arXiv subjects

Chak Man Lee

Publications and source records attributed to Chak Man Lee.

At least 19 recordsLinked to original sources

arXiv2025

Does the high-energy AMS-02 positron flux originate from the dark matter density spikes around nearby black holes?

Recent measurements made by the Alpha Magnetic Spectrometer (AMS) have detected accurate positron flux for energy range 1-1000 GeV. The energy spectrum can be best described by two source terms: the low-energy background diffusion term and an unknown high-energy source term. In this article, we discuss the possibility of the emission of positrons originating from dark matter annihilation in two nearby black hole X-ray binaries A0620-00 and XTE J1118+480. We show that the dark matter density spikes around these two black holes can best produce the observed AMS-02 high-energy positron flux due to dark matter annihilation with rest mass $m_{\rm DM} \approx 8000$ GeV via the $W^+W^-$ annihilation channel. This initiates a new proposal to account for the unknown high-energy source term in the AMS-02 positron spectrum.

astro-ph.HE↗

arXiv2024

Identifying dark matter signals by the radio continuum spectral data of the cool-core cluster RX J1720.1+2638

Investigating the signals of dark matter annihilation is one of the most popular ways to understand the nature of dark matter. In particular, many recent studies are focussing on using radio data to examine the possible signals of dark matter revealed in galaxies and galaxy clusters. In this article, we investigate on the spectral data of the central radio halo of the cool-core cluster RX J1720.1+2638. We show that the radio spectral data can be best accounted by the synchrotron emission due to dark matter annihilation via $τ$ lepton channel (with dark matter mass $m=15$ GeV) or $b$ quark channel (with dark matter mass $m=110$ GeV), although using the very coarse spectral data with notable errors. Despite the fact that cosmic-ray emission can also provide a good explanation for the observed radio spectrum, our results suggest a possible positive evidence for dark matter annihilation revealed in the form of radio emission in RX J1720.1+2638 cluster.

astro-ph.HE↗

arXiv2024

The first robust evidence showing a dark matter density spike around the supermassive black hole in OJ 287

Black hole dynamics suggests that dark matter would re-distribute near a supermassive black hole to form a density spike. However, no direct evidence of dark matter density spike around a supermassive black hole has been identified. In this letter, we present the first robust evidence showing a dark matter density spike around a supermassive black hole. We revisit the data of the well-known supermassive black hole binary OJ 287 and show that the inclusion of the dynamical friction due to a dark matter density spike around the supermassive black hole can satisfactorily account for the observed orbital decay rate. The derived spike index $γ_{\rm sp}=2.351^{+0.032}_{-0.045}$ gives an excellent agreement with the value $γ_{\rm sp}=2.333$ predicted by the benchmark model assuming an adiabatically growing supermassive black hole. This provides a strong verification of the canonical theory suggested two decades ago modeling the gravitational interaction between collisionless dark matter and supermassive black holes.

astro-ph.GA↗

arXiv2024

What if PSR J1910-5959A is an observable self-lensing binary?

In a binary, when the orbital plane of the companion star is almost edge-on along the line-of-sight direction, this would produce an observable self-gravitational lensing effect, which would slightly increase the overall optical intensity of the binary. However, the probability of getting one observable self-lensing binary (SLB) is very low. There are only five observed SLBs so far and all of them are eclipsing binaries. In this article, we theoretically show that the neutron star-white dwarf (NS-WD) binary PSR J1910-5959A could be an observable non-eclipsing SLB. It might be the first binary showing both periodic optical amplification and Shapiro time delay of radio signals, which is useful to verify our understanding about gravitational lensing in relativistic binaries. Moreover, we show that the observed peak amplification limit of the PSR J1910-5959A can help constrain the radius of the WD, which is a crucial parameter to examine the mass-radius and temperature-radius relationship for helium WD.

astro-ph.HE↗

arXiv2024

Constraining annihilating dark matter using the multi-frequency radio flux profiles of the M33 galaxy

