arXiv subjects

Qingzhong Liu

Publications and source records attributed to Qingzhong Liu.

16 recordsLinked to original sources

arXiv2026

An Explainable FFT-Based Spatial-Frequency Fusion Framework for Deepfake Detection

Deepfake generation has raised growing concerns regarding digital media authenticity, misinformation, identity fraud, and public trust. Recent studies show that combining spatial and frequency features leads to stronger detection results than using independently. This paper presents MSCA-FFT, a Fast Fourier Transform (FFT)-based multi-scale cross-attention framework for image-level deepfake detection. The model combines a partially fine-tuned Xception spatial branch with an FFT-based frequency branch. The frequency branch processes the log-scaled FFT magnitude spectrum through shallow convolutional layers, avoiding inverse frequency-to-image reconstruction used in DCT-based pipelines. The spatial and frequency representations are refined by transformer encoders, fused through cross-attention, and passed to an MLP classifier for real/fake prediction. Experimental results show that MSCA-FFT achieves consistently higher performance than the DCT-based state-of-the-art spatial-frequency fusion method and the compared baseline models. The ablation study further indicates that the FFT-based frequency branch provides complementary spectral cues when fused with spatial features. In addition, FFT-based frequency analysis and Grad-CAM/LIME explanations show consistent evidence around manipulation-sensitive facial regions, including the eyes, mouth, nose, and facial boundaries.

cs.CV↗

arXiv2024

An X-ray high-frequency quasi-periodic oscillation in NGC 1365

This study presents the detection of a high-frequency quasi-periodic oscillation (QPO) in the Seyfert galaxy NGC 1365 based on observational data obtained by \emph{XMM-Newton} in January 2004. Utilizing the weighted wavelet Z-transform (WWZ) and Lomb-Scargle periodogram (LSP) methods, a QPO signal is identified at a frequency of $2.19 \times 10^{-4}\ {\rm Hz}$ (4566 s), with a confidence level of 3.6\ $σ$. The signal is notably absent in the lower 0.2 -- 1.0 keV energy band, with the primary contribution emerging from the 2.0 -- 10.0 keV band, where the confidence level reaches 3.9 $σ$. Spectral analysis shows that there are multiple absorption and emission lines in the high-energy band (> 6\ keV). The correlation between the QPO frequency ($f_{\rm QPO}$) and the mass of the central black hole ($M_{\rm BH}$) of NGC 1365 aligns with the established logarithmic trend observed across black holes, indicating the QPO is of high frequency. This discovery provides new clues for studying the generation mechanism of QPOs in Seyfert galaxies, which helps us understand the accretion process around supermassive black holes and the characteristics of strong gravitational fields in active galactic nuclei.

astro-ph.GA↗

arXiv2024

Adiabatic Mass Loss in Binary Stars. V. Effects of Metallicity and Nonconservative Mass Transfer -- Application in High Mass X-ray Binaries

Binary stars are responsible for many unusual astrophysical phenomena, including some important explosive cosmic events. The stability criteria for rapid mass transfer and common-envelope evolution are fundamental to binary star evolution. They determine the mass, mass ratio, and orbital distribution of systems such as X-ray binaries and merging gravitational-wave sources. We use our adiabatic mass-loss model to systematically survey metal-poor and solar-metallicity donor thresholds for dynamical timescale mass transfer. The critical mass ratios qad are systematically explored, and the impact of metallicity and nonconservative mass transfer are studied. For metal-poor radiative-envelope donors, qad are smaller than those for solar-metallicity stars at the same evolutionary stage. However, qad do the opposite for convective-envelope donors. Nonconservative mass transfer significantly decreases qad for massive donors. This is because it matters how conservative mass transfer is during the thermal timescale phase immediately preceding a delayed dynamical mass transfer. We apply our theoretical predictions to observed high-mass X-ray binaries that have overfilled their Roche lobes and find a good agreement with their mass ratios. Our results can be applied to study individual binary objects or large samples of binary objects with binary population synthesis codes.

