Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a powerful way to probe dormant BHs over a wide mass range. In this study, we present our late-time observations and comprehensive multi-wavelength analyses of AT 2018cqh, a TDE at the center of a dwarf galaxy that exhibited successive flares in the optical, X-ray, and radio bands. We discovered an unexpected high-state X-ray plateau phase following the peak until the present time. Along with its reported prolonged rise lasting at least 550 days, these unique characteristics are consistent with the scenario of a TDE caused by an intermediate-mass black hole (IMBH) with a mass of approximately (1 − 6) × 105 solar masses. Furthermore, scaling relations derived from the host-galaxy properties indicated a similar BH mass in concert. This discovery highlights the invaluable role of TDEs in the search for elusive IMBHs. Black hole (BH) masses can be estimated from tidal disruption events (TDEs). Here, the authors show that AT 2018cqh, a TDE, exhibits unusual X-ray characteristics consistent with a TDE scenario involving an intermediate-mass BH.

Stars on bound orbits around a supermassive black hole may undergo repeating partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed case of periodicity after ASASSN-14ko. Uniquely, the flares from AT2023uqm show a nearly exponential increase in energy — a “runaway” phenomenon signaling the star’s progressive destruction. This behavior is consistent with rpTDEs of low-mass main-sequence stars or evolved giant stars. Multiwavelength observations and spectroscopic analysis of the two most recent flares reinforce its interpretation as an rpTDE. Intriguingly, each flare displays a similar double-peaked structure, potentially originating from a double-peaked mass fallback rate or two discrete collisions per orbit. The extreme ratio of peak separation to orbital period draws attention to the possibility of a giant star being disrupted, which could be distinguished from a low-mass main-sequence star by its future mass-loss evolution. Our analysis demonstrates the power of rpTDEs to probe the properties of disrupted stars and the physical processes of tidal disruption, though it is currently limited by our knowledge of these events. AT2023uqm emerges as the most compelling rpTDE thus far, serving as a crucial framework for modeling and understanding these phenomena.

We report the discovery of a radio-quiet to radio-loud transition in the narrow-line Seyfert 1 galaxy J1105+1452. The source has undergone a long-term evolution from a radio-quiet state in the 1990s to a persistently radio-bright state after 2017. Post-2017 flux densities in the 0.8-7 GHz range cluster between 32 and 43 mJy, whereas the 144 MHz flux density is only 1.94 +/- 0.23 mJy. This indicates strong low-frequency suppression from a compact, absorbed component. Modeling the radio spectral energy distribution with a synchrotron self-absorption model yields a turnover frequency nu p = 0.48 +/- 0.03 GHz and a peak flux density Sp = 38.9 +/- 4.7 mJy. These parameters classify J1105+1452 as a megahertz peaked-spectrum source, consistent with the new episode of an early-stage compact jet. Under the assumption of equipartition, we derive an intrinsic physical radius R similar to 0.68 pc and an average apparent expansion velocity beta app approximate to 0.64. The observed brightness temperature Tb approximate to 6.0 & times; 1011 K necessitates a Doppler factor delta approximate to 12, implying a relativistic jet viewed at theta less than or similar to 5 degrees. Despite the dramatic radio evolution, the X-ray spectrum remains stable and steep (Gamma similar or equal to 3.0), suggesting that the X-ray emission remains dominated by the disk/corona, while the radio band has become jet dominated. Our results identify J1105+1452 as a rare radio changing-state NLSy1, providing a unique laboratory for studying the birth and early evolution of relativistic jets at high Eddington ratios.

