A curious case of the accretion-powered X-ray pulsar GX 1+4

Gaurava K. Jaisawal*, Sachindra Naik, Shivangi Gupta, Jérôme Chenevez, Prahlad Epili

*Corresponding author for this work

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Abstract

We present detailed spectral and timing studies using a NuSTAR observation of GX 1+4 in 2015 October during an intermediate-intensity state. The measured spin period of 176.778 s is found to be one of the highest values since its discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar sharp peak is observed in profiles below ∼25 keV. The profiles at higher energies are found to be significantly phase shifted compared to the soft X-ray profiles. Broad-band energy spectra of GX 1+4, obtained from NuSTAR and Swift observations, are described with various continuum models. Among these, a two-component model consisting of a bremsstrahlung and a blackbody component is found to best fit the phase-averaged and phase-resolved spectra. Physical models are also used to investigate the emission mechanism in the pulsar, which allows us to estimate the magnetic field strength to be in ∼(5–10) × 1012 G range. Phase-resolved spectroscopy of NuSTAR observation shows a strong blackbody emission component in a narrow pulse phase range. This component is interpreted as the origin of the peculiar peak in the pulse profiles below ≤25 keV. The size of emitting region is calculated to be ∼400 m. The bremsstrahlung component is found to dominate in hard X-rays and explains the nature of simple profiles at high energies.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume478
Issue number1
Pages (from-to)448-459
ISSN0035-8711
DOIs
Publication statusPublished - 2018

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Keywords

  • Stars: neutron
  • pulsars: individual: GX 1+4
  • X-rays: stars

Cite this

Jaisawal, Gaurava K. ; Naik, Sachindra ; Gupta, Shivangi ; Chenevez, Jérôme ; Epili, Prahlad. / A curious case of the accretion-powered X-ray pulsar GX 1+4. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 478, No. 1. pp. 448-459.
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abstract = "We present detailed spectral and timing studies using a NuSTAR observation of GX 1+4 in 2015 October during an intermediate-intensity state. The measured spin period of 176.778 s is found to be one of the highest values since its discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar sharp peak is observed in profiles below ∼25 keV. The profiles at higher energies are found to be significantly phase shifted compared to the soft X-ray profiles. Broad-band energy spectra of GX 1+4, obtained from NuSTAR and Swift observations, are described with various continuum models. Among these, a two-component model consisting of a bremsstrahlung and a blackbody component is found to best fit the phase-averaged and phase-resolved spectra. Physical models are also used to investigate the emission mechanism in the pulsar, which allows us to estimate the magnetic field strength to be in ∼(5–10) × 1012 G range. Phase-resolved spectroscopy of NuSTAR observation shows a strong blackbody emission component in a narrow pulse phase range. This component is interpreted as the origin of the peculiar peak in the pulse profiles below ≤25 keV. The size of emitting region is calculated to be ∼400 m. The bremsstrahlung component is found to dominate in hard X-rays and explains the nature of simple profiles at high energies.",
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A curious case of the accretion-powered X-ray pulsar GX 1+4. / Jaisawal, Gaurava K.; Naik, Sachindra; Gupta, Shivangi; Chenevez, Jérôme; Epili, Prahlad.

In: Monthly Notices of the Royal Astronomical Society, Vol. 478, No. 1, 2018, p. 448-459.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - A curious case of the accretion-powered X-ray pulsar GX 1+4

AU - Jaisawal, Gaurava K.

AU - Naik, Sachindra

AU - Gupta, Shivangi

AU - Chenevez, Jérôme

AU - Epili, Prahlad

N1 - This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

PY - 2018

Y1 - 2018

N2 - We present detailed spectral and timing studies using a NuSTAR observation of GX 1+4 in 2015 October during an intermediate-intensity state. The measured spin period of 176.778 s is found to be one of the highest values since its discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar sharp peak is observed in profiles below ∼25 keV. The profiles at higher energies are found to be significantly phase shifted compared to the soft X-ray profiles. Broad-band energy spectra of GX 1+4, obtained from NuSTAR and Swift observations, are described with various continuum models. Among these, a two-component model consisting of a bremsstrahlung and a blackbody component is found to best fit the phase-averaged and phase-resolved spectra. Physical models are also used to investigate the emission mechanism in the pulsar, which allows us to estimate the magnetic field strength to be in ∼(5–10) × 1012 G range. Phase-resolved spectroscopy of NuSTAR observation shows a strong blackbody emission component in a narrow pulse phase range. This component is interpreted as the origin of the peculiar peak in the pulse profiles below ≤25 keV. The size of emitting region is calculated to be ∼400 m. The bremsstrahlung component is found to dominate in hard X-rays and explains the nature of simple profiles at high energies.

AB - We present detailed spectral and timing studies using a NuSTAR observation of GX 1+4 in 2015 October during an intermediate-intensity state. The measured spin period of 176.778 s is found to be one of the highest values since its discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar sharp peak is observed in profiles below ∼25 keV. The profiles at higher energies are found to be significantly phase shifted compared to the soft X-ray profiles. Broad-band energy spectra of GX 1+4, obtained from NuSTAR and Swift observations, are described with various continuum models. Among these, a two-component model consisting of a bremsstrahlung and a blackbody component is found to best fit the phase-averaged and phase-resolved spectra. Physical models are also used to investigate the emission mechanism in the pulsar, which allows us to estimate the magnetic field strength to be in ∼(5–10) × 1012 G range. Phase-resolved spectroscopy of NuSTAR observation shows a strong blackbody emission component in a narrow pulse phase range. This component is interpreted as the origin of the peculiar peak in the pulse profiles below ≤25 keV. The size of emitting region is calculated to be ∼400 m. The bremsstrahlung component is found to dominate in hard X-rays and explains the nature of simple profiles at high energies.

KW - Stars: neutron

KW - pulsars: individual: GX 1+4

KW - X-rays: stars

U2 - 10.1093/mnras/sty1049

DO - 10.1093/mnras/sty1049

M3 - Journal article

VL - 478

SP - 448

EP - 459

JO - Royal Astronomical Society. Monthly Notices

JF - Royal Astronomical Society. Monthly Notices

SN - 0035-8711

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ER -