Torque reversal and cyclotron absorption feature in HMXB 4U 1538-522

Abstract

We present a comprehensive timing and spectral analysis of the HMXB 4U 1538-522 by using the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory data. Using three archived observations made between 2019 and 2021, we have detected $\sim$ 526 s coherent pulsations up to 60 keV. We have found an instantaneous spin-down rate of $\dot{P}=6.6_{-6.0}^{+2.4}\times 10^{-6}$ s s${}^{-1}$ during the first observation. The pulse profiles had a double peaked structure consisting of a broad primary peak and an energy dependent, weak secondary peak. We have also analysed the long-term spin-period evolution of 4U 1538-522 from data spanning more than four decades, including the data from Fermi/GBM. Based on the recent spin trends, we have found that the third torque reversal in 4U 1538-522 happened around MJD 58800. The source is currently spinning up with $\dot{P}=-1.9(1)\times 10^{-9}$ s s${}^{-1}$. We also report a periodic fluctuation in the spin-period of 4U 1538-522. The broad-band persistent spectra can be described with a blackbody component and either powerlaw or Comptonization component along with a Fe K${}_{\alpha }$ line at 6.4 keV and a cyclotron absorption feature around 22 keV. We have also found a relatively weak absorption feature around 27 keV in the persistent spectra of 4U 1538-522 in all three observations. We have estimated a magnetic field strength of $1.84_{-0.06}^{+0.04}(1+z)\times 10^{12}$ and $2.33_{-0.24}^{+0.15}(1+z)\times 10^{12}$ G for the two features, respectively.

arXiv commentAccepted for publication in MNRAS

References in corpus (44)

• On the Absorption of X-rays in the Interstellar Medium
• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The Fermi Gamma-Ray Burst Monitor
• Broad-band gamma-ray and X-ray spectra of NGC 4151 and their implications for physical processes and geometry
• Observations of Accreting Pulsars
• Refined Neutron-Star Mass Determinations for Six Eclipsing X-Ray Pulsar Binaries
• Relativistic Lines and Reflection from the Inner Accretion Disks Around Neutron Stars
• The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs
• A model for cyclotron resonance scattering features
• Study of the accreting pulsar 4U 0115+634 with a bulk and thermal Comptonization model
• On the Correlation of Torque and Luminosity in GX 1+4
• On Timing and Spectral Characteristics of the X-ray Pulsar 4U 0115+63: Evolution of the Pulsation Period and the Cyclotron Line Energy
• On the Dramatic Spin-up/Spin-down Torque Reversals in Accreting Pulsars
• Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-ray Spectrum of 4U 0115+63
• Confirmation of Two Cyclotron Lines in Vela X-1
• The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor
• RXTE Discovery of Multiple Cyclotron Lines during the 2004 December Outburst of V0332+53
• Phase dependent view of Cyclotron lines from model accretion mounds on Neutron Stars
• 4U 0115+63: phase lags and cyclotron resonant scattering
• Spin period evolution of GX 1+4
• Strong outburst activity of the X-ray pulsar X Persei during 2001-2011
• Cyclotron resonant scattering feature simulations. II. Description of the CRSF simulation process
• The BeppoSAX 0.1 - 100 keV Spectrum of the X-ray Pulsar 4U 1538-52
• The first cyclotron harmonic of 4U 1538-52
• A Clumpy Stellar Wind and Luminosity-Dependent Cyclotron Line Revealed by The First Suzaku Observation of the High-Mass X-ray Binary 4U 1538-522
• Pulse phase resolved spectroscopy of Vela X-1 with Suzaku
• Multiple cyclotron line-forming regions in GX 301-2
• Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with INTEGRAL
• The First NuSTAR Observation of 4U 1538-522: Updated Orbital Ephemeris and A Strengthened Case for an Evolving Cyclotron Line Energy
• Detecting emission lines with XMM-Newton in 4U 1538-52
• Broadband spectroscopy of the eclipsing high mass X-ray binary 4U 1700-37 with Suzaku
• Recent Timing Studies on RXTE Observations of 4U 1538-52
• Evidence for an Evolving Cyclotron Line Energy in 4U 1538-522
• Understanding the LMXB X2127+119 in M15 I. X-ray eclipses and dips
• Probing the Cyclotron line characteristics of 4U 1538-522 using AstroSat-LAXPC
• An XMM-Newton view of the dipping low-mass X-ray binary XTE J1710-281
• Near-periodical spin period evolution in the binary system LMC X-4
• Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?
• Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR
• Broad-band spectral analysis of LMXB XTE J1710-281 with Suzaku
• Long-term developments in Her X-1: Correlation between the histories of the 35 day turn-on cycle and the 1.24 sec pulse period
• Broad-band spectral analysis of LMXB 2S 0921-63 with Suzaku

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