Context. Statistics on tidal disruption events (TDEs) may be contaminated by repeating TDEs (rTDEs), which have been widely discovered in recent years. However, no statistical study has yet examined rTDEs with time intervals longer than 5 years. In addition, the origin of rTDEs remains unclear. Aims. We aim to search for rTDEs with time intervals longer than 5 years in a well-defined TDE sample and to estimate the rTDE rate and fraction in the sample. Methods. We used a sample of 16 TDEs at z < 0.05 from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to search for flares 5–19 years before the ZTF TDEs using the Catalina Real-time Sky Survey (CRTS) light curves. We analyzed archival multi-band data to distinguish between TDEs and supernovae (SNe) and estimated the expected number of SNe that CRTS could detect in the sample. Results. We identify two rTDE candidates, AT 2019azh and AT 2024pvu, with time intervals of 13.2 and 17.1 years, respectively. The peak luminosities of the CRTS flares are close to those of ZTF flares. For the CRTS flare of AT 2024pvu, we used UV observations from the Galaxy Evolution Explorer (GALEX) near the peak to measure a blackbody temperature of ∼19 500 K, consistent with TDEs and higher than that of SNe. Moreover, we estimate the expected number of SNe in the sample to be ≲0.08, and hence the probability that both CRTS flares are SNe is only 0.3%. Therefore, we rule out the possibility that both CRTS flares are SNe and conclude that both are likely TDEs. Using the two rTDEs, we infer that the TDE rate is two to three orders of magnitude higher than the average over 5–19 years prior to TDE detection. Two rTDEs with intervals of ∼2 years in the sample, together with possible rTDEs missed by CRTS, suggest that rTDEs with intervals of < 20 years may account for 25%–60% of the TDE sample. We interpret rTDEs as repeating partial TDEs. If so, the high fraction of rTDEs suggests that the observed optical TDE rate is overestimated. However, the possibility of independent TDEs cannot be ruled out and requires future observational tests.

For over a century, the origin of low-energy cosmic rays (LECRs), the dominant heaters and ionizers of dense interstellar gas, has remained elusive owing to solar modulation and uncertain transport processes. In this study, we introduce a new astrophysical approach based on H i narrow self-absorption (HINSA) to obtain spatially resolved measurements of LECR ionization rates using high-fidelity H i observations toward the Orion region from the FAST telescope. The LECR ionization rate is found to scale with local star formation rate as log10 zeta=(1.4 +/- 0.70)log10SFR+(-10.5 +/- 2.9) . Moreover, it increases with visual extinction, and is found to exceed, toward active star-forming regions, the value predicted for diffuse regions based on Voyager measurements and an external propagation model. These findings demonstrate that LECRs are generated in situ by star-forming activities rather than penetrating from the broader Galactic cosmic-ray population. This is further supported by Fermi-LAT gamma-ray observations toward the Orion region. Together, these results resolve a key uncertainty in cosmic-ray origin and establish a new avenue for quantifying the energetic feedback that regulates the interstellar medium.

SDSS J1548+2208 is a unique partially obscured nuclear transient that exhibits multiwavelength outbursts in mid-infrared, X-rays, and radio. We present the results from multiwavelength photometric and spectroscopic follow-up observations with a time span of similar to 2500 days since its discovery. We find that the mid-infrared and X-ray emission (with a hard X-ray spectrum) are still at a high flux level relative to the pre-flare state, suggesting a sudden increase, and possibly long-sustained accreting activity from the central black hole. This is supported by the slowly evolving high-ionization coronal lines. The mid-infrared color turns blue slowly in the rising phase, which is distinct from stellar tidal disruption events (TDEs). All these properties point to the origin of outbursts from an extreme changing-look active galactic nucleus (AGN), and the scenario with a normal TDE seems disfavored. The radio spectral energy distribution (SED) in similar to 0.65-15 GHz is unusual, displaying a double-peak feature with distinct variability characteristics. In addition, we find evidence for the late-time radio rebrightening more than six years after the initial outburst, as well as a possibly new X-ray flare, though the significance for the latter is not high. The peculiar radio flux and SED evolution could be explained by a nascent outflow expanding into and shocking the circumnuclear diffuse medium filled by denser clouds. In this case, SDSS J1548+2208 represents a rare changing-look AGN that can launch radio outflows. Continued multiwavelength observations are required to map the dust and gas distribution on pc-scales, providing new insights into the environmental properties that could regulate AGN changing-look phenomenon.

