Letter to the Editor

INTEGRAL observation of hard X-ray variability of the TeV binary LS 5039/RX J1826.2-1450^*

¹ Kepler Zentrum für Astro- und Teilchenphysik, Institut für Astronomie und Astrophysik, University of Tübingen, Sand 1, 72076 Tübingen, Germany e-mail: hoffmann@astro.uni-tuebingen.de
² Universität Hamburg, Institut für Experimentalphysik, Hamburg, Germany
³ INAF IFC-Pa, via U. La Malfa 153, 90146 Palermo, Italy

Received: 21 November 2008
Accepted: 26 December 2008

Abstract

Context. LS 5039 / RX J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected.

Aims. We investigate the hard X-ray ( keV) spectral and timing properties of the source with the monitoring IBIS/ISGRI instrument on-board the INTEGRAL satellite.

Methods. We present the analysis of INTEGRAL observations for a total of about 3 Msec exposure time, including both public data and data from the Key Programme. We search for flux and spectral variability related to the orbital phase.

Results. The source is observed to emit from 25 up to 200 keV and the emission is concentrated around inferior conjunction. Orbital variability in the hard X-ray band is detected and established to be in phase with the orbitally modulated TeV emission observed with HESS. For this energy range we determine an average flux for the inferior conjunction phase interval of  erg cm^-2 s^-1, and a flux upper limit for the superior conjunction phase interval of  erg cm^-2 s^-1 (90% conf. level respectively). The spectrum for the inferior conjunction phase interval follows a power law with an index (90% conf. level).