arXiv subjects

J. Y. Wei

Publications and source records attributed to J. Y. Wei.

At least 19 recordsLinked to original sources

arXiv2026

XRF 241001A/SN 2024aiiq: A faint soft X-ray transient detected by SVOM with a broad-line type Ic supernova revealed by JWST

X-ray flashes (XRFs) are a type of gamma-ray burst (GRB) with prompt emission predominantly below 30 keV and have been poorly detected by previous missions. The advent of the SVOM mission, with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, subluminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigated the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. We analyzed the SVOM/ECLAIRs prompt emission and modeled its afterglow emission from X-ray to-radio. We present JWST/NIRSpec and SVOM/VT observations of the associated supernova (SN 2024aiiq), and we compared its properties with previously detected GRB/SNe. The event XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV with a duration of T90 = 3.14 seconds. Its spectrum is consistent with both thermal and nonthermal models, each implying a low Epeak < 10 keV and Eiso ~ 8x10^49 erg. The X-ray-to-radio afterglow modeling favors an origin from a relativistic jet viewed on-axis. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some eFXTs and inconsistent with synchrotron emission. The JWST/NIRSpec observations firmly established its collapsar origin by revealing a SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events. The event XRF 241001A is a soft low-luminosity collapsar event produced by a weak relativistic jet observed on-axis, supporting the view that part of the XRF population forms the low-energy soft tail of the long GRB population. Its observation demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population that remains largely unexplored.

astro-ph.HE↗

arXiv2026

OQ~208: A New Fe~II Changing-look Active Galactic Nucleus and Implications for the Nature of the Changing-look Phenomenon

In addition to the traditional hydrogen Balmer emission lines, here we extend the optical changing-look (CL) phenomenon occurring in some active galactic nuclei (AGNs) to the optical FeII complex. Multiepoch spectroscopy allows to identify OQ~208, a local flat-spectrum radio source, as a new FeII CL-AGN owing to the disappearance of both its strong FeII complex (RFe $\equiv$ FeII/H$β=0.64$) and its Balmer broad-line emission on a timescale of $\sim14$\,yr. The simultaneous disappearance implies that in this object, both the FeII and Balmer emission come from the same region exposed to the ionizing continuum. We further identify an anticorrelation between the FeII strength and the continuum (and also Eddington ratio) during the CL events in dozens of CL-AGNs recently studied by Panda \& Sniegowska (2024), suggesting a negative response of RFe to both $L_{5100}$ and $L_{\mathrm{bol}}/L_{\mathrm{Edd}}$; this can be understood by the Comptonization process in a hot, optically thin accretion flow.

astro-ph.GA↗

arXiv2026

The SVOM mission, its profile and its system

The SVOM (Space-based Variable Objects Monitor) mission, launched into low Earth orbit on 22 June 2024, is a French-Chinese multi-wavelength observatory dedicated to the study of the transient sky. Inspired by the Neil Gehrels Swift Observatory, it consists of an autonomous rapid-slewing satellite, linked in real time to several ground-based telescopes. The space segment comprises two X-ray/gamma-ray wide-field instruments (ECLAIRs and GRM) with real-time triggering capabilities combined with two narrow-field telescopes in X-ray (MXT) and in visible (VT). In addition, the SVOM collaboration has also developed a unique visible and NIR ground-based follow-up system to promptly respond to the gamma-ray transients detected on board. The core program of SVOM will provide new insights into the Gamma-Ray Burst physics by providing a homogeneous dataset covering both the prompt and afterglow emissions, as well as better studying the low luminosity and soft Gamma-Ray Burst populations. As a versatile satellite platform with fast slewing capabilities, SVOM also comprises a Target of Opportunity program and a General Program consisting in pointed observations scheduled over the year that will both significantly contribute to the multi-messenger and time-domain astronomy.

astro-ph.HE↗

arXiv2026

Are "Changing-Look" Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? II. The Case of Changing-Look Narrow-Line Seyfert 1 Galaxies

