Hasil untuk "Astrophysics"

C. Giunti, C. W. Kim

F. Melia

During a dramatic development of the field over the last decade, German groups and institutions have played central, often decisive, roles in high-energy astrophysics. Both spatially resolved and temporal studies of gamma-ray sources are conducted with unprecedented sensitivity, deciphering the physical processes in Galactic and extragalactic sources of high-energy emission, and providing new insights into fundamental physics. Radio observations of compact objects, especially black holes and neutron stars, permit exploring physics under extreme conditions and testing for fundamental properties such as the existence of event horizons around black holes. Observations of ultra-high energy cosmic rays provide information on particle acceleration at the highest energy. The first detection in 2013 of cosmic high-energy neutrinos was named the Physics World breakthrough of the year.

Yuhang Liu, Fei Mei, Jun Zhang et al.

The core component to ensure the refined and safe operation of distribution network scheduling is 10 kV bus load probabilistic prediction. However, existing probabilistic prediction methods suffer from insufficient dynamic feature extraction and compromised prediction reliability caused by quantile crossing. To address these issues, this paper proposes a 10 kV bus load probabilistic prediction method integrating multi-value quantile regression (MQR) and a temporal fusion ensemble learning model (ELM). Firstly, a temporal fusion ensemble learning model is constructed, which integrates multiple temporal fusion network (TFN) sub-models through a stacking framework to parallel extract multi-dimensional temporal features of loads, effectively enhancing its feature capture capability for complex load data. Secondly, MQR is introduced as the core objective function to synchronously generate multi-quantile load forecasting results, comprehensively depicting the load probability distribution. Finally, a Listwise Maximum Likelihood Estimation (ListMLE) ranking constraint mechanism is embedded, which optimizes quantile ordering through monotonicity constraints, significantly reducing the degree of quantile crossing and improving the interpretability of forecasting results. The results show that the MQR-ELM algorithm achieves a Prediction Interval Coverage Probability of 94.624% (close to the nominal coverage rate of 95%), a Prediction Interval Averaged Width of 588.526, a Crossing Degree Index of only 0.0476, and a Continuous Ranked Probability Score as low as 84.931. All core indicators are significantly superior to those of the comparative algorithms.

Yunlang Guo, Bo Wang, Xiangdong Li et al.

Eclipsing millisecond pulsars (MSPs) are a type of pulsar binaries with close orbits (≲1.0 day). They are important objects for studying the accretion history of neutron stars (NSs), pulsar winds, and the origin of isolated MSPs, etc. Recently, a new eclipsing MSP, PSR J1928+1815, was discovered by the Five-hundred-meter Aperture Spherical radio Telescope. It is the first known pulsar with a He star companion, as suggested in Yang et al. The system features a short orbital period of ∼0.15 days and a relatively massive companion ≳1.0 M _⊙ . However, the origin of PSR J1928+1815 remains highly uncertain. In this paper, we investigated the formation of the new subclass of eclipsing MSPs containing (evolved) He star companions through the NS + He star channel. We found that if an NS binary undergoes subsequent mass-transfer phases following Case BA or Case BB, it may appear as an eclipsing MSP during the detached phase. Additionally, we obtained the initial parameter space for producing eclipsing MSPs with He star companions. Using the binary population synthesis approach, we estimated their birth rate to be ∼2.1–4.7 × 10 ^−4 yr ^−1 , corresponding to a total number of ∼220 systems in the Galaxy. Moreover, we concluded that PSR J1928+1815 may originate from the evolution of an NS + He star system with an initial orbital period of ∼0.1 days, which can undergo the Case BB mass transfer.

Alice Knutas, Angela Adamo, Alex Pedrini et al.

