arXiv subjects

Tinggui Wang

Publications and source records attributed to Tinggui Wang.

At least 19 recordsLinked to original sources

arXiv2026

Extreme Multiwavelength Variability in the Recurrent Intermediate-type Changing-look Seyfert Galaxy SDSS J234728.73+242745.7

We report the discovery of the Seyfert galaxy J234728.73+242745.7 as a recurrent intermediate-type CLAGN with extreme optical/UV variability. Optical spectra spanning nearly three decades reveal Type 1.0$\rightarrow$1.5$\rightarrow$1.2 transitions, accompanied by the disappearance and reappearance of broad He II $\lambda4686$ and a broad-line Balmer decrement evolving from 4.5 to 7.2 and then 2.4. Monitoring reveals coordinated variability from X-rays to the MIR. SED decomposition yields a host-corrected g-band high-to-low-state flux ratio of $5.4\pm0.4$, exceeding the Swift/XRT ratio of $2.7\pm0.8$ across the changing-look transition. This discrepancy may arise from reduced dust extinction, as correcting for the low-state continuum reddening ($A_V^{\rm cont}=0.66\pm0.23$ mag) brings the optical/UV ratios close to the X-ray value, although the correction is model-dependent and intrinsically weaker X-ray variability may also contribute. However, X-ray spectra show no compelling evidence for intrinsic gas absorption or its variability ($N_{\rm H}^{\rm intr}\lesssim5\times10^{20}$ cm$^{-2}$). In contrast, EP/WXT monitoring during the recent high state reveals order-of-magnitude X-ray fluctuations on monthly-to-sub-year timescales, exceeding contemporaneous optical variations. Meanwhile, the radio flux density remains stable at $\sim2$ mJy across all ASKAP observations since mid-2020. Together with optical/UV and MIR variability and the broad He II transition, these results favor intrinsic accretion-state changes as the primary driver, while allowing a secondary contribution from variable obscuration. The source displays a loop-like MIR color--magnitude evolution, likely driven by the delayed response of an extended torus. This recurrent CLAGN offers a laboratory for probing the dynamic response of the broad-line region and circumnuclear dust to accretion-state transitions.

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arXiv2026

WFST Follow-up of S251112cm: Searching for an Optical Counterpart to a Subsolar-mass Compact-binary Merger Candidate

Electromagnetic counterparts to gravitational-wave (GW) sources probe the properties, environments, and evolution of compact-object mergers. S251112cm belongs to an emerging class of GW candidates with possible subsolar-mass components. We present an optical counterpart search for S251112cm with the Wide Field Survey Telescope (WFST). Observations began 20.2 hr after the GW trigger and lasted three nights, covering approximately 780 deg$^2$ and 51% of the localization probability in the updated skymap. Our search for newly emerging, rapidly evolving, off-nuclear optical transients yielded four candidates with host-galaxy distances broadly consistent with the GW distance estimate. All four evolve substantially more slowly than AT 2017gfo, ruling out an AT 2017gfo-like origin and disfavoring their association with S251112cm as rapidly evolving kilonova counterparts. Combining WFST and DECam increases the localization probability coverage to approximately 67%. Assuming the counterpart lies within this footprint, we constrain a grid of binary-neutron-star kilonova models. For viewing angles $θ_{\rm obs}<60^\circ$, with other parameters fixed to the AT 2017gfo best-fit values, models with dynamical ejecta mass $M_{\rm dyn}\gtrsim0.01 M_\odot$ or wind ejecta mass $M_{\rm wind}\gtrsim0.05 M_\odot$ are disfavored over most of the covered GW probability. Our phenomenological analysis further constrains rapidly evolving optical transients with $T_{\rm rise,1/2}\leq2$ days to peak absolute magnitudes fainter than approximately -13 mag. To our knowledge, WFST provides the strongest optical constraints to date in the northern sky on possible rapidly evolving counterparts to this new class of GW candidates with subsolar-mass components. The comparable depths and complementary sky coverage of WFST and DECam extend these constraints across more of the localization region at similar sensitivity.