The evolutionary role of the so-called ``changing-look'' (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within $\sim10$ yr, has been suggested in the past few years. By focusing on CL-AGNs having spectra similar to those of broad-line Seyfert 1 galaxies, some authors have proposed that CL-AGNs tend to be at a special evolutionary stage associated with intermediate-to-old stellar populations. Here we attempt to verify this evolutionary role by extending the sample to CL narrow-line Seyfert 1 (NLS1) galaxies, which are believed to be ``young'' AGNs with a less massive supermassive black hole and high accretion rate. Combining the recent large NLS1 catalog provided by Paliya et al. (2024) and the SDSS-V DR19 spectral survey returns only three CL-NLS1s out of a parent sample of 884 objects, reinforcing the rarity of CL-NLS1s. Subsequent spectral analysis shows that the evolutionary role mentioned above still holds, although CL-NLS1s tend to occupy the young end of the intermediate-old population. Finally, we propose that off-center SDSS spectra caused by the ``fiber drop'' effect have great potential for determining the properties of the narrow-line region of NLS1s.

astro-ph.GA↗

arXiv2026

Multi-wavelength Study of A Superflare on RS CVn-type Star HD22468 Triggered at Hard X-ray by SVOM

Detection of stellar flares at hard X-ray is still rare at the current stage. A transient was recently detected by the hard X-ray camera, ECLAIRs onboard the SVOM mission at 11:39:01.2UT on 2025, January 09. Simultaneous monitor in the optical band on the ground by SVOM/GWAC and follow-up spectroscopy enable us to confirm that the transient is caused by a superflare on HD~22468, a RS CVn-type star. The bolometric energy released in the flare is estimated to be $\sim7.2\times10^{37}-1.7\times10^{38}\ \mathrm{erg}$. The hard X-ray spectra of the event at the peak can be reproduced by the ``apec'' model of a hot plasma with a temperature of $106^{+27}_{-22}$~MK. In the optical range, the H$α$ emission-line profile obtained at $\sim1.7$ hrs after the trigger shows a bulk blueshift of $-96\pm20\ \mathrm{km\ s^{-1}}$, which can be explained by either a chromospheric evaporation or a prominence eruption. The ejected mass is estimated to be $3.9\times10^{20}$ g for the evaporating plasma, and to be $3.2\times10^{21}\ \mathrm{g}<M_{\mathrm{p}}<8.8\times10^{21}\ \mathrm{g}$ for the erupted prominence.

astro-ph.SR↗

arXiv2025

SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization

Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared afterglow discovery and the spectroscopic measurements of its redshift z $\simeq$ 7.3 . This burst happened when the Universe was only $\sim$ 5% of its current age. We discuss the signature of these rare events within the context of the SVOM operating model, and the ways to optimize their identification with adapted ground follow-up observation strategies.

astro-ph.HE↗

arXiv2025

JWST reveals a supernova following a gamma-ray burst at z $\simeq$ 7.3

The majority of energetic long-duration gamma-ray bursts (GRBs) are thought to arise from the collapse of massive stars, making them powerful tracers of star formation across cosmic time. Evidence for this origin comes from the presence of supernovae in the aftermath of the GRB event, whose properties in turn link back to those of the collapsing star. In principle, with GRBs we can study the properties of individual stars in the distant universe. Here, we present JWST/NIRCAM observations that detect both the host galaxy and likely supernova in the SVOM GRB 250314A with a spectroscopically measured redshift of z $\simeq$ 7.3, deep in the era of reionisation. The data are well described by a combination of faint blue host, similar to many z $\sim$ 7 galaxies, with a supernova of similar luminosity to the proto-type GRB supernova, SN 1998bw. Although larger galaxy contributions cannot be robustly excluded, given the evidence from the blue afterglow colours of low dust extinction, supernovae much brighter than SN 1998bw can be. These observations suggest that, despite disparate physical conditions, the star that created GRB 250314A was similar to GRB progenitors in the local universe.

