Showing 1–50 of 114 results for author: Jiang, N

A Tidal Disruption Event from an Intermediate-mass Black Hole Revealed by Comprehensive Multi-wavelength Observations

Authors: Jialai Wang, Mengqiu Huang, Yongquan Xue, Ning Jiang, Shifeng Huang, Yibo Wang, Jiazheng Zhu, Shifu Zhu, Lixin Dai, Chichuan Jin, Bin Luo, Xinwen Shu, Mouyuan Sun, Tinggui Wang, Fan Zou

Abstract: Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a novel and 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 an extraordinary TDE at the center of a dwarf galaxy, which exhibited successive flares in the optical,… ▽ More Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a novel and 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 an extraordinary TDE at the center of a dwarf galaxy, which exhibited successive flares in the optical, X-ray, and radio bands. Notably, 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 $(1-6) \times 10^5$ 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. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: 35 pages, 10 figures

EP250827b/SN 2025wkm: An X-ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction

Authors: Gokul P. Srinivasaragavan, Dongyue Li, Xander J. Hall, Ore Gottlieb, Genevieve Schroeder, Heyang Liu, Brendan O'Connor, Chichuan Jin, Mansi Kasliwal, Tomás Ahumada, Qinyu Wu, Christopher L. Fryer, Annabelle E. Niblett, Dong Xu, Maria Edvige Ravasio, Grace Daja, Wenxiong Li, Shreya Anand, Anna Y. Q. Ho, Hui Sun, Daniel A. Perley, Lin Yan, Eric Burns, S. Bradley Cenko, Jesper Sollerman , et al. (69 additional authors not shown)

Abstract: We present the discovery of EP250827b/SN 2025wkm, an X-ray Flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at $z = 0.1194$. EP250827b possesses a prompt X-ray luminosity of $\sim 10^{45} \, \rm{erg \, s^{-1}}$, lasts over 1000 seconds, and has a peak energy $E_{\rm{p}} < 1.5$ keV at 90% confidence. SN 2025wkm possesses a double-peaked lig… ▽ More We present the discovery of EP250827b/SN 2025wkm, an X-ray Flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at $z = 0.1194$. EP250827b possesses a prompt X-ray luminosity of $\sim 10^{45} \, \rm{erg \, s^{-1}}$, lasts over 1000 seconds, and has a peak energy $E_{\rm{p}} < 1.5$ keV at 90% confidence. SN 2025wkm possesses a double-peaked light curve (LC), though its bolometric luminosity plateaus after its initial peak for $\sim 20$ days, giving evidence that a central engine is injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted Fe II and Si II broad absorption features, allowing for a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet $\gtrsim 10^{50}~$erg. In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically-driven winds from the magnetar and the disk mix together, and break out with a velocity $\sim 0.35c$ from an extended circumstellar medium with radius $\sim 10^{13}$ cm, generating X-ray breakout emission through free-free processes. The disk outflows and magnetar winds power blackbody emission as they cool, producing the first peak in the SN LC. The spin-down luminosity of the magnetar in combination with the radioactive decay of $^{56}$Ni produces the late-time SN LC. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 43 pages, 20 Figures, Submitted to ApJ Letters

Long-term Mid-infrared Color Variations of Narrow-Line Seyfert 1 Galaxies

Authors: Jiahua Wu, Huifang Xie, Liming Dou, Yanli Ai, Tinggui Wang, Xinwen Shu, Ning Jiang, Luis C. Ho, Junhui Fan

Abstract: We present a systematic investigation of long-term mid-infrared (MIR) color variability in 1,718 Narrow-Line Seyfert 1 galaxies (NLSy1s) using 14-year \textit{WISE}/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-brighte… ▽ More We present a systematic investigation of long-term mid-infrared (MIR) color variability in 1,718 Narrow-Line Seyfert 1 galaxies (NLSy1s) using 14-year \textit{WISE}/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 1,323 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 $\rm \left<W1-W2\right>$ 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 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 MIR color variations 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 non-thermal synchrotron emission from relativistic jets obscures thermal dust signatures. △ Less

Submitted 4 December, 2025; originally announced December 2025.

Comments: Accepted for publication in The Astrophysical Journal

Inefficient Circularization, Delayed Stream-Disk Interaction and Reprocessing: A Five-Stage Model for the Intermediate-Mass Black Hole Tidal Disruption Event EP240222a

Authors: Wenkai Li, Ning Jiang, Tinggui Wang, Rongfeng Shen, Erlin Qiao, Lixin Dai, Di Luo, Dongyue Li, Chichuan Jin, Jiazheng Zhu

Abstract: EP240222a is the first intermediate-mass black hole (IMBH) tidal disruption event (TDE) captured in real-time with multi-wavelength observations and spectroscopic confirmation. However, its light curves deviate substantially from previous theoretical expectations. Motivated by these unique features, we have developed a novel model that successfully reproduces its peculiar evolution. Our model deli… ▽ More EP240222a is the first intermediate-mass black hole (IMBH) tidal disruption event (TDE) captured in real-time with multi-wavelength observations and spectroscopic confirmation. However, its light curves deviate substantially from previous theoretical expectations. Motivated by these unique features, we have developed a novel model that successfully reproduces its peculiar evolution. Our model delineates five stages: (1) Initial Stage of inefficient circularization; (2) Slow-Rising Stage with a faint X-ray precursor disk fed by successive self-crossings; (3) Fast-Rising Stage, where delayed stream-disk interaction at momentum flux matching drives a sharp luminosity rise; (4) Plateau Stage with super-Eddington accretion, outflow, reprocessing, and a clear polar line-of-sight; and (5) Decline Stage of sub-Eddington accretion and ongoing reprocessing. Our fit indicates the disruption of a $M_* \approx 0.4~M_\odot$ main-sequence (MS) star with a penetration factor $β\approx 1.0$. Our model, which incorporates key TDE processes, establishes EP240222a-like light curves as typical IMBH-TDE signatures. The distinctive identifier is a slow rise in X-rays and a corresponding slow rise/quasi-plateau in the UV/optical, followed by a brighter, super-Eddington plateau in both bands, though other forms exist, such as the rapid rise from white dwarf (WD) disruptions over minutes to days. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Comments: to be submitted, comments are welcome

The Faintest, Extremely Variable X-ray Tidal Disruption Event from a Supermassive Black Hole Binary?

Authors: Mengqiu Huang, Yongquan Xue, Shuo Li, Fukun Liu, Shifu Zhu, Jin-Hong Chen, Rong-Feng Shen, Yibo Wang, Yi Yang, Ning Jiang, Franz Erik Bauer, Cristian Vignali, Fan Zou, Jialai Wang, Alexei V. Filippenko, Bin Luo, Chen Qin, Jonathan Quirola-Vásquez, Jun-Xian Wang, Lulu Fan, Mouyuan Sun, Qingwen Wu, Qingling Ni, Thomas G. Brink, Tinggui Wang , et al. (8 additional authors not shown)

Abstract: Tidal disruption events (TDEs), which occur when stars enter the tidal radii of supermassive black holes (SMBHs) and are subsequently torn apart by their tidal forces, represent intriguing phenomena that stimulate growing research interest and pose an increasing number of puzzles in the era of time-domain astronomy. Here we report an unusual X-ray transient, XID 935, discovered in the 7 Ms Chandra… ▽ More Tidal disruption events (TDEs), which occur when stars enter the tidal radii of supermassive black holes (SMBHs) and are subsequently torn apart by their tidal forces, represent intriguing phenomena that stimulate growing research interest and pose an increasing number of puzzles in the era of time-domain astronomy. Here we report an unusual X-ray transient, XID 935, discovered in the 7 Ms Chandra Deep Field-South, the deepest X-ray survey ever. XID 935 experienced an overall X-ray dimming by a factor of more than 40 between 1999 and 2016. Not monotonically decreasing during this period, its X-ray luminosity increased by a factor $> 27$ within 2 months, from $L_{\rm 0.5-7\ keV}<10^{40.87}$ erg s$^{-1}$ (10 October 2014 -- 4 January 2015) to $L_{\rm 0.5-7\ keV}=10^{42.31\pm 0.20}$ erg s$^{-1}$ (16 March 2015). The X-ray position of XID 935 is located at the center of its host galaxy with a spectroscopic redshift of 0.251, whose optical spectra do not display emission characteristics associated with an active galactic nucleus. The peak 0.5--2.0 keV flux is the faintest among all the X-ray-selected TDE candidates to date. Thanks to a total exposure of $\sim 9.5$ Ms in the X-ray bands, we manage to secure relatively well-sampled, 20-year-long X-ray light curves of this deepest X-ray-selected TDE candidate. We find that a partial TDE model could not explain the main declining trend. An SMBH binary TDE model is in acceptable accordance with the light curves of XID 935; however, it fails to match short-timescale fluctuations exactly. Therefore, the exceptional observational features of XID 935 provide a key benchmark for refining quantitative TDE models and simulations. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Comments: 31 pages, 6 figures, 1 table, accepted by The Innovation

Journal ref: The Innovation 7(3), 101169 (2026)

Searching for Electromagnetic Counterpart Candidates to GW231123

Authors: Lei He, Liang-Gui Zhu, Zheng-Yan Liu, Rui Niu, Chao Wei, Bing-Zhou Gao, Ming-Shen Zhou, Run-Duo Liang, Ken Chen, Jian-Min Wang, Ning Jiang, Zhen-Yi Cai, Ji-an Jiang, Zi-Gao Dai, Ye-Fei Yuan, Jian Li, Wen Zhao

Abstract: The detection of GW231123, a gravitational-wave (GW) event with exceptionally massive and rapidly spinning black holes, suggests the possible formation within an active galactic nucleus (AGN) disk, which provides a favorable environment for potentially generating an observable electromagnetic (EM) counterpart. We conduct a search for such a counterpart by crossmatching the GW localization with a c… ▽ More The detection of GW231123, a gravitational-wave (GW) event with exceptionally massive and rapidly spinning black holes, suggests the possible formation within an active galactic nucleus (AGN) disk, which provides a favorable environment for potentially generating an observable electromagnetic (EM) counterpart. We conduct a search for such a counterpart by crossmatching the GW localization with a comprehensive catalog of AGN flares from the Zwicky Transient Facility. Our analysis yields six plausible optical flare candidates that are spatially and temporally coincident with GW231123 and exhibit significant deviations from their AGN baseline flux. Although these candidates represent a crucial first step, their true nature remains inconclusive. Confirming any one of these flares via future observations would provide a landmark validation of the AGN formation channel and unlock the multi-messenger potential of this extraordinary merger. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 10 pages, 3 figures, comments are welcome

A Star's Death by a Thousand Cuts: The Runaway Periodic Eruptions of AT2023uqm

Authors: Yibo Wang, Tingui Wang, Shifeng Huang, Jiazheng Zhu, Ning Jiang, Wenbin Lu, Rongfeng Shen, Shiyan Zhong, Dong Lai, Yi Yang, Xinwen Shu, Tianyu Xia, Di Luo, Jianwei Lyu, Thomas Brink, Alex Filippenko, Weikang Zheng, Minxuan Cai, Zelin Xu, Mingxin Wu, Xiaer Zhang, Weiyu Wu, Lulu Fan, Ji-an Jiang, Xu Kong , et al. (15 additional authors not shown)

Abstract: Stars on bound orbits around a supermassive black hole may undergo repeated 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… ▽ More Stars on bound orbits around a supermassive black hole may undergo repeated 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. △ Less

Submitted 30 October, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: Submitted. Comments are welcome

Joint Analysis of Optical, Near-Infrared And Mid-Infrared Variability of 4 Quasars at Redshift < 1

Authors: Lin Long, Zhen-ya Zheng, Ning Jiang, Chun Xu, Jiaqi Lin, Fang-Ting Yuan, Chunyan Jiang, Ruqiu Lin, Hai-Cheng Feng, Hengxiao Guo, Xiang Ji

