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In our previous study, we identified a shift in the synchrotron peak frequency of the blazar B2 1308+326 from 10 ^12.9 to 10 ^14.8 Hz during a flare, suggesting it could be a changing-look blazar (CLB). In this work, we investigate the changing-look behaviour of B2 1308+326 by analysing a newly acquired optical spectrum and comparing it with an archival spectrum. We find that between the two epochs, the continuum flux increased by a factor of ~4.4, while the Mg ii emission line flux decreased by a factor of 1.4 ± 0.2. Additionally, the equivalent width of the Mg ii line reduced from ~20 to ~3 Å, indicating an apparent shift from a flat-spectrum radio quasar (FSRQ) class to a BL Lacertae (BL Lac) class. Despite this apparent change, the ratio of accretion disk luminosity to Eddington luminosity remains >10 ^−2 during both epochs, indicating efficient accretion persists in B2 1308+326. The measured black hole mass remains consistent with an average $\mathrm{log}{M}_{{\rm{BH}}}=8.44$ M _⊙ . Our findings suggest that B2 1308+326 is not a genuine CLB but rather an intrinsic FSRQ that emerges as a BL Lac during high-flux states due to enhanced nonthermal emission.

Stars and compact objects embedded in accretion disks of active galactic nuclei (AGNs), dubbed accretion-modified stars (AMSs), often experience hyper-Eddington accretion in the dense gas environment, resulting in powerful outflows as the Bondi explosion and formation of cavities. The varying gas properties across different regions of the AGN disk can give rise to diverse and intriguing phenomena. In this paper, we conduct a study on the characteristics of AMSs situated in the outer, middle, and inner regions of the AGN disk, where the growth of the AMSs during the shift inward is considered. We calculate their multiwavelength spectral energy distributions (SEDs) and thermal light curves. Our results reveal that the thermal luminosity of the Bondi explosion occurring in the middle region leads to UV flares with a luminosity of ∼10 ^44 erg s ^−1 . The synchrotron radiation of Bondi explosion in the middle and inner regions peaks at the X-ray band with luminosities of ∼10 ^43 and ∼10 ^42 erg s ^−1 , respectively. The γ -ray luminosity of inverse Compton radiation spans from 10 ^42 –10 ^43 erg s ^−1 peaked at the ∼10 MeV (outer region) and ∼GeV (middle and inner regions) bands. The observable flares of AMS in the middle region exhibit a slow rise and rapid Gaussian decay with a duration of months, while in the inner region, it exhibits a fast rise and slow Gaussian decay with a duration of several hours. These various SED and light-curve features provide valuable insights into the various astronomical transient timescales associated with AGNs.

We conduct a reverberation mapping (RM) campaign to spectroscopically monitor a sample of selected bright active galactic nuclei with large anticipated broad-line region (BLR) sizes adequate for spectroastrometric (SA) observations by the GRAVITY instrument on the Very Large Telescope Interferometer. We report the first results for five objects, IC 4329A, Mrk 335, Mrk 509, Mrk 1239, and PDS 456, among which Mrk 1239 and PDS 456 are for the first time spectroscopically monitored. We obtain multiyear monitoring data and perform multicomponent spectral decomposition to extract the broad H β profiles. We detect significant time lags between the H β and continuum variations, generally obeying the previously established BLR size–luminosity relation. Velocity-resolved H β time lags illustrate diverse, possibly evolving, BLR kinematics. We further measure the H β line widths from mean and rms spectra and the resulting virial products show good consistency among different observing seasons. Adopting a unity virial factor and the FWHM of the broad H β line from the mean spectra as a measure of velocity, the obtained black hole masses averaged over seasons are $\mathrm{log}{M}_{\bullet }/{M}_{\odot }={8.02}_{-0.14}^{+0.09}$ , ${6.92}_{-0.12}^{+0.12}$ , ${8.01}_{-0.25}^{+0.16}$ , ${7.44}_{-0.14}^{+0.13}$ , and ${8.59}_{-0.11}^{+0.07}$ for the five objects, respectively. Black hole mass estimations using other line width measures are also reported. For objects with previous RM campaigns, our mass estimates are in agreement with earlier results. In a companion paper, we will employ BLR dynamical modeling to directly infer the black hole mass and thereby determine the virial factors.

Over the past three decades, multiple reverberation mapping (RM) campaigns conducted for the quasar PG 2130+099 have exhibited inconsistent findings with time delays ranging from ∼10 to ∼200 days. To achieve a comprehensive understanding of the geometry and dynamics of the broad-line region (BLR) in PG 2130+099, we continued an ongoing high-cadence RM monitoring campaign using the Calar Alto Observatory 2.2 m optical telescope for an extra four years from 2019 to 2022. We measured the time lags of several broad emission lines (including He ii , He i , H β , and Fe ii ) with respect to the 5100 Å continuum, and their time lags continuously vary through the years. Especially, the H β time lags exhibited approximately a factor of 2 increase in the last two years. Additionally, the velocity-resolved time delays of the broad H β emission line reveal a back-and-forth change between signs of virial motion and inflow in the BLR. The combination of negligible (∼10%) continuum change and substantial time-lag variation (over 2 times) results in a significant scatter in the intrinsic R _H _β – L _5100 relationship for PG 2130+099. Taking the consistent changes in the continuum variability time scale and the size of the BLR into account, we tentatively propose that the changes in the measurement of the BLR size may be affected by “geometric dilution”

Stochastic analytic continuation is an excellent numerical method for analytically continuing Green's functions from imaginary frequencies to real frequencies, although it requires significantly more computational time than the traditional MaxEnt method. We develop an alternate implementation of stochastic analytic continuation which expands the dimensionless field n(x) introduced by Beach using orthogonal polynomials. We use the kernel polynomial method (KPM) to control the Gibbs oscillations associated with truncation of the expansion in orthogonal polynomials. Our KPM variant of stochastic analytic continuation delivers improved precision at a significantly reduced computational cost. [ABSTRACT FROM AUTHOR]

We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel (F) and Wannier–Mott (WM) excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS2by J-aggregates. The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method. The calculation results show that strong couplings among F excitons, WM excitons, and localized surface plasmon resonances (LSPRs) lead to the appearance of three plexciton branches in the extinction spectra. The weighting efficiencies of the F exciton, WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system. Furthermore, the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances. [ABSTRACT FROM AUTHOR]

A symmetric plasmonic structure consisting of metal–insulator–metal waveguide, groove and slot cavities is studied, which supports double Fano resonances deriving from two different mechanisms. One of the Fano resonances originates from the interference between the resonances of groove and slot cavities, and the other comes from the interference between slot cavities. The spectral line shapes and the peaks of the double Fano resonances can be modulated by changing the length of the slot cavities and the height of the groove. Furthermore, the wavelength of the resonance peak has a linear relationship with the length of the slot cavities. The proposed plasmonic nanosensor possesses a sensitivity of 800 nm/RIU and a figure of merit of 3150, which may have important applications in switches, sensors, and nonlinear devices. [ABSTRACT FROM AUTHOR]