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arXiv · 1706.00236

Mode change of a gamma-ray pulsar, PSR J2021+4026

J. Zhao·C. W. Ng·L. C. C. Lin·J. Takata·Y. Cai·C. P. Hu·D. C. C. Yen·P. H. T. Tam·C. Y. Hui·A. K. H. Kong·K. S. Cheng
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Abstract

A glitch of a pulsar is known as a sudden increase in the spin frequency and spin-down rate (frequency time derivative), and it can be caused by a sudden rel\ ease of the stress built up in the solid crust of the star or pinned vortices in the superfluid interior. PSR J2021+4026 is the first pulsar that shows a significant change in the gamma-ray flux and pulse profile at the glitch that occurred around 2011 October 16. We report the results of timing and spectral analysis of PSR~J2021+4026 using $\sim$ 8~yr Fermi-LAT data. We find that the pulsar stayed at a high spin-down rate ($\sim 4\%$ higher than the pre-glitch value) and a low gamma-ray state ($\sim 18\%$ lower) for about 3~yr after the glitch. Around 2014 December, the spin-down rate and gamma-ray flux gradually returned to pre-glitch values within a time scale of a few months. The phase-resolved spectra and pulse profiles after the relaxation are also consistent with those before the glitch. The observed long-term evolution of the spin-down rate and the gamma-ray flux indicates that the glitch triggered a mode change in the global magnetosphere. We speculate that the glitch changed the local magnetic field structure around the polar cap and/or the inclination angle of the dipole axis, leading to a change in the electric current circulating in the magnetosphere.

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J. Zhao, C. W. Ng, L. C. C. Lin, J. Takata, Y. Cai, C. P. Hu, D. C. C. Yen, P. H. T. Tam, C. Y. Hui, A. K. H. Kong, K. S. Cheng. 2017-06-11. Mode change of a gamma-ray pulsar, PSR J2021+4026. https://doi.org/10.3847/1538-4357%2Faa74d8

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