astro-ph.SR↗

arXiv2023

Multiwavelength observations of KS 1947+300

KS 1947+300 is a Be/X-ray binary. Despite its nearly circular orbit, it displays both giant and regular less intense X-ray outbursts. According to the viscous decretion disk model, such low eccentric binaries should not show periodic outbursts. We have studied the long-term optical variability of KS 1947+300 and its relationship with X-ray activity. Our objective is to investigate the origin of this variability. KS 1947+300 exhibits changes in brightness and H$α$ emission on time scales from months to years. The optical and IR variability shows small amplitude changes during the active X-ray state, and a long, smooth decrease during the quiescent state. The fact that the amplitude of variability increased with wavelength suggests that the long-term decrease of the optical emission is due to the weakening of the circumstellar disk. Structural changes in the disk may also be the origin of the periodic signals with periods $\sim200$ days detected in the ZTF-{\it g} and {\it r} band light curves. We speculate that these changes are related to the mechanism that ejects matter from the photosphere of the Be star into the disk. We have also studied the X-ray variability that manifested as a series of type I outbursts after the two giant outburst in 2000 and 2013 and found that the intensity and peak orbital phase differ from outburst to outburst. The type I outbursts in KS 1947+300 are not strictly periodic. This irregularity could result from precession of the interacting points between the neutron star and the disk, namely the disk apastron and the two nodes of the disk. The long-term changes in optical continuum and line emission and the X-ray variability patterns are attributed to an evolving and distorted decretion disk.

astro-ph.HE↗

arXiv2023

Multiwavelength observation of 1A 0535+262=HD 245770 from 2010 to 2021

Context. 1A 0535+262 is a high-mass X-ray binary that went into a giant X-ray outburst in 2020. During this event, the X-ray luminosity reached the highest value measured over the last 30 years. Aims. Our aim is to study the long-term variability of 1A 0535+262 before and after the 2020 major X-ray outburst and to uncover the mechanism that led to the X-ray outburst. Methods. We used the long-term photometric light curve and the equivalent widths of the H$α$ and He I $λ$6678 lines to monitor the state of the Be star's circumstellar disk. The H$α$ line profiles show evidence for V/R variability, which we revealed by fitting the H$α$ spectral line profiles with two Gaussian functions. In addition, we divided our data into four periods according to the intensity of the X-ray, optical, and infrared emission. Results. The H$α$ line profiles show single-peaked profiles in most cases. This is consistent with the previously reported orbital inclination of ${i}$ = $37^{\circ} \pm 2^{\circ}$. Unlike the H$α$ lines, the He I $\lambda6678$ lines show a maximal intensity in October 2020, which is one month before the giant X-ray outburst in 2020. Based on the behavior of the equivalent widths of the H$α$ and He I $\lambda6678$ lines, and the ${V}$-band magnitude, we find two mass ejection processes from the Be star to the Be disk on MJD 55820 and MJD 56600. The V/R quasi-period is about two\, years during 2011--2015, which is different from 1994 to 1995. Furthermore, the periods I$\to$II$\to$III$\to$IV in the $(B-V)$ color index versus $V$-band magnitude diagram constitute a cycle. From the behavior of the V/R ratio of H$α$ lines, and the variability of the $V$ band, we believe that the precession of the density perturbation inside the disk is retrograde.

astro-ph.HE↗

arXiv2023

Sciences with the 2.5-meter Wide Field Survey Telescope (WFST)

The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China and the Purple Mountain Observatory. It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over an FOV of 6.5-square-degree. It is anticipated that WFST will be set up at the Lenghu site in the summer of 2023 and begin to observe the northern sky in four optical bands (u, g, r, and i) with a range of cadences, from hourly/daily in the Deep High-Cadence Survey (DHS) program to semiweekly in the Wide-Field Survey (WFS) program, three months later. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31 (AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low-z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23 (u) and 24 mag (g), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions, tidal disruption events and fast, luminous optical transients even beyond a redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g=25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of LSST that monitor the southern sky.

astro-ph.IM↗

arXiv2023

Sub-second periodic radio oscillations in a microquasar

Powerful relativistic jets are one of the ubiquitous features of accreting black holes in all scales. GRS 1915+105 is a well-known fast-spinning black-hole X-ray binary with a relativistic jet, termed as a ``microquasar'', as indicated by its superluminal motion of radio emission. It exhibits persistent x-ray activity over the last 30 years, with quasi-periodic oscillations of $\sim 1-10$ Hz and 34 and 67 Hz in the x-ray band. These oscillations likely originate in the inner accretion disk, but other origins have been considered. Radio observations found variable light curves with quasi-periodic flares or oscillations with periods of $\sim 20-50$ minutes. Here we report two instances of $\sim$5 Hz transient periodic oscillation features from the source detected in the 1.05-1.45 GHz radio band that occurred in January 2021 and June 2022, respectively. Circular polarization was also observed during the oscillation phase.

