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

¹ CEA Saclay, DSM/Dapnia/Service d'Astrophysique, 91191 Gif-sur-Yvette, France e-mail: diego.gotz@cea.fr
² SRON–Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands
³ University of Amsterdam, Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ, Amsterdam, The Netherlands
⁴ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Droking Surrey, RH5 6NT, UK
⁶ Università degli Studi di Pavia, Dipartimento di Fisica Nucleare e Teorica and INFN-Pavia, via Bassi 6, 27100 Pavia, Italy
⁷ INAF–Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via Bassini 15, 20133 Milano, Italy
⁸ Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
⁹ University of Padua, Department of Physics, via Marzolo 8, 35131 Padova, Italy

Received: 16 July 2007
Accepted: 17 September 2007

Abstract

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.