Dong-Wei Bao

We report a rapid optical changing-look event in the Seyfert galaxy NGC 3227: the optical continuum faded by ∼70%, and broad H β emission nearly disappeared within weeks before recovering within 2 months. Damped random walk simulations calibrated to the source’s normal variability show that such a decline is unlikely for stochastic accretion fluctuations. The optical decline coincides with an X-ray spectral hardening event detected by Swift, indicating additional line-of-sight absorption. During the dim state, reverberation mapping yields a clear 6–8 day lag between the continuum and broad H β , placing the obscurer interior to the broad-line region. Photoionization calculations require a fully ionized Compton-thick column with N _H ≈ 1.5 × 10 ²⁴ cm ⁻² to reproduce the optical continuum suppression. Together, these observations demonstrate that compact, high-column-density obscurers interior to the broad-line region can produce extreme optical changing-look behavior on timescales of weeks.

As the 15th paper in a series reporting on a large reverberation mapping (RM) campaign of super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs), we present the results of measurements of the Mg ii lines in 18 SEAMBHs monitored spectroscopically from 2017 to 2024. Among these, the time lags of Mg ii have been successfully determined for eight of the 18 objects, thereby expanding the current Mg ii RM sample, particularly at higher accretion rates. By incorporating measurements of the line widths, we determine the masses of their central supermassive black holes. Based on these new measurements, we update the relation between the Mg ii radius and the monochromatic luminosity at 3000 Å ( R _MgII – L ₃₀₀₀ relation), yielding a slope of 0.24 ± 0.03, which is slightly shallower than, yet still consistent with, previously reported values. Similar to the H β lines, the Mg ii time lags in SEAMBHs are shorter than those of AGNs with normal accretion rates at comparable luminosities. The deviation of AGNs from the best-fit R _MgII – L ₃₀₀₀ relation shows a strong correlation with the accretion rate, while no significant correlation is found between the deviation and the flux ratio of UV iron to Mg ii .

The physical origins of the diverse emission-line asymmetries observed in the spectra of active galactic nuclei (AGNs) are not completely understood. Monitoring the temporal variations of line profiles offers a promising approach to investigating the underlying physics. In this study, we present an analysis of the broad Hβ emission line profiles of eight AGNs observed from 2016–2023 May as part of the reverberation mapping campaign titled “Monitoring AGNs with Hβ Asymmetry,” utilizing data obtained from the Wyoming Infrared Observatory 2.3 m telescope. We measure the temporal variations of line asymmetry, width, and central velocity shift for the eight objects. Our findings reveal that the variation in asymmetry is positively correlated with Hβ flux in five of the eight objects, while the remaining objects exhibit negative or complex correlations. Furthermore, we observe anticorrelations between line width and Hβ flux for most objects, indicating the presence of the “breathing” phenomenon in their Hβ emission lines. In contrast, two objects demonstrate an “anti-breathing” phenomenon or complex behavior. We discuss the physical origins of the temporal variations in line profiles and propose the possibility of decomposing the variations in Hβ asymmetry and width into components: one that corresponds to short-term variations in Hβ flux and another that reflects long-term variations in continuum light curves, perhaps driven by radiation pressure.

We report on the optical spectroscopic observations of the host galaxy of the hyperactive repeating fast radio burst (FRB) FRB 20240114A. The host galaxy is a dwarf galaxy at a redshift of z = 0.1306 ± 0.0002. With a rest-frame coverage of 4300–7900 Å, we have detected Hα, Hβ, [O iii] λλ4959,5007, [N ii]λλ6548,6583, and [S ii] λ6716 emission lines. The emission line ratios suggest that the ionization in the host galaxy is dominated by star formation. The star formation rate (SFR) derived from the Hα emission line is (0.06 ± 0.01) M _⊙ yr⁻¹, and the spectral energy distribution fitting suggests the lower limit of the SFR(UV) is 0.09 M _⊙ yr⁻¹. The stellar mass is (4.0 ± 1.8) × 10⁸ M _⊙, making the specific SFR log sSFR ( H α ) = − 9.17 ± 0.07 yr − 1 . The line ratios indicate an upper limit of a metallicity of 12 + log₁₀([O/H]) ∼ 8.5. As the nearest dwarf host galaxy with a repeating FRB, the activity of FRB 20240114A and the properties of this host galaxy closely resemble those of FRB 20121102A and FRB 20190520B. The Hα-traced dispersion measure provided by the ionized gas of the host galaxy has a moderate contribution of ∼200 pc cm⁻³, assuming a warm ionized gas. We found that the distributions of the stellar mass versus SFR are significantly different between repeating and one-off FRBs, as determined by the MANOVA test with p = 0.0116.

