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Space-based optical lattice clocks as gravitational wave detectors in search for new physics

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Science China(Physics,Mechanics & Astronomy) 2025年第04期Mechanics & Astronomy) .卷 248-256页

作者： Bo Wang Bichu Li Qianqian Xiao Geyu Mo Yi-Fu Cai Department of Astronomy School of Physical SciencesUniversity of Science and Technology of China cas key Laboratory for research in galaxies and cosmology School of Astronomy and Space ScienceUniversity of Science and Technology of China Deep Space Exploration Laboratory

We investigate the sensitivity and performance of space-based optical lattice clocks（OLCs） in detecting gravitational waves,in particular the stochastic gravitational wave background（SGWB） at low frequencies(10-4, 1) Hz, which are inaccessible to ground-based detectors. We first analyze the response characteristics of a single OLC detector for SGWB detection and compare its sensitivity with that of laser interferometer space antenna（LISA）. Due to longer arm lengths, space-based OLC detectors can exhibit unique frequency responses and enhance the capability to detect SGWB in the low-frequency range, but the sensitivity of a single OLC detector remains insufficient overall compared with LISA. Then, as a preliminary plan, we adopt a method of crosscorrelation on two OLC detectors to improve the signal-to-noise ratio（SNR）. This method leverages the uncorrelated origins but statistically similar properties of noise in two detectors while the SGWB signal is correlated between them, thus achieving effective noise suppression and sensitivity enhancement. Future advancements in OLC stability are expected to further enhance their detection performance. This work highlights the potential of OLC detectors as a promising platform for SGWB detection,offering complementary capabilities to LISA, and opening an observational window into more astrophysical sources and the early universe.

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Wave effect of gravitational waves intersected with a microlens field II:An adaptive hierarchical tree algorithm and population study

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Science China(Physics,Mechanics & Astronomy) 2025年第1期68卷 237-250页

作者： Xikai Shan Guoliang Li Xuechun Chen Wen Zhao Bin Hu Shude Mao Purple Mountain Observatory Chinese Academy of SciencesNanjing 210023China Department of Astronomy Tsinghua UniversityBeijing 100084China Institute for Frontier in Astronomy and Astrophysics Beijing Normal UniversityBeijing 102206China School of Physics and Astronomy Beijing Normal UniversityBeijing 100875China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China cas key Laboratory for researches in galaxies and cosmology Department of AstronomyUniversity of Science and Technology of ChinaChinese Academy of SciencesHefei 230026China

The gravitational lensing wave effect generated by a microlensing field embedded in a lens galaxy is an inevitable phenomenon in strong lensed gravitational waves(SLGWs).This effect presents both challenges and opportunities for the detection and appli-cation of ***,investigating this wave effect requires computing a complete diffraction integral over each microlens in the *** is extremely time-consuming due to the large number of microlenses(10^(3)-10^(6)).Therefore,simply adding all the microlenses is ***,the complexity of the time delay surface makes the lens plane resolution a crucial factor in controlling numerical *** this paper,we propose a trapezoid approximation-based adaptive hierarchical tree algo-rithm to meet the challenges of calculation speed and *** find that this algorithm accelerates the calculation by four orders of magnitude compared to the simple adding method and is one order of magnitude faster than the fixed hierarchical tree algorithm proposed for electromagnetic *** importantly,our algorithm ensures controllable numerical errors,increasing confidence in the *** with our previous work(***.66,239511,2023),this paper addresses all numerical issues,including integral convergence,precision,and computational time1).Finally,we conducted a population study on the microlensing wave effect of SLGWs using this algorithm and found that the microlensing wave effect cannot be ignored,especially for Type II SLGWs(from saddle position of the time delay surface)due to their intrinsic geometric structures and their typical intersection with a denser microlensing ***,more than 33%(11%)of SLGWs have a mismatch larger than 1%(3%)compared to the unlensed ***,we found that the mismatch between signal pairs in a doubly imaged GW is generally larger than 10^(−3),and 61%(25%)of signal pairs have a mismatch larger than 1%(3%).Theref

