The magnetar candidate AX  J1818.8−1559

¹ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via E. Bassini 15, 20133 Milano, Italy
e-mail: sandro@iasf-milano.inaf.it
² IUSS – Istituto Universitario di Studi Superiori, viale Lungo Ticino Sforza 56, 27100 Pavia, Italy
³ AIM – CEA/Irfu/Service d’Astrophysique, Orme des Merisiers, 91191 Gif-sur-Yvette, France
⁴ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy

Received: 27 June 2012
Accepted: 31 July 2012

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 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.