GX 339−4 X-ray Binary Reveals Presence of Quasi-Periodic Oscillations

Chinese astronomers have utilized the Hard X-ray Modulation Telescope (HXMT) to observe the recent outburst of GX 339-4, a low-mass X-ray binary system. They have successfully identified new quasi-periodic oscillations (QPOs) in this source. The findings of their research have been published on the pre-print server arXiv.

X-ray binaries (XRBs) are comprised of a normal star or a white dwarf transferring mass onto a compact neutron star or a black hole. Astronomers categorize them as low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB) based on the mass of the companion star.

GX 339-4, located approximately 39,000 light years away from Earth, is a recurring black hole LMXB that was first detected in 1973. Its black hole is estimated to be at least 5.8 times as massive as the sun. Over the past thirty years, GX 339−4 has undergone numerous outbursts, exhibited quasi-periodic oscillations (QPOs), and displayed all the black hole accretion states. It has been extensively studied at all wavelengths, making it one of the most well-studied black hole LMXBs.

In early 2021, GX 339-4 experienced a new outburst, prompting a team of astronomers led by Wei Wang from Wuhan University in China to conduct HXMT observations of this event in order to gain further insight into the behavior of this system. As a result, they successfully detected new quasi-periodic oscillations (QPOs).

Quasi-periodic oscillations (QPOs) are generally observed when X-rays are emitted near the inner edge of an accretion disk in which gas swirls onto a compact object like a neutron star or a black hole. In black hole X-ray binary systems, QPOs are classified as Type-A, -B, or -C, depending on properties such as the quality factor and the shape of the noise associated with the oscillation.

“By analyzing the Insight-HXMT data from February to March 2021, we conducted X-ray timing analysis of this new outburst. Through the results of count rates, hardness-intensity diagram (HID), and power density spectrum (PDS), we have confirmed the source’s spectral transitions from the low-hard state (LHS) to the hard-intermediate state (HIMS). During the transition from the LHS to the HIMS, we observed low-frequency quasi-periodic oscillations (LFQPOs) in the PDS,” explained the researchers.

The observations revealed type-C QPOs with centroid frequencies ranging from 0.1 to 0.6 Hz in the low-hard state and in the frequency range of 1−3 Hz in the hard-intermediate state. The authors of the research paper emphasized that type-C QPOs are the most common type of QPOs in black hole XRBs and are primarily observed in the low-hard and hard-intermediate states.

Furthermore, Wang’s team has also identified a phase lag behavior (in the 50-100 keV band) in GX 339-4 for the first time. It was discovered that when the QPO centroid frequency is below 0.2 Hz, the lag is negative, but it becomes positive thereafter. However, further observations are necessary to fully understand the physical mechanisms behind these phase lags.

The study additionally found that in the root-mean-square (rms)-energy spectrum, the QPO rms remains relatively constant at lower energy and then decreases from around 10% below 10 keV to 2% above 50 keV. The researchers added that a similar correlation between the rms of QPOs and the photon energy above 10 keV was observed during the 2006/2007 outburst when the QPO frequency was less than 1 Hz.

© 2023 Science X Network

Denial of responsibility! SamacharCentrl is an automatic aggregator of Global media. In each content, the hyperlink to the primary source is specified. All trademarks belong to their rightful owners, and all materials to their authors. For any complaint, please reach us at – [email protected]. We will take necessary action within 24 hours.