关键词： gravitational lensing diffractional integral algorithm gravitational wave

Testing Cotton gravity as dark matter substitute with weak lensing

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Science China(Physics,Mechanics & Astronomy) 2025年第04期Mechanics & Astronomy) .卷 86-94页

作者： Geyu Mo Qingqing Wang Xin Ren Weitong Yan Qinxun Li Yen Chin Ong Wentao Luo cas key Laboratory for researches in galaxies and cosmology School of Astronomy and Space ScienceUniversity of Science and Technology of China Department of Astronomy School of Physical Sciences University of Science and Technology of China Department of Physics Tokyo Institute of Technology Universit?ts-Sternwarte Fakult?t für Physik Ludwig-Maximilians Universit?t München Center for Gravitation and cosmology College of Physical Science and Technology Yangzhou University School of Aeronautics and Astronautics Shanghai Jiao Tong University

Harada proposed a modified theory of gravity called Cotton gravity, and argued that it successfully explains the rotation curves of 84 galaxies without the need for dark matter. In this work, we use the galaxy-galaxy lensing technique to test whether the modification effect of Cotton gravity can indeed be a viable substitute for dark matter. Using the spherically symmetric solution of Cotton gravity, we obtain the deflection angle via the Gauss-Bonnet theorem and the weak lensing shear. We use five galaxy catalogs divided into 5 stellar mass bins from the Sloan Digital Sky Survey Data Release 7(SDSS DR7), each further divided into blue star-forming galaxy and red passive galaxy sub-catalogs. We find that Cotton gravity on its own has a significant deviation from the measured galaxy-galaxy lensing signals, thus it cannot replace the role of dark matter. If we consider the combination of dark matter and Cotton gravity, the modification is tightly constrained. Our analysis also applies to other modified gravity theories whose an additional linear term appears in the Schwarzschild solution.

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A sample of active galactic nuclei with strong soft X-ray variabilities

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Science China(Physics,Mechanics & Astronomy) 2015年第4期58卷 101-108页

作者： BI Da LIU Teng WANG JunXian cas key Laboratory for research in galaxies and cosmology Department of AstronomyUniversity of Science and Technology of China

Large-amplitude X-ray variation is a special feature of AGN, reflecting possible extreme change in the central engine or the ab- sorption along the line of sight. Till now there are only a few relevant studies on individual sources or rather small samples. In this work we aim to perform a systematic study of AGNs with strong soft X-ray variations at timescale of 〉 10 years. To build the sample, we compare the soft X-ray fluxes of AGNs measured in ROSAT All-Sky Survey （RASS） during 1990-1991 with those measured by XMM-Newton during 2000-2009. This investigation bings forth to a sample of 13 AGNs, which appeared bright in RASS era, and went into low states （flux dropped by a factor of 〉 10） when they were caught by XMM-Newton. Most of the 13 sources are type I Seyfert galaxies. 5 of them are noticed to have strong X-ray vai＇iation for the first time. We study the nature of their variations through performing XMM-Newton spectral analyses and by collecting reports from the existing literature. We find the sample could be divided into three categories according to the possible causes of the strong X-ray variations. The variations in MRK 0478 and 1H 0419-557 are consistent with strong light-bending effect, i.e., the observed X-ray flux drops significantly as the X-ray emitting corona gets much closer to the central black hole. The variations in ESO 140-G043 and NGC 7158 are caused by absorption changes along the line of sight. For one special case MRK 0335, the variation can be explained by either light-bending or absorption variation. In the rest 8 sources （- 60%）, the strong soft X-ray variations are likely to exist due to intrinsic changes in the activities of the corona, although in some of them without high quality X-ray spectra we are unable to rule out alternative models. This sample provides good targets for future monitoring campaigns with more extensive studies.

