X-ray Timing Study of Galactic Pulsating Ultraluminous X-ray Sources with NICER
Bryant Randolph (1*), Kiki Vierdayanti(2), Tiara Andamari Saraswati(2)

1) Astronomy Studi Program, Faculty of Mathematics and Natural Science, Institut Teknologi Bandung
*bryantrandolph03[at]gmail.com
2) Astronomy Research Group, Faculty of Mathematics and Natural Science, Institut Teknologi Bandung

Abstract

Ultraluminous X-ray Sources (ULXs) are accreting compact objects that are observed to be extremely luminous at the X-ray range, significantly exceeding the Eddington luminosity, indicating a potential new regime of accretion process. While majority of ULXs are extragalactic objects, recent studies have discovered such objects also within our own Galaxy which offered opportunity for a more in-depth study of ULXs. In this work, we performed timing study on two Galactic sources, Swift J0243.6+6124 and RX J0209.6-7427, during their super-Eddington outbursts observed using the Neutron Star Interior Composition ExploreR (NICER). Our timing analysis tracks the evolution of their Power Spectral Density (PSD), showing the presence of pulsation, Quasi Periodic Oscillations (QPOs) and time lags that correlates with the change in luminosity throughout the outburst, indicating significant structural change in the accretion disk. Additionally, spectral analysis was also performed with complementary data from NuSTAR mission to reach a wider energy range to provide a more detailed view on the super-Eddington accretion disk structure.

Keywords: ULX- accretion- outburst- super-Eddington- timing analysis- NICER

Topic: Stellar Physics