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How elevated sources can cause local increases of sound pressure levels in the upwind domain
No full textWhile increased sound levels near the ground in downwind conditions are a well-studied topic, comparatively little attention has been given in the literature to increased sound pressure levels in upwind propagation. This increase, however, typically occurs only under specific conditions, including an elevated source location, a non-linear (e.g., logarithmic) wind or temperature profile, and a focus on particular distances within the upwind domain. These conditions are known to be responsible for the formation of caustics. Simultaneously, the sound level enhancement may be disturbed by diffraction, ground reflection, and its characteristics depend on the source structure, being most readily derivable for point sources. Consequently, investigations using models and comparisons with observations are challenging. This work uses two fundamentally different modelling approaches in their ability to capture such phenomena. The goal is to provide an intuitive understanding of the complex interactions involved in sound propagation under real atmospheric conditions, thereby supporting the interpretation of acoustic simulation and measurements in applied contexts
Rebrightenings of gamma-ray burst afterglows from an increasing magnetic inclination angle of a nascent magnetar
No full textContext. A nascent magnetar, accompanying a gamma-ray burst (GRB) explosion, releases enormous rotational energy via magnetic dipole radiation. The energy loss rate of the magnetar is determined by the strength of the magnetic field at the pole.
Aims. We investigated the effect of the magnetic inclination angle on the energy loss rate. The released energy is injected into the GRB jet and shapes the light curves of GRB afterglow. Different evolutionary approaches lead to different curves shapes.
Methods. A shallow decay phase in GRB X-ray afterglow may result from energy injection from a magnetar with a fixed inclination angle. A two-plateau phase may result from a decreasing inclination angle scenario. In this study, we considered an increasing inclination angle scenario. The energy loss rate of the magnetar increases as the magnetic inclination angle grows.
Results. Our analysis reveals that as the lost rotational energy injected into the GRB jet increases, rebrightening phases occur in the GRB afterglows. The rebrightening features are slight and short-lived.
Conclusions. The observed afterglow rebrightening of GRB 170822A and GRB 230414B can be well explained within our framework. Some GRB X-ray afterglows that exhibit slight and early rebrightenings may result from an increasing magnetic inclination angle of a nascent magnetar
A wide-field X-ray search for the Geminga pulsar halo with SRG/ART-XC
No full textSearches for the putative large-scale X-ray halo around the Geminga pulsar have been extensively performed using various narrow field-of-view X-ray telescopes. In this paper, we present wide-field scanning observation of Geminga with SRG/ART-XC. Our X-ray analysis provides, for the first time, direct imaging of a 3.5° ×3.5° region in the 4−12 keV energy band, comparable in extent to the expected Geminga emission. The ART-XC observation provides a highly uniform sky coverage without strong vignetting effects. The synchrotron X-ray halo flux was predicted using a physical model based on particle injection, diffusion, and cooling over the pulsar’s lifetime, as well as the spectral and spatial properties of the synchrotron X-ray and inverse-Compton gamma-ray emissions. The model is tuned to reproduce existing multiwavelength data from X-ray upper limits and GeV to TeV gamma-ray observations. After accounting for the high particle background and its uncertainties, no significant emission is found in the assumed source region, and X-ray flux upper limits are derived. These limits are less constraining by up to a factor of three with respect to existing results obtained with narrow field-of-view telescopes and longer exposure times. Nonetheless, we place direct and independent constraints on Geminga’s ambient magnetic field strength, which are compatible with other studies. Our methodology, including simulation for longer observation times, is applied for the first time to the wide field-of-view search for pulsar halos. Using extensive simulations, we also show that a 68% probability of detecting the Geminga pulsar halo can be achieved with a 20-day SRG/ART-XC exposure for a 3 μG magnetic field
The environment of TeV halo progenitors
No full textContext. TeV haloes are extended sources of very-high-energy gamma rays found around some middle-aged pulsars. The emission spanning several tens of parsecs suggests an efficient confinement of the ultra-relativistic lepton pairs produced by pulsars in their vicinity. The physical mechanism responsible for this suppressed transport has not yet been identified. In some scenarios, pair confinement may be linked to the medium the pulsars are located in.