Abstract: Amid rapid advances in time-domain astronomy, multi-wavelength (e.g., optical and infrared) time-domain studies of quasars remain scarce. Here we present a systematic analysis of four quasars initially selected by their Ks-band variability amplitudes in the VISTA Variables in the Vía Láctea Survey (VVV/VVVX). For these objects, we obtain complementary optical light curves from Pan-STARRS1 (PS1) an… ▽ More Amid rapid advances in time-domain astronomy, multi-wavelength (e.g., optical and infrared) time-domain studies of quasars remain scarce. Here we present a systematic analysis of four quasars initially selected by their Ks-band variability amplitudes in the VISTA Variables in the Vía Láctea Survey (VVV/VVVX). For these objects, we obtain complementary optical light curves from Pan-STARRS1 (PS1) and the Zwicky Transient Facility (ZTF), and W1-band light curves from the Wide-field Infrared Survey Explorer (WISE). We perform correlation analysis to study the time lags between different bands, which may be directly related to the size of the dust torus. After correcting for infrared flux contamination from the accretion disk and accounting for the redshift effect, we measure the Ks-optical and W1-optical lags for the targets VVV J1834-2925 and VVV J1845-2426. Using typical sublimation temperatures and reverberation time lags, we obtain a graphite-to-silicate grain size ratio of $\frac{a_C}{a_S}\sim$ 0.4. Through SED fitting, we determine the luminosities of these quasars and find that their dust torus sizes follow the established $R_{dust}-L_{AGN}$ relation reported in previous studies. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions

Authors: Jiazheng Zhu, Ning Jiang, Yibo Wang, Tinggui Wang, Luming Sun, Shiyan Zhong, Yuhan Yao, Ryan Chornock, Lixin Dai, Jianwei Lyu, Xinwen Shu, Christoffer Fremling, Erica Hammerstein, Shifeng Huang, Wenkai Li, Bei You

Abstract: X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader… ▽ More X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader formation channels for QPEs. To further investigate Ansky's nature, we obtained a timely ultraviolet (UV) spectrum, which reveals a featureless, TDE-like spectrum devoid of broad optical or UV emission lines. Additionally, the steep UV continuum, fitted by a power law with an index of -2.6, aligns more closely with TDEs than with AGNs. Compared to other featureless TDEs, Ansky exhibits a significantly lower blackbody luminosity (10^43 erg s^-1) and much longer rise and decay timescales, suggesting a distinct TDE subclass. An offset TDE involving an intermediate-mass black hole is unlikely, given its position consistent with the galactic center with a 3 sigma upper limit of 54 pc. Instead, we propose that Ansky may result from the tidal disruption of a post-main-sequence star by a typical supermassive black hole. Our findings strengthen the growing evidence for TDE-QPE associations, although other formation channels for QPEs remain plausible and await future observational efforts. △ Less

Submitted 25 November, 2025; v1 submitted 25 October, 2025; originally announced October 2025.

Comments: 14 pages, 9 figures, Published in ApJL

Journal ref: ApJL 994 L16 (2025)

A fast powerful X-ray transient from possible tidal disruption of a white dwarf

Authors: Dongyue Li, Wenda Zhang, Jun Yang, Jin-Hong Chen, Weimin Yuan, Huaqing Cheng, Fan Xu, Xinwen Shu, Rong-Feng Shen, Ning Jiang, Jiazheng Zhu, Chang Zhou, Weihua Lei, Hui Sun, Chichuan Jin, Lixin Dai, Bing Zhang, Yu-Han Yang, Wenjie Zhang, Hua Feng, Bifang Liu, Hongyan Zhou, Haiwu Pan, Mingjun Liu, Stephane Corbel , et al. (75 additional authors not shown)

Abstract: Stars captured by black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser--and theref… ▽ More Stars captured by black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser--and therefore tougher--than gaseous stars, can only be disrupted by intermediate-mass black holes (IMBHs) of 10^2--10^5 solar masses. WD-TDEs are considered to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe. Its one-day-long X-ray peak as luminous as 10^(47-49) erg/s showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays, as detected by Fermi/GBM and Konus-Wind, indicating relativistic jet emission. The jet's X-ray dropped sharply from 3 x 10^49 erg/s to around 10^44 erg/s within 20 days (10 days in the source rest frame). These characteristics are inconsistent with any known transient phenomena other than a jetted-TDE evolving over an unprecedentedly short timescale, indicating the disruption of a WD by an IMBH. At late times, a new soft component progressively dominates the X-ray spectrum, exhibiting an extreme super-Eddington luminosity, which possibly originates from an accretion disc. WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments, and they are prime sources of gravitational waves in the band of space-based interferometers. △ Less

Submitted 23 December, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: submitted on 19 October 2025, accepted for publication in Science Bulletin on 12 December 2025

Outflow-cloud interaction as the possible origin of the peculiar radio emission in the tidal disruption event AT2018cqh

Authors: Lei Yang, Xinwen Shu, Guobin Mou, Yongquan Xue, Luming Sun, Fabao Zhang, Zhumao Zhang, Yibo Wang, Tao Wu, Ning Jiang, Hucheng Ding, Tinggui Wang

Abstract: AT2018cqh is a unique optical tidal disruption event (TDE) discovered in a dwarf galaxy exhibiting delayed X-ray and radio flares. We present the results from high-resolution VLBA and e-MERLIN radio observations of AT2018cqh extending to $δ$t $\sim$ 2250 days post discovery, which reveal a compact radio emission, unresolved at a scale of <~ 0.13 pc at 7.6 GHz, with a high brightness temperature of… ▽ More AT2018cqh is a unique optical tidal disruption event (TDE) discovered in a dwarf galaxy exhibiting delayed X-ray and radio flares. We present the results from high-resolution VLBA and e-MERLIN radio observations of AT2018cqh extending to $δ$t $\sim$ 2250 days post discovery, which reveal a compact radio emission, unresolved at a scale of <~ 0.13 pc at 7.6 GHz, with a high brightness temperature of $T_b$ ~> 4.03 $\times$ 10$^{9}$ K. The radio spectral energy distribution (SED) is found to gradually shift towards a higher peak flux density and frequency over a period of $\sim$1000 days. An equipartition analysis suggests that there is a little change in the radio emitting region over this period, while the electron density increases by a factor of 3. The radio light curve at 0.89 GHz continues to rise, with a bump feature lasting for 240 days. These properties are in contrast to the predictions of standard shockwave model from a diffuse circumnuclear medium, but could be explained if dense clouds exist in the circumnuclear environment. The latter scenario is supported by our hydrodynamic simulations of the interaction of TDE outflow with a cloud, which can reproduce the temporal evolution in the radio SED. This work highlights the importance of the outflow-cloud interaction in explaining the delayed, fast-rising radio emission observed in some TDEs, especially those occurring in galaxies with pre-existing AGN activity. △ Less

Submitted 25 September, 2025; v1 submitted 25 September, 2025; originally announced September 2025.

Comments: 12 pages, 6 figures, accepted for publication in ApJL; v2: corrected an author's name

A Systematic Search for AGN Flares in ZTF Data Release 23

Authors: Lei He, Zheng-Yan Liu, Rui Niu, Ming-Shen Zhou, Pu-Run Zou, Bing-Zhou Gao, Run-Duo Liang, Liang-Gui Zhu, Jian-Min Wang, Ning Jiang, Zhen-Yi Cai, Ji-an Jiang, Zi-Gao Dai, Ye-Fei Yuan, Yong-Jie Chen, Wen Zhao

Abstract: Active galactic nuclei (AGNs) are known to exhibit stochastic variability across a wide range of timescales and wavelengths. AGN flares are extreme outbursts that deviate from this typical behavior and may trace a range of energetic physical processes. Using six years of data from Zwicky Transient Facility (ZTF) Data Release 23, we conduct a systematic search for AGN flares among a sample of well-… ▽ More Active galactic nuclei (AGNs) are known to exhibit stochastic variability across a wide range of timescales and wavelengths. AGN flares are extreme outbursts that deviate from this typical behavior and may trace a range of energetic physical processes. Using six years of data from Zwicky Transient Facility (ZTF) Data Release 23, we conduct a systematic search for AGN flares among a sample of well-sampled AGNs and AGN candidates. We construct two catalogs: the AGN Flare Coarse Catalog (AGNFCC), containing 28,504 flares identified via Bayesian blocks and Gaussian Processes, and the AGN Flare Refined Catalog (AGNFRC), comprising 1,984 high-confidence flares selected using stricter criteria. We analyze their spatial distribution, temporal characteristics, host AGN type and potential origins. Some flares can be associated with known supernovae, tidal disruption events, or blazars, and a few may be linked to binary black hole mergers or microlensing events. These catalogs provide a valuable resource for studying transient phenomena in AGNs and are publicly available at https://github.com/Lyle0831/AGN-Flares. △ Less

Submitted 5 November, 2025; v1 submitted 27 July, 2025; originally announced July 2025.

Comments: 20 pages, 18 figures, accepted for publication in ApJS

A Torus Remnant Revealed by the Infrared Echo of Tidal Disruption Event AT 2019qiz: Implications for the Missing Energy and Quasiperiodic Eruption Formation

Authors: Mingxin Wu, Ning Jiang, Jiazheng Zhu, Di Luo, Liming Dou, Tinggui Wang

Abstract: AT 2019qiz is the first standard optical tidal disruption event (TDE) with detection of X-ray quasi-periodic eruptions (QPEs), providing strong evidence for TDE-QPE association. Moreover, it belongs to the rare subset of optical TDEs with prominent infrared (IR) echoes revealed by the multi-epoch photometry from the Wide-field Infrared Survey Explorer (WISE). The IR light curve shows an early bump… ▽ More AT 2019qiz is the first standard optical tidal disruption event (TDE) with detection of X-ray quasi-periodic eruptions (QPEs), providing strong evidence for TDE-QPE association. Moreover, it belongs to the rare subset of optical TDEs with prominent infrared (IR) echoes revealed by the multi-epoch photometry from the Wide-field Infrared Survey Explorer (WISE). The IR light curve shows an early bump, followed by a steady rise until the second-to-last epoch, after which it appears to enter a plateau phase. The dust temperature decreased until the fourth epoch and remains approximately constant for the subsequent five epochs. We have fitted the last five epochs using a convex dust ring model, resulting in an inner radius $>1.2$pc. Such a large radius greatly exceeds the inner radius of the active galactic nuclei (AGN) torus for a $10^6\,M_{\odot}$ black hole and thus could be a torus remnant with the inner part having vanished, further supporting the unified scenario of recently faded AGNs, TDEs, and QPEs. Consequently, a connection between QPEs and IR-bright TDEs is naturally expected. Moreover, the echo requires at least a peak bolometric luminosity of $(6.6, 9.5, 1.0)\times 10^{44} \,\text{erg}\,\text{s}^{-1}$ assuming silicate, silicon carbide, and graphite dust grains, respectively, all of which are significantly higher than the peak optical blackbody luminosity. It adds to the accumulating evidence that the missing energy of TDEs may lie in the unobservable extreme UV. This work highlights the unique value of IR echoes in the study of TDEs and QPEs, and a promising prospect in the era of the Near-Earth Object (NEO) Surveyor, the successor to WISE. △ Less

Submitted 1 August, 2025; v1 submitted 17 July, 2025; originally announced July 2025.

Comments: Publication in ApJL (988,L77). 1 Table and 11 Figure

Insights from the "Red devil" AT 2022fpx: A Dust-reddened Family of Tidal Disruption Events Excluded by Their Apparent Red Color?