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arXiv2026

EP241021a as An Off-nuclear Month-duration Transient in a Dwarf Starburst Galaxy

EP241021a is a peculiar fast X-ray transient exhibiting a long X-ray plateau and an optical rebrightening, both challenging the traditional jet afterglow model. Whether its nature is a stellar explosion or a tidal disruption event (TDE) remains debated. Here we present late-time HST/WFC3 and Gemini-N/GMOS observations of its host galaxy at $z=0.748$. After $\sim300$ days post-trigger, the transient emission had faded below detection, revealing a dwarf disk galaxy with an effective radius $R_e=1.7$ kpc, a stellar mass $M_\star\sim3\times10^8M_\odot$, and a high star formation rate of $\sim5\ M_\odot\ {\rm yr}^{-1}$. Combined with previous very long baseline interferometry measurements, the transient can be located in the galactic disk with a projected physical offset of $0.95\pm0.13$ kpc from the galaxy center. Host-subtracted optical light curves show that the rebrightening ceased at $\sim47$ days, followed by a sudden drop with a power-law index steeper than $-3.3$, coincident with a similar drop in the X-ray light curve. This synchronous drop in both bands is consistent with jet shut-off, and the required month-long jet activity suggests a persistently accreting compact object fed by a TDE. Among the TDE scenarios, the off-nuclear location and the starburst host galaxy slightly favor the post-supernova micro-TDE scenario in a binary system, in which a natal kick drives the newborn compact object into a tidal disruption of its companion. Nevertheless, an off-nuclear intermediate-mass black hole TDE or a stellar-mass black hole TDE induced by dynamical scattering in a dense stellar cluster cannot yet be excluded.

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arXiv2026

EP J062132.0+623837: A Multi-wavelength Study of a Changing-look Active Galactic Nucleus Discovered by Einstein Probe

EP J062132.0+623837 is a new X-ray source identified in 14-day binned survey data from the Wide-field X-ray Telescope aboard the Einstein Probe (EP). Subsequent X-ray observations with the Follow-up X-ray Telescope (FXT) on board EP localized the source to the central region of the galaxy 2MASX J06213207+6238390 at $z=0.084$. Here, we present a comprehensive analysis of the multi-wavelength data for this object. During the FXT and Swift/XRT follow-up, the source remained X-ray active, with observed luminosities of $(3-9)\times10^{43}$ erg s$^{-1}$, and its X-ray spectra were well described by power-law models with photon indices of $Γ\sim1.5$. The optical spectrum of the host galaxy clearly reveals a broad-line active galactic nucleus (AGN) exhibiting significantly enhanced broad Balmer emission lines compared to an archival spectrum obtained four years earlier, thereby marking a changing-look transition from Type 1.8 to Type 1.5. Furthermore, long-term optical and mid-infrared light curves indicate that the nucleus underwent dramatic brightening around 2010 and has since shown substantial variability. Given the spatial coincidence and multi-wavelength behavior, we identify EP J062132.0+623837 as a changing-look AGN, initially detected by EP and subsequently confirmed to exhibit large-amplitude variability across multiple bands. This case study demonstrates the great potential of wide-field time-domain X-ray surveys for discovering changing-look AGNs, paving a new avenue for their systematic identification as a powerful complement to ongoing optical surveys.

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arXiv2026

A Step-Like Transition Underlying the Life and Death of Galaxies

How galaxies stop forming stars is a complex and central problem in astrophysics. Numerous physical mechanisms have been proposed, yet a simple, unified framework connecting these mechanisms remains lacking. Here, we derive a step-function quenching response from the fundamental principle of gas mass conservation, governed by the competition between gas-supply and gas-depletion timescales. This response also enables the gas-supply timescale to be inferred from the observed quenched fraction. Applying this method to approximately 350,000 galaxies, we find a characteristic gas-supply timescale of ~1 Gyr, reveal distinct inside-out and outside-in quenching signatures associated with supermassive black holes and dark matter halos, respectively, and identify galaxies with intermediate stellar surface mass densities as occupying a critical state for quenching and rejuvenation. Our work establishes a unified physical framework in which a simple step-function response captures how diverse physical processes regulate galaxy quenching and the resumption of star formation through their effects on the competition between gas-supply and gas-depletion timescales.

