arXiv subjects

Ting-Gui Wang

Publications and source records attributed to Ting-Gui Wang.

At least 19 recordsLinked to original sources

arXiv2026

The atmospheric extinction curve at Lenghu site

In this study, we use a dedicated spectroscopic telescope to carry out low-resolution measurements of the optical atmospheric extinction curve at Lenghu astronomical site in Qinghai Province, China. Observations of A0-type stars are conducted over multiple nights between 2024 and 2026, covering airmasses from 1.0 to 2.0 and wavelengths in the range of 400 to 800 nm. We derive the extinction curve for the Lenghu site and compare it with those from Mauna Kea and Cerro Paranal.

astro-ph.IM↗

arXiv2026

The $γ$-ray-emitting blazar B3 1239+376 at $z$ = 3.82 identified in a multi-wavelength context

Among thousands of extragalactic $γ$-ray emitters, only a handful of distant ($z >$ 3) sources are detected. Yet, they are crucial probes shedding light on the cosmic evolution of jets of active galactic nuclei and the initial phase of mass growth of supermassive black holes. Here, we report on a multi-band study of the radio quasar B3 1239+376 with $z$ = 3.82. By analyzing the Fermi-LAT data, a significant (globally 7.7$σ$) $γ$-ray source in its direction, with an estimated association probability of 0.91, is observed in a half-year period of 2025. The analysis also reveals the emergence of co-spatial $γ$-ray residues in prior epochs. Moreover, the $γ$-ray and infrared light curves obtained from WISE and SPHEREx observations are likely correlated, as we observe that the emissions in both bands peak at the same time. The temporal coincidence establishes a firm association relationship between the $γ$-ray source and the quasar. Therefore, B3 1239+376 is proposed as the third most distant $γ$-ray detected blazar to date. Benefiting from the multi-wavelength observations, broadband spectral energy distributions in different flux states are compiled and reproduced by the classic one-zone leptonic radiation model to investigate the jet properties. Considering the recent brightening in $γ$ rays, prompt follow-up observations are encouraged, especially radio interferometry observations which may catch the potential ejection of a new jet blob.

astro-ph.HE↗

arXiv2024

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

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.

astro-ph.HE↗

arXiv2023

Limiting Magnitudes of the Wide Field Survey Telescope (WFST)

Expected to be of the highest survey power telescope in the northern hemisphere, the Wide Field Survey Telescope (WFST) will begin its routine observations of the northern sky since 2023. WFST will produce a lot of scientific data to support the researches of time-domain astronomy, asteroids and the solar system, galaxy formation and cosmology and so on. We estimated that the 5 $σ$ limiting magnitudes of WFST with 30 second exposure are $u=22.31$ mag, $g=23.42$ mag, $r=22.95$ mag, $i=22.43$ mag, $z=21.50$ mag, $w=23.61$ mag. The above values are calculated for the conditions of $airmass=1.2$, seeing = 0.75 arcsec, precipitable water vapour (PWV) = 2.5 mm and Moon-object separation = $45^{\circ}$ at the darkest New Moon night of the Lenghu site (V=22.30 mag, Moon phase $θ=0^{\circ}$). The limiting magnitudes in different Moon phase conditions are also calculated. The calculations are based on the empirical transmittance data of WFST optics, the vendor provided CCD quantum efficiency, the atmospherical model transmittance and spectrum of the site. In the absence of measurement data such as sky transmittance and spectrum, we use model data.

astro-ph.IM↗

arXiv2023

A γ-ray emitting NLS1 galaxy SDSS J095909.51+460014.3 identified by multiwavelength contemporaneous brightening

We report on an identification of a new gamma-ray emitting narrow-line Seyfert 1 galaxy (gamma-NLS1), SDSS J095909.51+460014.3 (z = 0.399), by establishing an association with a gamma-ray source 4FGL 0959.6+4606, although its low-energy counterpart was suggested to be a radio galaxy 2MASX J09591976+4603515. WISE long-term light curves of these two sources reveal diverse infrared variability patterns. Brightenings of 2.5 mag are detected for the former source, while flux decays of 0.5 mag are found for the other one. More importantly, the time that the infrared flux of the NLS1 rises, is coincident with the time of flux increase of 4FGL 0959.6+4606. At the same time, no infrared activity of the radio galaxy has been observed. A specific analysis of 15-month Fermi-LAT data, aiming at the high gamma-ray flux state, yields a significant source (TS =43). The corresponding gamma-ray localization analysis suggests that only the NLS1 falls into the uncertainty area, further supporting the updated association relationship. A broadband spectral energy distribution of SDSS J095909.51+460014.3 has been drawn and well described by the classic single-zone homogeneous leptonic jet model. Its jet properties are investigated and found to be comparable with the known gamma-NLS1s.

