arXiv subjects

Ruizhi Yang

Publications and source records attributed to Ruizhi Yang.

At least 37 records · Page 2Linked to original sources

arXiv2024

Extended GeV $γ$-ray emission around the star forming region of the W3 complex

We analyze the GeV $γ$-ray emission from the W3 complex using about 14 years of Pass 8 data recorded by the $\it Fermi$ Large Area Telescope (\textit{Fermi}-LAT). We resolve the $γ$-ray emissions around W3 into two components: an elliptical Gaussian overlapping with the molecular gas and a point-like source near the cluster W3 Main. The pion-bump feature of SED for the elliptical Gaussian together with the better fitting result of pion decay model favor the hadronic origin. We further argue that the cosmic rays (CRs) could originate from the interactions between cluster winds and the shock produced by the SNR HB3. The point-like source positionally coincident with the star cluster W3 Main indicates it may be directly powered by near clusters, while its fainter $γ$-ray emissions below 10 GeV is possibly due to the shelter from dense gas making the low-energy CRs incapable of penetrating the dense materials. Meanwhile, we cannot rule out that the $γ$-ray emissions originate from the interaction of accelerated protons in SNR with the ambient gas.

astro-ph.HE↗

arXiv2024

Precise measurement of pion-bump structure using future MeV gamma-ray detectors

The pion-bump structure in the gamma-ray spectrum is a direct proof for the hadronic origin of the gamma rays, and thus the decisive evidence for the acceleration of hadronic cosmic rays in astrophysical objects. However, the identification of such a spectral feature is limited by the resolution and energy coverage of current gamma-ray instruments. Furthermore, there are unavoidable bremsstrahlung emissions from secondary and primary electrons, which may dominate the gamma-ray emission below the pion-bump. Thus, the study of this gamma-ray emission component can provide unique information on the acceleration and confinement of high-energy particles. In this paper, we studied the predicted gamma-ray spectrum assuming both hadronic or leptonic origin in mid-aged supernova remnants W44, we discuss the detection potential of future MeV missions on these emissions and possible implications.

astro-ph.HE↗

arXiv2024

Detection of extended gamma-ray emission in the vicinity of Cl Danks 1 and 2

We report the detection of high-energy gamma-ray emission towards the G305 star-forming region. Using almost 15 years of observation data from {\sl Fermi} Large Area Telescope, we detected an extended gamma-ray source in this region with a significance of $\sim 13 σ$. The gamma-ray radiation reveals a clear pion-bump feature and can be fitted with the power law parent proton spectrum with an index of $-2.5$. The total cosmic ray (CR) proton energy in the gamma-ray production region is estimated to be the order of $10^{49}\ \rm erg$. We further derived the CR radial distribution from both the gamma-ray emission and gas distribution and found it roughly obeys the $1/r$ type profile, which is consistent with other similar systems and expected from the continuous injection of CRs by the central powerful young massive star cluster Danks 1 or Danks 2 in this region. Together with former detections of similar gamma-ray structures, such as Cygnus cocoon, Westerlund 1, Westerlund 2, NGC 3603, and W40, the detection supports the hypothesis that young massive star clusters are CR accelerators.

astro-ph.HE↗

arXiv2024

Stochastic Wave Dark Matter with Fermi-LAT $γ$-ray Pulsar Timing Array

Pulsar timing arrays (PTAs) can detect disturbances in the fabric of spacetime on a galactic scale by monitoring the arrival time of pulses from millisecond pulsars (MSPs). Recent advancements have enabled the use of $γ$-ray radiation emitted by MSPs, in addition to radio waves, for PTA experiments. Wave dark matter (DM), a prominent class of DM candidates, can be detected with PTAs due to its periodic perturbations of the spacetime metric. In response to this development, we perform in this Letter a first analysis of applying the $γ$-ray PTA to detect the ultralight axion-like wave DM, with the data of Fermi Large Area Telescope (Fermi-LAT). Despite its much smaller collecting area, the Fermi-LAT $γ$-ray PTA demonstrates a promising sensitivity potential. We show that the upper limits not far from those of the dedicated radio-PTA projects can be achieved. Moreover, we initiate a cross-correlation analysis using the data of two Fermi-LAT pulsars. The cross-correlation of phases, while carrying key information on the source of the spacetime perturbations, has been ignored in the existing data analyses for the wave DM detection with PTAs. Our analysis indicates that taking this information into account can improve the sensitivity to wave DM by $\gtrsim 50\%$ at masses below $10^{-23}$ eV.