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arXiv2026

Unravelling the Nature of AT 2025abao: From Precursor to Final Fate

Luminous red novae (LRNe) are potential signatures of common envelope evolution (CEE), a critical yet poorly understood phase in compact binary formation. AT 2025abao, an LRN in the Andromeda galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system's evolutionary fate remains unclear. Here, we unravel the binary nature of AT 2025abao by modeling its complete evolution, from precursor to final outcome. We show that the eight-year infrared precursor arises from a $\approx1.4^{+0.2}_{-0.3}\,M_{\odot}$ main-sequence companion inspiralling through the wind of a $\approx 6.9\,M_{\odot}$ AGB star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to $\approx 0.92\,M_{\odot}$ and energy to $\approx 1.25\times 10^{47}\,$erg, revealing that only $\approx 0.57\,M_{\odot}$ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT 2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact binary formation.

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arXiv2026

Mrk 382: A Narrow-line Seyfert 1 Galaxy with Recurrent X-ray State Transitions

We report recurrent X-ray state transitions in the nearby narrow-line Seyfert~1 galaxy Mrk~382 using multi-epoch observations from \textit{Swift}, \textit{Chandra}, \textit{XMM-Newton}, and eROSITA, together with archival ultraviolet, optical, and infrared data. The 0.3--2 keV flux varies by nearly an order of magnitude over the past $\sim15$ yr, with multiple transitions between bright and faint states. The source brightened by a factor of $\sim10$ between the 2010 \textit{Chandra} observation and the 2011 \textit{XMM-Newton} high state, then declined by $\sim6$--7 to a low state in 2019, followed by renewed brightening in recent \textit{Swift} monitoring. The X-ray spectrum shows strong state-dependent evolution, changing from a steep high-state continuum ($Γ=2.32\pm0.04$) to a much harder low-state spectrum ($Γ=1.39\pm0.06$). The low-state spectrum also exhibits a narrow Fe K$α$ line with an equivalent width of $\sim330$ eV. Reflection modeling indicates that the low-flux state is strongly reflection dominated, with the reflection fraction increasing from $R_{\rm refl}\sim4$ to $\sim34$, consistent with a compact corona subject to strong light-bending effects. The ultraviolet emission broadly follows the long-term X-ray variability but with smaller amplitude, while the optical and mid-infrared bands vary more mildly. Despite the dramatic X-ray variability, Mrk~382 does not enter an extreme X-ray-weak state, and we did not detect clear optical spectral-type changes based on the currently available observations. Mrk~382 is therefore a rare nearby Seyfert galaxy undergoing recurrent X-ray state transitions, providing a valuable laboratory for studying changing coronal geometry and multiwavelength AGN variability.

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arXiv2026

A systematic study of the long-term mid-infrared color variations of Seyfert 1 galaxies

