Observations explore the evolution of quasi-periodic oscillations in two X-ray binaries

Utilizing the Arduous X-ray Modulation Telescope (HXMT) and the Neutron star Inside Composition Explorer (NICER), astronomers from China and India have noticed two X-ray binaries often called GX 339−4 and EXO 1846−031. Outcomes of the observational marketing campaign, revealed Could 29 on the arXiv pre-print repository, reveal important info relating to the evolution of quasi-periodic oscillations (QPOs) recognized in these programs.

X-ray binaries (XRBs) are composed of a standard star or a white dwarf transferring mass onto a compact neutron star or a black hole. Based mostly on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB).

GX 339−4 and EXO 1846−031 are two black hole LMXBs found a long time in the past, each situated inside 39,000 mild years away from the Earth. The lots of black holes in these two programs are estimated to be between 4 and 11 solar masses.

Earlier observations of GX 339−4 and EXO 1846−031 have discovered that they exhibit QPOs. Typically, such oscillations are believed to happen when X-rays are emitted close to the inside fringe of an accretion disk during which gasoline swirls onto a compact object like a neutron star or a black hole. Low frequency quasi-periodic oscillations (with frequencies starting from a couple of mHz to 30 Hz) might be divided into three sorts: Kind-A, -B, and -C QPOs, based mostly on high quality issue, noise kind, fractional root-mean-square (rms), and phase delay.

GX 339−4 and EXO 1846−031 are identified to showcase Kind-C QPOs, that are characterised by a robust and slim peak with a centroid frequency starting from 0.01 Hz to 30 Hz superposed to a robust, 15%–30% fractional rms amplitude, broadband noise element. Lately, a crew of astronomers led by Zuobin Zhang of the Fudan College in Shanghai, China, have carried out HXMT and NICER monitoring of the Kind-C QPOs in these two programs, hoping to get extra insights into their evolution and properties.

The observations discovered that the evolution of the QPO frequency is intently associated to mass accretion charge and inside disk radius in GX 339−4 and likewise in EXO 1846−031. The astronomers famous that such correlation follows the prediction of the dynamic frequency mannequin. The dynamic frequency is the ratio of the sound propagation velocity of the inside disk to the truncation radius.

In response to the paper, the Kind-C QPOs in GX 339−4 and EXO 1846-031 seem on the finish of low-hard state and/or hard-intermediate state. The examine discovered a robust constructive correlation between QPO frequency and photon index of the power-law at first of observations, which flattens or begins reversing on the highest values of the QPO frequency.

The analysis additionally confirmed the excessive spin nature of the black hole in EXO 1846−031, which was advised by earlier research that analyzed the blurred reflection spectra of this technique.

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