关键词： soft X-ray active galactic nuclei variation

Spectral Synthesis via Mean Field approach to Independent Component Analysis

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research in Astronomy and Astrophysics 2016年第3期16卷 51-62页

作者： Ning Hu Shan-Shan Su Xu Kong cas key Laboratory for research in galaxies and cosmology Department of Astronomy University of Science and Technology of China

We apply a new statistical analysis technique, the Mean Field approach to Independent Component Analysis（MF-ICA） in a Bayseian framework, to galaxy spectral analysis. This algorithm can compress a stellar spectral library into a few Independent Components（ICs）, and the galaxy spectrum can be reconstructed by these ICs. Compared to other algorithms which decompose a galaxy spectrum into a combination of several simple stellar populations, the MF-ICA approach offers a large improvement in efficiency. To check the reliability of this spectral analysis method, three different methods are used：（1） parameter recovery for simulated galaxies,（2） comparison with parameters estimated by other methods, and（3） consistency test of parameters derived with galaxies from the Sloan Digital Sky Survey. We find that our MF-ICA method can not only fit the observed galaxy spectra efficiently, but can also accurately recover the physical parameters of galaxies. We also apply our spectral analysis method to the DEEP2 spectroscopic data, and find it can provide excellent fitting results for low signal-to-noise spectra.

关键词： methods: data analysis -- methods: statistical -- galaxies: evolution -- galaxies: fundamentalparameters -- galaxies: stellar content

Smoothing methods comparison for CMB E-and B-mode separation

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research in Astronomy and Astrophysics 2016年第4期16卷 55-62页

作者： Yi-Fan Wang Kai Wang Wen Zhao cas key Laboratory for research in galaxies and cosmology Department of Astronomy University of Science and Technology of China

The anisotropies of the B-mode polarization in the cosmic microwave background radiation play a crucial role in the study of the very early Universe. However, in real observations, a mixture of the E- mode and B-mode can be caused by partial sky surveys, which must be separated before being applied to a cosmological explanation. The separation method developed by Smith （2006） has been widely adopted, where the edge of the top-hat mask should be smoothed to avoid numerical errors. In this paper, we compare three different smoothing methods and investigate leakage residuals of the E-B mixture. We find that, if less information loss is needed and a smaller region is smoothed in the analysis, the sin- and cos-smoothing methods are better. However, if we need a cleanly constructed B-mode map, the larger region around the mask edge should be smoothed. In this case, the Gaussian-smoothing method becomes much better. In addition, we find that the leakage caused by numerical errors in the Gaussian-smoothing method is mostly concentrated in two bands, which is quite easy to reduce for further E-B separations.

关键词： cosmic microwave background radiation -- polarization -- statistics

On the nature of X-ray “unobscured” Seyfert 2 galaxies

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Science China(Physics,Mechanics & Astronomy) 2012年第12期55卷 2482-2491页

作者： TAN Ying WANG JunXian ZHANG Kai cas key Laboratory for research in galaxies and cosmology Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China

We present a systematic study to reveal the effect of host galaxy contamination to the identification of X-ray "unobscured" Seyfert 2 *** compiled a sample of 14 X-ray "unobscured" Seyfert 2 galaxies and 29 X-ray obscured Seyfert 2s,with infrared [Ne II] and [O IV] emission line flux *** this work we classify Seyfert 2s as "unobscured" or obscured in X-ray simply based on X-ray spectral *** find that our X-ay "unobscured" Seyfert 2s have statistically higher [Ne II]/[O IV] line ratios,compared with obscured *** the [Ne II]/[O IV] line ratio reflects the relative strength of star formation activity comparing with the SMBH accretion,the observed differences in [Ne II]/[O IV] line ratios clearly indicate relatively stronger X-ray contamination from star formation in the host galaxies in X-ray "unobscured" Seyfert *** we could attribute the X-ray "unobscured" appearance to host galaxy contamination for most(if not all) of our X-ray "unobscured" Seyfert *** analysis indicates that "unobscured" Seyfert 2s have intrinsically lower AGN luminosity but similar star formation rates,compared with obscured *** is also consistent with previous studies showing most X-ray "unobscured" Seyfert 2s are at lower luminosities,and relatively stronger contaminations from the host galaxies are thus *** we develop a screening criterion to distinguish potential pure Seyfert 2s from X-ray "unobscured" appearances which could be caused by strong host galaxy contamination.

