分类： 天文学 >> 天文学 提交时间： 2025-07-09
摘要： Five decades after the discovery of radio pulsars, main stream theories based on polar cap still suffer from difficulties in both self-consistency and confrontation with observations[1]. Increasing observation of individual subpulses of pulsars, i.e., high brightness temperature, highly polarized, and narrowband nanoshots of the Crab pulsar[2, 3] indicate that they relate with basic emission elements in a pulse window. Moreover, high degree of circular polarization, and rapid orthogonal jump in the position angle of linear polarization are observed in micropulses of both pulsars and Fast Radio Bursts (FRBs)[3–6], which further requires that such a small element of emission has a rapid variable conal-core pattern rather than a simple bunch of high energy density widely accepted. These are both unprecedented challenges and chances to understand the origin of pulsar coherent emission. This paper confronts with those difficulties by a simple model of alternative emission site and mechanism, in which pulsar wind is launched from open field line region and the coherent emission is triggered by a forced magnetic reconnection occurring at the tip of last closed field line near the light cylinder. The high energy density at such a tiny reconnection site automatically invokes Alfven waves, creates electron-positron pair, and accelerates them into relativistic speed. The resultant particle-wave interaction gives rise to coherent bunches inborn a conal-core structure responsible for observations on pulsars, magnetars and FRBs. For the first time, puzzles on coherency, polarization, correlation of coherent emission with wind, and energy budget of pulsars, magnetars, and FRBs are interpreted by a unified model.
分类： 天文学 >> 天体物理学 分类： 天文学 >> 天文学 提交时间： 2023-08-31
摘要： The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.
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