Radio data can give stringent constraints for annihilating dark matter. In general, radio observations can detect very accurate radio flux density with high resolution and different frequencies for nearby galaxies. We are able to obtain the radio flux density as a function of distance from the galactic center and frequencies $S(r,ν)$. In this article, we demonstrate a comprehensive radio analysis of the M33 galaxy, combining the radio flux density profile $S(r)$ and the frequency spectrum $S(ν)$ to get the constraints of dark matter annihilation parameters. By analyzing the archival radio data obtained from the Effelsberg telescope, we show that the dark matter annihilation contributing to the radio flux density might be insignificant in the disk region of the M33 galaxy. Moreover, by including the baryonic radio contribution, we constrain the $2σ$ conservative upper limits of the annihilation cross section, which can be complementary to the existing constraints based on neutrino, cosmic-ray, and gamma-ray observations. Our results indicate that analyzing the galactic multi-frequency radio flux profiles can give useful and authentic constraints on dark matter for the leptophilic annihilation channels.

astro-ph.GA↗

arXiv2023

A new method to constrain annihilating dark matter

Recent indirect searches of dark matter using gamma-ray, radio, and cosmic-ray data have provided some stringent constraints on annihilating dark matter. In this article, we propose a new indirect method to constrain annihilating dark matter. By using the data of the G2 cloud near the Galactic supermassive black hole Sgr A*, we can get stringent constraints on the parameter space of dark matter mass and the annihilation cross section, especially for the non-leptophilic annihilation channels $b\bar{b}$ and $W^{\pm}$. For the thermal annihilation cross section, the lower bounds of dark matter mass can be constrained up to TeV order for the non-leptophilic channels with the standard spike index $γ_{\rm sp}=7/3$.

hep-ph↗

arXiv2022

Indirect Evidence for Dark Matter Density Spikes around Stellar-Mass Black Holes

It has been suggested for a long time that dark matter would form a density spike around a black hole. However, no promising evidence has been observed so far to verify this theoretical suggestion. Here, we report the existence of a dark matter density spike around each of the two nearby stellar-mass black holes (A0620-00 and XTE J1118+480). The dynamical friction between dark matter and the companion stars can satisfactorily explain the abnormally fast orbital decays in the two binaries. The calculated spike index for A0620-00 and XTE J1118+480 are $γ=1.71^{+0.01}_{-0.02}$ and $γ=1.85^{+0.04}_{-0.04}$ respectively, which are close to the lower regime predicted by the stellar heating model. It may provide a possible indirect evidence for the existence of dark matter density spikes around stellar-mass black holes. We anticipate that analyzing observational data of nearby black hole X-ray binaries would be a new way to reveal the nature of dark matter.

astro-ph.HE↗

arXiv2022

Crossing the dark matter soliton core: a possible reversed orbital precession

The ultra-light dark matter (ULDM) model has become a popular dark matter scenario nowadays. The mass of the ULDM particles is extremely small so that they can exhibit wave properties in the central dark matter halo region. Numerical simulations show that a soliton core with an almost constant mass density would be formed inside the ULDM halo. If our Galactic Centre has a dark matter soliton core, some of the stars orbiting about the supermassive black hole (Sgr A*) would be crossing the soliton core boundary. In this article, we report the first theoretical study on how the dark matter soliton core near the Sgr A* could affect the surrounding stellar orbital precession. We show that some particular stellar orbital precession may become retrograde in direction, which is opposite to the prograde direction predicted by General Relativity. We anticipate that future orbital data of the stars S2, S12 and S4716 can provide crucial tests for the ULDM model for $m \sim 10^{-19}-10^{-17}$ eV.

astro-ph.GA↗

arXiv2022

The solar system test for the general modified gravity theories

In the past few decades, various versions of modified gravity theories were proposed to mimic the effect of dark matter. Compared with the conventional Newtonian or relativistic dynamics, these theories contain some extra apparent force terms in the dynamical equations to replace the role of dark matter. Generally speaking, the extra apparent force terms usually scale with radius so that the effect would be significant only on large scale to explain the missing mass in galaxies or galaxy clusters. Nevertheless, the apparent effect may still be observable in small structures like the solar system. In this article, we derive analytic general formulae to represent the contribution of the precession angle of the planets in the solar system due to the general modified gravity theories, in which the extra apparent force terms can be written in a power law of radius $r$ or an exponential function in $r$. We have tested three popular modified gravity theories, the Modified Newtonian Dynamics (MOND), the Emergent Gravity (EG), and the Modified Gravity (MOG). In particular, based on the solar system data, we have constrained the parameters involved for two popular general interpolating functions used in MOND. Our results can be generally applied to both of the modified inertia and modified gravity versions of MOND.

