arXiv subjects

X. Y. Zeng

Publications and source records attributed to X. Y. Zeng.

4 recordsLinked to original sources

arXiv2023

Intermittent QPO properties of MAXI J1820+070 revealed by Insight-HXMT

We investigate the dynamical properties of low frequency quasi-periodic oscillations (QPOs) observed from the black hole X-ray binary MAXI J1820+070 during the early part of its 2018 outburst, when the system was in a bright hard state. To this aim, we use a series of observations from the Hard X-ray Modulation Telescope Insight-HXMT, and apply a wavelet decomposition (weighted wavelet Z-transforms) to the X-ray light-curve. We find that the QPO phenomenon is intermittent within each individual observation, with some sub-intervals where the oscillation is strongly detected (high root-mean-square amplitude) and others where it is weak or absent. The average life time of individual QPO segments is ~ 5 oscillation cycles, with a 3 sigma tail up to ~ 20 cycles. There is no substantial difference between the energy spectra during intervals with strong and weak/absent QPOs. We discuss two possible reasons for the intermittent QPO strength, within the precessing jet model previously proposed for MAXI J1820+070. In the rigid precession model, intermittent QPOs are predicted to occur with a coherence Q ~ a few when the disk alignment time-scale is only a few times the precession time-scale. Alternatively, we suggest that changes in oscillation amplitude can be caused by changes in the jet speed. We discuss a possible reason for the intermittent QPO strength, within the precessing jet model previously proposed for MAXI J1820+070: we suggest that changes in oscillation amplitude are caused by changes in the jet speed. We argue that a misaligned, precessing jet scenario is also consistent with other recent observational findings that suggest an oscillation of the Compton reflection component in phase with the QPOs.

astro-ph.HE↗

arXiv2023

A measure of cosmological distance using the \civ\ Baldwin effect in quasars

We use the anticorrelation between the equivalent width (EW) of the C\,\textsc{iv} 1549 Å emission line and the continuum luminosity in the quasars rest frame (Baldwin effect) to measure their luminosity distance as well as estimate cosmological parameters. We obtain a sample of 471 Type I quasars with the UV/optical spectra and EW (C\,\textsc{iv}) measurements in the redshift range of $2.3< z< 7.1$ including 25 objects at $5 < z < 7.1$, which can be used to investigate the C\,\textsc{iv} Baldwin effect and determine cosmological luminosity distance. The relation $EW(C\,\textsc{iv}) \propto {(λ{L_λ})^γ}$ can be applied to check the inverse correlation between the C\,\textsc{iv} EW and ${L_λ}$ of quasars and give their distance, and the data suggest that the EW of C\,\textsc{iv} is inversely correlated with continuum monochromatic luminosities. On the other hand, we also consider dividing the Type I quasars sample into various redshift bins, which can be used to check if the C\,\textsc{iv} EW-luminosity relation depends on the redshift. Finally, we apply a combination of Type I quasars and SNIa Pantheon to test the property of dark energy concerning whether or not its density deviates from the constant, and give the statistical results.

astro-ph.CO↗

arXiv2019

Chinese Sunspot Drawing and Its Digitization-(I) Parameter Archives

Based on the Chinese historical sunspots drawings, a data set consisting of the scanned images and all their digitized parameters from 1925 to 2015 have been constructed. In this paper, we briefly describe the developmental history of sunspots drawings in China. This paper describes the preliminary processing processes that strat from the initial data (inputing to the scanning equipment) to the parameters extraction, and finally summarizes the general features of this dataset. It is the first systematic project in Chinese solar-physics community that the historical observation of sunspots drawings were digitized. Our data set fills in an almost ninety years historical gap, which span 60 degrees from east to west and 50 degrees from north to south and have no continuous and detailed digital sunspot observation information. As a complementary to other sunspots observation in the world, our dataset provided abundant information to the long term solar cycles solar activity research.

astro-ph.SR↗

arXiv2018

Thermal noise limited higher-order mode locking of a reference cavity

Higher-order mode locking has been proposed to reduce the thermal noise limit of reference cavities. By locking a laser to the HG02 mode of a 10-cm long all ULE cavity, and measure its performance with the three-cornered-hat method among three independently stabilized lasers, we demonstrate a thermal noise limited performance of a fractional frequency instability of 4.9E-16. The results match the theoretical models with higher-order optical modes. The achieved laser instability improves the all ULE short cavity results to a new low level.

physics.ins-det↗