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

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Serim M. M., Dönmez Ç. K., Serim D., Ducci L., Baykal A., Santangelo A.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, cilt.522, sa.4, ss.6115-6122, 2023 (SCI-Expanded) identifier identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 522 Sayı: 4
  • Basım Tarihi: 2023
  • Doi Numarası: 10.1093/mnras/stad1407
  • Dergi Adı: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Aerospace Database, Applied Science & Technology Source, Communication Abstracts, Compendex, INSPEC, Metadex, zbMATH, DIALNET, Civil Engineering Abstracts
  • Sayfa Sayıları: ss.6115-6122
  • Anahtar Kelimeler: accretion, accretion discs, methods: data analysis, pulsars: individual: Swift J0243.6+6124
  • Orta Doğu Teknik Üniversitesi Adresli: Evet

Özet

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 × 1036 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 × 1012 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.