In single-pulse observations of PSR B1919+21, we identify a previously unreported emission phenomenon, which we term phase-locked intermittent brightenings (PLIBs). We aim to characterise the phenomenology and polarimetric properties of PLIBs and to explore possible physical interpretations of their origin. Using highly sensitive, high time-resolution polarimetric observations of PSR B1919+21 obtained with the Arecibo Observatory, we analysed flux-density variations, pulse-phase stability, and polarisation-vector trajectories in the Stokes Q--U plane, with particular emphasis on episodes of enhanced emission. Phase-locked intermittent brightenings are characterised by flux enhancements up to an order of magnitude above the mean level, occurring intermittently but at a fixed rotational phase (l = -5 They appear in both polarised and unpolarised emission and are associated with a sim90 change in the linear polarisation position angle, a transition of the Q--U vector from quadrant IV to quadrant II, and a reversal in the handedness of circular polarisation (Stokes V). Following a PLIB event, the Q--U vector executed a complete 360 clockwise rotation before returning to quadrant II; the characteristic Q--U-plane `torus' structure at l = 0 is likewise consistently confined to quadrant II. We interpret PLIBs as signatures of spatially localised but temporally intermittent processes operating within the neutron-star magnetosphere. Possible mechanisms include magnetic reconnection or surface instabilities, acting within a magnetic configuration that can be represented schematically as a double-helix structure embedded in a cylindrical magnetic tube. Within this phenomenological framework, the rotation of the double-helix structure with a period of 2, P₃ provides a qualitative explanation for the observed evolution of the polarisation plane. Meanwhile, the rotational distortion of magnetic field lines associated with the neutron star’s spin offers a plausible interpretation of the observed orthogonal polarisation mode transitions. The occurrence and modulation properties further suggest that the underlying structure has relatively low magnetic helicity. Overall, we propose a phenomenological framework that integrates these elements and provides a unified, qualitative interpretation of the emission and polarisation behaviour associated with PLIBs.
Gulyaev et al. (Wed,) studied this question.