astro-ph.HE↗

arXiv2023

Ensemble Mapping the Inner Structure of Luminous Quasars

A simple prediction of the well-known unification model of active galactic nuclei is that a sample of sources should exhibit an anti-correlation between the solid angle of the dusty torus and of the ionization cone (as the sum of them shall equal 4$π$), which however has never been detected. In this work, we analyze the correlation between [OIII] 5007 narrow emission line equivalent width and $L_{\rm IR}(λ)/L_{\rm bol}$ for a large sample of luminous quasars. For the first time, we detect a clear intrinsic anti-correlation between them, which immediately verifies the torus/ionization-cone geometry in luminous quasars. More interestingly, the anti-correlation significantly weakens with increasing wavelength from $\sim$ 2 to 12 $μ$m, and disappears at $\sim$ 12 $μ$m. Simulations show a cool dust component (in addition to equatorial torus) with its strength positively correlating with the solid angle of the ionization cone is required to explain the observations. This shows that the polar dust seen in nearby active galaxies also exists in luminous quasars, with its contribution to total dust emission increasing with $λ$ (from $\sim$ 2 to 12 $μ$m) and reaching between 39%-62% (model dependent) at rest frame 12 $μ$m. Our findings provide a unique approach to map the otherwise spatially unresolvable inner structure of quasars.

astro-ph.GA↗

arXiv2022

GB6 J2113+1121: A multi-wavelength flaring gamma-ray blazar temporally and spatially coincident with the neutrino event IceCube-191001A

A radio-emitting tidal disruption event (AT2019dsg) is proposed as a likely counterpart of the IceCube neutrino event IC-191001A. In this work we have revisited the {\it Fermi}-LAT data in the direction of the neutrino and confirmed no signal at the site of AT2019dsg. Instead, at the edge of the 90\% confidential level error region of this neutrino there is a $γ$-ray transient source associated with a blazar GB6 J2113+1121. In May 2019, GB6 J2113+1121 was undergoing an unprecedented $γ$-ray flare since the start of the {\it Fermi}-LAT operation, with a variability amplitude about 20-fold. Similar violent flares of GB6 J2113+1121, unobserved before, have been also detected observed in optical bands. Moreover, the blazar remained in a high flux state in the infrared bands when IceCube-191001A arrived, though its $γ$-ray and optical activities has temporally ceased. Motivated by the spatial and temporal coincidence, we suggest that GB6 J2113+1121 is a candidate of the counterpart of IC-191001A. The jet properties of GB6 J2113+1121 are investigated, which are found to be comparable with that of the neutrino-emitting blazars (candidates). A specific analysis of archival IceCube data in this direction and future observations would put a further constraint on the origin of the neutrino.

astro-ph.HE↗

arXiv2019

An On-going Mid-infrared Outburst in the White Dwarf 0145+234: Catching in Action of Tidal Disruption of an Exoasteroid?

We report the detection of a large amplitude MIR outburst in the white dwarf (WD) 0145+234 in the NEOWISE Survey data. The source had a stable MIR flux before 2018, and was brightened by about 1.0 magnitude in the W1 and W2 bands within half a year and has been continuously brightening since then. No significant variations are found in the optical photometry data during the same period. This suggests that this MIR outburst is caused by recent replenishing or redistribution of dust, rather than intrinsic variations of the WD. SED modeling of 0145+234 suggests that there was already a dust disk around the WD in the quiescent state, and both of the temperature and surface area of the disk evolved rapidly since the outburst. The dust temperature was about 1770K in the initial rising phase, close to the sublimation temperature of silicate grains, and gradually cooled down to around 1150K, while the surface area increased by a factor of about 6 during the same period. The inferred closest distance of dust to the WD is within the tidal disruption radius of a gravitationally bounded asteroid. We estimated the dust mass to be between $3\times10^{15}$ to $3\times10^{17}$ $ρ/(1 \mathrm g~cm^{-3})$ kg for silicate grains of a power-law size distribution with a high cutoff size from 0.1 to 1000 microns. We interpret this as a possible tidal breakup of an exo-asteroid by the WD. Further follow-up observations of this rare event may provide insights on the origin of dust disk and metal pollution in some white dwarfs.