We present JWST NIRCam observations of the emerging young star clusters (eYSCs) detected in the nearby spiral galaxy M83. The NIRcam mosaic encompasses the nuclear starburst, the bar, and the inner spiral arms. The eYSCs, detected in Pa α and Br α maps, have been largely missed in previous optical campaigns of young star clusters (YSCs). We distinguish between eYSCI, if they also have compact 3.3 μ m polycyclic aromatic hydrocarbon (PAH) emission associated with them, and eYSCII, if they only appear as compact Pa α emitters. We find that the variations in the 3.3 μ m PAH feature are consistent with an evolutionary sequence where eYSCI evolve into eYSCII and then optical YSCs. This sequence is clear in the F300M​​​​​​−F335M (tracing the excess in the 3.3 μ m PAH feature) and the F115W−F187N (tracing the excess in Pa α ) colors, which become increasingly bluer as clusters emerge. The central starburst stands out as the region where the most massive eYSCs are currently forming in the galaxy. We estimate that only about 20% of eYSCs will remain detectable as compact YSCs. Combining eYSCs and YSCs (≤10 Myr), we recover an average clearing timescale of 6 Myr in which clusters transition from embedded to fully exposed. We see evidence of shorter emergence timescales (∼5 Myr) for more massive (>5 × 10 ^3 M _⊙ ) clusters, while star clusters of ∼10 ^3 M _⊙ about 7 Myr. We estimate that eYSCs remain associated with the 3.3 μ m PAH emission for 3–4 Myr. Larger samples of eYSC and YSC populations will provide stronger statistics to further test environmental and cluster mass dependencies on the emergence timescale.

Senbei Du, Merav Opher, Marc Kornbleuth

The evolution of the velocity distribution of pickup ions is crucial for understanding the energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer. Pickup ions in the heliosheath contain two main components: those transmitted across the heliospheric termination shock and those locally created within the heliosheath. In this work, we discuss the velocity distribution of the latter locally created component. We find that pickup ions created by the charge exchange of neutral solar wind (NSW) may be a significant source of the observed ENA fluxes between about 100 eV and 1 keV. Moreover, newborn pickup ions can maintain highly anisotropic velocity distribution in the heliosheath. This is because the kinetic instabilities are weak after the solar wind flow decelerates at the termination shock. Hybrid kinetic simulations show the mirror instability to be the dominant mode for conditions in the heliosheath close to the termination shock. We estimate that effects of NSW and anisotropy may enhance the expected phase space density of newborn pickup ions by more than a factor of 100.

R. Braun, T. Bourke, J. Green et al.

The Square Kilometre Array concept has grown from the answer to a simple question: What size radio telescope would it take to permit us to read the history of the Universe as written in the language of its most abundant constituent, Hydrogen? What has also become apparent, is that the same radio telescope that will answer fundamental questions about our cosmic origins and fate will permit a wealth of other discoveries to be made, in areas as diverse as the formation of planets similar to the Earth, detection of gravitational distortions of Space-Time, the origin of cosmic magnetic fields and understanding the formation and growth of Black Holes. In this paper we discuss a few of these headline science topics and refer the reader to the overview chapters within these proceedings for more details on the broad areas of anticipated impact, as well as the individual contributed chapters that focus on specific topics.

Chin-Chun Wu, Kan Liou, Brian E. Wood et al.

The propagation of interplanetary shocks, particularly those driven by coronal mass ejections (CMEs), is still an outstanding question in heliophysics and space weather forecasting. Here, we address the effects of the ambient solar wind on the propagation of two similar CME-driven shocks from the Sun to Earth. The two shock events (CME03, 2010 April 3; CME12, 2012 July 12) have the following properties. Both events (1) were driven by a halo CME (i.e., the source location is near the Sun–Earth line); (2) had a CME source in the southern hemisphere; (3) had a similar transit time (∼2 days) to Earth; (4) occurred in a nonquiet solar period; and (5) led to a severe geomagnetic storm. The initial (near the Sun) propagation speed, as measured by coronagraph images, was slower (by ∼300 km s ^−1 ) for CME03 than CME12, but it took about the same amount of traveling time for both events to reach Earth. According to the in situ solar wind observations from the Wind spacecraft, the CME03-driven shock was associated with a faster solar wind upstream of the shock than the CME12-driven shock. This is also demonstrated in our global MHD simulations. Analysis of our simulation result indicates that the drag force indirectly plays an important role in the shock propagation. The present study suggests that in addition to the initial CME propagation speed near the Sun, the shock speed (in the inertial frame) and the ambient solar wind conditions—in particular, the solar wind speed—are key to timing the arrival of CME-driven shock events.