astro-ph.HE↗

arXiv2025

Picking-up Local GRB Candidates Based on Their Host Galaxies

Rapid identification of candidates of high-value gamma-ray bursts (GRBs), including both high-$z$ and local events, is crucial for outlining subsequent observational strategy. In this paper, we present a model that enables an on-duty astronomer to rapidly identify candidates of local GRBs prior to spectroscopy, provided that these events have been localized at an arcseconds precision. After taking into account the mass distribution of the host galaxies of GRBs, the model calculates the two-dimensional cross-match probabilities between a localized GRB and its surrounding nearby galaxies, and then returns the best match with the highest probability. The model is evaluated not only by the observed GRB sample with redshifts up to $z=4$, but also through the simulated GRB samples. By using the recently published GLADE+ galaxies catalog with a completeness of 95\% up to 500Mpc, along with the NED-LVS catalog, the Precision and Recall of the model are determined to be 0.23-0.33 and 0.75, respectively, at the best performance. A dedicated web service, which will be integrated into the SVOM Science User Support System, has been developed to deploy the model.

astro-ph.HE↗

arXiv2025

Enhancing Fault Diagnosis in GWAC: A Monitoring System for Telescope Arrays

The Ground-based Wide-Angle Cameras array (GWAC) necessitates the integration of over 100 hardware devices, more than 100 servers, and upwards of 2500 software modules, all synchronized within a 3-second imaging cycle. However, the complexity of real-time and high concurrency processing of big data have historically resulted in a substantial failure rate, with estimated observation efficiency of less than 50% in 2023. To address these challenges, we developed a monitoring system aimed at enhancing fault diagnosis efficiency. The system features two innovative monitoring views: state evolution monitoring and transient lifecycle monitoring. These, combined with instantaneous state monitoring and key parameter monitoring views, create a comprehensive and holistic monitoring strategy. This paper details the system's architecture, data collection methods, and the design philosophy of monitoring views. After a year of practical fault diagnostics, the system has demonstrated the ability to identify and localize faults within minutes, achieving fault localization speeds nearly ten times faster than traditional methods. Additionally, the system's design exhibits high generalizability, making them applicable to other telescope array systems.

astro-ph.IM↗

arXiv2024

Potential Chromospheric Evaporation in A M-dwarf's Flare Triggered by Einstein Probe Mission

Although flares from late-type main-sequence stars have been frequently detected in multi-wavelength, the associated dynamical process has been rarely reported so far. Here, we report follow-up observations of an X-ray transient triggered by WXT onboard the Einstein Probe at UT08:45:08 in 2024, May 7. The photometry in multi-bands and time-resolved spectroscopy started at 3 and 7.5 hours after the trigger, respectively, which enables us to identify the transient as a flare of the M-dwarf 2MASS J12184187-0609123. The bolometric energy released in the flare is estimated to be $\sim10^{36}\ \mathrm{erg}$ from its X-ray light curve. The H$α$ emission-line profile obtained at about 7 hours after the trigger shows an evident blue asymmetry with a maximum velocity of $200-250\ \mathrm{km\ s^{-1}}$. The blue wing can be likely explained by the chromospheric temperature (cool) upflow associated with chromospheric evaporation, in which the mass of the evaporating plasma is estimated to be $1.2\times10^{18}$g. In addition, a prominence eruption with an estimated mass of $7\times10^{15}\mathrm{g}<M_{\mathrm{p}}<7\times10^{18}\mathrm{g}$ can not be entirely excluded.

astro-ph.SR↗

arXiv2024

Capability of Searching for Kilonova Associated with a Short Gamma-ray Burst by SVOM

In spite of the importance of studying the cosmic generation of heavy elements through the r-process, the detection of kilonova resulted from a merger of neutron star binaries is still a challenge task. In this paper, we show that the Visible Telescope (VT) onboard the on-going SVOM space mission is powerful for identifying kilonova candidates associated with short gamma-ray bursts (SGRBs) up to a distance of 600Mpc. A significant color variation, turn blue and then turn red, is revealed by calculating the light curves in both red and blue channels of VT by a linear combination of an afterglow and an associated kilonova. The maximum color variation is as high as $\sim0.5-1$ mag, which is far larger than the small photometry error of $\sim0.2$ mag of VT for a point source with a brightness of 23 mag. Up to a distance of 600Mpc, $\sim1-2$ kilonova candidates per year are predicted to be identified by VT.

astro-ph.HE↗

arXiv2024

GRB 221009A/SN 2022xiw: A Supernova Obscured by a Gamma-Ray Burst Afterglow?

