Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT. (arXiv:1910.03955v1 [astro-ph.HE])

Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT. (arXiv:1910.03955v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ji_L/0/1/0/all/0/1">L. Ji</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Doroshenko_V/0/1/0/all/0/1">V. Doroshenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Santangelo_A/0/1/0/all/0/1">A. Santangelo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gungor_C/0/1/0/all/0/1">C. Gungor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_S/0/1/0/all/0/1">S. Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ducci_L/0/1/0/all/0/1">L. Ducci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_S/0/1/0/all/0/1">S.-N. Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ge_M/0/1/0/all/0/1">M.-Y. Ge</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Qu_L/0/1/0/all/0/1">L.J. Qu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_Y/0/1/0/all/0/1">Y.P. Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bu_Q/0/1/0/all/0/1">Q.C.Bu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cao_X/0/1/0/all/0/1">X.L. 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We present a study of timing properties of the accreting pulsar 2S 1417-624
observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT
and NICER observations. We report a dramatic change of the pulse profiles with
luminosity. The morphology of the profile in the range 0.2-10.0keV switches
from double to triple peaks at $sim2.5$ $rm times 10^{37}{it D}_{10}^2
erg s^{-1}$ and from triple to quadruple peaks at $sim7$ $rm times
10^{37}{it D}_{10}^2 erg s^{-1}$. The profile at high energies (25-100keV)
shows significant evolutions as well. We explain this phenomenon according to
existing theoretical models. We argue that the first change is related to the
transition from the sub to the super-critical accretion regime, while the
second to the transition of the accretion disc from the gas-dominated to the
radiation pressure-dominated state. Considering the spin-up as well due to the
accretion torque, this interpretation allows to estimate the magnetic field
self-consistently at $sim7times 10^{12}$G.

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