The brightening of the pulsar wind nebula of PSR B0540−69 after its spin-down-rate transition

Abstract

It is believed that an isolated pulsar loses its rotational energy mainly through a relativistic wind consisting of electrons, positrons and possibly Poynting flux1,2,3. As it expands, this wind may eventually be terminated by a shock, where particles can be accelerated to energies of X-ray synchrotron emission, and a pulsar wind nebula (PWN) is usually detectable surrounding a young energetic pulsar1,2,3. However, the nature and/or energetics of these physical processes remain very uncertain, largely because they typically cannot be studied in a time-resolved fashion. Here we show that the X-ray PWN around the young pulsar PSR B0540−69 brightens gradually up to 32 ± 8% over the mean previous flux, after a sudden change in the spin-down rate of ~36% in December 2011. This spin-down-rate transition has very different properties from a traditional pulsar glitch4. No evidence is seen for any change in the pulsed X-ray emission. We conclude that the spin-down-rate transition results from a sudden change in the pulsar magnetosphere that increases the pulsar wind power and hence the PWN X-ray emission. The X-ray light curve of the PWN suggests a mean lifetime of the particles of 397 ± 374 d, corresponding to a magnetic field strength of \(0.78_{-0.28}^{+4.50}\ {\mathrm{mG}}\) in the PWN.

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Fig. 1: The unfolded X-ray spectra of PSR B054069 and its wind nebula (PSR + PWN) observed by XMM-Newton, Swift/XRT and NuSTAR.
Fig. 2: The luminosity evolution of PSR B054069 and its wind nebula (PSR + PWN).

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request. All the observational data used in this study are public and can be downloaded from the archives of these X-ray satellites.

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Acknowledgements

K. S. Cheng of Hongkong University, L. Zhang of Yunnan University, R. X. Xu of Peking University and H. Tong of Guangzhou University are appreciated for helpful discussions on the emission mechanism of pulsars. This work is supported by the National Key R&D Program of China (2016YFA0400800) and the National Natural Science Foundation of China under grants 11503027, 11673013, 11653004, U1838201, U1838201, 11673023 and U1838104. We thank the data support from the XMM-Newton, NuSTAR, RXTE and Swift teams.

Author information

M.Y.G., L.L.Y., S.S.W., Z.J.L. and W.Z. were involved in the data analysis. F.J.L., M.Y.G., L.J.W., S.N.Z. and Q.D.W. contributed to the theoretical discussions. The manuscript was produced by M.Y.G., F.J.L., L.J.W., Q.D.W., S.N.Z. and S.S.W.

Correspondence to M. Y. Ge or F. J. Lu.

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Supplementary Figs. 1–5, Tables 1–3, text and references.

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