astro-ph.SR↗

arXiv2019

Multi-wavelength variability of CGRaBS J0733+0456: identifying a distant $γ$-ray blazar at z = 3.01

We report on OVRO, WISE, Swift and Fermi-LAT observations of the high redshift blazar CGRaBS J0733+0456, from which significant flux variations in radio, infrared (IR) as well as $γ$-ray domains are detected. Particularly, the amplitude of long-term IR variation is over one order of magnitude and the IR variability timescale can be constrained as short as a few hours in the source frame. The IR and $γ$-ray light curves are found to be rather similar, and the strong quasi-simultaneous infrared and $γ$-ray flares are proved to be unique among the nearby $γ$-ray sources. This is the first time to identify a $γ-$ray blazar at redshift $z\geq 3$ with multi-wavelength flux variations (flares). Broadband spectral energy distributions in different flux states are constructed and theoretically described. The $γ-$ray flares from some blazars as distant as redshift $\sim$ 5 are expected to be detectable for Fermi-LAT.

astro-ph.HE↗

arXiv2016

X-ray spectral and temporal analysis of Narrow Line Seyfert 1 galaxy Was 61

We present an analysis of spectrum and variability of the bright reddened narrow line Seyfert 1 galaxy Was~61 using 90 ks archival {\it XMM-Newton} data. The X-ray spectrum in 0.2-10 keV can be characterized by an absorbed power-law plus soft excess and an Fe K$α$ emission line. The power-law spectral index remains constant during the flux variation. The absorbing material is mildly ionized, with a column density of 3.2$\times$10$^{21}$ cm$^{-2}$, and does not appear to vary during the period of the X-ray observation. If the same material causes the optical reddening (E(B-V)$\simeq$0.6 mag), it must be located outside the narrow line region with a dust-to-gas ratio similar to the average Galactic value. We detect significant variations of the Fe K$α$ line during the observational period. A broad Fe K$α$ line at $\simeq$6.7 keV with a width of $\sim$0.6 keV is detected in the low flux segment of the first 40 ks exposure, and is absent in the spectra of other segments; a narrow Fe K$α$ emission line $\sim$6.4 keV with a width of $\sim$0.1 keV is observed in the subsequent 20 ks segment, which has a count rate of 35% higher and is in the next day. We believe this is due to the change in geometry and kinematics of the X-ray emitting corona. The temperature and flux of soft X-ray excess appear to correlate with the flux of the hard power-law component. Comptonization of disc photons by a warm and optically thick inner disk is preferred to interpret the soft excess, rather than the ionized reflection.

astro-ph.HE↗

arXiv2015

A Comprehensive Study of Broad Absorption Line Quasars: I. Prevalence of HeI* Absorption Line Multiplets in Low-Ionization Objects

Neutral Helium multiplets, HeI*3189,3889,10830 are very useful diagnostics to the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of HeI* detections have been reported. Using a newly developed method, we detected HeI*3889 absorption line in 101 sources of a well-defined sample of 285 MgII BAL quasars selected from the SDSS DR5. This has increased the number of HeI* BAL quasars by more than one order of magnitude. We further detected HeI*3189 in 50% (52/101) quasars in the sample. The detection fraction of HeI* BALs in MgII BAL quasars is about 35% as a whole, and increases dramatically with increasing spectral signal-to-noise ratios, from 18% at S/N <= 10 to 93% at S/N >= 35. This suggests that HeI* BALs could be detected in most MgII LoBAL quasars, provided spectra S/N is high enough. Such a surprisingly high HeI* BAL fraction is actually predicted from photo-ionization calculations based on a simple BAL model. The result indicates that HeI* absorption lines can be used to search for BAL quasars at low-z, which cannot be identified by ground-based optical spectroscopic survey with commonly seen UV absorption lines. Using HeI*3889, we discovered 19 BAL quasars at z<0.3 from available SDSS spectral database. The fraction of HeI* BAL quasars is similar to that of LoBAL objects.

