1. Physics Department, McGill University, Montreal, Quebec H3W 2C4, Canada
2. Department of Physics and Center for Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Space Science Research Center, National Space Science and Technology Center, Huntsville, Alabama 35805, USA

Correspondence to: V. M. Kaspi^1,2 Correspondence and requests for materials should be addressed to V.M.K. (e-mail: Email: vkaspi@physics.mcgill.ca).

Abstract

Anomalous X-ray pulsars (AXPs) are a class of rare X-ray emitting pulsars whose energy source has been perplexing for some 20 years^{1, 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--ray repeaters (SGRs). But the defining property of the SGRs—their low-energy--ray and X-ray bursts—has not hitherto been observed for AXPs. Soft--ray repeaters are thought to be 'magnetars', which are young neutron stars whose emission is powered by the decay of an ultra-high magnetic field^{4, 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.

1. Physics Department, McGill University, Montreal, Quebec H3W 2C4, Canada
2. Department of Physics and Center for Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Space Science Research Center, National Space Science and Technology Center, Huntsville, Alabama 35805, USA

Correspondence to: V. M. Kaspi^1,2 Correspondence and requests for materials should be addressed to V.M.K. (e-mail: Email: vkaspi@physics.mcgill.ca).