Benjamin Mueck (University of Tuebingen, Germany)

4U 1735-44: The present with XMM and RXTE and the future with XMM and LOFT

Low mass X-ray binaries are interacting binary systems composed of a compact object, in the case of 4U
1735-44 a neutron star, and a companion star with typically one solar mass. The neutron star accretes
matter from the companion star and an accretion disc is formed. In such discs, features like the iron K-alpha
fluorescence line, possibly relativistically broadened, and high frequency Quasi-Periodic Oscillations (kHz
QPO) can be seen. The study of these features can lead to a proof of relativistic effects and gives indications
of the nature of the compact object. Furthermore, the mass and the radius of the compact object can
constrained and a distinction between a neutron star and a Black Hole is possible. Analysis results derived
from X-ray data from the neutron star low mass X-ray binary 4U 1735-44 will be discussed. The observations
reported here were performed with the satellites BeppoSAX, XMM-Newton and RXTE. The obtained data
allow a detailed study of both the spectral and timing features of the source. LOFT will offer the possibility to
detect weaker kHz QPOs with a higher significance and to put better constraints on the frequency and the
width of the QPOs. Simulations of the capability of LOFT will be presented and will be compared to the
results obtained with RXTE. Furthermore we will discuss the conclusions which can be drawn from a
potential simultaneous observation with XMM-Newton and LOFT.