We present optical photometry for the afterglow of GRB 221009A, in some respects the most extraordinary gamma-ray burst (GRB) ever observed. Good quality in the R-band light curve is obtained, covering 0.32-19.57 days since the Fermi-GBM trigger. We find that a weak bump emerges fromthe declining afterglow at $t \approx 11$ days; a supernova (SN) may be responsible. We use a smooth broken power-law and $^{56}\mathrm{Ni}$ model to fit the light curve. The best-fitting results reveal that the SN ejected a total mass of $M_\mathrm{ej} = 3.70 M_\odot$, a $^{56}\mathrm{Ni}$ mass of $M_\mathrm{Ni} = 0.23 M_\odot$, and a kinetic energy of $E_\mathrm{SN,K} = 2.35 \times 10^{52} \mathrm{erg}$. We also compare GRB 221009A with other GRB-SN events based on a GRB-associated SN sample, and find that only SN 2003lw and SN 2011kl can be obviously revealed in the afterglow of GRB 221009A by setting these objects at its distance. This suggests that a supernova (SN 2022xiw) is possibly obscured by the brighter afterglow emission from GRB 221009A.

astro-ph.HE↗

arXiv2024

Instability of Circumnuclear Gas Supply as An Origin of "Changing-look" Phenomenon of Supermassive Blackholes

The origin of the "Changing-look" (CL) phenomenon in supermassive black holes (SMBHs) remains an open issue. This study aims to shed light on this phenomenon by focusing on a sample that encompasses all known repeating CL active galactic nuclei (AGNs). Through the identification of a characteristic time scale for the CL phenomenon, it was observed that larger SMBHs possess shorter characteristic timescales, while smaller SMBHs exhibit longer timescales. These findings reveal a significant contrast to the traditional AGN variability that has been adequately explained by the AGN's disk instability model. This stark discrepancy highlights a distinct origin of the CL phenomenon, distinguishing it from traditional AGN variability. By properly predicting the characteristic time scale and its dependence on SMBH mass, we propose that the CL phenomenon is likely a result of a variation in accretion rate caused by a sudden change in the supply of circumnuclear gas during the transition between active and passive SMBH fueling stages.

astro-ph.GA↗

arXiv2024

Changing-look NLS1 galaxies, their detection with SVOM, and the case of NGC 1566

We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

astro-ph.GA↗

arXiv2023

Are "Changing-Look'' Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? I

The nature of the so-called ``changing-look'' (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within $\sim10$~yr, remains an open question. As the first in our series of studies, we here attempt to understand the CL phenomenon from a view of the coevolution of AGNs and their host galaxies (i.e., if CL-AGNs are at a specific evolutionary stage) by focusing on the SDSS local ``partially obscured'' AGNs in which the stellar population of the host galaxy can be easily measured in the integrated spectra. A spectroscopic follow-up program using the Xinglong 2.16~m, Lick/Shane 3~m, and Keck 10~m telescopes enables us to identify in total 9 CL-AGNs from a sample of 59 candidates selected by their mid-infrared variability. Detailed analysis of these spectra shows that the host galaxies of the CL-AGNs are biased against young stellar populations and tend to be dominated by intermediate-age stellar populations. This motivates us to propose that CL-AGNs are probably particular AGNs at a specific evolutionary stage, such as a transition stage from ``feast'' to ``famine'' fueling of the supermassive black hole. In addition, we reinforce the previous claim that CL-AGNs tend to be biased against both a high Eddington ratio and a high bolometric luminosity, suggesting that the disk-wind broad-line-region model is a plausible explanation of the CL phenomenon.

astro-ph.CO↗

arXiv2023

Does Feedback from Supermassive Blackhole Co-evolve With Host In Type 2 Quasars?