astro-ph.HE↗

arXiv2024

Limits on the Primordial Black Holes Dark Matter with future MeV detectors

Primordial black holes (PBHs) are a compelling candidate for Dark Matter (DM). There remain significant parameter spaces to be explored despite current astrophysical observations have set strong limits. Utilizing advanced MeV observation instruments, we have statistically established the upper limit of Hawking radiation emitted by PBHs in DM-dense systems, such as galaxy clusters or dwarf galaxies. These results can set a stringent upper limit on the ratio of PBH to DM, expressed as $f_{\rm PBH}$. Our results highlight the efficacy of MeV observations in DM-dense environments. The constraints on $f_{\rm PBH}$ for PBHs in the mass range of $10^{16}-10^{17} ~\rm g$ can be improved significantly compared with the current observations.

astro-ph.HE↗

arXiv2023

Semantic Connectivity-Driven Pseudo-labeling for Cross-domain Segmentation

Presently, self-training stands as a prevailing approach in cross-domain semantic segmentation, enhancing model efficacy by training with pixels assigned with reliable pseudo-labels. However, we find two critical limitations in this paradigm. (1) The majority of reliable pixels exhibit a speckle-shaped pattern and are primarily located in the central semantic region. This presents challenges for the model in accurately learning semantics. (2) Category noise in speckle pixels is difficult to locate and correct, leading to error accumulation in self-training. To address these limitations, we propose a novel approach called Semantic Connectivity-driven pseudo-labeling (SeCo). This approach formulates pseudo-labels at the connectivity level and thus can facilitate learning structured and low-noise semantics. Specifically, SeCo comprises two key components: Pixel Semantic Aggregation (PSA) and Semantic Connectivity Correction (SCC). Initially, PSA divides semantics into 'stuff' and 'things' categories and aggregates speckled pseudo-labels into semantic connectivity through efficient interaction with the Segment Anything Model (SAM). This enables us not only to obtain accurate boundaries but also simplifies noise localization. Subsequently, SCC introduces a simple connectivity classification task, which enables locating and correcting connectivity noise with the guidance of loss distribution. Extensive experiments demonstrate that SeCo can be flexibly applied to various cross-domain semantic segmentation tasks, including traditional unsupervised, source-free, and black-box domain adaptation, significantly improving the performance of existing state-of-the-art methods. The code is available at https://github.com/DZhaoXd/SeCo.

cs.CV↗

arXiv2023

DRL-based Energy-Efficient Baseband Function Deployments for Service-Oriented Open RAN

Open Radio Access Network (Open RAN) has gained tremendous attention from industry and academia with decentralized baseband functions across multiple processing units located at different places. However, the ever-expanding scope of RANs, along with fluctuations in resource utilization across different locations and timeframes, necessitates the implementation of robust function management policies to minimize network energy consumption. Most recently developed strategies neglected the activation time and the required energy for the server activation process, while this process could offset the potential energy savings gained from server hibernation. Furthermore, user plane functions, which can be deployed on edge computing servers to provide low-latency services, have not been sufficiently considered. In this paper, a multi-agent deep reinforcement learning (DRL) based function deployment algorithm, coupled with a heuristic method, has been developed to minimize energy consumption while fulfilling multiple requests and adhering to latency and resource constraints. In an 8-MEC network, the DRL-based solution approaches the performance of the benchmark while offering up to 51% energy savings compared to existing approaches. In a larger network of 14-MEC, it maintains a 38% energy-saving advantage and ensures real-time response capabilities. Furthermore, this paper prototypes an Open RAN testbed to verify the feasibility of the proposed solution.

