  Low-mass X-ray binary systems consist of a neutron star and a main-sequence
companion star. The compact object accretes matter via Roche-lobe overflow,
which leads to an accretion disk. In addition to a broad-band continuum
emission of a thermal component and a Comptonization part, evidence for a broad
iron K{\alpha} line is found in several sources. Some of them show an
asymmetric line profile as well, which could originate from relativistic
effects. To understand the spectral behavior of the system 4U 1735-44, we study
the broad-band spectrum and especially the iron line feature between 6.4 and
6.97 keV. The shape of the line allows one to determine the region where the
line is produced. Together with the continuum models, a geometrical model of
the source can be proposed. Furthermore, the effects of pile-up in the
XMM-Newton observation are investigated. We analyzed data obtained with the
X-ray satellites BeppoSAX and XMM-Newton. The XMM-Newton data were analyzed,
specifically taking into account pile-up effects. With the help of the data of
these two satellites, we performed a detailed spectral study in an energy range
from 0.2-24 keV. During the observations, the source was in the so-called
banana state of an atoll source. Fitting the BeppoSAX data, we found line
features that we were able to model with a reflection model, whereas the
continuum was modeled with a combination of a thermal component and a
Comptonization part. The analysis of the XMM-Newton data gave evidence for a
broad but not asymmetric iron line. We found no broadening or asymmetry of the
line because of pile-up.