We present a noteworthy transient AT 2021aeuk exhibiting three distinct optical flares between 2018 and 2023. It is hosted in a radio-loud narrow-line Seyfert 1 galaxy, with an optical image showing a minor tidal morphology and a red mid-infrared color (W1 − W2 = 1.1). Flares II and III exhibit rapid rises, and long-term decays (≳1000 days) with recurring after-peak bumps. The g − r color after subtracting the reference magnitude exhibited a rapid drop and recovery during Flare II, followed by a minor after-peak evolution in blue colors. We applied a canonical tidal disruption event (TDE) fitting on the light curves, which gives a decay index p of − 2.99 − 0.14 + 0.13 for Flare II and − 1.61 − 0.65 + 0.34 for Flare III. The blackbody fitting shows lower temperatures (∼10^3.8 K) with minor after-peak evolution. The blackbody radius (≳10¹⁶ cm) and luminosity (∼10⁴⁵ erg s⁻¹) are larger than the typical TDE sample’s. The time lag (in rest frame) between the ZTF g and r bands ( τ g , r = 3.4 − 0.9 + 1.0 days) significantly exceeds the prediction from the standard accretion disk. Pre-burst spectra reveal prominent Bowen fluorescence lines, indicating a vigorous or potentially long-lasting process that enriches the local metallicity. Additionally, we derived black hole masses of log M • = 7.09 − 0.31 + 0.18 M ⊙ and log M • = 7.52 − 0.10 + 0.08 M ⊙ using Hβ and Hα emission lines. The variation and recurring features of AT 2021aeuk are not likely induced by the radio-beaming effect or Type II superluminous supernova; however, we cannot rule out the possibility of TDE or enhanced active galactic nuclei accretion process. The unusually high occurrence of three flares within 5 yr may also induced by the complex local environment.

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, Hβ, and Fe ii) with respect to the 5100 Å continuum, and their time lags continuously vary through the years. Especially, the Hβ time lags exhibited approximately a factor of 2 increase in the last two years. Additionally, the velocity-resolved time delays of the broad Hβ 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 _Hβ –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”

We report first-time reverberation-mapping results for 14 active galactic nuclei (AGNs) from the ongoing Monitoring AGNs with Hβ Asymmetry campaign (MAHA). These results utilize optical spectra obtained with the Long Slit Spectrograph on the Wyoming Infrared 2.3 m Telescope between 2017 November and 2023 May. MAHA combines long-duration monitoring with high cadence. We report results from multiple observing seasons for nine of the 14 objects. These results include Hβ time lags, supermassive black hole masses, and velocity-resolved time lags. The velocity-resolved lags allow us to investigate the kinematics of the broad-line region.

We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 2617 carried out from 2016 until 2022 and covering the wavelength range from the X-ray to the near-IR. The facilities included the telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope, Swift, and others. We found significant variability at all wavelengths and, specifically, in the intensities and profiles of the broad Balmer lines. We measured time delays of ∼ 6 days (∼ 8 days) in the responses of the Hβ (Hα) line to continuum variations. We found the X-ray variations to correlate well with the UV and optical (with a small time delay of a few days for longer wavelengths). The K-band lagged the B band by 14 ± 4 days during the last 3 seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017–2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The HK-band variability is governed primarily by dust. The Balmer decrement of the broad-line components is inversely correlated with the UV flux. The change of the object’s type, from Sy1 to Sy1.8, was recorded over a period of ∼ 8 years. We interpret these changes as a combination of two factors: changes in the accretion rate and dust recovery along the line of sight.