BeppoSAX and XMM-Newton spectral study of 4U 1735-44

TL;DR

This study analyzes the broad-band X-ray spectrum of the low-mass X-ray binary 4U 1735-44 using BeppoSAX and XMM-Newton data, focusing on the iron line feature and pile-up effects to understand the system's spectral properties.

Contribution

It provides a detailed spectral analysis of 4U 1735-44, incorporating pile-up correction and comparing results from two satellites to characterize the iron line and continuum emission.

Findings

Detected broad iron line features consistent with reflection models

No significant line asymmetry or broadening due to pile-up in XMM-Newton data

Spectral modeling supports a thermal plus Comptonization continuum

Abstract

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.