astro-ph.HE↗

arXiv2022

Multiwavelength observations of Swift J0243.6+6124 from 2017 to 2022

We have obtained optical spectroscopy and photometry data during four years after the event. The long-term photometric light-curve and the equivalent widths of the Halpha and He I 6678 lines were used to monitor the state of the Be star disk. The Halpha line profiles show evidence for V/R variability that was accounted for by fitting the Halpha spectral line profile with two Gaussian functions. We divided our data into three phases according to the intensity of the X-ray, optical, and infrared emission. Phase I covers the rise and decay of the giant X-ray outburst that took place in October to November 2017. We interpret phase II as the dissipation of the Be star equatorial disk and phase III as its recovery. The timescale of a complete formation and dissipation process is about 1250 days. The epoch when the dissipation process stopped and the reformation period began is estimated to be around MJD 58530. We find a delay of about 100 to 200 days between the minimum of the optical or infrared intensity and the strength of the Halpha line after the X-ray outburst, which may indicate that the dissipation of the disk begins from the inner parts. The motion of the density perturbation inside the disk is prograde, with a V/R quasi-period of about four years. The source shows a positive correlation in the (B-V) color index versus V-band magnitude diagram, which implies that the system is seen at a small or moderate inclination angle.

astro-ph.SR↗

arXiv2022

A Survey of Deep Fake Detection for Trial Courts

Recently, image manipulation has achieved rapid growth due to the advancement of sophisticated image editing tools. A recent surge of generated fake imagery and videos using neural networks is DeepFake. DeepFake algorithms can create fake images and videos that humans cannot distinguish from authentic ones. (GANs) have been extensively used for creating realistic images without accessing the original images. Therefore, it is become essential to detect fake videos to avoid spreading false information. This paper presents a survey of methods used to detect DeepFakes and datasets available for detecting DeepFakes in the literature to date. We present extensive discussions and research trends related to DeepFake technologies.

cs.CV↗

arXiv2019

A wide star-black-hole binary system from radial-velocity measurements

All stellar mass black holes have hitherto been identified by X-rays emitted by gas that is accreting onto the black hole from a companion star. These systems are all binaries with black holes below 30 M$_{\odot}$$^{1-4}$. Theory predicts, however, that X-ray emitting systems form a minority of the total population of star-black hole binaries$^{5,6}$. When the black hole is not accreting gas, it can be found through radial velocity measurements of the motion of the companion star. Here we report radial velocity measurements of a Galactic star, LB-1, which is a B-type star, taken over two years. We find that the motion of the B-star and an accompanying H$α$ emission line require the presence of a dark companion with a mass of $68^{+11}_{-13}$ M$_{\odot}$, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. The gravitational wave experiments have detected similarly massive black holes$^{7,8}$, but forming such massive ones in a high-metallicity environment would be extremely challenging to current stellar evolution theories$^{9-11}$.

astro-ph.SR↗

arXiv2016

Long-term Optical Studies of the Be/X-ray Binary RX J0440.9+4431/LS V+44 17

We present the spectroscopic and photometric observations on the Be/X-ray binary RX~J0440.9+4431 from 2001 to 2014. The short-term and long-term variability of the H$α$ line profile indicates that one-armed global oscillations existed in the circumstellar disk. Several positive and negative correlations between the $V$-band brightness and the H$α$ intensity \textbf{were} found from the long-term photometric and spectroscopic observations. We suggest that the monotonic increase of the $V$-band brightness and the H$α$ brightness between our 2005-2007 observations might be the result of a continuous mass ejection from the central Be star, while the negative correlation in 2007-2010 should be caused by the cessation of mass loss from the Be star just before the decline in $V$-band brightness began (around our 2007 observations). With the extension of the ejection material, the largest circumstellar disk during the last two decades has been observed in our 2010 observations with an equivalent width of $\sim$$-12.88$ Å, which corresponds to a circumstellar disk with a size of 12.9 times the radius of the central Be star. Three consecutive X-ray outbursts peaking around MJD 55293, 55444, and 55591 might be connected with the largest circumstellar disk around the Be star. We also use the orbital motion of the neutron star as a probe to constrain the structure of the circumstellar disk and estimate the eccentricity of the binary system to be $\ge$ 0.4. After three years of the H$α$ intensity decline after the X-ray outbursts, a new circumstellar disk was being formed around the Be star after our 2013 observations.

