NuSTAR observations of the X-ray pulsar LMC X-4: A constraint on the magnetic field and tomography of the system in the fluorescent iron line

Abstract

We present results of the spectral and timing analysis of the X-ray pulsar LMC X-4 with the NuSTAR observatory in the broad energy range 3-79 keV. Along with the detailed analysis of the averaged source spectrum, the high-precision pulse phased-resolved spectra were obtained for the first time. It has been shown that the comptonization model gives the best approximation of the obtained spectra. The evolution of its parameters was traced depending on the pulse phase as well. The search for the possible cyclotron absorption line was performed for all energy spectra in the 5-55 keV energy range. The obtained upper limit for the depth of the cyclotron absorption line τ ∼ 0.15 (3σ) indicates no cyclotron absorption line in this energy range, which provides an estimate of the magnitude of the magnetic field on the surface of the neutron star: B < 3 × 10 11 G or B > 6.5 × 10 12 G. The latter one is agree with the estimate of the magnetic field obtained from the analysis of the power spectrum of the pulsar: B ∼ 3 × 10 13 G. Based on results of the pulse phase-resolved spectroscopy we revealed a delay between maxima of the emission and the equivalent width of the fluorescent iron line. This delay can be apparently associated with the travel time of photons between the emitting regions in the vicinity of the neutron star and the relatively cold regions where this emission is reflected (presumably, at the inflowing stream or at the place of an interaction of the stream and the outer edge of the accretion disk).

New Constraints on the Geometry and Kinematics of Matter Surrounding the Accretion Flow in X-Ray Binaries from Chandra High-energy Transmission Grating X-Ray Spectroscopy

“…In the last few years, a number of papers have presented analyses for some of these objects using broadband X-ray data from missions such as NuSTAR or Suzaku. Thus Jaisawal & Naik (2015) analyze Suzaku data for 4U1700−37; Sasano et al (2014) analyze Suzaku data for 4U1822−371; Naik et al (2011) analyze Suzaku, andFarinelli et al (2016) Suzaku and NuSTAR data for Cen X−3; Tomsick et al (2014) and Parker et al (2015) analyze Suzaku and NuSTAR data for Cyg X−1, while Walton et al (2016) NuSTAR-only data for the same object; Suchy et al (2012) analyze Suzaku data for GX 301−2; Yoshida et al (2017) analyze Suzaku data for GX 1+4; Fürst et al (2013) and Wolff et al (2016) analyze NuSTAR, andFarinelli et al (2016) Suzaku and NuS-TAR data for Her X−1; Shtykovsky et al (2017) analyze NuSTAR, and Hung et al (2010) Suzaku data for LMCX−4; Jaisawal & Naik (2014) and Pradhan et al (2014) analyze Suzaku data for OAO 1657−415;and Maitra & Paul (2013) analyze Suzaku data for Vela X−1.…”

“…Recently, Shtykovsky et al (2017) used NuSTAR data covering about half of the system's orbital cycle to carry out tomography of the narrow Fe Kα line. Based on the phase shift between the Fe Kα EW and the pulsing profile, they suggest that the line originates on the outer edge of the accretion disk (see also Neilsen et al 2009), and most likely either in the inflowing accretion stream that flows through the inner Lagrangian point and falls on the outer accretion disk edge or in the area where the flow interacts with the outer edge of the accretion disk (the so-called hot spot).…”

NuSTARobservations of the supergiant X-ray pulsar IGR J18027−2016: accretion from the stellar wind and possible cyclotron absorption line

“…Moreover, two models (the broken power law and powerlaw*highcut) suffer from the abrupt breaks at the break and cutoff energies, respectively. This can lead to artificial narrow line features around these energies (see, e.g., Shtykovsky et al 2016). Therefore, in the following analysis, we used the comptt model, which we consider to be the most reliable one.…”

Observational constraints on the magnetic field of the bright transient Be/X-ray pulsar SXP 4.78

“…To test finally the hypothesis of a possible presence of a cyclotron absorption line in the spectra of SXP 4.78, we used an approach proposed by Tsygankov & Lutovinov (2005) and recently updated by Shtykovsky et al (2017). The bestfitting model was modified by adding the gabs component.…”