The fifth edition of the Roma-BZCAT catalog (5BZCAT) contains 227 blazars of the uncertain type (BZU), whose available data do not support an unambiguous assignment to the BL Lacertae object (BZB), flat-spectrum radio quasar (BZQ), or host-galaxy-dominated blazar-like source (BZG) categories. We construct a machine-readable value-added catalog for these sources using 1151 BZB, 1909 BZQ, and 274 BZG catalog entries as the supervised reference sample. The compact input set contains redshift, optical magnitude, radio, X-ray, and gamma-ray measurements; missingness indicators; and spectral slopes connecting the radio, optical, and X-ray bands. Redshift and its availability are explicitly treated as optical-spectroscopy-related label proxies. Cross-validation shows that the Light Gradient Boosting Machine (LightGBM) provides the most reliable probability scores among the tested models, although the stacking ensemble gives a slightly higher balanced accuracy. The final catalog reports LightGBM probabilities and contains 61 BZB-like, 120 BZQ-like, and 46 BZG-like sources; 17 are flagged for low probability separation. These probabilities quantify similarity to existing 5BZCAT labels conditional on catalog measurements, rather than an independent physical taxonomy.

Despite the growing number of high-energy neutrinos (TeV-PeV) detected by IceCube, their astrophysical origins remain largely unidentified. Recent observations have linked a few tidal disruption events (TDEs) to the production of high-energy neutrino emission, all of which display dust-reprocessed infrared flares, indicating a dust- and gas-rich environment. By cross-matching the neutrino events and a sample of mid-infrared outbursts in nearby galaxies with transient radio flares, we uncover an optically obscured TDE candidate, SDSS J151345.75 + 311125.2, which shows both spatial and temporal coincidence with the sub-PeV neutrino event IC170514B. Using a standard equipartition analysis of the synchrotron spectral evolution spanning 605 days post mid-infrared discovery, we find a little evolution in the radio-emitting region, with a kinetic energy up to 10(51) erg, depending on the outflow geometry and shock acceleration efficiency assumed. High-resolution European VLBI Network imaging reveals a compact radio emission that is unresolved at a scale of < 2.1 pc, with a brightness temperature of T-b > 5 & times; 10(6) K, suggesting that the observed late-time radio emission might originate from the interaction between a decelerating outflow and a dense circumnuclear medium. If the association is genuine, the neutrino production is possibly related to the acceleration of protons through pp collisions during the outflow expanding process, implying that the outflow-cloud interaction could provide a physical site with a high-density environment for producing the sub-PeV neutrinos. Such a scenario can be tested with future identifications of radio transients coincident with high-energy neutrinos.

Context . SDSS J143016.05+230344.4 ( z = 0.08105) has been proposed as a candidate pre-coalescence supermassive black hole binary and shows remarkable multiwavelength variability. Its radio evolution provides a direct probe of the compact emitting region and of the physical origin of the late-time activity. Aims . We aim to localize the variable radio emission, characterize its spectral evolution, and constrain whether the radio brightening is produced by a newly emerging compact component, external absorption, or dissipation in a structured circumnuclear environment. Methods . We analyzed 4.7–22.2 GHz very long baseline interferometry (VLBI) observations obtained between 2022 February and 2024 February, together with quasi-simultaneous connected-array spectra covering 0.7–16.5 GHz. We combined the VLBI brightnesstemperature and compactness constraints with spectral decomposition and equipartition-based estimates of source size and ambient density structure. Results . At all epochs, the radio emission is dominated by a single unresolved milliarcsecond core with T B ≳ 10 7 K, constraining the variable emission to ≲0.3 pc. The broadband spectra require two synchrotron self-absorbed components: a persistent low-frequency component with ν p,steady ≈ 0.74 GHz and S p,steady ≈ 1.22 mJy, and a flare component whose turnover evolves from (6.35 GHz, 0.18mJy) in February–May 2022 to (8.61 GHz, 0.38 mJy) in December 2022, and then to (5.83 GHz, 0.25 mJy) in March–April 2023. The flare contribution at 15 GHz reaches ~80% and matches the near-epoch VLBI recovery fraction, showing that the high-frequency brightening arises from a newly formed compact synchrotron component. A second brightening of the 15.2 GHz VLBI core is detected between September 2023 and February 2024, while the source remains unresolved. Equipartition scalings imply characteristic radii of ~5 × 10 −4 pc for the flare and ~9 × 10 −3 pc for the steady component, and indicate a steep inner circumnuclear density profile, n ∝ R −1.7 . Conclusions . The delayed radio flare is best explained by dissipation in an outflow or jet-base disturbance propagating through a structured circumnuclear medium.