cs.NI↗

arXiv2023

Ultra-High-Energy Gamma-Ray Astronomy

Ultra-High Energy (UHE, $>$0.1\,PeV) $γ$-ray Astronomy is rapidly evolving into an expanding branch of the $γ$-ray astronomy with the surprising discovery of 12 PeVatrons and the detection of a handful of photons above 1 PeV. Nearly all known celestial object types that have emissions in the TeV band are found also emitting UHE photons. UHE $γ$-rays have a well-defined horizon inside our galaxy due to the absorption of infrared and cosmic microwave backgrounds in the universe. With the last 30 years, traditional cosmic ray (CR) detection techniques allow the detection of UHE $γ$-rays, and opened up the last observation window. For leptonic sources, UHE radiation is in the deep Klein-Nishina regime which is largely suppressed. Therefore UHE $γ$-ray detection will help to locate and identify hadronic radiation sources, tracing the historic pursuit for the origin of CRs around the knee of the spectrum. The Crab Nebula is again the focus of attention with measured photon emissions above 1\,PeV. In the absence of hadronic processes, this may indicate the existence of an extreme accelerator of e$^+$/e$^-$. Utilization of the CR extensive air shower detection techniques broadens the field of view of the source observations, enabling the measurement of UHE radiation surrounding the sources. These observations can probe the particle propagation inside and outside the accelerators and the subsequent injection/escape into the interstellar medium.

astro-ph.HE↗

arXiv2023

Analysis of the Gravitational Wave Background Using Gamma-Ray Pulsar Timing Arrays with Next-Generation Detectors

In this work, we investigate the potential of gamma-ray pulsar time array (PTA) on gravitational waves background (GWB) using future gamma-ray detectors with larger effective areas. We consider both spaceborne detectors and ground-based imaging air Cherenkov telescope arrays (IACTs). We simulated the detected photons from pulsars using the response of hypothetical detectors taking into account the backgrounds and analyzed the sensitivities. Our results showed that thanks to the higher statistics of IACTs, the PTA using IACTs can improve significantly the performance compared with the PTA using Fermi-LAT data.

astro-ph.HE↗

arXiv2023

Diffuse gamma-ray emission around the Rosette Nebula

The Rosette Nebula is a young stellar cluster and molecular cloud complex, located at the edge of the southern shell of a middle-aged SNR Monoceros Loop (G205.5+0.5). We revisited the GeV gamma-ray emission towards the Rosette Nebula using more than 13 years of Fermi-LAT data. We tested several spatial models and found that compared to the result using the CO gas template only, the inclusion of the HII gas template can significantly improve the likelihood fit. We performed spectral analysis using the new spatial template. With both the gamma-ray observation and CO+HII gas data, we derived the cosmic ray spectrum of different components in the vicinity of the Rosette Nebula. We found the gamma-ray emissions from Rosette Nebula are substantially harder than previously reported, which may imply that Rosette Nebula is another example of a gamma-ray emitting young massive star cluster.

astro-ph.HE↗

arXiv2023

Cosmic ray density variations in nearby giant molecular clouds

In this paper, we analyzed 12 years of Fermi LAT gamma-ray data towards three nearby giant molecular clouds (GMCs), i.e., R~CrA, Chamaeleon, and Lupus. We calibrated the gas column density of these regions by using the Planck dust opacity map as well as the Gaia extinction map. With both the gamma-ray observations and gas column density maps, we derived the cosmic ray densities in the three GMCs. We found the derived CR spectra have almost the same shape but significantly different normalizations, which may reflect that the distributions of CRs in the vicinity of solar systems are inhomogeneous.

astro-ph.HE↗

arXiv2022

Detailed study of extended gamma-ray morphology in the vicinity of the Coma cluster with Fermi-LAT

Galaxy clusters can be sources of high-energy (HE) $γ$-ray radiation, due to the efficient acceleration of particles exceeding EeV energies. At present, though, the only candidate for emitting HE $γ$-rays is the Coma cluster, towards which an excess of $γ$-ray emission has been detected by the Fermi Large Area Telescope (LAT). Using $\mathrm{\sim12.3}$ years of \textit{Fermi}-LAT data, we explored the region of the Coma cluster between energies 100 MeV and 1 TeV by detailed spectral and morphological analysis. In the region of the Coma cluster, we detected diffuse gamma-ray emission of energies between 100 MeV and 1 TeV with a 5.4$σ$ extension significance and a 68\% containment radius of $0.82^{+0.10}_{-0.05}$ degrees derived with a 2D homogeneous disk model. The corresponding gamma-ray spectrum extends up to $\sim50$ GeV, with a power-law index of $\mathrm{Γ=2.23\pm0.11}$ and flux of $\mathrm{(3.84\pm0.67)\times10^{-12}\,erg\,cm^{-2}\,s^{-1}}$. Using energy arguments we show that point-like sources such as radiogalaxies and star-forming galaxies are unlikely to explain the emission, and more likely, the emission is produced in the Coma cluster. Besides, we also identified three point-like sources in the region. However, due to the limited statistics of the detection, we could neither exclude nor conclude that the total extended emission is contributed to by these three-point like sources.

