Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL

Aims.We report on a multi-band high-energy observing campaign aimed at studying the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910, one of the magnetar candidates. Methods: We observed 1RXS J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy range. Furthermore, we also reanalyzed, using the latest calibration and software, all the publicly available INTEGRAL data since 2002, and the soft X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM-Newton and Swift/XRT, in order to study the soft and hard X-ray spectral variability of 1RXS J170849.0-400910. Results: We find a long-term variability of the hard X-ray flux, extending the hardness-intensity correlation proposed for this source over 2 orders of magnitude in energy