The magnetar candidate AX ?J1818.8?1559

摘要

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 Advanced Satellite for Cosmology and Astrophysics (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 (~2?×?10-12?erg?cm-2?s-1, 2–10?keV) did not show significant variations from those derived from archival data of various satellites obtained from 1993 to 2011. We discuss possible interpretations of the data 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.