Authors: Zheyu Lin, Ning Jiang, Yibo Wang, Xu Kong, Shifeng Huang, Zesen Lin, Chen Qin, Tianyu Xia

Abstract: We report unnoticed but intriguing features in the peculiar nuclear transient AT 2022fpx, and investigate its type. These features include the constantly red optical color of $g-r>0$, a stable soft X-ray flare ($kT\sim100$ eV) in the past $\sim$550 days, a prominent mid-infrared echo peaked at $\sim$$10^{43.3}$ erg s$^{-1}$ and the confirmation of a weak active galactic nucleus by weak flares in p… ▽ More We report unnoticed but intriguing features in the peculiar nuclear transient AT 2022fpx, and investigate its type. These features include the constantly red optical color of $g-r>0$, a stable soft X-ray flare ($kT\sim100$ eV) in the past $\sim$550 days, a prominent mid-infrared echo peaked at $\sim$$10^{43.3}$ erg s$^{-1}$ and the confirmation of a weak active galactic nucleus by weak flares in pre-event Wide-field Infrared Survey Explorer mid-infrared light curves with no contemporary optical, radio or X-ray counterparts. The combination of the optical red color and possible origin of a tidal disruption event (TDE) of AT 2022fpx is particularly attractive, as it challenges the most widely accepted and adopted "blue color" criterion for optical TDE selection. Although we still cannot confirm whether the red color is intrinsic, we do find that the "blue color" criterion can filter out normal TDEs whose optical-UV spectral energy distributions (SEDs) are either severely contaminated by prominent emission lines (especially H$α$) or heavily dust-reddened. Hence, its potential selection effect may have been imprinted on the whole optical TDE family. Blackbody fitting on the optical (rest-frame $\sim$$4000-7000$ Å) and optical-UV ($\sim$$2000-7000$ Å) SEDs of four TDEs with high-cadence UV observations shows that $T_\mathrm{bb}$ rise by $\sim$40$-$110 \% when the UV bands are included. The power-law models ($f_λ\proptoλ^{-α}$ with $α=2-3$) can fit the rest-frame $\sim$$2000-7000$ ÅSEDs more consistently, indicating that SEDs should peak at shorter wavelengths, but not simple blackbodies. Hence, the estimated released energy for the optical-UV bright but X-ray faint TDEs based on blackbody SED fitting should be significantly lower than the intrinsic energy. △ Less

Submitted 5 September, 2025; v1 submitted 7 July, 2025; originally announced July 2025.

Comments: 22 pages, 10 figures, 3 tables, accepted by ApJ

Journal ref: ApJ 990 22 (2025)

Introduction to the Chinese Space Station Survey Telescope (CSST)

Authors: CSST Collaboration, Yan Gong, Haitao Miao, Hu Zhan, Zhao-Yu Li, Jinyi Shangguan, Haining Li, Chao Liu, Xuefei Chen, Haibo Yuan, Jilin Zhou, Hui-Gen Liu, Cong Yu, Jianghui Ji, Zhaoxiang Qi, Jiacheng Liu, Zigao Dai, Xiaofeng Wang, Zhenya Zheng, Lei Hao, Jiangpei Dou, Yiping Ao, Zhenhui Lin, Kun Zhang, Wei Wang , et al. (97 additional authors not shown)

Abstract: The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific inst… ▽ More The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific instruments, i.e. Multi-band Imaging and Slitless Spectroscopy Survey Camera (SC), Multi-Channel Imager (MCI), Integral Field Spectrograph (IFS), Cool Planet Imaging Coronagraph (CPI-C), and THz Spectrometer (TS). Using these instruments, CSST is expected to make significant contributions and discoveries across various astronomical fields, including cosmology, galaxies and active galactic nuclei (AGN), the Milky Way and nearby galaxies, stars, exoplanets, Solar System objects, astrometry, and transients and variable sources. This review aims to provide a comprehensive overview of the CSST instruments, observational capabilities, data products, and scientific potential. △ Less

Submitted 19 September, 2025; v1 submitted 6 July, 2025; originally announced July 2025.

Comments: 48 pages, 12 figures, 1 table. Accepted for publication in SCIENCE CHINA Physics, Mechanics & Astronomy

Tracing the light: Identification for the optical counterpart candidates of binary black-holes during O3

Authors: Lei He, Zhengyan Liu, Rui Niu, Bingzhou Gao, Mingshen Zhou, Purun Zou, Runduo Liang, Wen Zhao, Ning Jiang, Zhen-Yi Cai, Zi-Gao Dai, Ye-Fei Yuan

Abstract: The accretion disks of active galactic nuclei (AGN) are widely considered the ideal environments for binary black hole (BBH) mergers and the only plausible sites for their electromagnetic (EM) counterparts. Graham et al.(2023) identified seven AGN flares that are potentially associated with gravitational-wave (GW) events detected by the LIGO-Virgo-KAGRA (LVK) Collaboration during the third observi… ▽ More The accretion disks of active galactic nuclei (AGN) are widely considered the ideal environments for binary black hole (BBH) mergers and the only plausible sites for their electromagnetic (EM) counterparts. Graham et al.(2023) identified seven AGN flares that are potentially associated with gravitational-wave (GW) events detected by the LIGO-Virgo-KAGRA (LVK) Collaboration during the third observing run. In this article, utilizing an additional three years of Zwicky Transient Facility (ZTF) public data after their discovery, we conduct an updated analysis and find that only three flares can be identified. By implementing a joint analysis of optical and GW data through a Bayesian framework, we find two flares exhibit a strong correlation with GW events, with no secondary flares observed in their host AGN up to 2024 October 31. Combining these two most robust associations, we derive a Hubble constant measurement of $H_{0}= 72.1^{+23.9}_{-23.1} \ \mathrm{km \ s^{-1} Mpc^{-1}}$ and incorporating the multi-messenger event GW170817 improves the precision to $H_{0}=73.5^{+9.8}_{-6.9} \ \mathrm{km \ s^{-1} Mpc^{-1}}$. Both results are consistent with existing measurements reported in the literature. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Comments: 16 pages, 5 figures, accepted for publication in ApJ

Unveiling the Cosmic Dance of Repeated Nuclear Transient ASASSN-14ko: Insights from Multiwavelength Observations

Authors: Shifeng Huang, Tinggui Wang, Ning Jiang, Rong-Feng Shen, Zhaohao Chen, Yuanming Wang, Jiazheng Zhu, Yibo Wang, Yunguo Jiang, Xinwen Shu, Hucheng Ding, Xiongjun Fang, Yifan Wang, Jie Lin, Jingran Xu, Xu Chen, Zheyu Lin, Zhengfeng Sheng

Abstract: ASASSN-14ko is a periodically repeating nuclear transient. We conducted high-cadence, multiwavelength observations of this source, revealing several recurrent early bumps and rebrightenings in its UV/optical light curves. The energy released during these bumps and rebrightenings shows a diminishing trend in recent UV/optical outbursts, which we monitored through multiwavelength observations. These… ▽ More ASASSN-14ko is a periodically repeating nuclear transient. We conducted high-cadence, multiwavelength observations of this source, revealing several recurrent early bumps and rebrightenings in its UV/optical light curves. The energy released during these bumps and rebrightenings shows a diminishing trend in recent UV/optical outbursts, which we monitored through multiwavelength observations. These features can be ascribed to the interaction between stream debris and the expanded disk in the repeated partial tidal disruption event. The X-ray light curve exhibits an inverse pattern compared to the UV/optical bands, displaying sporadic outbursts. Furthermore, our observations demonstrate that the blackbody temperature and radius in each outburst increase with the UV/optical luminosity, and such evolution resembles that observed in X-ray quasiperiodic eruptions, whereas distinguishing it from typical tidal disruption events. △ Less

Submitted 17 June, 2025; originally announced June 2025.

Comments: Accepted for publication in ApJ, 16 pages, 10 figures

Prospects for Time-Domain and Multi-Messenger Science with eXTP

Authors: Shu-Xu Yi, Wen Zhao, Ren-Xin Xu, Xue-Feng Wu, Giulia Stratta, Simone Dall'Osso, Yan-Jun Xu, Andrea Santangelo, Silvia Zane, Shuang-Nan Zhang, Hua Feng, Huan Yang, Junjie Mao, Junqiang Ge, Lijing Shao, Mi-Xiang Lan, He Gao, Lin Lin, Ning Jiang, Qingwen Wu, Tong Liu, Yun-Wei Yu, Xiang-Yu Wang, Jin Zhang, Dafne Guetta , et al. (53 additional authors not shown)

Abstract: In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including a… ▽ More In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology. △ Less

Submitted 8 September, 2025; v1 submitted 9 June, 2025; originally announced June 2025.

Comments: accepted for publication in the SCIENCE CHINA Physics, Mechanics & Astronomy

Early evolution of super-Eddington accretion flow in tidal disruption events

Authors: Erlin Qiao, Yongxin Wu, Yiyang Lin, Meng Guo, Jifeng Liu, Chenlei Guo, Chichuan Jin, Ning Jiang

Abstract: Tidal disruption events (TDEs) are luminous black hole (BH) transient sources, which are detected mainly in X-ray and optical bands. It is generally believed that the X-ray emission in TDEs is produced by an accretion disc formed as the stellar debris accreted onto the central BH. The origin of the optical emission is not determined, but could be explained by the `reprocessing' model with the X-ra… ▽ More Tidal disruption events (TDEs) are luminous black hole (BH) transient sources, which are detected mainly in X-ray and optical bands. It is generally believed that the X-ray emission in TDEs is produced by an accretion disc formed as the stellar debris accreted onto the central BH. The origin of the optical emission is not determined, but could be explained by the `reprocessing' model with the X-ray emission reprocessed into optical band by a surrounding optically thick envelope or outflow. In this paper, we performed radiation hydrodynamic simulations of super-Eddington accretion flow with Athena++ code in the environment of TDEs, i.e., injecting a continuous mass flow rate at the circularization radius in the form of $\dot M_{\rm inject} \propto t^{-5/3}$ for the mass supply rate. We show that a significant fraction of the matter in the accretion inflow are blowed off forming outflow, and the properties of the outflow are viewing-angle dependent. We further calculate the emergent spectra of such an inflow/outflow system for different viewing angles with the method of Monto Carlo radiative transfer. Based on the emergent spectra, we show that the observed features of TDEs, such as the X-ray and optical luminosities, the blackbody temperature of X-ray and optical emission and the corresponding emission radii, the ratio of X-ray luminosity to optical luminosity, as well as the evolution of these quantities can be explained in the framework of viewing-angle effect of super-Eddington accretion around a BH. △ Less

Submitted 5 May, 2025; originally announced May 2025.

Comments: 18 pages, 45 figures, accepted for publication by MNRAS

Dynamical Measurement of Supermassive Black Hole Masses: QPE Timing Method

Authors: Cong Zhou, Zhen Pan, Ning Jiang, Wen Zhao

Abstract: Quasi-periodic eruptions (QPEs) are intense repeating soft X-ray bursts with recurrence times about a few hours to a few weeks from galactic nuclei. More and more analyses show that (at least a fraction of) QPEs are the result of collisions between a stellar mass object (SMO, a stellar mass black hole or a main sequence star) and an accretion disk around a supermassive black hole (SMBH) in galacti… ▽ More Quasi-periodic eruptions (QPEs) are intense repeating soft X-ray bursts with recurrence times about a few hours to a few weeks from galactic nuclei. More and more analyses show that (at least a fraction of) QPEs are the result of collisions between a stellar mass object (SMO, a stellar mass black hole or a main sequence star) and an accretion disk around a supermassive black hole (SMBH) in galactic nuclei. Previous studies have shown the possibility of reconstructing the SMO trajectory from QPE timing data, consequently measuring the SMBH mass from tracing a single SMO. In this paper, we construct a comprehensive Bayesian framework for implementing the QPE timing method, explore the optimal QPE observation strategy for measuring SMBH masses, and forecast the measurement precision expected in the era of multi-target X-ray telescope, Chasing All Transients Constellation Hunters (CATCH). Simulations of CATCH observations of GSN 069 and eRO-QPE2 like QPEs confirm the possible applications of the QPE timing method in precise measurement of SMBH masses (and spins), especially in the lower mass end ($\lesssim 10^7 M_\odot$) where QPEs prevail and relevant dynamical timescales are reasonably short to be measured. △ Less

Submitted 15 September, 2025; v1 submitted 15 April, 2025; originally announced April 2025.

