We present the timing analysis results of MAXI J1803−298, a black hole candidate, during its 2021 outburst using data obtained from the Insight-HXMT and NICER telescopes. Our analysis reveals that the source undergoes a state transition from the low/hard state to the hard intermediate state, followed by the soft intermediate state, and ultimately reaching the high/soft state. We searched for the quasi-periodic oscillations (QPOs) and studied the characteristics of the outburst. At the beginning of the outburst, the source was in the hard state, many type-C QPOs were seen in the Insight-HXMT data, and the frequency of these QPOs increased from ∼0.16 to 2.6 Hz. Our analysis of the type-C QPOs’ rms–frequency relationship indicates a turning point in the frequency. We also analyzed the phase lag versus frequency and energy relationship and deduced that the source likely has a high inclination angle, consistent with previous research. The observed rms and phase lag features in type-C QPOs could be explained by the Lense-Thirring precession model, while the alternatives would be still viable. The lag spectrum of type-B QPO exhibits a ‘U-shaped’ pattern similar to many other sources, and the type-B QPOs’ rms increase as the energy rises. This phenomenon can be explained by the dual-corona model.
MAXI J1348-630 is a low-mass X-ray black hole binary located in the Galaxy and undergone the X-ray outburst in 2019. We analyzed the observation data in very soft state during the outburst between MJD 58588 and MJD 58596 based on the Insight-HXMT observations from 2 – 20 keV via the continuum fitting method to measure the spin of the stellar-mass black hole in MAXI J1348-630. The inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV$ and 5.33 ± 0.10 Rg from the observation data modeled by the multicolor disc blackbody model. Assuming the distance of the source $D\sim 3.4 \rm kpc$, the mass of the black hole M ∼ 11 M⊙, and the inclination of the system i ∼ 29.2○, the spin is determined to be a⋆ = 0.41 ± 0.03 for fixing hardening factor at 1.6 and $n_{H}=8.6\times 10^{21} \rm cm^{-2}$. Besides, considering the uncertainty of the parameters D, M, i of this system, with the Monte Carlo analysis, we still confirm the moderate spin of the black hole as $a_{\star }=0.42^{+0.13}_{-0.50}$. Some spectral parameters (e.g., column density and hardening factor) which could affect the measurements of the BH spin are also briefly discussed.
WC-Co coatings sprayed by HVOF attracted much attentions, benefiting from the satisfactory wear resistance and high bonding strength to the steel substrates. Nevertheless, high density of conventional coatings required excessive Co binder, which decreased the hardness and operation life. Based on this, a strengthened WC-30WB-10Co coating was developed with both high density and improved hardness, using high-qualified thermal sprayed composite powders. Comparison between the phase composition, microstructure, interfacial bonding strength and properties of the newly developed coatings and WC-12Co conventional coatings was clarified in detail. Compared to WC-12Co powders, spherical WC-30WB-10Co powders showed higher apparent density and flowability, due to the in situ formed CoWB and CoW2B2 phases during the accelerated metallurgy reaction. Oxidation and decarburization were confirmed during HVOF spraying with the formation of W2C, Co3W3C and Co6W6C phases in both coatings. Attracting WC-30WB-10Co coating with microhardness of 1639HV0.3 and relative density of 99.44% was achieved, higher than those of 1222 HV0.3 and 99.27% of WC-12Co. This was attributed to the formation of the ternary compounds and the consumption of the ductile Co binder in the WC-30WB-10Co coatings. The hard alloy coatings are expected to be well applied in aggressive wear and corrosion environments due to the high hardness and low metal phase content.
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