We report the discovery of a peculiar optical transient, AT2019ijn, that occurred in the nuclear region of a dwarf galaxy at z = 0.2729 +/- 0.0001. It rises rapidly to peak at a luminosity of Mg = -21.05 +/- 0.02 in 5.26 +/- 0.29 days, followed by a slow decline over more than a month, during which the optical emission has a persistently high blackbody temperature from TBB=1.45-0.13+0.16 to 1.59-0.51+1.68 & times;104 K. The radio emission is exceptional, peaking at 641 days after optical discovery with a high luminosity of (2.0 +/- 0.1) & times; 1031 erg s-1 Hz-1. The peak radio luminosity is at least two orders of magnitude brighter than known radio-bright fast blue optical transients and supernova explosions at similar epochs but comparable to jetted tidal disruption events. The luminous and long-lasting radio emission with a late-time peak can be explained by an off-axis relativistic jet with a viewing angle of 38.9-6.1+7.0 degrees . We discuss possible origins for AT2019ijn and favor a jetted tidal disruption event involving an intermediate-mass black hole of 1.32-0.67+1.19 & times;105 M circle dot, although a jetted magnetar model cannot be fully ruled out. AT2019ijn represents a new class of relativistic optical transients that highlights the importance of radio surveys for discovering off-axis jetted events.

The origin of radio afterglows or delayed radio flares in tidal disruption events is not fully understood. They could be generated either by a forward shock propagating into the diffuse circumnuclear medium or a bow shock around a dense cloud. Each of these scenarios is fundamentally different from the other and so, to elucidate the distinctions between the two, we conducted two-fluid simulations incorporating relativistic electrons to investigate the spatial evolution of these electrons after being accelerated by a shock. Based on their spatial distribution, we performed radiative transfer calculations to obtain the synchrotron spectra. In Paper I , we reported the results for the forward shock scenario and in this follow-up article, we focus on the bow shock scenario. Compared to the radio emission from the forward shock, whose peak frequency typically lies around 1 GHz and decreases with time, the radio emission from the bow shock peaks at higher frequencies (typically ∼1-20 GHz) and its flux rises more steeply than t^4 across our explored parameter space. The radio flux from the bow shock also responds to fluctuations in the outflow. The combined effects of the bow shock and forward shock substantially alter the radio spectra, causing significant deviations from the single-zone emission model and, in some cases, producing a multicomponent feature in the spectra. This study highlights the importance of the bow shock, inspiring a novel approach for probing dense gas on subparsec scales in galactic nuclei by decomposing the bow shock radio spectrum to reveal the conditions around circumnuclear dense gas. mou2026

SDSS J1548+2208 is a unique partially-obscured nuclear transient that exhibits multiwavelength outbursts in mid-infrared, X-ray and radio. We present the results from multiwavelength photometric and spectroscopic follow-up observations with a time span of 2500 days since its discovery. We find that the mid-infrared and X-ray emission (with a hard X-ray spectrum) are still in a high flux level relative to the pre-flare state, suggesting a sudden increased, and possibly long-sustained accreting activity from central black hole. This is supported by the slowly-evolving high-ionization coronal lines. The mid-infrared color turns blue slowly in the rising phase, which is distinct from stellar tidal disruption events (TDEs). All these properties point to the origin of outbursts from an extreme changing-look AGN and the scenario with a normal TDE seems disfavored. The radio spectral energy distribution (SED) in 0.65-15 GHz is unusual, displaying a double-peak feature with distinct variability characteristics. In addition, we find evidence for the late-time radio rebrightening more than six years since the initial outburst, as well as a possibly new X-ray flare, though the significance for the latter is not high. The peculiar radio flux and SED evolution could be explained by a nascent outflow expanding into and shocking circumnuclear diffuse medium filled by denser clouds. In this case, SDSS J1548+2208 represents a rare changing-look AGN which can launch radio outflows. Continued multiwavelength observations are required to map the dust and gas distribution on pc-scales, providing new insights into the environmental properties that could regulate AGN changing-look phenomenon.