Comments: 18 pages, 14 figures

Journal ref: MNRAS. 543, 1816 (2025)

Infant Core-collapse Supernovae with Circumstellar Interactions from KMTNet I: Luminous Transitional Case of KSP-SN-2022c

Authors: Nan Jiang, Dae-Sik Moon, Yuan Qi Ni, Maria R. Drout, Hong Soo Park, Santiago González-Gaitán, Sang Chul Kim, Youngdae Lee, Ernest Chang

Abstract: We present $BVi$ multi-band high-cadence observations of a Type II supernova (SN) KSP-SN-2022c from a star-forming galaxy at $z$ $\simeq$ 0.041 from its infant to nebular phase. Early light curve fitting with a single power-law is consistent with the first detection of roughly 15 minutes after shock breakout. The SN light curves feature a rapid rise and decline across its luminous ($V$ $\simeq$ -1… ▽ More We present $BVi$ multi-band high-cadence observations of a Type II supernova (SN) KSP-SN-2022c from a star-forming galaxy at $z$ $\simeq$ 0.041 from its infant to nebular phase. Early light curve fitting with a single power-law is consistent with the first detection of roughly 15 minutes after shock breakout. The SN light curves feature a rapid rise and decline across its luminous ($V$ $\simeq$ -18.41 mag) peak together with a short plateau. The presence of the short plateau and rapid post-peak decline place the SN within a small group of transitional type between Type II-P and II-L subtypes. Its (i) broad and asymmetric H profiles with large emission-to-absorption ratios and (ii) near-peak luminosity in excess of predictions from SN shock cooling models both point to circumstellar interactions in this SN. Early colour evolution exhibits a short-lived blueward motion in $B-V$ within the first few days and continuous reddening in $V-i$, inconsistent with simple blackbody heating. Our simulations of SN light curves estimate 13 $M_\odot$ and 680 $R_\odot$ for the mass and radius of the progenitor, respectively, together with CSM of 0.73 $M_\odot$ to account for the excess luminosity and rapid post-peak declines. We discuss the origin of its short plateau and early colour evolution in the context of partial envelope stripping of the progenitor star and a delayed SN shock breakout near the edge of the CSM, respectively, as indicated by our simulations. We establish a correlation between post-peak decline rates and CSM mass in Type II SNe, highlighting that CSM interactions play a major role in shaping the post-peak evolution of transitional types. △ Less

Submitted 29 March, 2025; originally announced March 2025.

Comments: Submitted to ApJ

Extended Emission-line Region in a Poststarburst Galaxy Hosting Tidal Disruption Event AT2019qiz and Quasiperiodic Eruptions

Authors: Yifei Xiong, Ning Jiang, Zhen Pan, Lei Hao, Zhenzhen Li

Abstract: We present a comprehensive analysis of the extended emission line region (EELR) in the host galaxy of the tidal disruption event (TDE) AT2019qiz, utilizing VLT/MUSE integral-field spectroscopy. The high spatial-resolution data reveal a bi-conical emission structure approximately $3.7~\mathrm{kpc}$ in scale within the galactic center, characterized by a prominent [OIII] line in the nucleus and sign… ▽ More We present a comprehensive analysis of the extended emission line region (EELR) in the host galaxy of the tidal disruption event (TDE) AT2019qiz, utilizing VLT/MUSE integral-field spectroscopy. The high spatial-resolution data reveal a bi-conical emission structure approximately $3.7~\mathrm{kpc}$ in scale within the galactic center, characterized by a prominent [OIII] line in the nucleus and significant [NII] line emission extending into the EELR. Spectral analysis of the EELR indicates line ratios consistent with Seyfert ionization in the center and LINER-type ionization in the outer diffuse region, suggesting ionization from galactic nuclear activity. The required ionizing luminosity, estimated from the H$\rmα$ and H$\rmβ$ luminosities based on the photoionization and recombination balance assumption, is $10^{41.8}$ $\mathrm{erg\,s^{-1}}$ for all spaxels classified as active galactic nucleus (AGN), and $10^{40.7}$ $\mathrm{erg\,s^{-1}}$ for spaxels in the central $0.9~\mathrm{kpc}$ Seyfert region. However, the current bolometric luminosity of the nucleus $L_{\text{bol}} \leq 10^{40.8}\,\mathrm{erg\,s^{-1}}$, estimated from quiescent-state soft X-ray observations, is insufficient to ionize the entire EELR, implying a recently faded AGN or a delayed response to historical activity. Stellar population analysis reveals a post-starburst characteristic in the EELR, and the gas kinematics show disturbances and non-circular components compared to the stellar kinematics. Notably, the recent detection of quasi-periodic eruptions (QPEs) in the X-ray light curve of AT2019qiz confirms the TDE-QPE association. Our findings provide direct evidence for an AGN-like EELR in the host galaxy of the nearest TDE with QPE detection, offering new insights into the complex interplay between TDEs, QPEs, AGN activity, and host galaxy evolution. △ Less

Submitted 11 August, 2025; v1 submitted 25 March, 2025; originally announced March 2025.

Comments: Publication in ApJ (989,49),17 pages, 11 figures

Journal ref: The Astrophysical Journal, 2025, 989(1): 49

Embers of Active Galactic Nuclei: Tidal Disruption Events and Quasiperiodic Eruptions

Authors: Ning Jiang, Zhen Pan

Abstract: Recent observations have confirmed the direct association between tidal disruption events (TDEs) and quasiperiodic eruptions (QPEs). In addition, TDE hosts and QPE hosts are statistically found to be similar in their morphological properties and in the strong overrepresentation of poststarburst galaxies. Particularly, both of them show an intriguing preference for extending emission line regions (… ▽ More Recent observations have confirmed the direct association between tidal disruption events (TDEs) and quasiperiodic eruptions (QPEs). In addition, TDE hosts and QPE hosts are statistically found to be similar in their morphological properties and in the strong overrepresentation of poststarburst galaxies. Particularly, both of them show an intriguing preference for extending emission line regions (EELRs), which are indicative of recently faded active galactic nuclei (AGNs). This further suggests that QPEs might be produced following TDEs involving supermassive black holes at a particular stage, when the AGN activity has recently ceased. Moreover, in the framework of "QPEs=extreme mass ratio inspiral (EMRI) + accretion disk" model, a large fraction of QPE EMRIs are inferred to be quasi-circular from the QPE timing, indicating that they are wet EMRIs that were formed in the AGN disk during a previous AGN phase. Based on these facts, we propose a unified scenario that connects these three phenomena: AGN activities boost both the TDE rate and the formation rate of low-eccentricity EMRIs, consequently TDEs are preferentially found in recently faded AGNs instead of in ongoing AGNs due to selection effects, and QPEs are also preferentially found in recently faded AGNs where TDEs frequently feed a misaligned accretion disk to the EMRI. △ Less

Submitted 14 April, 2025; v1 submitted 21 March, 2025; originally announced March 2025.

Comments: Publication in ApJL (983,L18). 2 Tables and 1 Figure

Distinguishing Tidal Disruption Events and Changing-look Active Galactic Nuclei via Variation of Mid-infrared Color

Authors: Yujun Yao, Jingjing Ye, Luming Sun, Ning Jiang, Megan Masterson, Xinwen Shu

Abstract: At present, there is a lack of effective probes to distinguish between mid-infrared (MIR) outbursts induced by tidal disruption events (TDEs) and changing-look active galactic nuclei (CLAGNs) based on only MIR data. Here, we propose that the time variation of MIR color (K-corrected W1-W2 after subtracting the quiescent fluxes) is a promising probe. With an optically selected sample containing TDEs… ▽ More At present, there is a lack of effective probes to distinguish between mid-infrared (MIR) outbursts induced by tidal disruption events (TDEs) and changing-look active galactic nuclei (CLAGNs) based on only MIR data. Here, we propose that the time variation of MIR color (K-corrected W1-W2 after subtracting the quiescent fluxes) is a promising probe. With an optically selected sample containing TDEs, ambiguous nuclear transients (ANTs), and CLAGNs, we studied the MIR color variation of their MIR counterparts using NEOWISE-R data. We found that the MIR color of TDEs and ANTs turns red faster than CLAGNs during the rising phase, and TDEs have a redder color than ANTs at the earliest phase. The former may be caused by the difference between the ultraviolet light curves of TDEs/ANTs and CLAGNs, or be related to no or relatively weak underlying AGN in TDEs/ANTs, while the latter may be related to the difference in the dust geometry. Based on color variation rate, we selected high-probability TDE, ANT, and CLAGN candidates from MIR outbursts in samples of Jiang et al. (2021) and Masterson et al. (2024). We found that both samples are mixtures of TDEs/ANTs and CLAGNs. For MIR outbursts whose hosts are not Seyfert galaxies, we estimated that $\sim50\%-80\%$ are TDEs and inferred a rate of infrared TDEs of $1.5-2.8\times10^{-5}$ galaxy$^{-1}$ yr$^{-1}$, comparable with that of optical TDEs. The rest are CLAGNs, suggesting the presence of weak AGNs that cannot be identified using common diagnoses. We predicted that with our method, a large amount of dust-obscured TDEs could be selected from future infrared surveys with higher data quality and cadence. △ Less

Submitted 8 September, 2025; v1 submitted 13 March, 2025; originally announced March 2025.

Comments: 32 pages, 20 figures, accepted for publication in ApJS

An 85-s X-ray quasi-periodicity after a stellar tidal disruption by a candidate intermediate-mass black hole

Authors: Wenjie Zhang, Xinwen Shu, Luming Sun, Rongfeng Shen, Liming Dou, Ning Jiang, Tinggui Wang

Abstract: It is still in dispute the existence of intermediate-mass black holes (IMBHs) with a mass of ~10^3-10^5 solar masses (Msun), which are the missing link between stellar-mass black holes (5-50 Msun) and supermassive black holes (10^6-10^10 Msun). The bright flares from tidal disruption events (TDEs) provide a new and direct way to probe IMBHs. 3XMM J215022.4-055108 is a unique off-nuclear X-ray tran… ▽ More It is still in dispute the existence of intermediate-mass black holes (IMBHs) with a mass of ~10^3-10^5 solar masses (Msun), which are the missing link between stellar-mass black holes (5-50 Msun) and supermassive black holes (10^6-10^10 Msun). The bright flares from tidal disruption events (TDEs) provide a new and direct way to probe IMBHs. 3XMM J215022.4-055108 is a unique off-nuclear X-ray transient which can be best explained as the TDE by an IMBH in a massive star cluster, though its mass is not well determined. Here, we report the discovery of a transient X-ray quasi-periodicity signal from 3XMM J215022.4-055108 with a period of ~85 seconds (at a significance of >3.51sigma) and fractional root-mean-squared amplitude of ~10%. Furthermore, the signal is coherent with a quality factor ~16. The significance drops to >3.13sigma if considering all light curves with sufficient quality for QPO search. Combining with the results from X-ray continuum fittings, the detection of QPO allows for joint constraints on the black hole mass and dimensionless spin in the range [9.9*10^3-1.6*10^4 Msun]$ and [0.26-0.36], respectively. This result supports the presence of an IMBH in an off-nuclear massive star cluster and may open up the possibility of studying IMBHs through X-ray timing of TDEs. △ Less

Submitted 2 March, 2025; originally announced March 2025.