astro-ph.GA↗

arXiv2014

A Search for Double-peaked narrow emission line Galaxies and AGNs in the LAMOST DR1

LAMOST has released more than two million spectra, which provide the opportunity to search for double-peaked narrow emission line (NEL) galaxies and AGNs. The double-peaked narrow-line profiles can be well modeled by two velocity components, respectively blueshifted and redshifted with respect to the systemic recession velocity. This paper presents 20 double-peaked NEL galaxies and AGNs found from LAMOST DR1 using a search method based on multi-gaussian fit of the narrow emission lines. Among them, 10 have already been published by other authors, either listed as genuine double-peaked NEL objects or as asymmetric NEL objects, the remaining 10 being first discoveries. We discuss some possible origins for double-peaked narrow-line features, as interaction between jet and narrow line regions, interaction with companion galaxies and black hole binaries. Spatially resolved optical imaging and/or follow-up observations in other spectral bands are needed to further discuss the physical mechanisms at work.

astro-ph.GA↗

arXiv2013

Quasar-Galaxy Clustering through Projected Galaxy Counts at z=0.6-1.2

We investigate the spatial clustering of galaxies around quasars at redshifts from 0.6 to 1.2 using the photometric data from Sloan Digital Sky Survey (SDSS) Stripe 82. The quasar and galaxy cross-correlation functions are measured through the projected galaxy number density n(r_p) on scales $0.05<r_p<20 h^-1 Mpc around quasars for a sample of 2300 quasars from Schneider et al. (2007). We detect strong clustering signals at all redshifts, and find that the clustering amplitude increases significantly with redshift. We examine the dependence of the quasar-galaxy clustering on quasar and galaxy properties and find that the clustering amplitude is significantly larger for quasars with more massive black holes, or with bluer colors, while the dependence on quasar luminosity is absent. We also show that quasars have a stronger correlation amplitude with blue galaxies than with red galaxies. We finally discuss the implication of our finding.

astro-ph.CO↗

arXiv2013

Connection Between Mid-Infrared Emission Properties and Narrow Line Region Outflows in Type 1 Active Galactic Nuclei

The location of warm dust producing the Mid-infrared (MIR) emission in Type 1 Active Galactic Nuclei (AGNs) is complex and not yet fully known. We explore this problem by studying how the MIR covering factor (CF_{MIR} =L_{MIR}/L_{bol}) correlates with the fundamental parameters of AGN accretion process (such as L_{bol}, black hole mass MBH, and Eddington ratio L/LEdd) and the properties of narrow emission lines (as represented by [O III] 5007), using large data sets derived from the Sloan Digital Sky Spectroscopic Survey (SDSS) and the Wide Infrared Sky Survey (WISE). Firstly we find that the luminosity of the [O III] wing component (Lwing) correlates more tightly with the continuum luminosity (L5100) than the luminosity of the line core component (Lcore) does, which is in line with our previous conclusion that the wing component, generally blueshifted, originates from the polar outflows in the inner narrow-line region (NLR). We then find that the MIR CF shows the strongest correlation with Lwing/L_{bol} rather than with Lcore/L_{bol} or the above fundamental AGN parameters, and the correlation becomes stronger as the infrared wavelength increases. We also confirm the anti-correlations of CF_{MIR} with L_{bol} and MBH, and the lack of dependence of CF_{MIR} on the Eddington ratio. These results suggest that a large fraction of the warm dust producing MIR emission in AGNs is likely embedded in polar outflows in the NLR instead of in the torus.

astro-ph.CO↗

arXiv2013

The Covering Factor of Warm Dust in Quasars: View from WISE All-Sky Data Release

By combining the newly infrared photometric data from the All-Sky Data Release of the Wide-field Infrared Survey Explorer with the spectroscopic data from the Seventh Data Release of the Sloan Digital Sky Survey, we study the covering factor of warm dust ($\CF$) for a large quasar sample, as well as the relations between $\CF$ and other physical parameters of quasars. We find a strong correlation between the flux ratio of mid-infrared to near-ultraviolet and the slope of near-ultraviolet spectra, which is interpreted as the dust extinction effect. After correcting for the dust extinction utilizing the above correlation, we examine the relations between $\CF$ and AGN properties: bolometric luminosity ($\Lbol$), black hole mass ($\MBH$) and Eddington ratio ($L/L_{\rm Edd}$). We confirm the anti-correlation between $\CF$ and $\Lbol$. Further we find that $\CF$ is anti-correlated with $\MBH$, but is independent of $L/L_{\rm Edd}$. Radio-loud quasars are found to follow the same correlations as for radio-quiet quasars. Monte Carlo simulations show that the anisotropy of UV-optical continuum of the accretion disc can significantly affect, but is less likely to dominate the $\CF$--$\Lbol$ correlation.

