Radio emission physics in the Crab pulsar

Abstract

We review our high-time-resolution radio observations of the Crab pulsar and compare our data to a variety of models for the emission physics. The Main Pulse and the Low Frequency Interpulse come from regions somewhere in the high-altitude emission zones (caustics) that also produce pulsed X-ray and γ -ray emission. Although no emission model can fully explain these two components, the most likely models suggest they arise from a combination of beam-driven instabilities, coherent charge bunching and strong electromagnetic turbulence. Because the radio power fluctuates on a wide range of time scales, we know the emission zones are patchy and dynamic. It is tempting to invoke unsteady pair creation in high-altitude gaps as the source of the variability, but current pair cascade models cannot explain the densities required by any of the likely models. It is harder to account for the mysterious High Frequency Interpulse. We understand neither its origin within the magnetosphere nor the striking emission bands in its dynamic spectrum. The most promising models are based on analogies with solar zebra bands, but they require unusual plasma structures which are not part of our standard picture of the magnetosphere. We argue that radio observations can reveal much about the upper magnetosphere, but work is required before the models can address all of the data.

Pulsar Radio Emission Mechanism: Radio Nanoshots as a Low-frequency Afterglow of Relativistic Magnetic Reconnection

“…Type II emission should naturally coincide in phase with the magnetospheric gamma-ray emission, which also originates in the current layer (Lyubarskii 1996;Uzdensky & Spitkovsky 2014;Cerutti et al 2016;Kalapotharakos et al 2018). This emerging picture is motivated by the recent observations of the Crab pulsar, several other young energetic pulsars, and a few millisecond pulsars, which clearly show a radio emission source that is coincident with the location of the pulsed high-energy radiation source (Johnston & Romani 2004;Johnson et al 2014;Eilek & Hankins 2016). In the Crab, this radio emission component (identified here with Type-II emission) is sometimes resolved into discrete bright pulses of nanosecond duration, "nanoshots" (Eilek & Hankins 2016).…”

Constraints on pulsed emission model for repeating FRB 121102

“…Note that the radio efficiency of GRP has been poorly understood (Eilek & Hankins 2016). The radio efficiency of normal pulse increases as the spin-down luminosity decreases in Galactic pulsars whose ages are older than the spin-down timescale (Szary et al 2014).…”

Phase-resolved gamma-ray spectroscopy of the Crab pulsar observed by POLAR

“…These features make it one of the best studied celestial objects, and thus a common calibration source for astronomical missions [4]. The Crab pulsar shows a double-pulse structure, with the main pulse (MP) and the inter pulse (IP) separated by the pulse phase of ∼ 144 • (0.4 in 1) approximately aligned in absolute phase in every energy band [5,6,7,8,9,10, and references therein]. The studies for the origin and structure of the particle acceleration region of pulsars (PSRs) over the past fifty years have evolved with multiple theoretical models (see review paper [11, and references therein]) that suggesting different radiation regions and mechanisms.…”