Comments: 21 pages, 14 figures, published in Nature Astronomy on 28 February 2025

The Extraordinary Long-lasting Infrared Echo of PS16dtm Reveals an Extremely Energetic Nuclear Outburst

Authors: Ning Jiang, Di Luo, Jiazheng Zhu, Roc M. Cutri

Abstract: PS16dtm is one of the earliest reported candidate tidal disruption events (TDEs) in active galactic nuclei (AGNs) and displays a remarkably bright and long-lived infrared (IR) echo revealed by multi-epoch photometry from the Wide-field Infrared Survey Explorer (WISE). After a rapid rise in the first year, the echo remains persistently at a high state from July 2017 to July 2024, the latest epoch,… ▽ More PS16dtm is one of the earliest reported candidate tidal disruption events (TDEs) in active galactic nuclei (AGNs) and displays a remarkably bright and long-lived infrared (IR) echo revealed by multi-epoch photometry from the Wide-field Infrared Survey Explorer (WISE). After a rapid rise in the first year, the echo remains persistently at a high state from July 2017 to July 2024, the latest epoch, and keeps an almost constant color. We have fitted the extraordinary IR emission with a refined dust echo model by taking into account the dust sublimation process. The fitting suggests that an extremely giant dust structure with a new inner radius of $\sim1.6$ pc and an ultra-high peak bolometric luminosity, i.e., $\sim6\times10^{46} \rm erg~s^{-1}$ for typical 0.1$μ$m-sized silicate grain, is required to account for the IR echo. This work highlights the distinctive value of IR echoes in measuring the accurate intrinsic bolometric luminosity, and thus the total radiated energy of TDEs, which could be severely underestimated by traditional methods, i.e. probably by more than an order of magnitude in PS16dtm. Such large energetic output compared to normal TDEs could be boosted by the pre-existing accretion disk and gas clouds around the black hole. Our model can be validated in the near future by IR time-domain surveys such as Near-Earth Object (NEO) Surveyor, given the recent retirement of WISE. In addition, the potential for spatially resolving a receding dusty torus after a TDE could also be an exciting subject in the era of advanced IR interferometry. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Comments: Accepted for publication in ApJL, 11 pages, 6 figures. This work is inspired by and dedicated to the recently retired WISE satellite

An Intermediate-mass Black Hole Lurking in A Galactic Halo Caught Alive during Outburst

Authors: C. -C. Jin, D. -Y. Li, N. Jiang, L. -X. Dai, H. -Q. Cheng, J. -Z. Zhu, C. -W. Yang, A. Rau, P. Baldini, T. -G. Wang, H. -Y. Zhou, W. Yuan, C. Zhang, X. -W. Shu, R. -F. Shen, Y. -L. Wang, S. -X. Wen, Q. -Y. Wu, Y. -B. Wang, L. L. Thomsen, Z. -J. Zhang, W. -J. Zhang, A. Coleiro, R. Eyles-Ferris, X. Fang , et al. (116 additional authors not shown)

Abstract: Stellar-mass and supermassive black holes abound in the Universe, whereas intermediate-mass black holes (IMBHs) of ~10^2-10^5 solar masses in between are largely missing observationally, with few cases found only. Here we report the real-time discovery of a long-duration X-ray transient, EP240222a, accompanied by an optical flare with prominent H and He emission lines revealed by prompt follow-up… ▽ More Stellar-mass and supermassive black holes abound in the Universe, whereas intermediate-mass black holes (IMBHs) of ~10^2-10^5 solar masses in between are largely missing observationally, with few cases found only. Here we report the real-time discovery of a long-duration X-ray transient, EP240222a, accompanied by an optical flare with prominent H and He emission lines revealed by prompt follow-up observations. Its observed properties evidence an IMBH located unambiguously in the halo of a nearby galaxy and flaring by tidally disrupting a star -- the only confirmed off-nucleus IMBH-tidal disruption event so far. This work demonstrates the potential of sensitive time-domain X-ray surveys, complemented by timely multi-wavelength follow-ups, in probing IMBHs, their environments, demographics, origins and connections to stellar-mass and supermassive black holes. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: 64 pages, 15 figures, submitted

Discovery of a years-delayed radio flare from an unusually slow-evolved tidal disruption event

Authors: Zhumao Zhang, Xinwen Shu, Lei Yang, Luming Sun, Hucheng Ding, Lin Yan, Ning Jiang, Fangxia An, Walter Silima, Fabao Zhang, Yogesh Chandola, Zhongzu Wu, Daizhong Liu, Liming Dou, Jianguo Wang, Yibo Wang, Chenwei Yang, Di Li, Tianyao Zhou, Wenjie Zhang, Fangkun Peng, Tinggui Wang

Abstract: SDSS J1115+0544 is a unique low-ionization nuclear emission-line region (LINER) galaxy with energetic ultraviolet (UV), optical and mid-infrared outbursts occurring in its nucleus. We present the results from an analysis of multi-wavelength photometric and radio follow-up observations covering a period of ~9 years since its discovery. We find that following a luminosity plateau of ~500 days, the U… ▽ More SDSS J1115+0544 is a unique low-ionization nuclear emission-line region (LINER) galaxy with energetic ultraviolet (UV), optical and mid-infrared outbursts occurring in its nucleus. We present the results from an analysis of multi-wavelength photometric and radio follow-up observations covering a period of ~9 years since its discovery. We find that following a luminosity plateau of ~500 days, the UV/optical emission has decayed back to the pre-outburst level, suggesting that the nuclear outburst might be caused by a stellar tidal disruption event (TDE). In this case, SDSS J1115+0544 could be an unusually slow-evolved 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 5.5 GHz luminosity as high as ~1.9x10^39 erg/s. Using a standard equipartition analysis, we find the outflow powering the radio emission was launched at t~1260 days with a velocity of beta<~0.1 and kinetic energy of E_K~>10^50 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 displaying both a short-lived UV/optical plateau emission and a late-time radio brightening. Future radio observations of these TDEs in the post-plateau decay phase will help to establish the connection between outflow launching and changes in accretion rate. △ Less

Submitted 15 January, 2025; originally announced January 2025.

Comments: 13 pages, 5 figures, comments are welcome

Science Opportunities of Wet Extreme Mass-Ratio Inspirals

Authors: Zhenwei Lyu, Zhen Pan, Junjie Mao, Ning Jiang, Huan Yang

Abstract: Wet extreme mass-ratio inspirals (wet EMRIs), which arise from stellar-mass black holes (sBHs) inspiral into supermassive black holes (SMBHs) within the gas-rich environments of Active Galactic Nuclei (AGN), are primary sources of gravitational waves (GWs) for space-borne detectors like LISA, TianQin, and Taiji. Unlike "dry EMRIs", which form through gravitational scattering in nuclear star cluste… ▽ More Wet extreme mass-ratio inspirals (wet EMRIs), which arise from stellar-mass black holes (sBHs) inspiral into supermassive black holes (SMBHs) within the gas-rich environments of Active Galactic Nuclei (AGN), are primary sources of gravitational waves (GWs) for space-borne detectors like LISA, TianQin, and Taiji. Unlike "dry EMRIs", which form through gravitational scattering in nuclear star clusters, wet EMRIs are naturally accompanied by interactions with accretion disks, offering rich multi-messenger science opportunities. They are distinct in generating transient electromagnetic (EM) signals, such as quasi-periodic eruptions (QPEs), which serve as valuable probes of accretion disk physics and SMBH environments. Their GW signals provide an unprecedented precision of the order of $O(10^{-4}\sim 10^{-6})$ in measuring SMBH mass and spin, enabling the calibration of traditional EM techniques and offering insights into jet formation models. Additionally, wet EMRIs serve as bright and dark sirens for cosmology, facilitating percent-level precision measurements of Hubble parameter through AGN host identification or statistical association. These systems hold immense potential for advancing our understanding of black hole dynamics, accretion physics, and cosmology. △ Less

Submitted 20 August, 2025; v1 submitted 27 December, 2024; originally announced January 2025.

Comments: 19 pages, 6 figures, 3 tables

Minute-cadence observations on Galactic plane with Wide Field Survey Telescope (WFST): Overview, methodology and early results

Authors: Jie Lin, Tinggui Wang, Minxuan Cai, Zhen Wan, Xuzhi Li, Lulu Fan, Qingfeng Zhu, Ji-an Jiang, Ning Jiang, Xu Kong, Zheyu Lin, Jiazheng Zhu, Zhengyan Liu, Jie Gao, Bin Li, Feng Li, Ming Liang, Hao Liu, Wei Liu, Wentao Luo, Jinlong Tang, Hairen Wang, Jian Wang, Yongquan Xue, Dazhi Yao , et al. (4 additional authors not shown)

Abstract: As the time-domain survey telescope of the highest survey power in the northern hemisphere currently, Wide Field Survey Telescope (WFST) is scheduled to hourly/daily/semi-weekly scan northern sky up to ~23 mag in four optical (ugri) bands. Unlike the observation cadences in the forthcoming regular survey missions, WFST performed "staring" observations toward Galactic plane in a cadence of… ▽ More As the time-domain survey telescope of the highest survey power in the northern hemisphere currently, Wide Field Survey Telescope (WFST) is scheduled to hourly/daily/semi-weekly scan northern sky up to ~23 mag in four optical (ugri) bands. Unlike the observation cadences in the forthcoming regular survey missions, WFST performed "staring" observations toward Galactic plane in a cadence of $\approx$1 minute for a total on-source time of about 13 hours, during the commissioning and pilot observation phases. Such an observation cadence is well applied in producing densely sampling light curves and hunting for stars exhibiting fast stellar variabilities. Here we introduce the primary methodologies in detecting variability, periodicity, and stellar flares among a half million sources from the minute-cadence observations, and present the WFST g-/r-band light curves generated from periodic variable stars and flaring stars. Benefit from high photometric precisions and deep detection limits of WFST, the observations have captured several rare variable stars, such as a variable hot white dwarf (WD) and an ellipsoidal WD binary candidate. By surveying the almost unexplored parameter spaces for variables, WFST will lead to new opportunities in discovering unique variable stars in the northern sky. △ Less

Submitted 16 March, 2025; v1 submitted 17 December, 2024; originally announced December 2024.

Comments: 20 pages, 12 figures, accepted by ApJS

A Systematic Search for Candidate Supermassive Black Hole Binaries Using Periodic Mid-Infrared Light Curves of Active Galactic Nuclei

Authors: Di Luo, Ning Jiang, Xin Liu

Abstract: Periodic variability in active galactic nuclei (AGNs) is a promising method for studying sub-parsec supermassive black hole binaries (SMBHBs), which are a challenging detection target. While extensive searches have been made in the optical, X-ray and gamma-ray bands, systematic infrared (IR) studies remain limited. Using data from the Wide-field Infrared Survey Explorer (WISE), which provides uniq… ▽ More Periodic variability in active galactic nuclei (AGNs) is a promising method for studying sub-parsec supermassive black hole binaries (SMBHBs), which are a challenging detection target. While extensive searches have been made in the optical, X-ray and gamma-ray bands, systematic infrared (IR) studies remain limited. Using data from the Wide-field Infrared Survey Explorer (WISE), which provides unique decade-long mid-IR light curves with a six-month cadence, we have conducted the first systematic search for SMBHB candidates based on IR periodicity. Analyzing a parent sample of 48,932 objects selected from about half a million AGNs, we have identified 28 candidate periodic AGNs with periods ranging from 1,268 to 2,437 days (in the observer frame) by fitting their WISE light curves with sinusoidal functions. However, our mock simulation of the parent sample indicates that stochastic variability can actually produce a similar number of periodic sources, underscoring the difficulty in robustly identifying real periodic signals with WISE light curves, given their current sampling. Notably, we found no overlap between our sample and optical periodic sources, which can be explained by a distinct preference for certain periods due to selection bias. By combining archived data from different surveys, we have identified SDSS J140336.43+174136.1 as a candidate exhibiting periodic behavior in both optical and IR bands, a phenomenon that warrants further validation through observational tests. Our results highlight the potential of IR time-domain surveys, including future missions such as the Nancy Grace-Roman Space Telescope, for identifying periodic AGNs, but complementary tests are still needed to determine their physical origins such as SMBHBs. △ Less

Submitted 11 November, 2024; v1 submitted 11 November, 2024; originally announced November 2024.

Comments: Accepted for publication in ApJ. 24 pages

A neutrino flare potentially associated with X-ray emission from tidal disruption event ATLAS17jrp

Authors: Rong-Lan Li, Chengchao Yuan, Hao-Ning He, Yun Wang, Ben-Yang Zhu, Yun-Feng Liang, Ning Jiang, Da-Ming Wei

Abstract: Tidal disruption events (TDEs), in which stars are disrupted by supermassive black holes, have been proposed as potential sources of high-energy neutrinos through hadronic interactions. X-ray-bright TDEs provide dense photon fields conducive to neutrino production via proton-photon ($pγ$) processes. We conducted a time-dependent unbinned likelihood analysis of ten years (2008-2018) of IceCube muon… ▽ More Tidal disruption events (TDEs), in which stars are disrupted by supermassive black holes, have been proposed as potential sources of high-energy neutrinos through hadronic interactions. X-ray-bright TDEs provide dense photon fields conducive to neutrino production via proton-photon ($pγ$) processes. We conducted a time-dependent unbinned likelihood analysis of ten years (2008-2018) of IceCube muon-track data, focusing on ten TDEs with confirmed spatially and temporally coincident with the TDE ATLAS17jrp, occurring 19 days after the onset of its X-ray activity and lasting for 56 days, with a post-trial $p$-value of 0.01. This result is consistent with a scenario in which X-ray photons serve as target fields for hadronic interactions. Although constrained by the sample size of X-ray-detected TDEs, these results underscore the need for high-cadence X-ray monitoring and future neutrino observatories to further explore the connection between TDEs and high-energy neutrinos. △ Less

Submitted 28 July, 2025; v1 submitted 10 November, 2024; originally announced November 2024.

