The magnetar candidate AX J1818.8-1559

Abstract

In October 2007 a hard X-ray burst was detected by the INTEGRAL satellite from a direction consistent with the position of AX J1818.8-1559, an X-ray source at low Galactic latitude discovered with the ASCA satellite in 1996-1999. The short duration (0.8 s) and soft spectrum (power law photon index of 3.0+/-0.2) of the burst in the 20-100 keV range are typical of Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We report on the results of an observation of AX J1818.8-1559 obtained with the Suzaku satellite in October 2011. The source spectrum, a power law with photon index 1.5, and flux 2x10^{-12} erg cm^-2 s^-1 (2-10 keV), do not show significant variations with respect to the values derived from archival data of various satellites (ROSAT, XMM-Newton, Chandra, Swift) obtained from 1993 to 2011. We discuss possible interpretations for AX J1818.8-1559 and, based on its association with the INTEGRAL burst, we propose it as a new member of the small class of magnetar candidates.