We present a comparative analysis of long-term mid-infrared (MIR) color variations (MCVs) for 1,977 narrow-line Seyfert 1 (NLSy1) and 4,113 broad-line Seyfert 1 (BLSy1) galaxies at $z < 0.3$. Using 14 years of WISE and NEOWISE data, we quantify the correlation between $W1-W2$ color and $W1$ magnitude. We categorize sources into bluer-when-brighter (BWB), redder-when-brighter (RWB), and weak/no MCV populations. Our results show that the MCV properties of BLSy1s are consistent with those of NLSy1s. This suggests that host-contaminated dust reprocessing is a universal mechanism across Seyfert 1s. Bolometric luminosity ($\Lbol$) is the primary driver of MCV behavior. However, at fixed $\Lbol$, the fraction of RWB sources decreases with increasing Eddington ratio ($\REdd$). This reveals a secondary dependence on the accretion state. Ensemble structure function analysis further shows that higher-$\REdd$ sources exhibit flatter structure functions at a given $\Lbol$, indicating smaller dust torus radii. These findings suggest that the central engine's radiation and accretion state shape the circumnuclear dust geometry. Radio-loud sources follow the same trends as radio-quiet counterparts, implying that jet emission does not significantly impact long-term MIR variability. Finally, modified blackbody modeling indicates that grains with sizes $a \gtrsim 0.1~μ$m are responsible for the observed MCVs. Our results establish a unified framework for MCVs in Seyfert~1s, where the Eddington ratio modulates both variability patterns and the physical scale of the dust torus. Furthermore, given the similarity between the MCV distributions of CLAGNs and RWB sources, we estimate that $\lesssim 6\%$ of Seyfert~1s may be CLAGN candidates, offering a potential MIR-based pre-selection.

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arXiv2026

A Unified Timescale Relation for Quasi-Periodic Eruptions and Repeated Nuclear Transients

Quasi-periodic eruptions (QPEs) and recurrent nuclear transients (RNTs) exhibit recurrent high-amplitude flares from galactic nuclei, yet their characteristic timescales remain poorly understood. In this work, we compile a sample of these systems and investigate empirical scaling relations between flare timescales and black hole masses. We find that the recurrence timescale exhibits a positive but highly scattered dependence on black hole mass in the combined QPE and RNT sample, approximately following $t_{\rm rec}\propto M_{\rm BH}^{1.19^{+0.52}_{-0.47}}$ with an intrinsic scatter of 0.95 dex. Remarkably, we uncover a tight nearly linear relation between recurrence time and flare timescale for QPEs and RNTs, described by $t_{\rm rec}\propto t_{\rm rise}^{1.00\pm0.07}$ with an intrinsic scatter of 0.29 dex. This relation extends across timescales from hours for QPEs to months and years for nuclear transients. We further find that QPEs and RNTs approximately follow a common empirical relation between recurrence time and flare rise time, although the physical origin of this relation remains uncertain. Our findings reveal a common phenomenological timescale link across RNTs, providing a practical framework for characterizing their temporal behavior.

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arXiv2026

Dynamically driven collapse of a thermally stable accretion disk in a nova-like system

While standard disk instability theory predicts thermal-steady, outburst-free disks in nova-like variables due to their high mass transfer rates, mass transfer variations are prevailingly invoked to explain the occasional flaring/fading phenomena observed in these systems. Here we report the observational evidence for a dynamical collapse of a thermally stable accretion disk, captured serendipitously by TESS during a fading episode of the VY Scl-type nova-like system MASTER OT J072703.91-631952.8, and traced by the emergence of an unusual negative superhump that evolves toward its orbital frequency. Simultaneously, the system underwent an anomalous eruptive event featuring a remarkably symmetric 45-day light-curve profile, indicative of a mild energy-release mechanism fundamentally distinct from documented eruptive events in cataclysmic variables. Notably, the concurrence of the eruption and the disk collapse is difficult to reconcile with the paradigm of mass transfer variations: the eruption implies enhanced mass transfer, whereas the disk collapse indicates a decline. The morphological disk evolution over $\sim 700$ days, characterized by both negative and positive superhumps, indicates a transition from a circular disk to an eccentric disk, followed by a tilted state and ultimately a minimal disk configuration. This evolutionary sequence provides evidence for a previously unrecognized dynamics-driven cycle operating in the thermally stable accretion disk of a VY Scl-type nova-like star.

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arXiv2026

Radio and X-ray flux rebrightening six years after outburst in a partially-obscured extreme changing-look AGN

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.

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arXiv2026

Exploring Tidal Disruption Events with SKA and VLBI: Unveiling the Mystery of Black Hole Feeding and Outflows

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.

