Discovery of a transient magnetar: XTE J1810-197

Alaa I. Ibrahim, Craig B. Markwardt, Jean H. Swank, Scott Ransom, Mallory Roberts, Victoria Kaspi, Peter M. Woods, Samar Safi-Harb, Solen Balman, William C. Parke, Chryssa Kouveliotou, Kevin Hurley, Thomas Cline

Research output: Contribution to journalArticlepeer-review


We report the discovery of a new X-ray pulsar, XTE J1810-197, that was serendipitously discovered on 2003 July 15 by the Rossi X- Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum (with a photon index of ≈4), and is detectable in earlier RXTE observations back to 2003 January but not before. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the source's persistent X-ray flux has been declining since then. The pulsar exhibits a high spin-down rate ̇P ≈ 10-11 s s-1 with no evidence of Doppler shifts due to a binary companion. The rapid spin-down rate and slow spin period imply a supercritical characteristic magnetic field B ≃ 3 × 1014 G and a young age ≳T ̃ 7600 yr. Follow-up Chandra observations provided an accurate position of the source. Within its error radius, the 1.5 m Russian-Turkish Optical Telescope found a limiting magnitude RC = 21.5, All such properties are strikingly similar to those of anomalous X-ray pulsars and soft gamma repeaters, providing strong evidence that the source is a new magnetar. However, archival ASCA and ROSAT observations found the source nearly 2 orders of magnitude fainter. This transient behavior and the observed long-term flux variability of the source in absence of an observed SGR-like burst activity make it the first confirmed transient magnetar and suggest that other neutron stars that share the properties of XTE J1810 - 197 during its inactive phase may be unidentified transient magnetars awaiting detection via a similar activity. This implies a larger population of magnetars than previously surmised and a possible evolutionary connection between magnetars and other neutron star families.

Original languageEnglish (US)
Pages (from-to)L21-L24
JournalAstrophysical Journal
Issue number1 II
StatePublished - Jul 1 2004


  • Pulsars: general
  • Pulsars: individual (XTE J1810-197)
  • Stars: magnetic fields
  • Stars: neutron
  • X-rays: stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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