gr-qc↗

arXiv2022

Investigating the nature of mass distribution surrounding the Galactic supermassive black hole

In the past three decades, many stars orbiting about the supermassive black hole (SMBH) at the Galactic Centre (Sgr A*) were identified. Their orbital nature can give stringent constraints for the mass of the SMBH. In particular, the star S2 has completed at least one period since our first detection of its position, which can provide rich information to examine the properties of the SMBH, and the astrophysical environment surrounding the SMBH. Here, we report an interesting phenomenon that if a significant amount of dark matter or stellar mass is distributed around the SMBH, the precession speed of the S2 stellar orbit could be `slow down' by at most 27\% compared with that without dark matter surrounding the SMBH, assuming the optimal dark matter scenario. We anticipate that future high quality observational data of the S2 stellar orbit or other stellar orbits can help reveal the actual mass distribution near the SMBH and the nature of dark matter.

astro-ph.GA↗

arXiv2022

Constraining annihilating dark matter by radio continuum spectrum of the Large Magellanic Cloud

Recent radio observations have obtained stringent constraints for annihilating dark matter. In this article, we use the radio continuum spectral data of the Large Magellanic Cloud (LMC) to analyze the dark matter annihilation signals. We have discovered a slightly positive signal of dark matter annihilation with a $1.5σ$ statistical significance. The overall best-fit dark matter mass is $m_{\rm DM} \approx 90$ GeV, annihilating via $b\bar{b}$ channel. We have also constrained the $3σ$ lower limits of dark matter mass with the standard thermal dark matter annihilation cross section for the $e^+e^-$, $μ^+μ^-$, $τ^+τ^-$ and $b\bar{b}$ channels.

astro-ph.GA↗

arXiv2022

Constraints on annihilating dark matter in the Omega Centauri cluster

Recent gamma-ray and radio studies have obtained some stringent constraints on annihilating dark matter properties. However, only a few studies have focussed on using X-ray data to constrain annihilating dark matter. In this article, we perform the X-ray analysis of annihilating dark matter using the data of the Omega Centauri cluster. If dark matter is the correct interpretation of the non-luminous mass component derived in the Omega Centauri cluster, the conservative lower limits of thermal dark matter mass annihilating via the $τ^+τ^-$, $b\bar{b}$ and $W^+W^-$ channels can be significantly improved to 104(43) GeV, 650(167) GeV and 480(137) GeV respectively, assuming the diffusion coefficient $D_0 \le 10^{26}(10^{27})$ cm$^2$/s. These constraints can safely rule out the recent claims of dark matter interpretation of the gamma-ray excess and anti-proton excess seen in our Galaxy. Generally speaking, the conservative lower limits obtained for non-leptophilic annihilation channels are much more stringent than that obtained by gamma-ray analysis of nearby dwarf galaxies. We anticipate that this would open a new window for constraining annihilating dark matter.

astro-ph.GA↗

arXiv2022

Constraining dark matter-nucleon scattering cross section by the background electron anti-neutrino flux data

Celestial objects such as stars and planets might be able to capture a large amount of dark matter particles through dark matter-nucleon scattering. Many previous studies have considered different celestial objects such as the Sun and the Earth as natural dark matter detectors and obtained some stringent bounds of the dark matter-nucleon scattering cross section. In this study, we use the $\sim 10$ MeV electron neutrino flux limits obtained by the Super-Kamiokande experiment and consider the Earth as a large natural dark matter detector to constrain the dark matter-nucleon scattering cross section. We show that this method can generally get more stringent limits. For certain ranges of dark matter mass annihilating via the $b\bar{b}$ channel, the limits of cross section for the isospin-independent scattering and proton-only scattering could be more stringent than that obtained in the PICO direct-detection experiment.