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arXiv2026

Local Analogs of Little Red Dots: Optical Variability and Evidence for an Active Galatic Nucleus Origin

Little red dots (LRDs) draw extensive attention because of their unique observational characteristics and apparent overabundance in the early Universe, raising new insights into early black hole formation and growth. Early studies show that LRDs exhibit weak variability in broad-band photometry and emission-line fluxes, suggesting a preference for super-Eddington accretion or disfavouring an AGN origin. However, the cadence of the current data, and therefore, the resulting light curves for LRDs, is limited, preventing us from placing strong constraints on their variability. Based on Zwicky Transient Facility (ZTF) light curves with a baseline of $\sim6$ years, we here study the optical variability of seven previously reported local analogs of LRDs at $z \sim 0.3$, offering an insight into LRDs from a low-redshift sample. Three out of seven local analogs show excess variances on all three bands of their light curves, and two of them can be fitted with the damping random walk model, supporting their AGN origins for the variability. The remaining sources show weak variance in at least one band, but no detectable variability at the current sensitivity level, exhibiting $\rm SF_\infty$ upper limits consistent with estimates from high-redshift (high-$z$) LRDs. Their non-detection of variability is likely due to the large photometric uncertainty. As an implication, by simulating long baseline light curves with the variability amplitude of local analogs and adopting JWST observation cadence, we investigate the limitation of the variability amplitude estimate for LRDs. Our mock observations imply that the current constraints on LRDs' variability are probably underestimated. This underestimation might be induced by the short temporal baseline of observations, as well as the intrinsic scatter of the empirical $M_{\rm BH}-τ$ relation.

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arXiv2026

X-ray variability of SDSS J000532.84+200717.4: from a normal state to an X-weak state

We present a multi-epoch study of the extreme X-ray variability of the type~1 quasar SDSS~J000532.84+200717.4 using archival observations from \textit{XMM-Newton}, \textit{Swift}/XRT, \textit{EP-FXT}, and \textit{ROSAT}, together with new optical spectroscopy and multi-wavelength photometry. The 0.2--10~keV X-ray flux exhibits a transition from a high state to a subsequent low state, declining by more than an order of magnitude and placing the source in the X-ray--weak regime ($Δα_{\rm ox} \lesssim -0.3$). Significant variability on timescales of days to weeks persists within the low state. In contrast, the optical and mid-infrared emission remain stable over decade-long timescales, while the UV continuum varies only mildly and broadly tracks the X-ray evolution. Multi-epoch optical spectroscopy shows no significant long-term changes in either the continuum shape or the broad emission-line profiles. The \ion{Mg}{2} emission is relatively weak compared with typical quasars, suggesting similarities to weak-line quasars. The pronounced wavelength-dependent variability indicates that the accretion disk remains largely intact while the X-ray emission undergoes dramatic changes. The spectral hardening in the low state and the viability of ionized partial-covering models are consistent with variable, largely dust-free absorbing gas, possibly associated with clumpy inner disk winds, although intrinsic coronal variations cannot be excluded. SDSS~J0005+200717.4 therefore provides evidence that extreme X-ray weakness can arise as a transient phase in otherwise normal quasars.

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arXiv2026

Discovery of a Featureless Tidal Disruption Event at z~1 with the Wide Field Survey Telescope

We report the discovery of tidal disruption event (TDE) WFST250820mmsw/AT2025wet by the 2.5-meter Wide Field Survey Telescope (WFST). It exhibits a blue nuclear flare throughout the observed evolution with a g-band peak magnitude ~22, which is about 3 magnitudes brighter than its host galaxy. A Keck/LRIS spectrum taken near the optical peak reveals a featureless blue continuum, with no discernible emission lines. However, its redshift can be accurately determined to be 1.037 by its host galaxy absorption lines. Blackbody fits to the multiband spectral energy distribution (SED) of AT2025wet yield a constant temperature of ~19,000K and a peak luminosity of (8.27 +0.92 -0.71)*10^44 erg s^-1 while actually the SED likely peaks at a much shorter wavelength than a 19,000K blackbody. The SED modeling of the host galaxy implies a stellar mass of ~10^11.2 M_odot and an estimated central black hole mass of ~10^8 M_odot, with no evidence of significant active galactic nucleus activity prior to the flare. All of these observations are well consistent with a featureless TDE scenario, making it the highest-redshift non-jetted TDE known to date. TDEs at such high redshift provide us a unique opportunity to explore the intrinsic SEDs of TDEs, particularly to test whether they peak in the extreme-UV regime, thereby addressing the missing energy puzzle and the origin of optical emission in TDEs. Ongoing surveys represented by WFST and the Legacy Survey of Space and Time (LSST) are expected to discover an increasing number of TDEs at higher redshifts, which will extend our census of SMBHs across redshift space and help unravel the mysteries of optical TDEs through direct probes of their UV emission.

