Detecting emission lines withXMM-Newtonin 4U 1538–52

Abstract

Context. The properties of the X-ray emission lines are a fundamental tool for studying the nature of the matter surrounding the neutron star and the phenomena that produce these lines. Aims. The aim of this work is to analyse the X-ray spectrum of 4U 1538−52 obtained by the XMM-Newton observatory and to look for the presence of diagnostic lines in the energy range 0.3−11.5 keV. Methods. We used a 54 ks PN & MOS/XMM-Newton observation of the high-mass X-ray binary 4U 1538−52 covering the orbital phase between 0.75 to 1.00 (the eclipse ingress). We modelled the 0.3−11.5 keV continuum emission with three absorbed power laws and looked for the emission lines. Results. We found previously unreported recombination lines in this system at ∼2.4 keV, ∼1.9 keV, and ∼1.3 keV, which is consistent with the presence of highly ionized states of S XV Heα, Si XIII Heα, and either Mg Kα or Mg XI Heα. On the other hand, in spectra that are both out of eclipse and in eclipse, we detect a fluorescence iron emission line at 6.4 keV, which is resolved into two components: a narrow (σ ≤ 10 eV) fluorescence Fe Kα line plus one hot line from highly photoionized Fe XXV. Conclusions. The detection of new recombination lines during eclipse ingress in 4U 1538−52 indicates that there is an extended ionized region surrounding the neutron star.

High-mass X-ray binaries in the Milky Way

“…The X-ray spectrum (Robba et al, 1992) displays two cyclotron absorption features (Clark et al, 1990;Robba et al, 2001;Rodes-Roca et al, 2009). Emission lines from an extended ionised region have been detected during eclipses (Rodes-Roca et al, 2011). Small spin-up and down have been detected .…”

Orbital phase-resolved spectroscopy of 4U 1538−52 with MAXI

“…thanks the Matsumae International Foundation Research Fellowship. (Clark 2000), BeppoSAX (Robba et al 2001), XMM-Newton (Rodes-Roca et al 2011), INTEGRAL (Hemphill et al 2013), and Suzaku (Hemphill et al 2014). The X-ray characteristics derived from these analyses suggest that the mass accretion onto the neutron star is consistent with a spherically symmetric stellar wind from the companion star (Mukherjee et al 2006).…”

“…Previous works in this direction have been carried out for only one or two orbits (Makishima et al 1987;Robba et al 2001;Mukherjee et al 2006;Rodes-Roca 2007) or for a shorter orbital phase (Rodes-Roca et al 2011). We obtained orbital phaseresolved spectra of the HMXB pulsar 4U 1538−52, accumulating the 60 s duration scans into six ∼0.5 day orbital phase bins outside of eclipse (Nakahira et al 2012;Doroshenko et al 2013;Islam & Paul 2014).…”

A CLUMPY STELLAR WIND AND LUMINOSITY-DEPENDENT CYCLOTRON LINE REVEALED BY THE FIRSTSUZAKUOBSERVATION OF THE HIGH-MASS X-RAY BINARY 4U 1538–522

“…An absorption feature at ∼22 keV in the spectrum of 4U 1538−522 was discovered and identified as a CRSF by Clark et al (1990); another absorption feature at ∼50 keV was observed by Robba et al (2001) and identified as the harmonic of the 22 keV CRSF by Rodes-Roca et al (2009). The spectrum also features a 6.4 keV emission feature, identified as the Fe Kα line (Makishima et al 1987), as well as other emission lines in the ∼1-3 keV and ∼6-7 keV range (Rodes-Roca et al 2010). Until now, the parameters of the cyclotron line have not displayed any detectable correlation with luminosity; however, conclusions in this area have been difficult to arrive at due to previous work using a mix of different empirical models for the continuum and the cyclotron line shape, with Clark et al (1990), Mihara et al (1998), and Rodes-Roca et al (2009) using Lorentzian-shaped line profiles for the CRSF and Coburn (2001), Robba et al (2001), and Hemphill et al (2013) adopting Gaussian profiles.…”