arXiv subjects

Tian-Yong Cao

Publications and source records attributed to Tian-Yong Cao.

6 recordsLinked to original sources

arXiv2026

Gravitational Wave Evidence of Spin Energy Extraction from Black Holes

Relativistic jets have been found for decades as a key phenomenon in active galactic nuclei (AGNs), compact binary systems, and gamma-ray bursts (GRBs), yet their energy resources remain a mystery. Two competing ideas prevail: one attributes jet energy to accretion power of the black hole (BH), the other, more interestingly, to magnetic extraction of rotational energy from the BH. A decisive observational distinction between them is still elusive. We propose that BHs remnant from their natal GRB activity can serve as a critical testbed to discriminate between these two scenarios. Via analytical approaches, we demonstrate that extraction of rotational energy to power jets during the GRB phase drives the remnant BH to a universal equilibrium spin, independent of accretion history, initial spin, and mass. This model predicts a stellar-mass BH population with this universal spin, a hallmark of BH spin energy extraction. Testing against the 4th gravitational wave (GW) catalogue (GWTC-4.0), we find a statistically robust dominant population where secondary BH spins are narrowly centered at $\sim0.05$. These findings provide strong new evidence for BH spin energy extraction.

astro-ph.HE↗

arXiv2025

Constraining the Nanohertz Gravitational Wave Background with an X-ray Pulsar Timing Array from NICER observations

We present constraints on the nanohertz gravitational wave background (GWB) using X-ray pulsar timing data from the Neutron Star Interior Composition Explorer(\textit{NICER}). By analyzing six millisecond pulsars over a six-year observational baseline, we employed a Bayesian framework to model noise components and search for a common red signal consistent with a GWB from supermassive black hole binaries (assuming a spectral index $γ_{\rm gwb}=13/3$). Our results show no significant evidence for a GWB, yielding a 95\% upper limit of $\log_{10}(A_{\rm gwb})<-13.4$. Weak evidence for Hellings-Downs spatial correlations was found (S=2.5), though the signal remains statistically inconclusive. Compared to radio and $γ$-ray pulsar timing arrays, the \textit{NICER} constraint is currently less stringent but demonstrates the feasibility of X-ray timing with \textit{NICER} for GWB studies and highlights the potential for improved sensitivity with future X-ray missions.

astro-ph.HE↗

arXiv2025

Probing Gravitational Wave Speed and Dispersion with LISA Observations of Supermassive Black Hole Binary Populations

According to General Relativity (GR), gravitational waves (GWs) should travel at the speed of light $c$. However, some theories beyond GR predict deviations of the velocity of GWs $c_{\rm gw}$ from $c$, and some of those expect vacuum dispersion. Therefore, probing the propagation effects of GWs by comparing the wave format detectors against the one at emission excepted from GR. Since such propagation effects accumulate through larger distance, it is expected that super-massive black holes binary (SMBHB) mergers serve as better targets than their stellarmass equivalent. In this paper, we study with simulations on how observations on a population of SMBHs can help to study this topic. We simulate LISA observations on three possible SMBHB merger populations, namely Pop\MakeUppercase{\romannumeral 3}, Q3-nod and Q3-d over a 5-year mission. The resulting constraints on the graviton mass are $9.50$, $9.33$, and $9.05 \times 10^{-27} \, \mathrm{eV}/c^2$, respectively. We also obtain the corresponding constraints on the dispersion coefficients assuming different dispersion scenarios. If the electromagnetic wave counterparts of SMBHB merger can be detected simultaneously, the $c_{\rm gw}$ can be constrained waveform-independently to $Δc/c$ to $10^{-13}-10^{-12}$, corresponding to graviton mass constraints of $10^{-26}-10^{-24} \mathrm{eV}/c^2$.

gr-qc↗

arXiv2025

Prospects for Time-Domain and Multi-Messenger Science with eXTP

In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology.

astro-ph.HE↗

arXiv2025

A systematic study of binary neutron star merger rate density history using simulated gravitational wave and short gamma-ray burst observations

Measuring the merger rate density history of binary neutron stars (BNS) can greatly aid in understanding the history of heavy element formation in the Universe. Currently, second-generation Gravitational Wave (GW) detectors can only measure the BNS merger rate density history at low redshifts ($z$ $\sim$ 0.1). Short gamma-ray bursts (sGRBs) may trace the BNS merger to higher redshifts ($z$ $\sim$ 3). However, not all BNS mergers result in sGRBs, and it is not certain that all sGRBs originate from BNS mergers. In this study, we simultaneously utilize simulated BNS merger GW signals detected by the advanced LIGO design and sGRB signals detected by {\it Fermi}/GBM to constrain the BNS merger rate density history up to $z$ $\sim$ 3. The results indicate that with $\sim$ 8 GWs and 571 sGRBs, the BNS merger rate density can be measured with an accuracy of about 50\% through $z=0$ to $z=1$. The ratio of the jet opening angle-corrected sGRB event rate density to the BNS merger rate density, denoted as $η$, can be constrained to a relative uncertainty of 45\%. With $\sim$ 21 GWs and 761 sGRBs, the BNS merger rate density can be measured to approximately 35\% and 40\% at $z=0$ and $z=1$, respectively. Meanwhile, $η$ can be constrained to a relative uncertainty of 28\%. Additionally, in our parameterized simulation, we find that at least approximately $\sim$550 sGRBs are needed to constrain the characteristic delay time in the star formation rate model, given a relative error of 50\% in the estimated redshift.

astro-ph.HE↗

arXiv2024

Constraining gravitational wave velocities using gravitational and electromagnetic wave observations of white dwarf binaries

Although the general theory of relativity (GR) predicts that gravitational waves (GWs) have exactly the same propagation velocity as electromagnetic (EM) waves, many theories of gravity beyond GR expect otherwise. Accurate measurement of the difference in their propagation speed, or a tight constraint on it, could be crucial to validate or put limits on theories beyond GR. The proposed future space-borne GW detectors are poised to detect a substantial number of Galactic white dwarf binaries (GWDBs), which emit the GW as semi-monochromatic signals. Concurrently, these GWDBs can also be identified as optical variable sources. Here we proposed that allocating a GWDB's optical light curve and contemporaneous GW signal can be used to trace the difference between the velocity of GW and EM waves. Simulating GW and EM wave data from 14 verification binaries (VBs), our method constrains propagation-originated phase differences, limiting the discrepancy between the speed of light ($c$) and GW ($c_{GW}$). Through the utilization of LISA's design sensitivity and the current precision in optical observation on GWDB, our study reveals that a four-year observation of the 14 recognized VBs results in a joint constraint that confines $Δc/c$ ($Δc = c_{\mathrm{GW}} - c$) to the range of $-2.1\times10^{-12}$ and $4.8\times10^{-12}$. Additionally, by incorporating this constraint on $c_{\mathrm{GW}}$, we are able to establish boundaries for the mass of the graviton, limiting it to $m_{\mathrm{g}}\le3\times10^{-23}\,e\mathrm{V}/c^{2}$, and for the parameter associated with local Lorentz violation, $\bar{s}_{00}$, constrained within the range of $-3.4\times10^{-11}\le\bar{s}_{00}\le1.5\times10^{-11}$.

gr-qc↗