关键词： active galactic nuclei X-rays absorption star formation

Weighing super-massive black holes with narrow Fe Kα line

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Science China(Physics,Mechanics & Astronomy) 2011年第7期54卷 1354-1358页

作者： JIANG Peng WANG JunXian SHU XinWen cas key Laboratory for research in galaxies and cosmology Department of Astronomy University of Science and Technology of China Hefei 230026 China

It has been suggested that the narrow cores of the Fe Ka emission lines in Active Galactic Nuclei （AGNs） are likely produced in the torus, the inner radius of which can be measured by observing the lag time between the V and K band flux variations. In this paper, we compare the virial products of the infrared time lags, and the narrow Fe Ka widths for 10 type 1 AGNs, with the black hole masses from other techniques. We found the narrow Fe Ka line width is in average 2.6＋0.9-0.4 times broader than expected, assuming an isotropic velocity distribution of the torus at the distance measured by the infrared lags. We propose the thick disk model of the torus may explain the observed larger line width. Another possibility is the contamination by emission from the broad line region or the outer accretion disk. Alternatively, the narrow iron line might originate from the inner most part of the obscuring torus within the sublimation radius, while the infrared emission may be from the outer cooler part. We note the correlations between the black hole masses based on this new technique and those based on other known techniques are statistically insignificant. We argue that this could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths. The next generation of X-ray observatories could help verify the origin of the narrow iron Ka line and the reliability of this new technique.

关键词： black hole physics galaxies: active galaxies: nuclei galaxies: Seyfert X-rays: galaxies infrared: galaxies

The study of Seyfert 2 galaxies with and without infrared broad lines

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research in Astronomy and Astrophysics 2010年第5期10卷 427-437页

作者： Hong-Bing Cai Xin-Wen Shu Zhen-Ya Zheng Jun-Xian Wang cas key Laboratory for research in galaxies and cosmology Department of AstronomyUniversity of Science and Technology of China Hefei 230026 China National Time Service Center CAS Xi＇an 710600 China

From the literature, we construct a sample of 25 Seyfert 2 galaxies （S2s）with a broad line region （BLR） detected in near infrared （NIR） spectroscopy and 29with NIR BLRs which were not detected. We find no significant difference betweenthe nuclei luminosity （extinction-corrected [OIII] 5007） and infrared color f 60/f25between the two populations, suggesting that the non-detections of NIR BLRs couldnot be due to low AGN luminosity or contamination from the host galaxy. As ex-pected, we find significantly lower X-ray obscurations in Seyfert 2s with NIR BLRdetection, supporting the unification scheme. However, such a scheme was challengedby the detection of NIR BLRs in heavily X-ray obscured sources, especially in sixof them with Compton-thick X-ray obscuration. The discrepancy could be solved bythe clumpy torus model and we propose a toy model demonstrating that IR-thin X-ray-thick S2s could be viewed at intermediate inclinations and compared with thoseIR-thick X-ray-thick S2s. We note that two of the IR-thin X-ray-thick S2s （NGC 1386and NGC 7674） experienced X-ray transitions, i.e. from Compton-thin to Compton-thick appearance or vice versa based on previous X-ray observations, suggesting thatX-ray transitions could be common in this special class of objects.

关键词： galaxies: active — galaxies: Seyfert — infrared: galaxies