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

Hemphill, Paul; Rothschild, R. E.; Cheatham, Diana M.; Fürst, Felix; Kretschmar, P.; Kühnel, Matthias; Pottschmidt, K.; Staubert, R.; Wilms, J.; Wolff, M. T.

doi:10.3847/1538-4357/ab03d3

Cited by 19 publications

(23 citation statements)

References 62 publications

(121 reference statements)

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“…It is therefore of interest to study the CRSF with different instruments at different epochs, and intensity states of the sources. Pulse phaseaveraged and pulse phase-resolved measurements of the CRSF have been carried out previously with AstroSat-LAXPC for 4U 1538-52 (Varun et al 2019) and results were found to be consistent with NuStar measurements (Hemphill et al 2019).…”

Section: Introductionmentioning

confidence: 63%

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

Varun

Pradhan

Maitra

et al. 2019

ApJ

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We present timing and spectral analysis of data from an observation of the High Mass X-ray Binary pulsar 4U 1907+09 with the LAXPC instrument onboard AstroSat. The light curve consisted of a flare at the beginning of the observation, followed by persistent emission. The pulsar continues to spin down, and the pulse profile is found to be double-peaked up to 16 keV with the peaks separated by a phase of ∼ 0.45. Significant energy dependence of the pulse profile is seen with diminishing amplitude of the secondary peak above 16 keV, and increasing amplitude of the main peak upto 40 keV and a sharp decline after that. We confirm earlier detections of the Cyclotron Resonance Scattering Feature (CRSF) in 4U 1907+09 at ∼ 18.5 ± 0.2 keV in the phase-averaged spectrum with a high detection significance. An intensity resolved spectral analysis of the initial flare in the light curve shows that the CRSF parameters do not change with a change in luminosity by a factor of 2.6. We also performed pulse phase-resolved spectral analysis with ten independent phase bins. The energy and the strength of the cyclotron line show pulse phase dependence that is in agreement with previous measurements. Two features from the current observation: different energy dependence of the two pulse peaks and a strong CRSF only around the secondary peak, both indicate a deviation from a dipole geometry of the magnetic field of the neutron star, or complex beaming pattern from the two poles.

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Section: Introductionmentioning

confidence: 63%

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

Varun

Pradhan

Maitra

et al. 2019

ApJ

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“…This indicates a trailing accretion stream or wakes from the supergiant companion. A cyclotron resonance scattering feature at around 22 keV has been observed in 4U 1538−52 in detail with Suzaku (Hemphill et al 2014), AstroSat (Varun et al 2019) and NuStar (Hemphill et al 2019).…”

Section: Introductionmentioning

confidence: 91%

X-Ray Reprocessing: Through the Eclipse Spectra of High-mass X-Ray Binaries with XMM-Newton

Aftab¹,

Paul²,

Kretschmar³

2019

ApJS

Self Cite

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The study of X-ray reprocessing is one of the key diagnostic tools to probe the environment in X-ray binary systems. One difficult aspect of studying X-ray reprocessing is the presence of much brighter primary radiation from the compact star together with the reprocessed radiation. In contrast for eclipsing systems, the X-rays we receive during eclipse are only those produced by reprocessing of the emission from the compact star by the surrounding medium. We report results from a spectral study of the X-ray emission during eclipse and outside eclipse (when available) in 9 high mass X-ray binaries (HMXBs) with XMM-Newton EPIC pn to investigate different aspects of the stellar wind in these HMXBs. During eclipse the continuum component of the spectrum is reduced by a factor of ∼8-237, but the count-rate for 6.4 keV Iron emission line or complex of Iron emission lines in HMXBs are reduced by a smaller factor leading to large equivalent widths of the Iron emission lines. This indicates a large size for the line emission region, comparable to or larger than the companion star in these HMXB systems. However there are significant system to system differences. 4U 1538−52, in spite of having a large absorption column density, shows a soft emission component with comparable flux during the eclipse and out-of-eclipse phases. Emission from Hydrogen-like Iron has been observed in LMC X-4 for the first time, in the out-of-eclipse phase in one of the observations. Overall, we find significant differences in the eclipse spectrum of different HMXBs and also in their eclipse spectra against out-of-eclipse spectra.

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“…Clark (2000) and few more observers suggest that the orbit is probably eccentric, with an eccentricity approximately 0.18. This source shows many interesting properties, like significant evolution in the orbital period and cyclotron lines (Hemphill et al 2019) but as stated earlier, our main interest is to do spectroscopic study of the highly ionised X-ray lines.…”

Section: U 1538-522mentioning

confidence: 98%

Spectroscopic modelling of two high-mass X-ray binaries, Cyg X--3 and 4U 1538--522

Shaw,

Bhattacharyya

2021

Preprint

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We report a detailed modelling of soft X-ray emission lines from two stellar-wind fed Galactic high mass X-ray binary (HMXB) systems, Cyg X-3 and 4U 1538-522, and estimate physical parameters, e.g., hydrogen density, radiation field, chemical abundances, wind velocity, etc. The spectral synthesis code CLOUDY is utilized for this modelling. We model highly ionised X-ray spectral lines such as Fe XXV (6.700 keV), Fe XXVI (6.966 keV), and reproduce the observed line flux values. We find that for Cyg X-3 and 4U 1538-522, the inner radius of the ionised gas is at a distance of 10 12.25 cm and 10 10.43 cm respectively from the primary star, which is the main source of ionisation. The densities of the ionised gas for Cyg X-3 and 4U 1538-522 are found to be ∼ 10 11.35 cm −3 and 10 11.99 cm −3 , respectively. The corresponding wind velocities are 2000 km s −1 and 1500 km s −1 . The respective predicted hydrogen column densities for Cyg X-3 and 4U 1538-522 are 10 23.2 cm −2 and 10 22.25 cm −2 . In addition, we find that magnetic field affects the strength of the spectral lines through cyclotron cooling. Hence, we perform separate model comparisons including magnetic field for both the sources. Most of the parameters, except the hydrogen column density, have similar values with and without magnetic field. We estimate that the most probable strength of the magnetic field for Cyg X-3 and 4U 1538-522, where the Fe XXV and Fe XXVI lines originate, is ∼ 10 2.5 G.

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

Cited by 19 publications

References 62 publications

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

X-Ray Reprocessing: Through the Eclipse Spectra of High-mass X-Ray Binaries with XMM-Newton

Spectroscopic modelling of two high-mass X-ray binaries, Cyg X--3 and 4U 1538--522

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