Aims. We aim at understanding the type of medium pulsars probe over their lifetime.
Methods. We developed a model for the environment probed by moving pulsars, from their birth in core-collapse explosions – where they receive a natal kick – until their entry into the interstellar medium. The model involves: (i) a Monte-Carlo sampling of the properties of the massive-star progenitors of pulsars; (ii) a calculation of the structure of the surrounding medium shaped by these progenitors for the two cases of isolated stars and star clusters; and (iii) a computation of the evolution of supernova remnants in these parent environments. Ultimately, from a distribution of neutron star kick velocities, we assess the medium in which pulsars are located as a function of time. We first derived the statistical properties of a fully synthetic Galactic population and then applied the model to a selection of known pulsars to assess the likely nature of their environment.
Results. We show that pulsars escape into the interstellar medium at around 300 kyr, significantly later than assumed in the literature. Given our assumptions, all known pulsars with a confirmed TeV halo have high probabilities of still being in their parent environment, which suggests that efficient pair confinement is connected to the region influenced by progenitor stars. To test this, we provide the probability that known pulsars still reside in their parent environment for a list of known pulsars
The SPIRou Legacy Survey
No full textContext. M dwarfs are prime targets in the search for exoplanets because of their prevalence and because low-mass planets can be better detected with radial velocity (RV) methods. In particular, the near-infrared (NIR) spectral domain offers an increased RV sensitivity and potentially reduced stellar activity signals. Precise NIR RV measurements are strongly affected by telluric absorption lines from the Earth’s atmosphere, however.
Aims. We searched for planets orbiting Gl 725 B, a nearby late-M dwarf located at 3.5 pc, using high-precision SPIRou RV observations. We also assessed the effect of telluric contamination on these measurements and evaluated the performance of the weighted principal component analysis reconstruction (wapit
A one-parameter two-zone leptonic model for the blazar sequence
No full textBlazars, a subclass of radio-loud active galactic nuclei with relativistic jets aligned close to our line of sight, emit highly variable nonthermal radiation across the electromagnetic spectrum. The physical origin of their emission and the blazar sequence remain open questions. We present a self-consistent two-zone leptonic model in which relativistic electrons accelerate in a compact region, losing energy via synchrotron and inverse Compton processes, and escape into a larger zone permeated by an external photon field associated with magnetohydrodynamic winds from the accretion disk. By varying only the mass accretion rate onto the central black hole, the model naturally reproduces the blazar sequence, including Compton dominance, γ-ray spectral indices, and the positions of synchrotron and inverse Compton peaks, while variations in the secondary parameters account for the observed spread in the data. Flat-spectrum radio quasars exhibit strong external Compton emission from the extended zone, whereas BL Lac objects are dominated by synchrotron and synchrotron self-Compton emission from the compact acceleration region. This framework highlights the key role of accretion rate and spatially structured emission zones in shaping blazar spectra and provides a unified interpretation of their diverse phenomenology
The light curve model fitting of Large Magellanic Cloud Cepheids: MESA-RSP versus Stellingwerf’s code predictions
No full textContext. A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional (3D) process is typically approximated in one-dimensional (1D) hydrocodes, using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features, such as the light curve amplitudes, secondary bumps, and the red edge of the instability strip (IS).