The feedback from accretion of central supermassive black holes (SMBHs) is a hot topic in the co-evolution of the SMBHs and their host galaxies. By tracing the large scale outflow by the line profile and bulk velocity shift of $[ \rm O~{\scriptsize III}]~ λ5007$, the evolutionary role of outflow is studied here on a large sample of 221 type 2 quasars (QSO2s) extracted from Reyes et al. By following our previous study on local Seyfert 2 galaxies, the current spectral analysis on the SDSS spectroscopic database enables us to arrive at following results: (1) by using the Lick indices, we confirm that QSO2s are on average associated with younger stellar populations than Seyfert galaxies; (2) QSO2s with a stronger outflow are tend to be associated with a younger stellar population, which implies a coevolution between the feedback from SMBH and the host in QSO2s; (3) although an occupation at the high $L_{\rm bol}/L_{\rm Edd}$ end, the QSO2s follow the $L_{\rm bol}/L_{\rm Edd}$-$D_{n}(4000)$ sequence established from local, less-luminous Seyfert galaxies, which suggests a decrease of accretion activity of SMBH and feedback as the circumnuclear stellar population continuously ages.

astro-ph.GA↗

arXiv2023

Nonreciprocal Charge and Spin Transport Induced by Non-Hermitian Skin Effect in Mesoscopic Heterojunctions

The pursuit of the non-Hermitian skin effect (NHSE) in various physical systems is of great research interest. Compared with recent progress in non-electronic systems, the implementation of the NHSE in condensed matter physics remains elusive. Here, we show that the NHSE can be engineered in the mesoscopic heterojunctions (system plus reservoir) in which electrons in two channels of the system moving towards each other have asymmetric coupling to those of the reservoir. This makes electrons in the system moving forward and in the opposite direction have unequal lifetimes, and so gives rise to a point-gap spectral topology. Accordingly, the electron eigenstates exhibit NHSE under the open boundary condition, consistent with the description of the generalized Brillouin zone. Such a reservoir-engineered NHSE visibly manifests itself as the nonreciprocal charge current that can be probed by the standard transport measurements. Further, we generalize the scenario to the spin-resolved NHSE, which can be probed by the nonreciprocal spin transport. Our work opens a new research avenue for implementing and detecting the NHSE in electronic mesoscopic systems, which will lead to interesting device applications.

cond-mat.mes-hall↗

arXiv2022

Flaring-associated Complex Dynamics in Two M-dwarfs Revealed by Fast, Time-resolved Spectroscopy

Habitability of an exoplanet is believed to be profoundly affected by activities of the host stars, although the related coronal mass ejections (CMEs) are still rarely detected in solar-like and late-type stars. We here report an observational study on flares of two M-dwarfs triggered by the high-cadence survey performed by the Ground Wide-angle Camera system. In both events, the fast, time-resolved spectroscopy enables us to identify symmetric broad H$α$ emission with not only a nearly zero bulk velocity, but also a large projected maximum velocity as high as $\sim700-800\ \mathrm{km\ s^{-1}}$. This broadening could be resulted from either Stark (pressure) effect or a flaring-associated CME at stellar limb. In the context of the CME scenario, the CME mass is estimated to be $\sim4\times10^{18}$ g and $2\times10^{19}$ g. In addition, our spectral analysis reveals a temporal variation of the line center of the narrow H$α$ emission in both events. The variation amplitudes are at tens of $\mathrm{km\ s^{-1}}$, which could be ascribed to the chromospheric evaporation in one event, and to a binary scenario in the other one. With the total flaring energy determined from our photometric monitor, we show a reinforced trend in which larger the flaring energy, higher the CME mass is.

astro-ph.SR↗