hep-ph↗

arXiv2021

The evaporating primordial black hole fraction in cool-core galaxy clusters

Recent studies of gamma-ray, cosmic-ray and radio data put stringent constraints on the fraction of primordial black holes (PBHs) in our universe. In this article, we propose a new indirect method in using the X-ray luminosity data of cool-core clusters to constrain the evaporating PBH fraction for the monochromatic, log-normal and power-law mass distributions. The present results show that the amount of evaporating PBHs only constitutes a minor component of dark matter for a large parameter space. The constraints are consistent with and close to that obtained from other cosmic-ray and multi-wavelength observations.

astro-ph.HE↗

arXiv2020

Constraining annihilating dark matter mass by the radio continuum spectral data of NGC4214 galaxy

Recent gamma-ray and radio observations provide stringent constraints for annihilating dark matter. The current $2σ$ lower limits of dark matter mass can be constrained to $\sim 100$ GeV for thermal relic annihilation cross section. In this article, we use the radio continuum spectral data of a nearby galaxy NGC4214 and differentiate the thermal contribution, dark matter annihilation contribution and cosmic-ray contribution. We can get more stringent constraints of dark matter mass and annihilation cross sections. The $5σ$ lower limits of thermal relic annihilating dark matter mass obtained are 300 GeV, 220 GeV, 220 GeV, 500 GeV and 600 GeV for $e^+e^-$, $μ^+μ^-$, $τ^+τ^-$, $W^+W^-$ and $b\bar{b}$ channels respectively. These limits challenge the dark matter interpretation of the gamma-ray, positron and antiproton excess in our Milky Way.

astro-ph.HE↗

arXiv2020

A possible radio signal of annihilating dark matter in the Abell 4038 cluster

In the past decade, some telescopes (e.g. Fermi-LAT, AMS and DAMPE) were launched to detect the signals of annihilating dark matter in our Galaxy. Although some excess of gamma rays, anti-protons and electrons/positrons have been reported and claimed as dark matter signals, the uncertainties of Galactic pulsars' contributions are still too large to confirm the claims. In this letter, we report a possible radio signal of annihilating dark matter manifested in the archival radio continuum spectral data of the Abell 4038 cluster. By assuming the thermal annihilation cross section and comparing the dark matter annihilation model with the null hypothesis (cosmic ray emission without dark matter annihilation), we get very large Test Statistic values TS $>45$ for four popular annihilation channels, which correspond to more than $6.5 σ$ statistical preference. This provides a very strong evidence for the existence of annihilating dark matter. In particular, our results also support the recent claims of dark matter mass $m \approx 30-50$ GeV annihilating via the $b\bar{b}$ quark channel with the thermal annihilation cross section.

astro-ph.HE↗

arXiv2020

Constraining Primordial Black Hole Fraction at the Galactic Centre using radio observational data

Recent gamma-ray and cosmic-ray observations have put strong constraints on the amount of primordial black holes (PBHs) in our universe. In this article, we use the archival radio data of the inner Galactic Centre to constrain the PBH to dark matter ratio for three different PBH mass distributions including monochromatic, log-normal and power-law. We show that the amount of PBHs only constitutes a very minor component of dark matter at the Galactic Centre for a large parameter space.

astro-ph.HE↗

arXiv2020

Constraining annihilating dark matter mass by the radio continuum spectral data of a high-redshift galaxy cluster

In the past decade, the properties of annihilating dark matter models were examined by various kinds of data, including the data of gamma rays, radio waves, X-ray, positrons, electrons, antiprotons and neutrinos. In particular, most of the studies focus on the data of our Galaxy, nearby galaxies (e.g. M31 galaxy) or nearby galaxy clusters (e.g. Fornax cluster). In this article, we examine the archival radio continuum spectral data of a relatively high-redshift galaxy cluster (A697 cluster) to constrain the properties of annihilating dark matter. We find that leptophilic annihilation channels ($e^+e^-$, $μ^+μ^-$ and $τ^+τ^-$) can give very good fits to the radio continuum spectrum of the A697 cluster.

astro-ph.HE↗