astro-ph.HE↗

arXiv2022

The Large High Altitude Air Shower Observatory (LHAASO) Science Book (2021 Edition)

Since the science white paper of the Large High Altitude Air Shower Observatory (LHAASO) published on arXiv in 2019 [e-Print: 1905.02773 (astro-ph.HE)], LHAASO has completed the transition from a project to an operational gamma-ray astronomical observatory LHAASO is a new generation multi-component facility located in Daocheng, Sichuan province of China, at an altitude of 4410 meters. It aims at measuring with unprecedented sensitivity the spectrum, composition, and anisotropy of cosmic rays in the energy range between 10$^{12}$ and 10$^{18}$~eV, and acting simultaneously as a wide aperture (one stereoradiant) continuously operating gamma-ray telescope in the energy range between 10$^{11}$ and $10^{15}$~eV with the designed sensitivity of 1.3\% of the Crab Unit (CU) above 100 TeV. LHAASO's capability of measuring simultaneously different shower components (electrons, muons, and Cherenkov/fluorescence light), will allow it to investigate the origin, acceleration, and propagation of CR through measurement of the energy spectrum, elemental composition, and anisotropy with unprecedented resolution. The remarkable sensitivity of LHAASO will play a key role in CR physics and gamma-ray astronomy for a general and comprehensive exploration of the high energy universe and will allow important studies of fundamental physics (such as indirect dark matter search, Lorentz invariance violation, quantum gravity) and solar and heliospheric physics. The LHAASO Collaboration organized an editorial working group and finished all editorial work of this science book, to summarize the instrumental features and outline the prospects of scientific researches with the LHAASO experiment.

astro-ph.HE↗

arXiv2021

A radiation transfer model for the Milky Way. II The global properties and large scale structure

We obtained an axi-symmetric model for the large-scale distribution of stars and dust in the Milky Way (MW) using a radiative transfer code that can account for the existing near-infrared (NIR)/mid-infrared/submm all-sky emission maps of our Galaxy. We find that the MW has a star-formation rate of ${ SFR}=1.25\pm0.2\,{ M}_{\odot}$/yr, a stellar mass $M_{*}=(4.9\pm 0.3)\times10^{10}\,{ M}_{\odot}$, and a specific SFR that is relatively constant with radius (except for the inner 1 kpc). We identified an inner radius $R_{ in}= 4.5$\,kpc beyond which the stellar emissivity and dust distribution fall exponentially. For $R<R_{ in}$ the emissivities fall linearly towards the centre. The old stellar populations in the disk have an exponential scalelength that increases monotonically from $h_{ s}^{ disk}(K)=2.2\pm 0.6$\,kpc in the NIR, to $h_{ s}^{ disk}(B)=3.2\pm 0.9$\,kpc at the shorter optical bands, and a scaleheight that varies with radial distance, from $z_{ s}^{ disk}(0)=140\pm 20$\,pc in the centre to $z_{ s}^{ disk}(R_{\odot})=300\pm 20$\,pc at the solar radius. The young stellar populations have a scalelength of $h_{ s}^{ tdisk}=3.2\pm 0.9$\,kpc and a scaleheight that varies from $z_{ s}^{ tdisk}(0)=50\pm 10$\,pc in the centre to $z_{ s}^{ tdisk}(R_{\odot})=90\pm 10$\,pc at the solar radius. We discovered an inner stellar disk within the central 4.5 kpc, which we associate with the extended long bar of the MW. Most of the obscured star formation happens within this inner thin disk. The diffuse dust is mainly distributed in a disk with scalelength $h_{ d}^{ disk}=5.2\pm 0.8$\,kpc and scaleheight $z_{ d}^{ disk}=0.14\pm 0.02$\,kpc. We give the first derivation of the MW attenuation curve and present it as a functional fit to the model data. We find the MW to lie in the Green Valley of the main sequence relation for spiral galaxies.