A. R. Rao

Stephanie L. Yardley, Christopher J. Owen, David M. Long et al.

The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilize the extensive suite of remote-sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote-sensing and in situ measurements of slow wind originating at open–closed magnetic field boundaries. The SOOP ran just prior to Solar Orbiter’s first close perihelion passage during two remote-sensing windows (RSW1 and RSW2) between 2022 March 3–6 and 2022 March 17–22, while Solar Orbiter was at respective heliocentric distances of 0.55–0.51 and 0.38–0.34 au from the Sun. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low-latency in situ data and full-disk remote-sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Postobservation analysis using the magnetic connectivity tool, along with in situ measurements from MAG and SWA/PAS, showed that slow solar wind originating from two out of three of the target regions arrived at the spacecraft with velocities between ∼210 and 600 km s ^−1 . The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter.

Boris Galitsky

It is well known that deep learning (DNN) has strong limitations due to a lack of explainability and weak defense against possible adversarial attacks. These attacks would be a concern for autonomous teams producing a state of high entropy for the team’s structure. In our first article for this Special Issue, we propose a <i>meta-learning/DNN</i> → <i>kNN</i> architecture that overcomes these limitations by integrating deep learning with explainable nearest neighbor learning (kNN). This architecture is named “shaped charge”. The focus of the current article is the empirical validation of “shaped charge”. We evaluate the proposed architecture for summarization, question answering, and content creation tasks and observe a significant improvement in performance along with enhanced usability by team members. We observe a substantial improvement in question answering accuracy and also the truthfulness of the generated content due to the application of the shaped-charge learning approach.

Xiaomin Ruan, Mingchun Chen, Zhendong Liu et al.

Seismic exploration is a key method for the study of underground structures. Active seismic surveys can acquire high signal-to-noise ratio reflection data; however, the operation of active seismic surveys is complicated, and the exploration cost is high. Passive seismic exploration is another type of seismic exploration, which requires no active human build source but utilizes the natural noise recorded by seismograph stations or geophones. As a low-cost and environmentally friendly method, passive seismic reflection exploration can be used to create higher resolution seismic profiles than the surface wave method and plays an increasingly important role in underground mineral exploration, dynamic monitoring of carbon storage, and urban underground structure detection. However, passive source reflection imaging technology faces several challenges. For example, because ambient noise is mainly controlled by surface wave energy, the reflected body wave signal can be weak and difficult to extract. Actual underground sources are limited in number and are unevenly distributed, which leads to artifacts in the virtual shot gathers reconstructed by seismic interference. There are also constraints of massive data computation and storage for long-term observation by a large number of geophones. With the rapid development of portable node geophones and high-performance computing, passive seismic reflection exploration has achieved considerable progress in both method research and practical applications in recent years. This paper briefly reviews the history of seismic interferometry and the construction of virtual shot gathers using various seismic interferometry methods and then introduces in detail how the reflection signals from ambient noise records dominated by surface waves are identified and extracted. We discuss the identification and extraction of weak body wave reflection signals based on various characteristics of surface and body waves, such as differences in signal-to-noise ratio, velocity, and azimuth angle. We then focus on the processing of passive source reflection data, including the beginning of raw data preprocessing, virtual shot gather static correction, coherent noise suppression, multiple suppression, velocity analysis, and direct migration imaging. We also introduce examples of passive seismic reflection applications, including CO2 storage site monitoring, metal mining, and coal mine underground structure research. Finally, we give an outlook for research prospects in passive seismic reflection exploration.