Aims. In this work, we calibrate the TC parameters adopted from the publicly available Modules for Experiments in Stellar Astrophysics-Radial Stellar Pulsations (MESA-RS
Optimal multi-round portfolio crowdfunding financing and capital structure
No full textThis study investigates the start-up firm’s optimal decision in multi-round equity and debt portfolio crowdfunding financing and the design of risk-sharing mechanism. A crowdfunding platform serves as an intermediary between a start-up firm with limited initial capital and external investors seeking debt and equity investments. When the funding target is not met, the crowdfunding platform provides loans to bridge the start-up firm’s capital gap, which also gives chance to adjust its capital structure. Firstly, a decision-making model is established to derive optimal financing strategies for a startup firm and a crowdfunding platform, while also derived the financing ratio between equity and debt crowdfunding channels. A numerical analysis further examines how key parameterssuch as fundraising rate and loan interest rateaffect the startup’s capital structure. More importantly, a novel debt-to-equity swap arrangement (DTE) is proposed for sharing debt risk between the start-up firm and the platform. The findings reveal that startup firms primarily rely on equity crowdfunding when the fundraising rate is moderate, while the low fundraising rate leads to a single equity crowdfunding approach. Similarly, the high loan interest rate drive startup firms to favor equity crowdfunding, whereas low rates may prompt platform to discontinue loans, leaving startup firms to rely solely on equity financing. Additionally, the DTE facilitates coordination among parties requires balanced adjustments from platforms (moderate commission rates), startup firm (capital structure optimization), and investors (appropriate success rates) to ensure effective risk-sharing and profit distribution
Mn-doped Bi
No full textThe current research investigates the influence of manganese (Mn) doping on the structural, optical, and dielectric properties of Bi2-xMnxO3 thin films for optoelectronic applications. The prepared thin films with different Mn content (x = 0, 0.025, 0.05, 0.075, and 0.1) were synthesized, and their characteristics were thoroughly analyzed. Our findings demonstrate that increasing manganese content enhances light absorption by creating new electronic states, which is reflected in higher absorbance and lower transmittance values. The direct optical band gap decreases with higher Mn incorporation (from 3.60 eV for x = 0–3.29 eV for x = 0.1), suggesting a tunable electronic structure. Furthermore, the Urbach energy increases with Mn concentration from 1.23 eV for x = 0–3.33 eV for x = 0.1, indicating enhanced structural disorder and broadening of the band tail, which can benefit photovoltaic applications. Analysis of refractive index, extinction coefficient, and dielectric parameters (ε1, ε2, Tanδ) demonstrates improved optical density, dielectric polarization, and reduced dielectric losses with Mn doping. These results establish clear correlations between Mn concentration and the resulting physical properties, providing crucial insights for optimizing Bi2O3-based materials for high-performance optoelectronic applications
HST pre-imaging of a free-floating planet candidate microlensing event
No full textHigh-cadence microlensing observations uncovered a population of very short-timescale microlensing events, which are believed to be caused by the population of free-floating planets (FFPs) roaming the Milky Way. Unfortunately, the light curves of such events are indistinguishable from those caused by wide-orbit planets. To properly differentiate both cases, one needs high-resolution observations that would allow one to resolve a putative luminous companion to the lens long before or after the event. Usually, the baseline between the event and high-resolution observations needs to be quite long (∼10 yr), hindering potential follow-up efforts. However, there is a chance to use archival data if they exist. Here, we present an analysis of the microlensing event OGLE-2023-BLG-0524, the site of which was captured in 1997 with the Hubble Space Telescope (HST). Hence, we achieve a record-breaking baseline length of 25 years. A very short duration of the event (tE = 0.346 ± 0.008 d) indicates an FFP as the explanation. Based on the finite-source effects in the light curve, we measure an angular Einstein radius value of θE = 4.78 ± 0.23 μas, suggesting a super-Earth in the Galactic disk or a sub-Saturn-mass planet in the Galactic bulge. We have not detected any potential companion to the lens with the HST data, which is consistent with the FFP origin of the event. Though we detect no potential companion to the lens in the HST imaging, we find that the HST imaging is insufficient to constrain beyond 25-48% of potential companions (depending on whether or not the occurrence rate of wide-orbit planets is correlated with the host mass); hence, we are unable to confidently confirm this event as an FFP. Despite this, our results show that archival high-resolution images should be available for many microlensing events, providing a potential new avenue to confirm FFP candidates in future observations