Mode Change of a Gamma-Ray Pulsar, PSR J2021+4026

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 release 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 th...

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Bibliographic Details
Published in:The Astrophysical journal 2017-06, Vol.842 (1), p.53
Main Authors: Zhao, J., Ng, C. W., Lin, L. C. C., Takata, J., Cai, Y., Hu, C.-P., Yen, D. C. C., Tam, P. H. T., Hui, C. Y., Kong, A. K. H., Cheng, K. S.
Format: Article
Language:English
Subjects:
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
DIPOLES
Electric currents
Fluctuations
Fluids
Flux
GAMMA RADIATION
Gamma ray fluxes
Gamma rays
gamma rays: stars
INCLINATION
Inclination angle
MAGNETIC FIELDS
Magnetospheres
methods: observational
NEUTRON STARS
Polar caps
PULSARS
pulsars: individual (J2021+4026)
radiation mechanisms: non-thermal
RELAXATION
SPECTRA
Spectral analysis
Spectrum analysis
stars: neutron
STRESSES
SUPERFLUIDITY
TELESCOPES
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Summary: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 release 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 ∼8 yr Fermi Large Area Telescope data. We find that the pulsar stayed at a high spin-down rate ( higher than the pre-glitch value) and a low gamma-ray state ( 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 timescale 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aa74d8