ABSTRACT IC 10 X-1, NGC 300 X-1, and Cyg X-3 constitute a unique class of X-ray binaries in which a stellar-mass black hole (BH) accretes material from a Wolf–Rayet (WR). These systems are particularly intriguing because of their short orbital periods, which make them promising progenitors of gravitational-wave (GW) sources detectable by the LIGO–Virgo–KAGRA (LVK) network. Adopting a revised accretion efficiency within the standard Bondi–Hoyle–Lyttleton framework, we perform detailed binary evolution calculations using mesa to characterize their properties at different evolutionary stages and to assess their ultimate fates as potential LVK-detectable GW sources. By applying additional constraints from the observed properties of IC 10 X-1 and NGC 300 X-1, we find that the upper limits on the BH masses in these systems ($M_{\rm BH} \lesssim 25\, \rm M_\odot$ for IC 10 X-1 and $M_{\rm BH} \lesssim 15\, \rm M_\odot$ for NGC 300 X-1) are significantly lower than previous estimates. Both systems are expected to form binary black holes (BBHs) that will merge within a Hubble time, except in the case where the BH in NGC 300 X-1 has a mass of $9\, \rm M_\odot$, corresponding to the lower limit inferred in a previous study using the continuum-fitting method with a relativistic slim-disc model. For Cyg X-3, we find that the BH spin magnitude is constrained to be $\lesssim$0.6. Moreover, the WR star in Cyg X-3 is likely to form a lower-mass-gap BH, and the resulting BBH system is also expected to merge within a Hubble time.

SDSS J1115+0544 is a unique low-ionization nuclear emission-line region galaxy with energetic ultraviolet (UV), optical, and mid-infrared outbursts occurring in its nucleus. We present the results from an analysis of multiwavelength photometric and radio follow-up observations with a time span of ≈9 yr since its discovery. We find that following a luminosity plateau of ≈500 days, the UV/optical emission has decayed back to the preoutburst level, suggesting that the nuclear outburst might be caused by a stellar tidal disruption event (TDE). In this case, J1115+0544 could be an unusually slowly evolving optical TDE with longest rise and decline time scales ever found. Three years later than the optical peak, a delayed radio brightening was found with a luminosity as high as νL _ν (5.5 GHz) ∼ 1.9 × 10 ^39 erg s ^−1 . Using a standard equipartition analysis, we find that the outflow powering the radio emission was launched at t ≳ 1150 days with a velocity of v ≲ 0.1 c and a minimal kinetic energy of E _K ≳ 3 × 10 ^49 erg. The delayed radio brightening coupled with the disappearing plateau in the UV/optical light curves is consistent with the scenario involving delayed ejection of an outflow from a state transition in the disk. SDSS J1115+0544 is the first TDE candidate displaying both a short-lived UV/optical plateau emission and a late-time radio brightening. Future radio observations of these TDEs in the postplateau decay phase will help to establish the connection between outflow launching and changes in accretion rate.