astro-ph.GA↗

arXiv2021

Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2

Star-forming regions have been proposed as potential Galactic cosmic-ray accelerators for decades. Cosmic ray acceleration can be probed through observations of gamma-rays produced in inelastic proton-proton collisions, at GeV and TeV energies. We analyze more than 11 years of Fermi-LAT data from the direction of Westerlund 2, one of the most massive and best-studied star-forming regions in our Galaxy. The spectral and morphological characteristics of the LAT source agree with the ones in the TeV regime (HESS J1023-575), allowing the description of the gamma-ray source from a few hundreds of MeV to a few tens of TeVs. We will present the results and discuss the implications of the identification with the stellar cluster and the radiation mechanism involved.

astro-ph.HE↗

arXiv2021

Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2

Star-forming regions have been proposed as potential Galactic cosmic-ray accelerators for decades. Cosmic-ray acceleration can be probed through observations of gamma-rays produced in inelastic proton-proton collisions, at GeV and TeV energies. In this paper, we analyze more than 11 years of Fermi-LAT data from the direction of Westerlund 2, one of the most massive and best-studied star-forming regions in our Galaxy. In particular, we investigate the characteristics of the bright pulsar PSR J1023-5746 that dominates the gamma-ray emission below a few GeV at the position of Westerlund 2, and the underlying extended source FGES J1023.3-5747. The analysis results in a clear identification of FGES J1023.3-5747 as the GeV counterpart of the TeV source HESS J1023-575, through its morphological and spectral properties. This identification provides new clues about the origin of the HESS J1023-575 gamma-ray emission, favouring a hadronic origin of the emission, powered by Westerlund 2, rather than a leptonic origin related to either the pulsar wind nebula associated with PSR J1023-5746 or the cluster itself. This result indirectly supports the hypothesis that star-forming regions can contribute to the cosmic-ray sea observed in our Galaxy

astro-ph.HE↗

arXiv2021

Probing the Cosmic Ray density in the inner Galaxy

The galactic diffuse $γ$-ray emission, as seen by Fermi Large Area Telescope (LAT), shows a sharp peak in the region around 4 kpc from the Galactic center, which can be interpreted either as due to an enhanced density of cosmic-ray accelerators or to a modification of the particle diffusion in that region. Observations of $γ$-rays originating in molecular clouds are a unique tool to infer the cosmic-ray density point by point, in distant regions of the Galaxy. We report here the analysis of 11 yr Fermi-LAT data, obtained in the direction of nine molecular clouds located in the 1.5--4.5 kpc region. The cosmic-ray density measured at the locations of these clouds is compatible with the locally measured one. We demonstrate that the cosmic-ray density gradient inferred from the diffuse gamma-ray emission is the result of the presence of cosmic-ray accelerators rather than a global change of the sea of Galactic cosmic rays due to their propagation.

astro-ph.HE↗

arXiv2021

Electrocardiogram Classification and Visual Diagnosis of Atrial Fibrillation with DenseECG

Atrial Fibrillation (AF) is a common cardiac arrhythmia affecting a large number of people around the world. If left undetected, it will develop into chronic disability or even early mortality. However, patients who have this problem can barely feel its presence, especially in its early stage. A non-invasive, automatic, and effective detection method is therefore needed to help early detection so that medical intervention can be implemented in time to prevent its progression. Electrocardiogram (ECG), which records the electrical activities of the heart, has been widely used for detecting the presence of AF. However, due to the subtle patterns of AF, the performance of detection models have largely depended on complicated data pre-processing and expertly engineered features. In our work, we developed DenseECG, an end-to-end model based on 5 layers 1D densely connected convolutional neural network. We trained our model using the publicly available dataset from 2017 PhysioNet Computing in Cardiology(CinC) Challenge containing 8528 single-lead ECG recordings of short-term heart rhythms (9-61s). Our trained model was able to outperform the other state-of-the-art AF detection models on this dataset without complicated data pre-processing and expert-supervised feature engineering.

eess.SP↗