Yufeng Li

Bio: Yufeng Li is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Physics & Gravitational wave. The author has an hindex of 3, co-authored 8 publications receiving 43 citations.

Constraining Cosmological Parameters in the FLRW Metric with Lensed GW+EM Signals

Abstract: We proposed a model-independent method to constrain cosmological parameters using the Distance Sum Rule of the Friedmann–Lemaitre–Robertson–Walker metric by combining the time delay distances and the comoving distances through a multi-messenger approach. The time delay distances are measured from lensed gravitational wave (GW) signals together with their corresponding electromagnetic wave (EM) counterparts, while the comoving distances are obtained from a parameterized fitting approach with independent supernova observations. With a series of simulations based on the Einstein Telescope, Large Synoptic Survey Telescope, and The Dark Energy Survey, we find that only 10 lensed GW+EM systems can achieve the constraining power comparable to and even stronger than 300 lensed quasar systems due to the more precise time delay from lensed GW signals. Specifically, the cosmological parameters can be constrained to and (1σ).5 Our results show that more precise time delay measurements could provide more stringent cosmological parameter values, and lensed GW+EM systems therefore can be applied as a powerful tool in the future precision cosmology.

Constraining cosmological parameters in FLRW metric with lensed GW+EM signals

Abstract: We proposed a model-independent method to constrain the cosmological parameters using the Distance Sum Rule of the FLRW metric by combining the time delay distances and the comoving distances through a multi-messenger approach. The time delay distances are measured from lensed gravitational wave~(GW) signals together with their corresponding electromagnetic wave~(EM) counterpart, while the comoving distances are obtained from a parametrized fitting approach with independent supernova observations. With a series of simulations based on Einstein Telescope, Large Synoptic Survey Telescope and The Dark Energy Survey, we find that only 10 lensed GW+EM systems can achieve the constraining power comparable to and even stronger than 300 lensed quasar systems due to more precise time delay from lensed GW signals. Specifically, the cosmological parameters can be constrained to ~$k=0.01_{-0.05}^{+0.05}$ and ~$H_0=69.7_{-0.35}^{+0.35}$ (1$\sigma$). Our results show that more precise time delay measurements could provide more stringent cosmological parameter values, and lensed GW+EM systems therefore can be applied as a powerful tool in the future precision cosmology.

Estimating the Black Hole Spin for the X-Ray Binary MAXI J1820+070

Abstract: MAXI J1820+070 is a newly-discovered black hole X-ray binary, whose dynamical parameters, namely the black hole mass, the inclination angle and the source distance, have been estimated recently. \emph{Insight}-HXMT have observed its entire outburst from 2018 March 14. In this manuscript, we fitted the spectra obtained by \emph{Insight}-HXMT in the soft state to a fully-relativistic thin disk model {\sc kerrbb2}, and found a slowly-spin black hole of $a_*=0.13^{+0.07}_{-0.10}$ ($1\sigma$) with the continuum-fitting method.

Detailed analysis on the reflection component for the black hole candidate MAXI J1348-630

Abstract: The black hole candidate MAXI J1348-630 was discovered on January 26th, 2019, with the Gas Slit Camera (GSC) on-board MAXI. We report a detailed spectral analysis of this source by using the archived data of NuSTAR. A total of 9 observations covered the complete outburst evolution of MAXI J1348-630 from the hard state to the soft state and finally back to the hard state. Additionally, the intermediate state is found in the transition from the hard state to the soft state. We use the state-of-art reflection model relxill family to fit all the 9 spectra, and the spectra from two focal plane module detectors of NuSTAR are jointly fitted for each observation. In particular, we concentrate on the results of the black hole spin parameter and the inclination of the accretion disk. Based on the analysis of the inner radius of the accretion disk, we obtain the spin parameter 0∗ = 0.78 +0.04 −0.04 , and the inclination angle of the inner disk 8 = 29.2 −0.5 degrees. Furthermore, we also find that when the black hole is in the hard state, the accretion disk would show a significant truncation. The high iron abundance and ionization of the accretion disk obtained in the fitting results can be possibly explained by the high density of the accretion disk.

Estimating the black hole spin for the X-ray binary MAXI J1820+070

Abstract: MAXI J1820+070 is a newly-discovered black hole X-ray binary, whose dynamical parameters, namely the black hole mass, the inclination angle and the source distance, have been estimated recently. \emph{Insight}-HXMT have observed its entire outburst from March 14th, 2018. In this work, we attempted to estimate the spin parameter~$a_*$, using the continuum-fitting method and applying a fully-relativistic thin disk model to the soft-state spectra obtained by \emph{Insight}-HXMT. It is well know that $a_*$ is strongly dependent on three dynamical parameters in this method, and we have examined two sets of parameters. Adopting our preferred parameters: $M$ = $8.48^{+0.79}_{-0.72}~M_\odot$, $i=63^\circ\pm3^\circ$ and $D=2.96\pm0.33$ kpc, we found a slowly-spinning black hole of $a_*=0.14 \pm 0.09$ ($1\sigma$), which give a prograde spin parameter as majority of other systems show. While it is also possible for the black hole to have a retrograde spin (less than 0) if different dynamical parameters are taken.

