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.

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.