Timing and spectral analysis of 2S 1417-624 during its 2018 outburst

Serim M. M., Ozudogru O. C., Donmez Ç. K., Sahiner S., Serim D., Baykal A., ...Daha Fazla

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, cilt.510, sa.1, ss.1438-1449, 2022 (SCI-Expanded) identifier identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 510 Sayı: 1
  • Basım Tarihi: 2022
  • Doi Numarası: 10.1093/mnras/stab3547
  • 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, INSPEC, Metadex, zbMATH, DIALNET, Civil Engineering Abstracts
  • Sayfa Sayıları: ss.1438-1449
  • Anahtar Kelimeler: accretion, accretion discs, stars: neutron, pulsars: individual: 2S 1417-624, RED POWER SPECTRA, SWIFT J0243.6+6124, RAY, PULSAR, ACCRETION, NOISE, STARS, TORQUE, NICER, VIEW
  • Orta Doğu Teknik Üniversitesi Adresli: Evet

Özet

We investigate timing and spectral characteristics of the transient X-ray pulsar 2S 1417-624 during its 2018 outburst with NICER follow up observations. We describe the spectra with high-energy cut-off and partial covering fraction absorption (PCFA) model and present flux-dependent spectral changes of the source during the 2018 outburst. Utilizing the correlation-mode switching of the spectral model parameters, we confirm the previously reported sub-critical to critical regime transitions and we argue that secondary transition from the gas-dominated to the radiation pressure-dominated disc do not lead us to significant spectral changes below 12 keV. Using the existing accretion theories, we model the spin frequency evolution of 2S 1417-624 and investigate the noise processes of a transient X-ray pulsar for the first time using both polynomial and luminosity-dependent models for the spin frequency evolution. For the first model, the power density spectrum of the torque fluctuations indicate that the source exhibits red noise component (Gamma similar to -2) within the time-scales of outburst duration which is typical for disc-fed systems. On the other hand, the noise spectrum tends to be white on longer time-scales with high timing noise level that indicates an ongoing accretion process in between outburst episodes. For the second model, most of the red noise component is eliminated and the noise spectrum is found to be consistent with a white noise structure observed in wind-fed systems.