Could the inter-band lag of active galactic nucleus vary randomly?

Authors: Zhen-Bo Su, Zhen-Yi Cai, Jun-Xian Wang, Tinggui Wang, Yongquan Xue, Min-Xuan Cai, Lulu Fan, Hengxiao Guo, Zhicheng He, Zizhao He, Xu-Fan Hu, Ji-an Jiang, Ning Jiang, Wen-Yong Kang, Lei Lei, Guilin Liu, Teng Liu, Zhengyan Liu, Zhenfeng Sheng, Mouyuan Sun, Wen Zhao

Abstract: The inter-band lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show th… ▽ More The inter-band lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show that, owing to the random nature of AGN variability, the inter-band lags of an individual AGN would vary from one campaign with a finite baseline to another. Specifically, the thermal fluctuation scenario implies larger variations in the lags than the reprocessing scenario. Moreover, the former predicts a positive correlation between the lag and variation amplitude, while the latter does not result in such a correlation. For both scenarios, averaging the lags of an individual AGN measured with repeated and non-overlapping campaigns would give rise to a stable lag, which is larger for a longer baseline and gets saturation for a sufficiently long baseline. However, obtaining the stable lag for an individual AGN is very time-consuming. Alternatively, it can be equivalently inferred by averaging the lags of a sample of AGNs with similar physical properties, thus can be properly compared with predictions of AGN models. In addition, discussed are several new observational tests suggested by our simulations as well as the role of the deep high-cadence surveys of the Wide Field Survey Telescope in enriching our knowledge of the lags. △ Less

Submitted 13 October, 2024; originally announced October 2024.

Comments: 16 pages, 10 figures. Accepted for publication in Astrophysical Journal, comments are welcome!

Recurring tidal disruption events a decade apart in IRAS F01004-2237

Authors: Luming Sun, Ning Jiang, Liming Dou, Xinwen Shu, Jiazheng Zhu, Subo Dong, David Buckley, S. Bradley Cenko, Xiaohui Fan, Mariusz Gromadzki, Zhu Liu, Jianguo Wang, Tinggui Wang, Yibo Wang, Tao Wu, Lei Yang, Fabao Zhang, Wenjie Zhang, Xiaer Zhang

Abstract: We report the discovery of a second optical flare that occurred in September 2021 in IRAS F01004-2237, where the first flare occurred in 2010 has been reported, and present a detailed analysis of multi-band data. The position of the flare coincides with the galaxy centre with a precision of 650 pc. The flare peaks in $\sim50$ days with an absolute magnitude of $\sim-21$ and fades in two years roug… ▽ More We report the discovery of a second optical flare that occurred in September 2021 in IRAS F01004-2237, where the first flare occurred in 2010 has been reported, and present a detailed analysis of multi-band data. The position of the flare coincides with the galaxy centre with a precision of 650 pc. The flare peaks in $\sim50$ days with an absolute magnitude of $\sim-21$ and fades in two years roughly following $L\propto t^{-5/3}$. It maintains a nearly constant blackbody temperature of $\sim$22,000 K in the late time. Its optical and UV spectra show hydrogen and helium broad emission lines with full width at half maxima of 7,000--21,000 km s$^{-1}$ and He II/H$α$ ratio of 0.3--2.3. It shows weak X-ray emission relative to UV emission, with X-ray flares lasting for $<2-3$ weeks, during which the spectrum is soft with a power-law index $Γ=4.4^{+1.4}_{-1.3}$. These characters are consistent with a tidal disruption event (TDE), ruling out the possibilities of a supernova or an active galactic nuclei flare. With a TDE model, we infer a peak UV luminosity of $3.3\pm0.2\times10^{44}$ erg s$^{-1}$ and an energy budget of $4.5\pm0.2\times10^{51}$ erg. The two optical flares separated by $10.3\pm0.3$ years can be interpreted as repeating partial TDEs, double TDEs, or two independent TDEs. Although no definitive conclusion can be drawn, the partial TDEs interpretation predicts a third flare around 2033, and the independent TDEs interpretation predicts a high TDE rate of $\gtrsim10^{-2}$ yr$^{-1}$ in F01004-2237, both of which can be tested by future observations. △ Less

Submitted 28 October, 2024; v1 submitted 13 October, 2024; originally announced October 2024.

Comments: 22 pages, 16 figures, 9 tables, accepted for publication in A&A

Journal ref: A&A 692, A262 (2024)

Intermediate-Mass Black Holes in Green Pea Galaxies (IMBH-GP) I: a Candidate Sample from LAMOST and SDSS

Authors: Ruqiu Lin, Zhen-Ya Zheng, Fang-Ting Yuan, Jun-Xian Wang, Chunyan Jiang, Ning Jiang, Lingzhi Wang, Linhua Jiang, Xiang Ji, Shuairu Zhu, Xiaodan Fu

Abstract: The scaling relation of central massive black holes (MBHs) and their host galaxies is well-studied for supermassive BHs (SMBHs, $M_{\rm BH}\ \ge 10^6\, M_{\rm \odot}$). However, this relation has large uncertainties in the mass range of the intermediate-mass BHs (IMBHs, $M_{\rm BH}\ \sim10^3-10^{6}\, M_{\rm \odot}$). Since Green Pea (GP) galaxies are luminous compact dwarf galaxies, which may be l… ▽ More The scaling relation of central massive black holes (MBHs) and their host galaxies is well-studied for supermassive BHs (SMBHs, $M_{\rm BH}\ \ge 10^6\, M_{\rm \odot}$). However, this relation has large uncertainties in the mass range of the intermediate-mass BHs (IMBHs, $M_{\rm BH}\ \sim10^3-10^{6}\, M_{\rm \odot}$). Since Green Pea (GP) galaxies are luminous compact dwarf galaxies, which may be likely to host less massive SMBHs or even IMBHs, we systematically search for MBHs in a large sample of 2190 GP galaxies at $z < 0.4$, selected from LAMOST and SDSS spectroscopic surveys. Here, we report a newly discovered sample of 59 MBH candidates with broad H$α$ lines. This sample has a median stellar mass of $10^{8.83\pm0.11}\, M_{\rm \odot}$ and hosts MBHs with single-epoch virial masses ranging from $M_{\rm BH}\ \sim 10^{4.7}$ to $10^{8.5}\, M_{\rm \odot}$ (median $10^{5.85\pm0.64}\, M_{\rm \odot}$). Among the 59 MBH candidates, 36 have black hole masses $M_{\rm BH} \le 10^{6}\, M_{\rm \odot}$ (IMBH candidates), one of which even has $M_{\rm BH} \ \lesssim 10^{5}\, M_{\rm \odot}$. We find that the $M_{\rm BH}-M_{\rm *}$ relation of our MBH sample is consistent with the $M_{\rm BH}-M_{\rm bulge}$ relation for SMBHs, while is above the $M_{\rm BH}-M_{\rm *}$ relation for MBHs in dwarf galaxies in the same mass range. Furthermore, we show that 25 MBH candidates, including 4 IMBH candidates, have additional evidence of black hole activities, assessed through various methods such as the broad-line width, BPT diagram, mid-infrared color, X-ray luminosity, and radio emission. Our studies show that it is very promising to find IMBHs in GP galaxies, and the BH sample so obtained enables us to probe the connection between the MBHs and compact dwarf galaxies in the low-redshift Universe. △ Less

Submitted 30 September, 2024; originally announced September 2024.

Comments: 17 pages, 8 figures, 2 tables; Accepted for pubulication in SCPMA

Journal ref: 2024SCPMA..6709811L

The unluckiest star: A spectroscopically confirmed repeated partial tidal disruption event AT 2022dbl

Authors: Zheyu Lin, Ning Jiang, Tinggui Wang, Xu Kong, Dongyue Li, Han He, Yibo Wang, Jiazheng Zhu, Wentao Li, Ji-an Jiang, Avinash Singh, Rishabh Singh Teja, D. K. Sahu, Chichuan Jin, Keiichi Maeda, Shifeng Huang

Abstract: The unluckiest star orbits a supermassive black hole elliptically. Every time it reaches the pericenter, it shallowly enters the tidal radius and gets partially tidal disrupted, producing a series of flares. Confirmation of a repeated partial tidal disruption event (pTDE) requires not only evidence to rule out other types of transients, but also proof that only one star is involved, as TDEs from m… ▽ More The unluckiest star orbits a supermassive black hole elliptically. Every time it reaches the pericenter, it shallowly enters the tidal radius and gets partially tidal disrupted, producing a series of flares. Confirmation of a repeated partial tidal disruption event (pTDE) requires not only evidence to rule out other types of transients, but also proof that only one star is involved, as TDEs from multiple stars can also produce similar flares. In this letter, we report the discovery of a repeated pTDE, AT 2022dbl. In a quiescent galaxy at $z=0.0284$, two separate optical/UV flares have been observed in 2022 and 2024, with no bright X-ray, radio or mid-infrared counterparts. Compared to the first flare, the second flare has a similar blackbody temperature of ~26,000 K, slightly lower peak luminosity, and slower rise and fall phases. Compared to the ZTF TDEs, their blackbody parameters and light curve shapes are all similar. The spectra taken during the second flare show a steeper continuum than the late-time spectra of the previous flare, consistent with a newly risen flare. More importantly, the possibility of two independent TDEs can be largely ruled out because the optical spectra taken around the peak of the two flares exhibit highly similar broad Balmer, N III and possible He II emission lines, especially the extreme ~4100Å emission lines. This represents the first robust spectroscopic evidence for a repeated pTDE, which can soon be verified by observing the third flare, given its short orbital period. △ Less

Submitted 29 July, 2024; v1 submitted 17 May, 2024; originally announced May 2024.

Comments: 17 pages, 10 figures, accepted by ApJ Letters on 2024 July 15

Magnetically arrested disks in FR I radio galaxies

Authors: Han He, Bei You, Ning Jiang, Xinwu Cao, Jingfu Hu, Zhenfeng Sheng, Su Yao, Bozena Czerny

Abstract: A sample of 17 FR I radio galaxies constructed from the 3CR catalog, which is characterized by edge-darkened radio structures, is studied. The optical core luminosities derived from Hubble Space Telescope observation are used to estimate the Eddington ratios which are found to be below $10^{-3.4}$ for this sample. This is supported by the Baldwin-Phillips-Terlevich optical diagnostic diagrams deri… ▽ More A sample of 17 FR I radio galaxies constructed from the 3CR catalog, which is characterized by edge-darkened radio structures, is studied. The optical core luminosities derived from Hubble Space Telescope observation are used to estimate the Eddington ratios which are found to be below $10^{-3.4}$ for this sample. This is supported by the Baldwin-Phillips-Terlevich optical diagnostic diagrams derived with the spectroscopic observation of Telescopio Nazionale Galileo, suggesting that these sources are of low ionization nuclear Emission-line Regions (LINERs). It implies that the accretion in these FR I sources can be modeled as advection-dominated accretion flows (ADAFs). Given the low accretion rate, the predicted jet power with a fast-spinning black hole (BH) $a=0.95$ in the Blandford-Znajek mechanics is lower than the estimated one for almost all the sources in our sample. Such powerful jets indicate the presence of magnetically arrested disks (MAD) in the inner region of the ADAF, in the sense that the magnetic fields in the inner accretion zone are strong. Moreover, we show that, even in the MAD scenario, the BH spins in the sample are most likely moderate and/or fast with $a\gtrsim0.5$. △ Less

Submitted 22 March, 2024; originally announced March 2024.

