Timing analysis of Swift J0243.6+6124 with NICER and Fermi/GBM during the decay phase of the 2017–2018 outburst

Date

2023-05-01

Author

Serim, Muhammed Miraç
Dönmez, Çağatay Kerem
Serim, Danjela
Ducci, Lorenzo
Baykal, Altan
Santangelo, Andrea

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We present a timing and noise analysis of the Be/X-ray binary system Swift J0243.6+6124 during its 2017–2018 super-Eddington outburst using NICER/XTI observations. We apply a synthetic pulse timing analysis to enrich the Fermi/GBM spin frequency history of the source with the new measurements from NICER/XTI. We show that the pulse profiles switch from double-peaked to single-peaked when the X-ray luminosity drops below ∼7×10^36 erg s^−1. We suggest that this transitional luminosity is associated with the transition from a pencil beam pattern to a hybrid beam pattern when the Coulomb interactions become ineffective to decelerate the accretion flow, which implies a dipolar magnetic field strength of ∼5×10^12 G. We also obtained the power density spectra (PDS) of the spin frequency derivative fluctuations. The red noise component of the PDS is found to be steeper (ω^−3.36) than the other transient accreting sources. We find significantly high noise strength estimates above the super-Eddington luminosity levels, which may arise from the torque fluctuations due to interactions with the quadrupole fields at such levels.

Subject Keywords

Accretion, Accretion discs, Methods: data analysis, Pulsars: individual: Swift J0243.6+6124

URI

https://academic.oup.com/mnras/article-pdf/522/4/6115/50404727/stad1407.pdf
https://hdl.handle.net/11511/103381

Collections

Department of Physics, Article