Floyd W. Stecker

This book chapter presents an overview of the historical experimental and theoretical developments in neutrino physics and astrophysics and also the physical properties of neutrinos, as well as the physical processes involving neutrinos. It also discusses the role of neutrinos in astrophysics and cosmology. Correction to tex file made.

M. Rengel

This paper corresponds to an invited oral contribution to the session 5A organised by the IAU inter-commission B2-B5 working group (WG) "Laboratory Astrophysics Data Compilation, Validation and Standardization: from the Laboratory to FAIR usage in the Astronomical Community" at the IAU 2022 General Assembly (GA). This WG provides a platform where to discuss the Findability, Accessibility,Interoperability, Reuse (FAIR) usage of laboratory Atomic and Molecular (A&M) data in astronomy and astrophysics. A&M data play a key role in the understanding of the physics and chemistry of processes in several research topics, including planetary science and interdisciplinary research in particular the atmospheres of planets and planetary explorations, etc. Databases, compilation of spectroscopic parameters, and facility tools are used by computer codes to interpret spectroscopic observations and simulate them. In this talk I presented existing A&M databases of interest to the planetary community focusing on access, organisation, infrastructures, limitations and issues, etc.

R. Belvedere, F. Cipolletta, C. Cherubini et al.

Fatemeh Naeimipour, Behrouz Mirza, Fatemeh Masoumi Jahromi

Abstract In this paper, we formulate two new classes of black hole solutions in higher curvature quartic quasitopological gravity with nonabelian Yang–Mills theory. At first step, we consider the SO(n) and $$SO(n-1,1)$$ S O ( n - 1 , 1 ) semisimple gauge groups. We obtain the analytic quartic quasitopological Yang–Mills black hole solutions. Real solutions are only accessible for the positive value of the redefined quartic quasitopological gravity coefficient, $$\mu _{4}$$ μ 4 . These solutions have a finite value and an essential singularity at the origin, $$r=0$$ r = 0 for space dimension higher than 8. We also probe the thermodynamic and critical behavior of the quasitopological Yang–Mills black hole. The obtained solutions may be thermally stable only in the canonical ensemble. They may also show a first order phase transition from a small to a large black hole. In the second step, we obtain the pure quasitopological Yang–Mills black hole solutions. For the positive cosmological constant and the space dimensions greater than eight, the pure quasitopological Yang–Mills solutions have the ability to produce both the asymptotically AdS and dS black holes for respectively the negative and positive constant curvatures, $$k=-1$$ k = - 1 and $$k=+1$$ k = + 1 . This is unlike the quasitopological Yang–Mills theory which can lead to just the asymptotically dS solutions for $$\Lambda >0$$ Λ > 0 . The pure quasitopological Yang–Mills black hole is not thermally stable.

M. Hidalgo-Soria, E. Barkai, S. Burov

We study a two state “jumping diffusivity” model for a Brownian process alternating between two different diffusion constants, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>D</mi><mo>+</mo></msub><mo>></mo><msub><mi>D</mi><mo>−</mo></msub></mrow></semantics></math></inline-formula>, with random waiting times in both states whose distribution is rather general. In the limit of long measurement times, Gaussian behavior with an effective diffusion coefficient is recovered. We show that, for equilibrium initial conditions and when the limit of the diffusion coefficient <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>D</mi><mo>−</mo></msub><mo>⟶</mo><mn>0</mn></mrow></semantics></math></inline-formula> is taken, the short time behavior leads to a cusp, namely a non-analytical behavior, in the distribution of the displacements <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mo>(</mo><mi>x</mi><mo>,</mo><mi>t</mi><mo>)</mo></mrow></semantics></math></inline-formula> for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>x</mi><mo>⟶</mo><mn>0</mn></mrow></semantics></math></inline-formula>. Visually this cusp, or tent-like shape, resembles similar behavior found in many experiments of diffusing particles in disordered environments, such as glassy systems and intracellular media. This general result depends only on the existence of finite mean values of the waiting times at the different states of the model. Gaussian statistics in the long time limit is achieved due to ergodicity and convergence of the distribution of the temporal occupation fraction in state <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>D</mi><mo>+</mo></msub></semantics></math></inline-formula> to a <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>δ</mi></semantics></math></inline-formula>-function. The short time behavior of the same quantity converges to a uniform distribution, which leads to the non-analyticity in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mo>(</mo><mi>x</mi><mo>,</mo><mi>t</mi><mo>)</mo></mrow></semantics></math></inline-formula>. We demonstrate how super-statistical framework is a zeroth order short time expansion of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mo>(</mo><mi>x</mi><mo>,</mo><mi>t</mi><mo>)</mo></mrow></semantics></math></inline-formula>, in the number of transitions, that does not yield the cusp like shape. The latter, considered as the key feature of experiments in the field, is found with the first correction in perturbation theory.

