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The high-energy cyclotron line in 2S 1417-624 discovered with Insight-HXMT during the 2018 outburst.

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Title: The high-energy cyclotron line in 2S 1417-624 discovered with Insight-HXMT during the 2018 outburst.
Authors: Liu, Q., Santangelo, A., Kong, L. D., Ducci, L., Ji, L., Wang, W., Serim, M. M., Güngör, C., Tuo, Y. L., Serim, D.
Source: Astronomy & Astrophysics / Astronomie et Astrophysique; 2024, Vol. 691, p1-10, 10p
Subject Terms: CYCLOTRON resonance, X-ray astronomy, PARTICLE physics, LIGHT curves, SPECTRUM analysis, ASTRONOMY, X-ray binaries
Abstract: We report a detailed timing and spectral analysis of the X-ray pulsar 2S 1417−624 using the data from Insight-HXMT during the 2018 outburst. The pulse profiles are highly variable with respect to both unabsorbed flux and energy. A double-peaked pulse profile from the low flux evolved to a multi-peaked shape in the high-flux state. The pulse fraction is negatively correlated to the source flux in the range of ∼(1 − 6)×10−9 erg cm−2 s−1, consistent with Rossi X-ray Timing Explorer (RXTE) studies during the 2009 giant outburst. The energy-resolved pulse profiles around the peak outburst showed a four-peak shape in the low-energy bands and gradually evolved to triple peaks at higher energies. The continuum spectrum is well described by typical phenomenological models, such as the cut-off power law and the power law with high-energy cut-off models. Notably, we discovered high-energy cyclotron resonant scattering features (CRSFs) for the first time, which are around 100 keV with a statistical significance of ∼7σ near the peak luminosity of the outburst. This CRSF line is significantly detected with different continuum models and provides very robust evidence for its presence. Furthermore, pulse-phase-resolved spectroscopy confirmed the presence of the line, whose energy varied from 97 to 107 keV over the pulse phase and appeared to have a maximum value at the narrow peak phase of the profiles. [ABSTRACT FROM AUTHOR]
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Abstract:We report a detailed timing and spectral analysis of the X-ray pulsar 2S 1417−624 using the data from Insight-HXMT during the 2018 outburst. The pulse profiles are highly variable with respect to both unabsorbed flux and energy. A double-peaked pulse profile from the low flux evolved to a multi-peaked shape in the high-flux state. The pulse fraction is negatively correlated to the source flux in the range of ∼(1 − 6)×10<sup>−9</sup> erg cm<sup>−2</sup> s<sup>−1</sup>, consistent with Rossi X-ray Timing Explorer (RXTE) studies during the 2009 giant outburst. The energy-resolved pulse profiles around the peak outburst showed a four-peak shape in the low-energy bands and gradually evolved to triple peaks at higher energies. The continuum spectrum is well described by typical phenomenological models, such as the cut-off power law and the power law with high-energy cut-off models. Notably, we discovered high-energy cyclotron resonant scattering features (CRSFs) for the first time, which are around 100 keV with a statistical significance of ∼7σ near the peak luminosity of the outburst. This CRSF line is significantly detected with different continuum models and provides very robust evidence for its presence. Furthermore, pulse-phase-resolved spectroscopy confirmed the presence of the line, whose energy varied from 97 to 107 keV over the pulse phase and appeared to have a maximum value at the narrow peak phase of the profiles. [ABSTRACT FROM AUTHOR]
ISSN:00046361
DOI:10.1051/0004-6361/202451062