this picture, FRB 20191221A is a factor ∼1012 scaled up version of galactic pulsars with one major difference, whereas pulsars convert rotational kinetic energy to EM waves and the outbursts of 20191221A require conversion of magnetic energy to radiation. 

ABSTRACT One widely discussed mechanism to produce highly coherent radio emission of fast radio bursts (FRBs) is coherent emission by bunches, either via curvature radiation or inverse Compton scattering (ICS). It has been suggested that the plasma oscillation effect can significantly suppress coherent emission power by bunches. We examine this criticism in this paper. The suppression factor formalism was derived within the context of radio pulsars in which radio waves are in the low-amplitude, linear regime and cannot directly be applied to the large-amplitude, non-linear regime relevant for FRBs. Even if one applies this linear treatment, plasma suppression is not important for two physical reasons. First, for an efficient radiation mechanism, such as ICS, the required plasma density is not high so that a high-density plasma may not exist. Secondly, both bunched coherent mechanisms demand that a large global parallel electric field (E∥) must exist in the emission region in order to continuously inject energy to the bunches to power an FRB. In order to produce typical FRB duration via coherent curvature or ICS radiation, a parallel electric field must be present to balance the acceleration and radiation back reaction. The plasma suppression factor should be modified with the existence of E∥. We show that the correction factor for curvature radiation, fcur, increases with E∥ and becomes 1 when E∥ reaches the radiation-reaction-limited regime. We conclude that the plasma suppression effect can be ignored for realistic FRB emission models invoking bunched coherent radio emission. 

ABSTRACT We present numerical simulation results for the propagation of Alfvén waves in the charge starvation regime. This is the regime where the plasma density is below the critical value required to supply the current for the wave. We analyse a conservative scenario where Alfvén waves pick up charges from the region where the charge density exceeds the critical value and advect them along at a high Lorentz factor. The system consisting of the Alfvén wave and charges being carried with it, which we call charge-carrying Alfvén wave (CC-AW), moves through a medium with small, but non-zero, plasma density. We find that the interaction between CC-AW and the stationary medium has a two-stream like instability which leads to the emergence of a strong electric field along the direction of the unperturbed magnetic field. The growth rate of this instability is of the order of the plasma frequency of the medium encountered by the CC-AW. Our numerical code follows the system for hundreds of wave periods. The numerical calculations suggest that the final strength of the electric field is of the order of a few per cent of the AW amplitude. Little radiation is produced by the sinusoidally oscillating currents associated with the instability during the linear growth phase. However, in the non-linear phase, the fluctuating current density produces strong EM radiation near the plasma frequency and limits the growth of the instability.