Tidal disruption events (TDEs) probe the birth and evolution of black hole accretion flows and jets on human timescales. Radio emission traces shocks and outflows from thermal TDEs and powerful relativistic jets in the rare jetted class. SKA Mid, phased for VLBI and used together with global networks, will deliver milliarcsecond imaging, tens of microarcsecond astrometry, and microJy sensitivity, enabling: (i) proper motion measurements that discriminate off axis relativistic jets from subrelativistic winds; (ii) resolved morphologies and magnetic field diagnostics via polarimetry; and (iii) precise nuclear localization to distinguish SMBH vs. IMBH and to reveal recoiling or binary systems. SKA's wide frequency coverage (0.35 to 15.4 GHz) and 1h continuum sensitivities of 3 to 10 microJy per beam, together with multibeam tiedarray VLBI and a transient buffer for rapid triggers, are transformational. LSST, Einstein Probe, and SVOM will increase TDE alerts to hundreds per year, and late time radio flares appear common, ensuring rich SKA VLBI samples. We provide observing strategies, detection forecasts, and predictions, e.g., about 5 proper motion detections of jetted (or off axis) TDEs per year and routine core shift constraints at the microarcsecond level. This program will establish TDEs as laboratories for exploring jet launching, particle acceleration (including neutrinos), black hole accretion history and demographics, and properties of circumnuclear medium.

We present 4.7–22.2 GHz Very Long Baseline Interferometry (VLBI) monitoring of the candidate pre-coalescence supermassive black hole binary SDSS J143016.05+230344.4 (z=0.08105) from 2022 February to 2024 February, together with quasi-simultaneous 0.7–16.5 GHz connected-array spectra. At all epochs, the radio emission is dominated by a single unresolved milliarcsecond core with T_ B≳10^7 K, confining the variable emission to ≲0.3 pc. The spectra require two self-absorbed synchrotron components: a persistent low-frequency component with ν_ p,steady≈0.74 GHz and S_ p,steady≈1.22 mJy, and a flare component whose turnover evolves from (6.35 GHz,0.18 mJy) in 2022 February–May to (8.61 GHz,0.38 mJy) in 2022 December and then to (5.83 GHz,0.25 mJy) in 2023 March–April. The 15 GHz flare fraction peaks at ≃80% and matches the near-epoch VLBI recovery fraction, showing that the high-frequency brightening arises from a new compact synchrotron component. A second 15.2 GHz VLBI-core brightening is detected from 2023 September to 2024 February while the source remains unresolved. Equipartition scalings imply characteristic radii of R_ eq∼5×10^-4 pc for the flare and ∼9×10^-3 pc for the steady component, and a steep inner circumnuclear density profile, n∝ R^-1.7. The delayed radio peak is consistent with dissipation of an outflow or jet-base disturbance in a structured circumnuclear medium, while a uniform free–free absorber is disfavored.

We present a comprehensive study of an infrared (IR) flare in the star-forming galaxy SDSS J010320.39+140152.5, which is selected from the sample of mid-IR (MIR) outbursts in nearby galaxies. Its MIR luminosity rose rapidly to a peak of similar to(5-6) & times; 1043 erg s-1, remained in the high state for about a year, and decreased continuously afterward. No optical variability was detected throughout the IR flare. Near-IR follow-up observations around the peak pinpointed the flare's location to spatially coincide with the galactic nucleus, with a 3 sigma upper limit of the offset of less than or similar to 100 pc. The IR spectral energy distribution of the flare is consistent with thermal emission of dust with temperatures of similar to 900 K. Using a dust radiative transfer model, we inferred a peak UV luminosity of similar to(4-10) & times; 1044 erg s-1 and a total energy of similar to(0.9-2) & times; 1052 erg released. We ruled out the possibility of a supernova, and prefer that the IR flare originated from an obscured tidal disruption event (TDE) rather than a changing-look active galactic nucleus. This flare stands as one of the most compelling cases to date for the class of dust-obscured TDEs that has emerged in recent years. They are missed by optical surveys, which partly accounts for the observed bias in TDE host galaxies, and they represent a crucial, yet often overlooked, component for a complete understanding of the TDE population.

