Long-term X-ray variability of the microquasar system LS 5039/RX J1826.2-1450

Abstract

We report on the results of the spectral and timing analysis of a BeppoSAX observation of the microquasar system LS 5039/RX J1826.2−1450. The source was found in a low-flux state with FX(1-10 keV)= 4.7× 10 −12 erg cm −2 s −1 , which represents almost one order of magnitude lower than a previous RXTE observation 2.5 years before. The 0.1-10 keV spectrum is described by an absorbed power-law continuum with photon-number spectral index = 1.8± 0.2 and hydrogen column density of NH = 1.0 +0.4 −0.3 × 10 22 cm −2 . According to the orbital parameters of the system the BeppoSAX observation covers the time of an X-ray eclipse should one occur. However, the 1.6-10 keV light curve does not show evidence for such an event, which allows us to give an upper limit to the inclination of the system. The low X-ray flux detected during this observation is interpreted as a decrease in the mass accretion rate onto the compact object due to a decrease in the mass-loss rate from the primary.