LOFAR observations of PSR B0943 10: profile evolution and discovery of a systematically changing profile delay in Bright modeReport as inadecuate

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1 IMAPP - Institute for Mathematics, Astrophysics and Particle Physics 2 ASTRON - ASTRON 3 Jodrell Bank Centre for Astrophysics 4 School of Physics and Astronomy Southampton 5 Centre for Astrophysics and Supercomputing 6 USN - Unité Scientifique de la Station de Nançay 7 LPC2E - Laboratoire de Physique et Chimie de l-Environnement et de l-Espace 8 Sub-department of Astrophysics, Department of Physics, University of Oxford

Abstract : We present broadband, low-frequency 25-80 MHz and 110-190 MHz LOFAR observations of PSR B0943+10, with the goal of better illuminating the nature of its enigmatic mode-switching behaviour. This pulsar shows two relatively stable states: a Bright B and Quiet Q mode, each with different characteristic brightness, profile morphology, and single-pulse properties. We model the average profile evolution both in frequency and time from the onset of each mode, and highlight the differences between the two modes. In both modes, the profile evolution can be well explained by radius-to-frequency mapping at altitudes within a few hundred kilometres of the stellar surface. If both B and Q-mode emission originate at the same magnetic latitude, then we find that the change of emission height between the modes is less than 6%. We also find that, during B-mode, the average profile is gradually shifting towards later spin phase and then resets its position at the next Q-to-B transition. The observed B-mode profile delay is frequency-independent at least from 25-80 MHz and asymptotically changes towards a stable value of about 0.004 in spin phase by the end of mode instance, much too large to be due to changing spin-down rate. Such a delay can be interpreted as a gradual movement of the emission cone against the pulsar-s direction of rotation, with different field lines being illuminated over time. Another interesting explanation is a possible variation of accelerating potential inside the polar gap. This explanation connects the observed profile delay to the gradually evolving subpulse drift rate, which depends on the gradient of the potential across the field lines.

Author: A. Bilous - J. Hessels - V. Kondratiev - J. Leeuwen - B. Stappers - P. Weltevrede - H. Falcke - T. Hassall - M. Pilia - E. Keane

Source: https://hal.archives-ouvertes.fr/


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