A curious case of the accretion-powered X-ray pulsar GX 1+4
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 Swiftobservations, 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) × 10^(12) 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.
Additional Information
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2018 April 24. Received 2018 April 24; in original form 2017 November 2. Published: 26 April 2018. We sincerely thank the referee for suggestions on the paper. GKJ thanks C. Ferrigno and M. Wolff for discussions on the physical models. The research work at Physical Research Laboratory is funded by the Department of Space, Government of India. The research leading to these results has received funding from the European Union's Seventh Framework Programme and Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Actions grant no. 609405 (FP7) and 713683 (H2020; COFUNDPostdocDTU). This research has made use of data obtained through HEASARC Online Service, provided by the NASA/GSFC, in support of NASA High Energy Astrophysics Programs.Attached Files
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- Eprint ID
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- CaltechAUTHORS:20180425-093642490
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2018-04-25Created from EPrint's datestamp field
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2021-11-15Created from EPrint's last_modified field
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- NuSTAR