Comments: 10 pages, 10 figures, 3 tables, Accepted for publication in MNRAS

AT2023lli: A Tidal Disruption Event with Prominent Optical Early Bump and Delayed Episodic X-ray Emission

Authors: Shifeng Huang, Ning Jiang, Jiazheng Zhu, Yibo Wang, Tinggui Wang, Shan-Qin Wang, Wen-Pei Gan, En-Wei Liang, Yu-Jing Qin, Zheyu Lin, Lin-Na Xu, Min-Xuan Cai, Ji-An Jiang, Xu Kong, Jiaxun Li, Long Li, Jian-Guo Wang, Ze-Lin Xu, Yongquan Xue, Ye-Fei Yuan, Jingquan Cheng, Lulu Fan, Jie Gao, Lei Hu, Weida Hu , et al. (20 additional authors not shown)

Abstract: High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The… ▽ More High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The bump represents the longest separation time from the main peak among known TDEs to date. The main UV/optical outburst declines as $t^{-4.10}$, making it one of the fastest decaying optically selected TDEs. Furthermore, we detected sporadic X-ray emission 30 days after the UV/optical peak, accompanied by a reduction in the period of inactivity. It is proposed that the UV/optical bump could be caused by the self-intersection of the stream debris, whereas the primary peak is generated by the reprocessed emission of the accretion process. In addition, our results suggest that episodic X-ray radiation during the initial phase of decline may be due to the patched obscurer surrounding the accretion disk, a phenomenon associated with the inhomogeneous reprocessing process. The double TDE scenario, in which two stars are disrupted in sequence, is also a possible explanation for producing the observed early bump and main peak. We anticipate that the multicolor light curves of TDEs, especially in the very early stages, and the underlying physics can be better understood in the near future with the assistance of dedicated surveys such as the deep high-cadence survey of the 2.5-meter Wide Field Survey Telescope (WFST). △ Less

Submitted 26 March, 2024; v1 submitted 3 March, 2024; originally announced March 2024.

Comments: 14 pages, 8 figures,accepted for publication by ApJL

Awakening of A Blazar at Redshift 2.7 Temporally Coincident with Arrival of Cospatial Neutrino Event IceCube-201221A

Authors: Xiong Jiang, Neng-Hui Liao, Yi-Bo Wang, Rui Xue, Ning Jiang, Ting-Gui Wang

Abstract: We report on multiwavelength studies of a blazar NVSS J171822+423948, which is identified as the low-energy counterpart of 4FGL J1718.5+4237, the unique $γ$-ray source known to be cospatial with the IceCube neutrino event IC-201221A. After a 12-year long quiescent period undetected by Fermi-LAT, $γ$-ray activities with a tenfold flux increase emerge soon (a few tens of days) after arrival of the n… ▽ More We report on multiwavelength studies of a blazar NVSS J171822+423948, which is identified as the low-energy counterpart of 4FGL J1718.5+4237, the unique $γ$-ray source known to be cospatial with the IceCube neutrino event IC-201221A. After a 12-year long quiescent period undetected by Fermi-LAT, $γ$-ray activities with a tenfold flux increase emerge soon (a few tens of days) after arrival of the neutrino. Associated optical flares in the ZTF $g$, $r$, and $i$ bands are observed together with elevated WISE infrared fluxes. Synchronized variations suggest that both the $γ$-ray emission and the neutrino event are connected to the blazar. Furthermore, the optical spectrum reveals emission lines at a redshift $z$ = 2.68 $\pm$ 0.01. Thus, it is the first candidate for a neutrino-emitting blazar at the redshift above 2. Discussions of theoretical constraints of neutrino production and comparisons with other candidates are presented. △ Less

Submitted 21 March, 2024; v1 submitted 22 January, 2024; originally announced January 2024.

Comments: 16 pages, 4 figures, ApJL in press

ASASSN-18ap: A Dusty Tidal Disruption Event Candidate with an Early Bump in the Light Curve

Authors: Yibo Wang, Tingui Wang, Ning Jiang, Xiaer Zhang, JiaZheng Zhu, XinWen Shu, Shifeng Huang, FaBao Zhang, Zhenfeng Sheng, Zheyu Lin

Abstract: We re-examined the classification of the optical transient ASASSN-18ap, which was initially identified as a supernova (SNe) upon its discovery. Based on newly emerged phenomena, such as a delayed luminous infrared outburst and the emergence of luminous coronal emission lines, we suggest that ASASSN-18ap is more likely a tidal disruption event (TDE) in a dusty environment, rather than a supernova.… ▽ More We re-examined the classification of the optical transient ASASSN-18ap, which was initially identified as a supernova (SNe) upon its discovery. Based on newly emerged phenomena, such as a delayed luminous infrared outburst and the emergence of luminous coronal emission lines, we suggest that ASASSN-18ap is more likely a tidal disruption event (TDE) in a dusty environment, rather than a supernova. The total energy in the infrared outburst is $\rm 3.1\times10^{51}$ erg, which is an order of magnitude higher than the total energy in the optical-to-ultraviolet range, indicating a large dust extinction, an extra-EUV component, or anisotropic continuum emission. A bumpy feature appeared in the optical light curve at the start of brightening, which was reported in a couple of TDEs very recently. This early bump may have been overlooked in the past due to the lack of sufficient sampling of the light curves of most TDEs during their ascending phase, and it could provide insight into the origin of optical emission. △ Less

Submitted 10 March, 2024; v1 submitted 19 December, 2023; originally announced December 2023.

Comments: Accepted to be published in ApJ

Reverberation evidence for Stream Collision and Delayed Disk Formation in Tidal Disruption Events

Authors: Hengxiao Guo, Jingbo Sun, Shuang-Liang Li, Yan-Fei Jiang, Tinggui Wang, Defu Bu, Ning Jiang, Yanan Wang, Yuhan Yao, Rongfeng Shen, Minfeng Gu, Mouyuan Sun

Abstract: When a star passes through the tidal disruption radius of a massive black hole (BH), it can be torn apart by the tidal force of the BH, known as the Tidal Disruption Event (TDE). Since the observed UV/optical luminosity significantly exceeds the predictions of the compact disk model in classical TDE theory, two competing models, stream collision and envelope reprocessing, have been proposed to add… ▽ More When a star passes through the tidal disruption radius of a massive black hole (BH), it can be torn apart by the tidal force of the BH, known as the Tidal Disruption Event (TDE). Since the observed UV/optical luminosity significantly exceeds the predictions of the compact disk model in classical TDE theory, two competing models, stream collision and envelope reprocessing, have been proposed to address this discrepancy. To distinguish between these models, we investigate the continuum reverberation behaviors for $\sim$30 TDEs with high-quality multi-band light curves. We found that over half of them exhibit a positive lag by a few days in UV/optical bands, indicating that their inferred sizes are significantly larger than the envelope sizes in reprocessing. Moreover, X-ray emissions not only significantly delay relative to the primary UV/optical peak but also lag behind the rebrightening bump by up to several tens of days, completely different from the X-ray illumination reprocessing. Additionally, the anti-correlated UV-optical continuum in ASASSN-15lh further disfavors the reprocessing scenario. In contrast, the model of stream collisions, combined with delayed accretion disk formation, can provide a unified explanation for the diverse TDE observations, e.g., the optical/X-ray population, the frequently observed rebrightening bump. This model describes a unification scheme wherein the UV/optical emission originates from stream collisions during the early-stage of TDE evolution and gradually transitions to being dominated by accretion disk with detectable X-ray emission in the late stage. After transitioning to a quiescent state, recurrent flares may be observed in some cases, possibly related to repeating partial TDEs. △ Less

Submitted 15 January, 2025; v1 submitted 11 December, 2023; originally announced December 2023.

Comments: 25 pages, 17 figures, 4 tables. ApJ accepted version

An Explanation for Overrepresentation of Tidal Disruption Events in Post-starburst Galaxies

Authors: Mengye Wang, Yiqiu Ma, Qingwen Wu, Ning Jiang

Abstract: Tidal disruption events\,(TDEs) provide a valuable probe in studying the dynamics of stars in the nuclear environments of galaxies. Recent observations show that TDEs are strongly overrepresented in post-starburst or "green valley" galaxies, although the underlying physical mechanism remains unclear. Considering the possible interaction between stars and active galactic nucleus\,(AGN) disk, the TD… ▽ More Tidal disruption events\,(TDEs) provide a valuable probe in studying the dynamics of stars in the nuclear environments of galaxies. Recent observations show that TDEs are strongly overrepresented in post-starburst or "green valley" galaxies, although the underlying physical mechanism remains unclear. Considering the possible interaction between stars and active galactic nucleus\,(AGN) disk, the TDE rates can be greatly changed compared to those in quiescent galactic nuclei. In this work, we revisit TDE rates by incorporating an evolving AGN disk within the framework of the "loss cone" theory. We numerically evolve the Fokker-Planck equations by considering the star-disk interactions, in-situ star formation in the unstable region of the outer AGN disk and the evolution of the accretion process for supermassive black holes\,(SMBHs). We find that the TDE rates are enhanced by about two orders of magnitude shortly after the AGN transitions into a non-active stage. During this phase, the accumulated stars are rapidly scattered into the loss cone due to the disappearance of the inner standard thin disk. Our results provide an explanation for the overrepresentation of TDEs in post-starburst galaxies. △ Less

Submitted 29 December, 2023; v1 submitted 12 November, 2023; originally announced November 2023.

Comments: Published in ApJ

Journal ref: The Astrophysical Journal. 2024, 960(2): 69

Dissonance in harmony: The UV/optical periodic outbursts of ASASSN-14ko exhibit repeated bumps and rebrightenings

Authors: Shifeng Huang, Ning Jiang, Rong-Feng Shen, Tinggui Wang, Zhenfeng Sheng

Abstract: ASASSN-14ko was identified as an abnormal periodic nuclear transient with a potential decreasing period. Its outbursts in the optical and UV bands have displayed a consistent and smooth "fast-rise and slow-decay" pattern since its discovery, which has recently experienced an unexpected alteration in the last two epochs, as revealed by our proposed high-cadence Swift observations. The new light cur… ▽ More ASASSN-14ko was identified as an abnormal periodic nuclear transient with a potential decreasing period. Its outbursts in the optical and UV bands have displayed a consistent and smooth "fast-rise and slow-decay" pattern since its discovery, which has recently experienced an unexpected alteration in the last two epochs, as revealed by our proposed high-cadence Swift observations. The new light curve profiles show a bump during the rising stages and a rebrightening during the declining stages, making them much broader and symmetrical than the previous ones. In the last two epochs, there is no significant difference in the X-ray spectral slope compared to the previous one, and its overall luminosity is lower than those of the previous epochs. The energy released in the early bump and rebrightening phases ($\sim10^{50}$ erg) could be due to collision of the stripped stream from partial tidal disruption events (pTDEs) with an expanded accretion disk. We also discussed other potential explanations, such as disk instability and star-disk collisions. Further high-cadence multi-wavelength observations of subsequent cycles are encouraged to comprehend the unique periodic source with its new intriguing features. △ Less

Submitted 15 October, 2023; v1 submitted 4 October, 2023; originally announced October 2023.

Comments: Accepted for publication in ApJL, 10 pages, 6 figures

A Gigantic Mid-Infrared Outburst in an Embedded Class-I Young Stellar Object J064722.95+031644.6

Authors: Tinggui Wang, Jiaxun Li, Gregory M. Mace, Tuo Ji, Ning Jiang, Qingfeng Zhu, Min Fang

Abstract: We report the serendipitous discovery of a giant mid-infrared (MIR) outburst from a previously unknown source near a star-forming region in the constellation Monoceros. The source gradually brightened by a factor of 5 from 2014 to 2016 before an abrupt rise by a factor of more than 100 in 2017. A total amplitude increase of >500 at 4.5 microns has since faded by a factor of about 10. Prior to the… ▽ More We report the serendipitous discovery of a giant mid-infrared (MIR) outburst from a previously unknown source near a star-forming region in the constellation Monoceros. The source gradually brightened by a factor of 5 from 2014 to 2016 before an abrupt rise by a factor of more than 100 in 2017. A total amplitude increase of >500 at 4.5 microns has since faded by a factor of about 10. Prior to the outburst, it was only detected at wavelengths longer than 1.8 microns in UKIDSS, Spitzer, and Herschel with a spectral energy distribution of a Class I Young Stellar Object (YSO). It has not been detected in recent optical surveys, suggesting that it is deeply embedded. With a minimum distance of 3.5 kpc, the source has a bolometric luminosity of at least 9 $L_\odot$ in the quiescent state and 400 $L_\odot$ at the peak of the eruption. The maximum accretion rate is estimated to be at least a few $10^{-5}$ $M_\odot$ year$^{-1}$. It shares several common properties with another eruptive event, WISE~J142238.82-611553.7: exceptionally large amplitude, featureless near-infrared spectrum with the exception of H_2 lines, intermediate eruption duration, an embedded Class I YSO, and a low radiative temperature (<600-700 K) in outburst. We interpret that the radiation from the inner accretion disk and young star is obscured and reprocessed by either an inflated outer disk or thick dusty outflow on scales > 6.5 AU during the outburst. △ Less

Submitted 19 September, 2023; originally announced September 2023.

