2002A&A...381...98H

The isolated neutron star candidate RBS 1223 was observed with the Advanced CCD Imaging Spectrometer aboard the Chandra X-ray observatory on 2000 June 24. A timing analysis of the data yielded a periodic modulation with a period P=5.1571696(+1.57x10^–4,-1.36x10^–4)s. Using ROSAT HRI archived observations we detected a period P=5.1561274±4.4x10^–4s and determined period derivative {dot}(P)=(0.7-2.0)x10^–11s/s. The detection of this period and {dot}(P) indicates that RBS 1223 has a ``characteristic'' age of 6000-12000 years and huge magnetic field at the surface (B_dipole≃(1.7-3.2)x10⁺¹⁴G) typical for anomalous X-ray pulsars (AXPs).