高能暂现源 · 每日文献综述

We present the first high-resolution near-infrared spectroscopy of the nucleus of the nearby, well-known Seyfert galaxy NGC 4151 (the 'Eye of Sauron'). Past studies of this source have revealed that it exhibits a variable absorption feature associated with the He Iλ10 830 Å emission line, that is potentially indicative of obscuration events affecting the central engine. Here, we took advantage of the IRTF/iSHELL and TNG/GIANO-B spectrographs to observe this feature with unprecedented spectral resolution (λ/∆λ &gt; 50 000); these allowed us to study the structure of the absorption trough and its variations in detail over a time span of ∼700 days. In order to infer a connection between the He I absorption variability and that of the X-ray ionising continuum, we also analysed the publicly available data collected by the Swift-XRT instrument over the same period of time, unveiling a potential driving mechanism in the changes of the outflow ionisation state due to the X-ray flux variations. We also derive outflow physical parameters ─ Ṁ<SUB>out</SUB> ≲ 10<SUP>−1</SUP> M<SUB>⊙</SUB> yr<SUP>−1</SUP>, r<SUB>out</SUB> ∼ 3 pc, v<SUB>max</SUB> ∼ 1000 km s<SUP>−1</SUP> ─ that are in line with those of comparable ionised winds found in similar targets, where the outflow is not powerful enough to trigger a significant feedback from the active galactic nucleus (Ė<SUB>kin</SUB>/L<SUB>bol</SUB> ∼ 0.001%). Such findings point at a scenario in which a dusty and clumpy outflow that obscures NGC 4151 up to galactic scales responds to changes in the ionising X-ray flux; this is similar to what happens in quasars with broad absorption lines and Seyferts with multi-phase outflows such as NGC 5548.

Coronal Mass Ejections (CMEs) are among the most energetic solar eruptions, expelling magnetized plasma from the corona into interplanetary space. Their interplanetary counterparts, known as Interplanetary Coronal Mass Ejections (ICMEs), retain distinct compositional signatures that reflect the physical conditions of their solar source regions. This study presents a statistical analysis of ICME composition dependence on solar activity during 2009--2025, covering Solar Cycle (SC) 24 and the ascending phase of SC~25 through its maximum, and compares the results with SC~23 studied by \citet{Song+etal+2021}. Using data from the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE), we examined the average iron charge state ($\langle Q_{\rm Fe}\rangle$), ionic ratios (C$^{6+}$/C$^{5+}$ and O$^{7+}$/O$^{6+}$), and the elemental abundance ratio (Fe/O) for 307 ICMEs listed in the Richardson and Cane ICME catalog. The results show strong positive correlations of $\langle Q_{\rm Fe}\rangle$ ($r$~=~0.86) and O$^{7+}$/O$^{6+}$ ($r$~=~0.85) with the annual sunspot number (SSN), whereas C$^{6+}$/C$^{5+}$ exhibits a weak correlation ($r$~=~0.17) primarily due to SWICS~2.0 upper-end saturation truncation that suppresses the solar maximum signal, and Fe/O a moderate correlation ($r$~=~0.57). The Fe/O ratio, a proxy for the First Ionization Potential (FIP) effect, displayed elevated values during the maxima of both SC~24 and SC~25, suggesting enhanced elemental fractionation during periods of increased magnetic activity. Comparing with SC~23, we find that the overall solar cycle dependence of ICME composition persists across cycles, though with notable quantitative differences attributed to the different magnetic activity levels between cycles. These findings confirm that ICME compositional signatures are strongly modulated by the solar cycle.

This study investigates the ionospheric response to the moderate geomagnetic storm of 25-26 August 2018 (Dst<SUB>min</SUB> ≈ -174 nT), using GPS-derived Total Electron Content (TEC) observations from six stations distributed across low and mid latitudes in the Indian and Asian sectors. A systematic detrending approach was applied to remove diurnal trends and long-period background variations, thereby isolating storm-driven disturbances. Continuous Wavelet Transform (CWT) analysis of the detrended TEC revealed statistically significant (95% confidence against first-order autoregressive (AR1) red-noise background) storm-associated oscillations in the 30-90-min range, corresponding to atmospheric gravity waves (AGWs) and medium-scale traveling ionospheric disturbances (MSTIDs). Low-latitude stations exhibited the strongest signatures, consistent with equatorial electrodynamic coupling and Equatorial Ionization Anomaly (EIA) modulation. A segmented CWT analysis effectively captured the pre-storm, main-phase, and recovery-phase evolution. These findings highlight coherent equatorward propagation of storm-induced AGWs/TIDs and demonstrate the utility of multi-station TEC-wavelet diagnostics for storm-ionosphere coupling studies.

A neutron star is born as a hot, lepton-rich protoneutron star (PNS) and cools via neutrino emission, eventually allowing heavy ions in the outer layers to crystallize into a solid crust. We develop a simple analytic estimate for the onset time of this crust formation during the late, post-convective PNS cooling phase. Using a diffusion-based neutrino luminosity and the resulting entropy evolution together with an approximately isentropic interior structure, we obtain the time-dependent density and temperature at the neutrinosphere. We then impose the Coulomb crystallization condition for heavy nuclei, expressed through the Coulomb coupling parameter, and determine when the neutrinosphere temperature first falls below the crystallization threshold evaluated at the neutrinosphere density. This procedure yields closed expressions for the entropy at crystallization and the corresponding crust-formation time, with explicit dependence on the PNS mass and radius, an effective diffusion/cooling normalization, and composition parameters such as the ionic charge Z and heavy-nuclei mass fraction. For canonical microphysics, we find that the first solid phase typically appears at <inline-formula><tex-math>$t_{\mathrm{crust}}\sim 100$</tex-math></inline-formula>─500 s. These closed-form scalings provide a useful late-time analytic benchmark for the onset of crust formation and clarify its dependence on PNS and composition parameters.

We present an optical analysis of BISOU (Balloon Interferometer for Spectral Observations of the primordial Universe), an astronomical balloon-borne pathfinder spectrometer developed as part of a preparatory study for a future space mission aiming at measuring spectral distortions of the cosmic microwave background (CMB). The BISOU optical system is based on a differential polarizing Fourier Transform Spectrometer (FTS) that receives inputs from both a sky-facing telescope and an internal calibration source. The FTS focal planes are equipped with bolometric detectors coupled to multimode feed horns, with distinct focal planes dedicated to the low (90 - 300GHz) and high (0.3 - 1.5THz) frequency bands. The optical analysis first relies on ray-tracing simulations to establish the overall configuration of the system, before proceeding to more advanced Gaussian beam and physical optics analyses.