Discovery of a recurrent spectral evolutionary cycle in the ultra-luminous X-ray sources Holmberg II X-1 and NGC 5204 X-1
arXiv:2106.05708 · doi:10.1051/0004-6361/202140781
Abstract
Most ultra-luminous X-ray sources (ULXs) are now thought to be powered by stellar-mass compact objects accreting at super-Eddington rates. While the discovery of evolutionary cycles have marked a breakthrough in our understanding of the accretion flow changes in the sub-Eddington regime in Galactic Black Hole Binaries, their evidence in the super-Eddington regime remained elusive. However, recent circumstantial evidence had hinted the presence of a recurrent evolutionary cycle in two archetypal ULXs: Holmberg II X-1 and NGC 5204 X-1. Here we build on our previous work and exploit the long-term high-cadence monitoring of Swift-XRT in order to provide evidence of the evolutionary cycle in these two sources and investigate the main physical parameters inducing their spectral transitions. We study the long-term evolution of both sources using hardness-intensity diagrams (HID) and by means of Lomb-Scargle periodograms and Gaussian processes modelling to look for periodic variability. We show that both sources follow a recurrent evolutionary pattern in the HID that can be characterized by the hard ultraluminous (HUL) and soft ultraluminous (SUL) spectral regimes, and a third state with characteristics similar to the supersoft ultraluminous (SSUL) state. The transitions between the soft states seem aperiodic, as revealed by timing analysis of the light curve of Holmberg II X-1, albeit further investigation is warranted. The light curve of NGC 5204 X-1 shows a periodicity of 200 days, possibly associated with the duration of the evolutionary cycle. We support a scenario in which the spectral changes from HUL to SUL are due to a periodic increase of the mass-transfer rate and subsequent narrowing of the opening angle of the supercritical funnel. The narrower funnel, combined with stochastic variability imprinted by the wind, might explain the SUL--SSUL spectral changes.
16 pages, 10 Figures, Accepted for publication to A&A, replaced with revised version matching published version
References in corpus (33)
- X-ray Properties of Black-Hole Binaries
- HI4PI: A full-sky HI survey based on EBHIS and GASS
- An online repository of Swift/XRT light curves of GRBs
- An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
- Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
- An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907
- Discovery of coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
- XMM-Newton observations of the brightest Ultraluminous X-ray sources
- Observational evidence for intermediate-mass black holes
- Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
- A spectral-timing model for ULXs in the super-critical regime
- The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
- Analysing the atolls: X-ray spectral transitions of accreting neutron stars
- XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows
- Why Is Supercritical Disk Accretion Feasible?
- Long-term X-ray spectral evolution of Ultraluminous X-ray sources: implications on the accretion flow geometry and the nature of the accretor
- NICER observations reveal that the X-ray transient MAXI J1348-630 is a Black Hole X-ray binary
- The superorbital variability and triple nature of the X-ray source 4U 1820-303
- M51 ULX-7: super-orbital periodicity and constraints on the neutron star magnetic field
- Nature of the soft ULX in NGC 247: super-Eddington outflow and transition between the supersoft and soft ultraluminous regimes
- A ~60-day super-orbital period originating from the ultraluminous X-ray pulsar in M82
- Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1
- X-ray spectral state is not correlated with luminosity in Holmberg II X-1
- Modeling the light curves of ultraluminous X-ray sources as precession
- A new candidate pulsating ULX in NGC 7793
- Orbital and super-orbital periods in ULX pulsars, disc-fed HMXBs, Be/X-ray binaries and double-periodic variables
- Uncovering Red and Dusty Ultraluminous X-ray Sources with Spitzer
- Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1
- Optical Spectroscopy of the environment of a ULX in NGC 7331
- A Possible 55-day X-ray Period of the Ultraluminous Accreting Pulsar M82 X-2
- No periodicity revealed for an "eclipsing" ultraluminous supersoft X-ray source in M81
- Spectral state transitions in Circinus ULX5
- Thick-disc model to explain the spectral state transition in NGC 247
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