Comments: 15 pages, 7 figures, accepted to ApJ

AT2018dyk Revisited: a Tidal Disruption Event Candidate with Prominent Infrared Echo and Delayed X-ray Emission in a LINER Galaxy

Authors: Shifeng Huang, Ning Jiang, Zheyu Lin, Jiazheng Zhu, Tinggui Wang

Abstract: The multiwavelength data of nuclear transient AT2018dyk, initially discovered as a changing-look low-ionization nuclear emission-line region (LINER) galaxy, has been revisited by us and found being in agreement with a tidal disruption event (TDE) scenario. The optical light curve of AT2018dyk declines as a power-law form approximately with index -5/3 yet its X-ray emission lags behind the optical… ▽ More The multiwavelength data of nuclear transient AT2018dyk, initially discovered as a changing-look low-ionization nuclear emission-line region (LINER) galaxy, has been revisited by us and found being in agreement with a tidal disruption event (TDE) scenario. The optical light curve of AT2018dyk declines as a power-law form approximately with index -5/3 yet its X-ray emission lags behind the optical peak by $\sim140$ days, both of which are typical characteristics for TDEs. The X-ray spectra are softer than normal active galactic nuclei (AGNs) although they show a slight trend of hardening. Interestingly, its rising time scale belongs to the longest among TDEs while it is nicely consistent with the theoretical prediction from its relatively large supermassive black hole (SMBH) mass ($\sim10^{7.38} M_{\odot}$). Moreover, a prominent infrared echo with peak luminosity $\sim7.4\times10^{42}~\text{erg}~\text{s}^{-1}$ has been also detected in AT2018dyk, implying an unusually dusty subparsec nuclear environment in contrast with other TDEs. In our sample, LINERs share similar covering factors with AGNs, which indicates the existence of the dusty torus in these objects. Our work suggests that the nature of nuclear transients in LINERs needs to be carefully identified and their infrared echoes offer us a unique opportunity for exploring the environment of SMBHs at low accretion rate, which has been so far poorly explored but is crucial for understanding the SMBH activity. △ Less

Submitted 31 August, 2023; v1 submitted 18 August, 2023; originally announced August 2023.

Comments: 9 pages, 6figures, 1 table. Accepted for publication in MNRAS

Two Candidate Obscured Tidal Disruption Events Coincident with High-energy Neutrinos

Authors: Ning Jiang, Ziying Zhou, Jiazheng Zhu, Yibo Wang, Tinggui Wang

Abstract: Recently, three optical tidal disruption event (TDE) candidates discovered by the Zwicky Transient Facility (ZTF) have been suggested to be coincident with high-energy neutrinos. They all exhibit unusually strong dust infrared (IR) echoes, with their peak times matching the neutrino arrival time even better than the optical peaks. We hereby report on two new TDE candidates that are spatially and t… ▽ More Recently, three optical tidal disruption event (TDE) candidates discovered by the Zwicky Transient Facility (ZTF) have been suggested to be coincident with high-energy neutrinos. They all exhibit unusually strong dust infrared (IR) echoes, with their peak times matching the neutrino arrival time even better than the optical peaks. We hereby report on two new TDE candidates that are spatially and temporally coincident with neutrinos by matching our sample of mid-infrared outbursts in nearby galaxies (MIRONG) with Gold alerts of IceCube high-energy neutrino events up to June 2022. The two candidates show negligible optical variability according to their ZTF light curves and can therefore be classified as part of the growing population of obscured TDE candidates. The chance probability of finding two such candidates about $\sim3\%$ by redistributing the MIRONG sources randomly in the SDSS footprint, which will be as low as $\sim0.1\%$ (or $\sim0.2\%$) if we limit to sources with increased fluxes (or variability amplitudes) comparable with the matched two sources. Our findings further support the potential connection between high-energy neutrinos and TDEs in dusty environments by increasing the total number of neutrino-associated TDE and TDE candidates to five, although the underlying physics remains poorly understood. △ Less

Submitted 20 August, 2023; v1 submitted 31 July, 2023; originally announced July 2023.

Comments: Published, ApJL, 953, L12

AT 2023clx: the Faintest and Closest Optical Tidal Disruption Event Discovered in Nearby Star-forming Galaxy NGC 3799

Authors: Jiazheng Zhu, Ning Jiang, Tinggui Wang, Shifeng Huang, Zheyu Lin, Yibo Wang, Jian-Guo Wang

Abstract: We report the discovery of a faint optical tidal disruption event (TDE) in the nearby star-forming galaxy NGC 3799. Identification of the TDE is based on its position at the galaxy nucleus, a light curve declining as t^-5/3, a blue continuum with an almost constant blackbody temperature of ~12,000K, and broad (~15,000kms^-1) Balmer lines and characteristic He~II 4686A emission. The light curve of… ▽ More We report the discovery of a faint optical tidal disruption event (TDE) in the nearby star-forming galaxy NGC 3799. Identification of the TDE is based on its position at the galaxy nucleus, a light curve declining as t^-5/3, a blue continuum with an almost constant blackbody temperature of ~12,000K, and broad (~15,000kms^-1) Balmer lines and characteristic He~II 4686A emission. The light curve of AT 2023clx peaked at an absolute magnitude of -17.16mag in the g-band and a maximum blackbody bolometric luminosity of 4.56*10^42 ergs^-1, making it the faintest TDE discovered to date. With a redshift of 0.01107 and a corresponding luminosity distance of 47.8Mpc, it is also the closest optical TDE ever discovered to our best knowledge. Furthermore, our analysis of Swift/XRT observations of AT 2023clx yields a very tight 3 sigma upper limit of 9.53*10^39 ergs^-1 in the range 0.3--10keV. AT 2023clx, together with very few other faint TDEs such as AT 2020wey, prove that there are probably a large number of faint TDEs yet to be discovered at higher redshifts, which is consistent with the prediction of luminosity functions (LFs). The upcoming deeper optical time-domain surveys, such as the Legacy Survey of Space and Time (LSST) and the Wide-Field Survey Telescope (WFST) will discover more TDEs at even lower luminosities, allowing for a more precise constraint of the low-end of the LF. △ Less

Submitted 9 July, 2023; originally announced July 2023.

Comments: 9 pages, 6 figures; Accepted for ApJL (July, 2023)

Sciences with the 2.5-meter Wide Field Survey Telescope (WFST)

Authors: WFST Collaboration, Tinggui Wang, Guilin Liu, Zhenyi Cai, Jinjun Geng, Min Fang, Haoning He, Ji-an Jiang, Ning Jiang, Xu Kong, Bin Li, Ye Li, Wentao Luo, Zhizheng Pan, Xuefeng Wu, Ji Yang, Jiming Yu, Xianzhong Zheng, Qingfeng Zhu, Yi-Fu Cai, Yuanyuan Chen, Zhiwei Chen, Zigao Dai, Lulu Fan, Yizhong Fan , et al. (38 additional authors not shown)

Abstract: The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China and the Purple Mountain Observatory. It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over an FOV of 6.5-s… ▽ More The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China and the Purple Mountain Observatory. It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over an FOV of 6.5-square-degree. It is anticipated that WFST will be set up at the Lenghu site in the summer of 2023 and begin to observe the northern sky in four optical bands (u, g, r, and i) with a range of cadences, from hourly/daily in the Deep High-Cadence Survey (DHS) program to semiweekly in the Wide-Field Survey (WFS) program, three months later. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31 (AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low-z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23 (u) and 24 mag (g), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions, tidal disruption events and fast, luminous optical transients even beyond a redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g=25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of LSST that monitor the southern sky. △ Less

Submitted 14 September, 2023; v1 submitted 13 June, 2023; originally announced June 2023.

Comments: 48 pages

Journal ref: SCPMA-Vol. 66 No. 10: 109512 (2023)

SN2017egm: A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves

Authors: Jiazheng Zhu, Ning Jiang, Subo Dong, Alexei V. Filippenko, Richard J. Rudy, A. Pastorello, Christopher Ashall, Subhash Bose, R. S. Post, D. Bersier, Stefano Benetti, Thomas G. Brink, Ping Chen, Liming Dou, N. Elias-Rosa, Peter Lundqvist, Seppo Mattila, Ray W. Russell, Michael L. Sitko, Auni Somero, M. D. Stritzinger, Tinggui Wang, Peter J. Brown, E. Cappellaro, Morgan Fraser , et al. (6 additional authors not shown)

Abstract: When discovered, SN~2017egm was the closest (redshift $z=0.03$) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has since been extensively observed and studied. We report spectroscopic data showing strong emission at around He~I $λ$10,830 and four He~I absorption lines in the optical. Consequently, we classify SN~2017egm as… ▽ More When discovered, SN~2017egm was the closest (redshift $z=0.03$) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has since been extensively observed and studied. We report spectroscopic data showing strong emission at around He~I $λ$10,830 and four He~I absorption lines in the optical. Consequently, we classify SN~2017egm as a member of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We also present our late-time photometric observations. By combining them with archival data, we analyze high-cadence ultra-violet, optical, and near-infrared light curves spanning from early pre-peak ($\sim -20\,d$) to late phases ($\sim +300\,d$). We obtain its most complete bolometric light curve, in which multiple bumps are identified. None of the previously proposed models can satisfactorily explain all main light-curve features, while multiple interactions between the ejecta and circumstellar material (CSM) may explain the undulating features. The prominent infrared excess with a blackbody luminosity of $10^7$--$10^8\,L_{sun}$ detected in SN~2017egm could originate from the emission of either an echo of a pre-existing dust shell, or newly-formed dust, offering an additional piece of evidence supporting the ejecta-CSM interaction model. Moreover, our analysis of deep $Chandra$ observations yields the tightest-ever constraint on the X-ray emission of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio $\lesssim 10^{-3}$ at late phases ($\sim100-200\,d$), which could help explore its close environment and central engine. △ Less

Submitted 6 March, 2023; originally announced March 2023.

Comments: 25 pages, 14 Figures, 4 Tables; accepted for publication in ApJ (Mar. 2023)

The radio detection and accretion properties of the peculiar nuclear transient AT 2019avd

Authors: Yanan Wang, Ranieri D. Baldi, Santiago del Palacio, Muryel Guolo, Xiaolong Yang, Yangkang Zhang, Chris Done, Noel Castro Segura, Dheeraj R. Pasham, Matthew Middleton, Diego Altamirano, Poshak Gandhi, Erlin Qiao, Ning Jiang, Hongliang Yan, Marcello Giroletti, Giulia Migliori, Ian McHardy, Francesca Panessa, Chichuan Jin, Rongfeng Shen, Lixin Dai

Abstract: AT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/Swift photometries revealed two plateaus: one observed after the peak and the other one appeared ~240 days lat… ▽ More AT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/Swift photometries revealed two plateaus: one observed after the peak and the other one appeared ~240 days later. Meanwhile, our NICER and XRT/Swift campaigns show two declines in the X-ray emission, one during the first optical plateau and one 70-90 days after the optical/UV decline. The evidence suggests that the optical/UV could not have been primarily originated from X-ray reprocessing. Furthermore, we detected a timelag of ~16-34 days between the optical and UV emission, which indicates the optical likely comes from UV reprocessing by a gas at a distance of 0.01-0.03 pc. We also report the first VLA and VLBA detection of this source at different frequencies and different stages of the second flare. The information obtained in the radio band - namely a steep and a late-time inverted radio spectrum, a high brightness temperature and a radio-loud state at late times - together with the multiwavelength properties of AT 2019avd suggests the launching and evolution of outflows such as disc winds or jets. In conclusion, we propose that after the ignition of black hole activity in the first flare, a super-Eddington flaring accretion disc formed and settled to a sub-Eddington state by the end of the second flare, associated with a compact radio outflow. △ Less

Submitted 9 January, 2023; v1 submitted 16 December, 2022; originally announced December 2022.

Comments: 20 pages, 10 figures, 1 table. Accepted for publication in MNRAS