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arXiv2026

An Obscured Tidal Disruption Event Uncovered by Its Mid- and Near-Infrared Dust Echo in a Star-Forming Galaxy

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 (MIRONG). Its MIR luminosity rose rapidly to a peak of $\sim5.4\times10^{43}$ \lum, maintained 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 $3σ$ upper limit of the offset of $\lesssim100$ pc. The IR spectral energy distribution (SED) of the flare is consistent with thermal emission of dust with temperatures of $\sim900$ K. Using a dust radiative transfer model, we inferred a peak UV luminosity of $\sim(4-10)\times10^{44}$ erg s$^{-1}$ and a total energy of $\sim(0.9-2)\times10^{52}$ ergs 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 (AGN). This flare stands as one of the most compelling cases to date for the emerging class of dust-obscured TDEs in recent years. They are missed by optical surveys, partly accounting for the observed bias in TDE host galaxies, and represent a crucial, yet often overlooked, component for a complete understanding of the TDE population.

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arXiv2026

Characterizing and spectrally modeling embedded FUor eruptions in the near-infrared

Context. Episodic accretion in young stellar objects (YSOs) is thought to play a critical role in addressing the "luminosity problem" associated with star formation. However, optical surveys tend to bias against sources that are heavily obscured. Infrared time-domain surveys, such as unTimely WISE, facilitate the identification of such sources within the dense star formation regions of our Galaxy. Aims. We aim to systematically identify and characterize FUor outbursts in infrared-selected YSOs using high-resolution spectroscopy and detailed disk modeling. Methods. We conducted follow-up high-resolution spectroscopy with Gemini South/IGRINS for four FUor candidates discovered in infrared time-domain surveys. Using a combination of photometric and spectroscopic observations, we constructed spectral energy distributions and fit them with a disk model that incorporates an actively accreting inner disk together with a passively irradiated outer disk. Results. All objects show CO and H$_2$O absorption bands at 2.3$μ$m, and their positions in the Na + Ca versus CO equivalent width diagram further corroborate their classification as FUors. The best-fitting model spectra closely match both the observed spectral features and the overall continuum, providing additional confirmation of the FUor classification. The best-fit models reveal high extinction values ($A_V$ = 10-20 mag), with $M_*\dot{M}$ comparable to those of classical FUors such as FU Orionis. Among 18 sources initially selected via infrared light curves, $6-$7 out of 8 with available spectra exhibit FUor characteristics, implying a high selection efficiency.

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arXiv2026

A Radio Changing-state Jet in the Narrow-line Seyfert 1 Galaxy J1105+1452

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 $1.94 \pm 0.23$ 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 $ν_{\rm p} = 0.48 \pm 0.03$ GHz and a peak flux density $S_{\rm p} = 38.9 \pm 4.7$ 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 $R \sim 0.68$ pc and an average apparent expansion velocity $β_{\rm app} \approx 0.64$. The observed brightness temperature $T_b \approx 6.0 \times 10^{11}$ K necessitates a Doppler factor $δ\approx 12$, implying a relativistic jet viewed at $θ\lesssim 5^\circ$. Despite the dramatic radio evolution, the X-ray spectrum remains stable and steep ($Γ\simeq 3.0$), 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.

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