Magnetar-like X-ray bursts from an anomalous X-ray pulsar

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Abstract

Anomalous X-ray pulsars (AXPs) are a class of rare X-ray emitting pulsars whose energy source has been perplexing for some 20 years1,2,3. Unlike other X-ray emitting pulsars, AXPs cannot be powered by rotational energy or by accretion of matter from a binary companion star, hence the designation ‘anomalous’. Many of the rotational and radiative properties of the AXPs are strikingly similar to those of another class of exotic objects, the soft-γ-ray repeaters (SGRs). But the defining property of the SGRs—their low-energy-γ-ray and X-ray bursts—has not hitherto been observed for AXPs. Soft-γ-ray repeaters are thought to be ‘magnetars’, which are young neutron stars whose emission is powered by the decay of an ultra-high magnetic field4,5; the suggestion that AXPs might also be magnetars has been controversial6. Here we report two X-ray bursts, with properties similar to those of SGRs, from the direction of the anomalous X-ray pulsar 1E1048.1 - 5937. These events imply a close relationship (perhaps evolutionary) between AXPs and SGRs, with both being magnetars.

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Figure 1: Light curves for the observed bursts.
Figure 2: X-ray spectrum in the 2–40 keV range for the 1 s after the onset of burst 1.

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Acknowledgements

P.M.W. is affiliated to the Universities Space Research Association. We thank E. Kuulkers, K. Hurley, K. Jahoda, C. Kouveliotou, W. Lewin, M. Lyutikov, M. Muno, D. Psaltis, S. Ransom, M. Roberts, D. Smith and C. Thompson for discussions. This work was supported in part by a NASA LTSA grant, an NSERC research grant, and an NSF career award. V.M.K. is a Canada Research Chair and an Alfred P. Sloan Fellow. This work made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center.

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Correspondence to V. M. Kaspi.

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Gavriil, F., Kaspi, V. & Woods, P. Magnetar-like X-ray bursts from an anomalous X-ray pulsar. Nature 419, 142–144 (2002) doi:10.1038/nature01011

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