Łukasz Dębowski

We present a hypothetical argument against finite-state processes in statistical language modeling that is based on semantics rather than syntax. In this theoretical model, we suppose that the semantic properties of texts in a natural language could be approximately captured by a recently introduced concept of a perigraphic process. Perigraphic processes are a class of stochastic processes that satisfy a Zipf-law accumulation of a subset of factual knowledge, which is time-independent, compressed, and effectively inferrable from the process. We show that the classes of finite-state processes and of perigraphic processes are disjoint, and we present a new simple example of perigraphic processes over a finite alphabet called Oracle processes. The disjointness result makes use of the Hilberg condition, i.e., the almost sure power-law growth of algorithmic mutual information. Using a strongly consistent estimator of the number of hidden states, we show that finite-state processes do not satisfy the Hilberg condition whereas Oracle processes satisfy the Hilberg condition via the data-processing inequality. We discuss the relevance of these mathematical results for theoretical and computational linguistics.

K. Kotorashvili, N. L. Shatashvili

We have shown the simultaneous generation of macro-scale fast flows and strong magnetic fields in the 2-temperature relativistic electron-ion plasmas of astrophysical objects due to Unified Reverse Dynamo/Dynamo mechanism. The resulting dynamical magnetic field amplification and/or flow acceleration is directly proportional to the initial turbulent kinetic/magnetic (magnetic) energy; the process is very sensitive to relativistically hot electron-ion fraction temperature and magneto-fluid coupling. It is shown, that for realistic physical parameters of White Dwarfs accreting hot astrophysical flow / Binary systems there always exists such a real solution of dispersion relation for which the formation of dispersive strong super-Alfvénic macro-scale flow/outflow with Alfvén Mach number $> 10^6$ and/or generation of super-strong magnetic fields is guaranteed.

M. Martinelli, C. J. A. P. Martins, S. Nesseris et al.

In physically realistic scalar-field based dynamical dark energy models (including, e.g., quintessence) one naturally expects the scalar field to couple to the rest of the model's degrees of freedom. In particular, a coupling to the electromagnetic sector leads to a time (redshift) dependence of the fine-structure constant and a violation of the Weak Equivalence Principle. Here we extend the previous Euclid forecast constraints on dark energy models to this enlarged (but physically more realistic) parameter space, and forecast how well Euclid, together with high-resolution spectroscopic data and local experiments, can constrain these models. Our analysis combines simulated Euclid data products with astrophysical measurements of the fine-structure constant, $α$, and local experimental constraints, and includes both parametric and non-parametric methods. For the astrophysical measurements of $α$ we consider both the currently available data and a simulated dataset representative of Extremely Large Telescope measurements and expected to be available in the 2030s. Our parametric analysis shows that in the latter case the inclusion of astrophysical and local data improves the Euclid dark energy figure of merit by between $8\%$ and $26\%$, depending on the correct fiducial model, with the improvements being larger in the null case where the fiducial coupling to the electromagnetic sector is vanishing. These improvements would be smaller with the current astrophysical data. Moreover, we illustrate how a genetic algorithms based reconstruction provides a null test for the presence of the coupling. Our results highlight the importance of complementing surveys like Euclid with external data products, in order to accurately test the wider parameter spaces of physically motivated paradigms.