astro-ph.SR↗

arXiv2014

Long-term Optical Observations of the Be/X-ray Binary X Per

We present the optical spectroscopic observations of X Per from 1999 to 2013 with the 2.16m telescope at Xinglong Station and the 2.4m telescope at Lijiang station, National Astronomical Observatories of China. Combining with the public optical photometric data, we find certain epochs of anti-correlations between the optical brightness and the intensity of the Hα and HeI 6678 lines, which may be attributed to the mass ejections from the Be star. Alternative explanations are however also possible. The variability of FeII 6317 line in the spectra of X Per might be also caused by the shocked waves formed after the mass ejections from the Be star. The X-ray activities of the system might also be connected with the mass ejection events from the Be star. When the ejected materials were transported from the surface of the Be star to the orbit of neutron star, an X-ray flare could be observed in its X-ray light curves. We use the neutron star as a probe to constrain the motion of the ejected material in the circumstellar disk. With the diffusion time of the ejected material from the surface of Be star to the orbit of neutron star, the viscosity parameter α of the circumstellar disk is estimated to be 0.39 and 0.28 for the different time, indicating that the disk around Be star may be truncated by the neutron star at the 2:1 resonance radius and Type I X-ray outburst is unlikely to be observed in X Per.

astro-ph.SR↗

arXiv2012

Multi-wavelength study of the Be/X-ray binary MXB 0656-072

We present and analyze the optical photometric and spectroscopic data of the Be/X-ray binary MXB 0656-072 from 2006 to 2009. A 101.2-day orbital period is found, for the first time, from the present public X-ray data(Swift/BAT and RXTE/ASM). The anti-correlation between the H$α$ emission and the $UBV$ brightness of MXB 0656$-$072 during our 2007 observations indicates that a mass ejection event took place in the system. After the mass ejection, a low-density region might develop around the Oe star. With the outward motion of the circumstellar disk, the outer part of the disk interacted with the neutron star around its periastron passage and a series of the X-ray outbursts were triggered between MJD 54350 and MJD 54850. The PCA--HEXTE spectra during the 2007-2008 X-ray outbursts could be well fitted by a cut-off power law with low energy absorption, together with an iron line around 6.4 keV, and a broad cyclotron resonance feature around 30 keV. The same variability of the soft and hard X-ray colors in 2.3-21 keV indicated that there were no overall changes in the spectral shape during the X-ray outbursts, which might be only connected with the changes of the mass-accretion rate onto the neutron star.

astro-ph.HE↗

arXiv2011

Discrete Mass Ejections from the Be/X-ray Binary A0535+26/HD245770

We present the long-term optical spectroscopic observations on the Be/X-ray binary A0535+26 from 1992 to 2010. Combining with the public V-band photometric data, we find that each giant X-ray outburst occurred in a fading phase of the optical brightness. The anti-correlation between the optical brightness and the H$α$ intensity during our 2009 observations indicates a mass ejection event had taken place before the 2009 giant X-ray outburst, which might cause the formation of a low-density region in the inner part of the disk. The similar anti-correlation observed around 1996 September indicates the occurrence of the mass ejection, which might trigger the subsequent disk loss event in A0535+26.

astro-ph.HE↗

arXiv2008

Optical Spectroscopic Observations of CI Camelopardalis

We present the results of optical spectroscopic observations of CI Cam. Double-peaked profiles were simultaneously observed for the first time in the hydrogen Balmer, He {\small I} $λ$6678 and Fe {\small II} lines during an observational run in 2001 September. An intermediate viewing angle of the circumstellar disk around the B[e] star is consistent with our data. A significant decrease in the intensity of the H$α$ and He {\small I} lines in our 2004 September observations might have been the precursor of a line outburst at the end of 2004. The remarkable increase in the intensity of all lines and the decrease in visual brightness in 2005 might be due to the environment filling with new material ejected during the outburst. The environment of CI Cam is influenced by mass loss from the B[e] star and the outburst of its compact companion.

astro-ph↗

arXiv2008

Optical Spectroscopic Observations of Cyg X-1=HDE 226868

We present the results of the spectroscopic observations of HDE 226868, the optical counterpart to the black hole X-ray binary Cyg X-1, from 2001 to 2006. We analyze the variabilities of the two components in the complex H$α$ line: one P-Cygni shaped component which follows the motion of the supergiant and another emission component moving with an antiphase orbital motion relative to the supergiant, which is attributed to a focused-stellar wind. The results of KOREL disentangling of our spectra indicate that the focused stellar wind is responsible for the major part of the variability of the H$α$ emission line. The emission of the supergiant component had a small difference between the low/hard and high/soft states, while the focused wind component became strong in the low/hard state and weak in the high/soft state. The wind is nearly undisturbed by the X-ray photoionization during the low/hard state. However, during the high/soft state, the X-rays from the compact object could decelerate the line-driven wind and result in a high mass accretion rate, due to the effect of the X-ray photoionization. The X-ray illuminating could also change the temperature profile of the stellar wind and increase its temperature, and thus decrease the H$α$ emissivity of the wind, which could explain the H$α$ variabilities of Cyg X-1 during different X-ray states.

astro-ph↗