astro-ph.CO↗

arXiv2012

The Baldwin effect in the narrow emission lines of AGNs

The anti-correlations between the equivalent widths of emission lines and the continuum luminosity in AGNs, known as the Baldwin effect are well established for broad lines, but are less well studied for narrow lines. In this paper we explore the Baldwin effect of narrow emission lines over a wide range of ionization levels and critical densities using a large sample of broad-line, radio-quiet AGNs taken from Sloan Digital Sky Survey (SDSS) Data Release 4. These type1 AGNs span three orders of magnitude in continuum luminosity. We show that most narrow lines show a similar Baldwin effect slope of about -0.2 while the significant deviations of the slopes for [NII] 6583, [OII] 3727, [NeV] 3425, and the narrow component of Ha can be explained by the influence of metallicity, star-formation contamination and possibly by difference in the shape of the UV-optical continuum. The slopes do not show any correlation with either the ionization potential or the critical density. We show that a combination of 50% variations in continuum near 5100A and a log-normal distribution of observed luminosity can naturally reproduce a constant Baldwin effect slope of -0.2 for all narrow lines. The variations of the continuum could be due to variability, intrinsic anisotropic emission, or an inclination effect.

astro-ph.CO↗

arXiv2012

A Metal-Strong and Dust-Rich Damped \lya Absorption System toward the Quasar SDSS J115705.52+615521.7

(Abridged for arXiv) We report the discovery of an unusual, extremely dust-rich and metal-strong damped \lya absorption system (DLA) at a redshift $z_{a}=2.4596$ toward the quasar SDSS J115705.52+615521.7 (hereafter J1157+6155) with an emission-line redshift $z_{e}=2.5125$. Its neutral hydrogen column density $N_{\hi} = 10^{21.8\pm0.2}$ cm$^{-2}$ is among the highest values measured in quasar DLAs. The measured metal column density is $N_{ZnII}\approx 10^{13.8}$ cm$^{-2}$, which is about 1.5 times larger than the largest value in any previously observed quasar DLAs. The best-fit curve is a MW-like law with a significant broad feature centered around 2175 Å in the rest frame of the absorber. The measured extinction $A_V \approx 0.92$ mag is unprecedentedly high in quasar DLAs. After applying an extinction correction, the $i$ band absolute magnitude of the quasar is as high as $M_{i} \approx -29.4$ mag, placing it one of the most luminous quasars ever known. This discovery is suggestive of the existence of a rare yet important population of dust-rich DLAs with both high metallicities and high column densities, which may have significant impact on the measurement of the cosmic evolution of neutral gas mass density and metallicity.

astro-ph.GA↗

arXiv2012

Rapid Infrared Variability of Three Radio-loud Narrow-line Seyfert 1 Galaxies: A View from the Wide-field Infrared Survey Explorer

Using newly released data from the Wide-field Infrared Survey Explorer, we report the discovery of rapid infrared variability in three radio-loud narrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in the sample of Yuan et al. (2008). J0849+5108 and J0948+0022 clearly show intraday variability, while J1505+0326 has a longer measurable time scale within 180 days. Their variability amplitudes, corrected for measurement errors, are $\sim 0.1-0.2$ mag. The detection of intraday variability restricts the size of the infrared-emitting region to $\sim 10^{-3}$ pc, significantly smaller than the scale of the torus but consistent with the base of a jet. The three variable sources are exceptionally radio-loud, have the highest radio brightness temperature among the whole sample, and all show detected $γ$-ray emission in Fermi/LAT observations. Their spectral energy distributions resemble those of low-energy-peaked blazars, with a synchrotron peak around infrared wavelengths. This result strongly confirms the view that at least some radio-loud NLS1s are blazars with a relativistic jet close to our line of sight. The beamed synchrotron emission from the jet contributes significantly to and probably dominates the spectra in the infrared and even optical bands.

astro-ph.HE↗