Multitude of iron lines including a Compton-scattered component in OAO 1657 – 415 detected with<i>Chandra</i>

Pradhan, Pragati; Raman, Gayathri; Paul, Biswajit

doi:10.1093/mnras/sty3441

Cited by 10 publications

(24 citation statements)

References 33 publications

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“…Presence of multiple emission lines has been detected in the spectrum of OAO 1657-415 with Fe K 𝛼 line as the most abundant (Kamata et al 1990;Orlandini et al 1999;Jaisawal & Naik 2014;Pradhan et al 2014Pradhan et al , 2019. We detect Fe K 𝛼 emission line in the spectra from all three segments.…”

Section: Discussionsupporting

confidence: 59%

“…Values for the column density in the three segments were found to be similar (Segment 1: 5.33 +6.00 −4.84 ×10 22 , Segment 2: < 8.26×10 22 , Segment 3: 12.35 +4.73 −2.76 × 10 22 cm −2 ). The 𝑁 H values from previous works show a large range from 1.29 ± 0.04 × 10 22 to 75.74 ± 5.91 × 10 22 cm −2 (Orlandini et al 1999;Baykal 2000;Audley et al 2006;Jaisawal & Naik 2014;Pradhan et al 2019). So, for the subsequent analysis, we have fixed 𝑁 H = 5 × 10 21 cm −2 , the lowest value obtained for the first segment.…”

Section: Spectral Analysismentioning

confidence: 98%

“…Pradhan et al (2014) studied the time-resolved spectrum of OAO 1657-415 by using the Suzaku observation from 2011 and discussed the possibility of a clumpy stellar cloud as the reason for X-ray variability. Pradhan et al (2019) have indicated the presence of Compton shoulder around 6.4 keV.…”

Section: Introductionmentioning

confidence: 97%

“…The X-ray spectrum of OAO 1657-415 is highly absorbed due to its low galactic location and is generally described by using a power law model modified with either an exponential cutoff or a high energy cutoff component (Kamata et al 1990;Orlandini et al 1999;Barnstedt et al 2008). Additionally, Fe emission lines at 6.4, 6.7, 6.97, 7.1 keV and Ni K𝛼 line at 7.4 keV have also been reported in the source spectrum (Kamata et al 1990;Orlandini et al 1999;Audley et al 2006;Pradhan et al 2014Pradhan et al , 2019Jaisawal et al 2021). The study of ASCA observation revealed the presence of a dustscattered X-ray halo with decaying intensity through the eclipse and an estimated source distance of 7.1 ± 1.3 kpc.…”

Section: Introductionmentioning

confidence: 99%

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Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR

Sharma,

Jain

et al. 2021

Preprint

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This work presents a comprehensive timing and spectral analysis of high-mass X-ray binary pulsar, OAO 1657-415 by using the observation made with Nuclear Spectroscopic Telescope Array (NuSTAR) on June 2019. During this observation, OAO 1657-415 exhibited X-ray variability by a factor of about 3. X-ray pulsations at 37.03322(14) s were observed up to 70 keV. OAO 1657-415 was undergoing a spin-down phase with 𝑃 = 9(1) × 10 −8 s s −1 . This is an order of about 100 larger than the long-term spin-up rate. The pulse profile evolved marginally during the observation. We have discussed the long-term pulse period history of the source spanning a time-base of 43 years, including the latest Fermi/GBM data. The 3-70 keV source spectrum is described by a partially covered cutoff power-law, an Fe K 𝛼 line at 6.4 keV and a Compton shoulder at 6.3 keV. We report the presence of a cyclotron absorption feature around 40 keV, which is indicative of a surface magnetic field strength of 3.59 ± 0.06 (1 + 𝑧) −1 × 10 12 and 3.29 +0.23 −0.22 (1 + 𝑧) −1 × 10 12 G. This work shows the first robust presence of cyclotron absorption feature in the source.

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Section: Discussionsupporting

confidence: 59%

Section: Spectral Analysismentioning

confidence: 98%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR

Sharma,

Jain

et al. 2021

Preprint

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“…Being located at a low galactic latitude, OAO 1657-415 is highly absorbed with a column density of 10 23 cm À2 (Polidan et al 1978;Kamata et al 1990). The energy spectrum of the pulsar can be described by a power law continuum with an exponential high energy cutoff along with a soft excess and prominent emission lines at 6.4, 6.7 and 7.1 keV (Kamata et al 1990;Audley et al 2006;Barnstedt et al 2008;Pradhan et al 2014Pradhan et al , 2019Jaisawal & Naik 2014).…”

Section: Introductionmentioning

confidence: 99%

AstroSat observations of eclipsing high mass X-ray binary pulsar OAO 1657-415

et al. 2021

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We present the results obtained from analysis of two AstroSat observations of the high mass Xray binary pulsar OAO 1657-415. The observations covered 0.681-0.818 and 0.808-0.968 phases of the $ 10.4 day orbital period of the system, in March and July 2019, respectively. Despite being outside the eclipsing regime, the power density spectrum from the first observation lacks any signature of pulsation or quasi-periodic oscillations. However, during July observation, X-ray pulsations at a period of 37.0375 s were clearly detected in the light curves. The pulse profiles from the second observation consist of a broad single peak with a dip-like structure in the middle across the observed energy range. We explored evolution of the pulse profile in narrow time and energy segments. We detected pulsations in the light curves obtained from 0.808-0.92 orbital phase range, which is absent in the remaining part of the observation. The spectrum of OAO 1657-415 can be described by an absorbed power-law model along with an iron fluorescent emission line and a blackbody component for out-of-eclipse phase of the observation. Our findings are discussed in the frame of stellar wind accretion and accretion wake at late orbital phases of the binary.

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A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line

Saavedra

Fogantini²,

Combi³

et al. 2022

A&A

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Context. OAO 1657-415 is an accreting X-ray pulsar with a high-mass companion that has been observed by several telescopes over the years, in different orbital phases. Back in 1999, observations performed with Beppo-SAX lead to the detection of a cyclotron-resonant-scattering feature, which has not been found again with any other instrument. A recent NuSTAR X-ray observation performed during the brightest phase of the source allows us to perform sensitive searches for cyclotron-resonant-scattering features in the hard X-ray spectrum of the source. Aims. We aim to characterise the source by means of temporal and spectral X-ray analysis, and to confidently search for the presence of cyclotron-resonant-scattering features. Methods. The observation was divided into four time intervals in order to characterise each one. Several timing analysis tools were used to obtain the pulse of the neutron star, and the light curves folded into the time intervals. The NuSTAR spectrum in the energy range 3–79 keV was used, which was modelled with a power-law continuum emission model with a high-energy cutoff. Results. We identify the pulsations associated with the source in the full observation, and find these to be shifted due to the orbital Doppler effect. We show evidence that a cyclotron line at 35.6 ± 2.5 keV is present in the spectrum. We use this energy to estimate the dipolar magnetic field at the pulsar surface to be 4.0 ± 0.2 × 1012 G. We further estimate a lower limit on the distance to OAO 1657-415 of ≃1 kpc. We also find a possible positive correlation between the luminosity and the energy associated with the cyclotron line. Conclusions. We conclude that the cyclotron line at 35.6 ± 2.5 keV is the same as that detected by Beppo-SAX. Our detection has a significance of ∼ 3.4σ.

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Multitude of iron lines including a Compton-scattered component in OAO 1657 – 415 detected withChandra

Cited by 10 publications

References 33 publications

Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR

Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR

AstroSat observations of eclipsing high mass X-ray binary pulsar OAO 1657-415

A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line

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