The First NuSTAR Observation of 4U 1538-522: Updated Orbital Ephemeris and A Strengthened Case for an Evolving Cyclotron Line Energy

Abstract

We have performed a comprehensive spectral and timing analysis of the first NuSTAR observation of the high-mass X-ray binary 4U 1538-522. The observation covers the X-ray eclipse of the source, plus the eclipse ingress and egress. We use the new measurement of the mid-eclipse time to update the orbital parameters of the system and find marginally-significant evolution in the orbital period, with ${\dot{P}}_{\mathrm{orb}}/P_{\mathrm{orb}}=\left(-0.95\pm 0.37\right)\times 10^{-6}$ yr${}^{-1}$. The cyclotron line energy is found approximately 1.2 keV higher than RXTE measurements from 1997--2003, in line with the increased energy observed by Suzaku in 2012 and strengthening the case for secular evolution of 4U 1538-522's CRSF. We additionally characterize the behavior of the iron fluorescence and emission lines and line-of-sight absorption as the source moves into and out of eclipse.

18 pages, 11 figures

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• The first cyclotron harmonic of 4U 1538-52
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• The pre-outburst flare of the A 0535+26 August/September 2005 outburst
• The Swift-BAT monitoring reveals a long term decay of the cyclotron line energy in Vela X-1
• Inversion of the decay of the cyclotron line energy in Her X-1
• Probing the Cyclotron line characteristics of 4U 1538-522 using AstroSat-LAXPC

Cited by in corpus (12)

• A catalogue of high-mass X-ray binaries in the Galaxy: from the INTEGRAL to the Gaia era
• A new radio census of neutron star X-ray binaries
• New measurements of the cyclotron line energy in Cen X-3
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• Superorbital Modulation in the High-Mass X-ray Binary 4U 1538-52, and Possible Modulation in IGR J16393-4643
• Torque reversal and cyclotron absorption feature in HMXB 4U 1538-522
• Investigating the superorbital modulations in 4U 1909+07, IGR J16418-4532 and IGR J16479-4514 with Swift XRT, BAT and NuSTAR observations
• Long-term evolution of Cyclotron Line energy in an eclipsing pulsar 4U 1538-522
• Exploring polarization and geometry in the X-ray pulsar 4U 1538-52
• Spectroscopic modelling of two high-mass X-ray binaries, Cyg X--3 and 4U 1538--522
• On the origin of super-global spin-up trends of X-ray pulsars in HMXB systems
• Multiwavelength study of 1eRASS J085039.9-421151 with eROSITA NuSTAR and X-shooter