Active galactic nucleus (AGN) feedback is a key ingredient in galaxy evolution, yet its impact on the cold atomic gas reservoir-the neutral hydrogen (H i) phase-remains poorly constrained. We present the most extensive spatially resolved H i 21 cm survey of Seyfert AGN hosts to date, based on observations with the Giant Metrewave Radio Telescope (GMRT). We measure H i masses and sizes for eight Seyfert galaxies, and map the detailed kinematics and surface densities for two representative targets. We find that AGN-host galaxies exhibit a slightly shallower H i mass-size relation than the canonical relation or the Simba simulation predictions; however, the measured slope remains consistent with the canonical value within 2 sigma uncertainties. This result suggests that AGN feedback does not significantly disrupt the global extent or large-scale structure of atomic gas reservoirs. To investigate the internal H i kinematics in greater detail, we perform a 3D kinematic forward modeling of the H i disk in UGC 4503. Our analysis reveals an elevated intrinsic velocity dispersion of sigma=14.9-3.8+6.1 km s-1 and a reduced level of rotational support, with V/sigma=14.28-4.17+4.97 , compared to large-sample star-forming spirals. These kinematic signatures, together with localized residuals in the velocity field, indicate that AGN-driven outflows or jets may inject or indirectly affect the turbulence in the atomic gas disk, potentially regulating the cold gas reservoir. Future GMRT observations, combined with optical integral-field spectroscopy from Mapping Nearby Galaxies at Apache Point Observatory, will enable quantitative constraints on the role of AGN feedback in regulating star formation efficiency across a larger and more representative galaxy sample.

We present a systematic investigation of long-term mid-infrared (MIR) color variability in 1718 narrow-line Seyfert 1 galaxies (NLSy1s) using 14 yr of Wide-field Infrared Survey Explorer/NEOWISE monitoring data. Through Pearson correlation analysis between photometric magnitude and color, we identify (1) a radio-quiet NLSy1 (RQ-NLSy1) population comprising 230 bluer-when-brighter (BWB) sources, 131 redder-when-brighter (RWB) sources, and 1323 objects showing weak or statistically insignificant color variations; and (2) a radio-loud NLSy1 (RL-NLSy1) population containing 5 BWBs, 2 RWBs, and 27 sources with weak/no color variations. Our analysis reveals that the BWB tendency strengthens significantly in galaxies with redder mean MIR colors W1 -W2 and lower starlight contamination. Furthermore, this color-change pattern demonstrates that the most bolometric luminous sources exhibit the most pronounced BWB behavior. While similar trends exist for black hole mass and Eddington ratio, bolometric luminosity appears to be the primary physical driver. Potential origins of these variations (e.g., host galaxy contribution, accretion disk variability, and dust reprocessing) are discussed. We conclude that temperature-dependent dust reprocessing dominates the observed BWB, RWB, and no/weak variation patterns. This interpretation may also apply to similar MIR color variations (MCVs) observed in other extragalactic MIR transients, such as tidal disruption events, ambiguous nuclear transients, and changing-look AGNs. In addition, we find no significant difference in long-term MCVs between RL-NLSy1s and RQ-NLSy1s; however, RL-NLSy1s show significantly greater dispersion in intrinsic variability amplitude compared to RQ-NLSy1s due to jet-induced complexity, where nonthermal synchrotron emission from relativistic jets obscures thermal dust signatures.

Quasi-periodic eruptions (QPEs) are rapid, recurring soft X-ray bursts, whose nature is still in dispute. A compelling case of QPEs has emerged in the slowly evolving optical transient AT2019wzc, possibly associated with the tidal disruption of a post-main-sequence star by a supermassive black hole. Further evidence of a tidal disruption event (TDE) is crucial to understand the nature of AT2019wzc and establish the link between TDE and QPEs. Here we report the detection of a narrow, blueshifted N VI absorption line in its high-resolution X-ray spectra obtained by XMM-Newton, but weak or undetectable absorption lines from other elements of similar ionization states such as carbon and oxygen. The absorption line features can be reproduced by an ionized gas with ionization parameter log ξ∼ 0.3 erg cm s^-1 and column density N_ H∼ 10^20 cm^-2, under the condition of a nitrogen abundance of 11.6_-7.8^+19.6 times the solar value. This abnormal nitrogen abundance favors a TDE origin for AT2019wzc, and the absorbing gas may originate from the outflow induced by self-collision of the TDE's debris stream.