The Observation of Gravitational Waves from a Binary Black Hole Merger

Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

The Distance, Inclination, and Spin of the Black Hole Microquasar H1743-322

Abstract: During its 2003 outburst, the black-hole X-ray transient H1743-322 produced two-sided radio and X-ray jets. Applying a simple and symmetric kinematic model to the trajectories of these jets, we determine the source distance, 8.5 \pm 0.8 kpc, and the inclination angle of the jets, 75 \pm 3 degrees. Using these values, we estimate the spin of the black hole by fitting its RXTE spectra, obtained during the 2003 outburst, to a standard relativistic accretion-disk model. For its spin, we find a*=0.2 \pm 0.3 (68% limits); -0.3 < a* < 0.7 at 90% confidence. We rule strongly against an extreme value of spin: a* < 0.92 at 99.7% confidence. H1743-322 is the third known microquasar (after A0620-00 and XTE J1550-564) that displays large-scale ballistic jets and has a moderate value of spin. Our result, which depends on an empirical distribution of black hole masses, takes into account all known sources of measurement error.

Direct test of the FLRW metric from strongly lensed gravitational wave observations.

Abstract: The assumptions of large-scale homogeneity and isotropy underly the familiar Friedmann-Lemaitre-Robertson-Walker (FLRW) metric that appears to be an accurate description of our Universe. In this paper, we propose a new strategy of testing the validity of the FLRW metric, based on the galactic-scale lensing systems where strongly lensed gravitational waves and their electromagnetic counterparts can be simultaneously detected. Each strong lensing system creates opportunity to infer the curvature parameter of the Universe. Consequently, combined analysis of many such systems will provide a model-independent tool to test the validity of the FLRW metric. Our study demonstrates that the third-generation ground based GW detectors, like the Einstein Telescope (ET) and space-based detectors, like the Big Bang Observer (BBO), are promising concerning determination of the curvature parameter or possible detection of deviation from the FLRW metric. Such accurate measurements of the FLRW metric can become a milestone in precision GW cosmology.

Strong gravitational lensing of explosive transients.

Abstract: Recent rapid progress in time domain surveys makes it possible to detect various types of explosive transients in the Universe in large numbers, some of which will be gravitationally lensed into multiple images. Although a large number of strongly lensed distant galaxies and quasars have already been discovered, strong lensing of explosive transients opens up new applications, including improved measurements of cosmological parameters, powerful probes of small scale structure of the Universe, and new observational tests of dark matter scenarios, thanks to their rapidly evolving light curves as well as their compact sizes. In particular, compact sizes of emitting regions of these transient events indicate that wave optics effects play an important role in some cases, which can lead to totally new applications of these lensing events. Recently we have witnessed first discoveries of strongly lensed supernovae, and strong lensing events of other types of explosive transients such as gamma-ray bursts, fast radio bursts, and gravitational waves from compact binary mergers are expected to be observed soon. In this review article, we summarize the current state of research on strong gravitational lensing of explosive transients and discuss future prospects.

Model-Independent Determination of H 0 and Ω K 0 from Strong Lensing and Type Ia Supernovae

Abstract: We present the first determination of the Hubble constant ${H}_{0}$ from strong lensing time delay data and type Ia supernova luminosity distances that is independent of the cosmological model. We also determine the spatial curvature model independently. We assume that light propagation over long distances is described by the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) metric and geometrical optics holds, but make no assumption about the contents of the Universe or the theory of gravity on cosmological scales. We find ${H}_{0}={75.7}_{\ensuremath{-}4.4}^{+4.5}\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ and ${\mathrm{\ensuremath{\Omega}}}_{K0}=0.1{2}_{\ensuremath{-}0.25}^{+0.27}$. This is a 6% determination of ${H}_{0}$. A weak prior from the cosmic microwave background on the distance to the last scattering surface improves this to ${H}_{0}={76.8}_{\ensuremath{-}3.8}^{+4.2}\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ and ${\mathrm{\ensuremath{\Omega}}}_{K0}=0.1{8}_{\ensuremath{-}0.18}^{+0.25}$. Assuming a zero spatial curvature, we get ${H}_{0}={74.2}_{\ensuremath{-}2.9}^{+3.0}\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, a precision of 4%. The measurements also provide a consistency test of the FLRW metric: we find no evidence against it.