arXiv subjects

Ting-Feng Yi

Publications and source records attributed to Ting-Feng Yi.

14 recordsLinked to original sources

arXiv2026

Day-timescale Quasi-periodic Oscillations of the Gev BL Lac RX J0805.4+7534 with TESS

This paper reports for the first time the detection of quasi-periodic oscillations (QPOs) in the light curves of the BL Lacertae object RX J0805.4+7534. The Transiting Exoplanetary Survey Satellite (TESS) observed this source in seven sectors of the sky, and we extracted the light curves for these sectors using a custom method. The presence of QPO signals was found in these light curves. To detecte the periodicity and assess the statistical significance of the QPO signals, we employed two methods: Lomb-Scargle periodograms and Weighted Wavelet \textit{Z}-transform. Both of these different methods yielded consistent results. \textcolor{red}{\sout{The results showed signals with day-timescale QPO in sectors 20, 26, 53, and 73, with confidence levels exceeding $3\sigma$, and three of the sectors exhibited a ~3.8 days QPO. To explain these rapid quasi-periodic changes, we discuss several possible explanations. We propose that the QPO signal might be due to the rotation of hot spots on circular orbits within the accretion disk.}}\textcolor{blue}{The results show that QPO signals exist in sectors 20, 26, and 53, with the confidence levels exceeding 99.73\%. The QPOs in sectors 20 and 26 are $\sim 3.8$ days and have a global significance of 95\%. To explain these rapid quasi-periodic variations, we discussed several possible physical scenarios. The most possible one is the kink instability in relativistic jets. The other possible scenario is the rotation of hot-spots in the innermost accretion disk. Based on the hot-spot orbital model hypothesis, the mass of the black hole at the center of this BL Lac object wes estimated. The validity of these two explanations requires further observational data to verify. However, since the radiation of BL Lac objects primarily originates from jets, we prefer the kink instability in relativistic jets to be the cause of this rapid QPO.

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arXiv2025

The relation between the optical variability timescale, magnetic field of jets and black hole spin in active galactic nuclei

We investigate the relationship among the jet magnetic field, black hole spin, black hole mass, Eddington ratio, and optical variability timescales in jetted active galactic nuclei (AGNs). By fitting a damped random walk (DRW) model to the g-band light curves, we obtain the characteristic variability timescale ($\tau_{\rm DRW}$) for 41 jetted AGNs with precise supermassive black hole (SMBH) mass measurements. Our main results are as follows: (i) Our analysis reveals a significant correlation between the jet magnetic field ($B_{\rm 1pc}$), black hole spin ($j$) and the characteristic variability timescale within our sample. These findings suggest that the optical variability of jetted AGNs is influenced by the jet magnetic field and black hole spin. Furthermore, the characteristic variability timescale aligns with the electron escape timescale, as evidenced by the relationship between the characteristic variability timescale and jet magnetic field ($\tau_{\rm DRW}\propto B_{\rm 1pc}^{0.76\pm0.22}$). (ii) We confirm a significant correlation between the characteristic variability timescale and SMBH mass, expressed as: $\log \rm \tau_{\rm DRW} = 0.52(\pm0.21)\log M _{\rm BH}/M_{\rm \odot}-3.12(\pm1.90)$, with an intrinsic scatter of 0.08 dex. The slope of this relationship is consistent with that between the thermal timescale and black hole mass. Our results support the hypothesis that magnetorotational instability (MRI) fluctuations drive the intrinsic variability observed in the light curves emitted by the AGNs accretion disk.

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arXiv2025

Optical Monitoring and Long-term Optical Spectral Variability of BL Lacertae Object S5 0716+714

We present photometric observations of the BL Lacertae object S5 0716+714 with a temporal resolution of 120 s in the Sloan i' and r' bands. These observations were conducted using the Comet Search Program telescope at Xingming Observatory from 2018 December 22 to 2020 February 15, and more than 5600 effective images were obtained on each filter across 79 nights. Additionally, we compiled long-term variability data spanning 34 yr in the optical UBVRI bands. Using the power-enhanced F-test and nested ANOVA test, we found intraday variability (IDV) on 31 nights and possible IDV on 20 nights in the i' band. Similarly, IDV was detected on 35 nights in the r' band, while possible IDV was observed on 22 nights. The minimum variability timescale is 7.33 minutes, and the estimated black hole masses are (0.68- 5.12)*10^8 Msun. The spectral variability and long-term optical light curves reveal a bluer-when-brighter trend on intraday timescales. The long-term optical flux density and spectral index exhibit periodic variability with a timescale of about 1038 days. An anticorrelation between optical flux and spectral index was observed, with a time delay of -140 days. Variability across different optical bands exhibited a strong correlation, with no discernible time lag. From the IDV, spectral variability, correlation, and time delays between different bands, we conclude that these radiation characteristics may result from the shock-in-jet model scenario.

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arXiv2025

Two repeated quasi-periodic oscillations in the FSRQ S5 1044+71 observed by TESS

In this work, we report for the first time two repeated quasi-periodic oscillations (QPOs) in the light curve of the Flat Spectrum Radio Quasar (FSRQ) S5 1044+71. This source was observed by the Transiting Exoplanet Survey Satellite (TESS) in multiple sectors. We used the generalized Lomb-Scargle periodogram method and weighted wavelet Z-transform method to search for significant periodic signals. The main results are as follows: We found QPOs of $\sim$ 7.0 days (persisted for 4 cycles, with a significance of $\sim3.5σ$) and $\sim$ 7.3 days (persisted for 5 cycles, with a significance of $\sim3.8σ$) in the light curves of Sector 47 and EP1, respectively. Considering range of error, we consider them to be the same. We discussed two likely models of these rapid quasi-periodic variations: One comes from the jet and the other from the accretion disk. For the first one, we consider kink instability of the jet as a plausible explanation. Second, the QPO is probable to come from the main hot spots in the accretion disk, which is located approximately within the innermost stable circular orbit allowed by general relativity. Based on this model, we estimate the mass of the black hole in S5 1044+71 to be $3.49 \times 10^9 M_{\odot}$.

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arXiv2023

Comprehensive study of the blazars from Fermi-LAT LCR: The log-normal flux distribution and linear RMS-Flux relation

Fermi-LAT LCR provide continuous and regularly-sampled gamma-ray light curves, spanning about 14 years, for a large sample of blazars. The log-normal flux distribution and linear RMS-Flux relation of the light curves for a few of Fermi blazar have been examined in previous studies. However, the probability that blazars exhibit log-normal flux distribution and linear RMS-Flux relation in their gamma-ray light curves has not been systematically explored. In this study, we comprehensively research on the distribution of gamma-ray flux and the statistical characteristics on a large sample of 1414 variable blazars from the Fermi-LAT LCR catalog, including 572 FSRQs, 477 BL Lacs, and 365 BCUs, and statistically compare their flux distributions with normal and log-normal distributions. The results indicate that the probability of not reject log-normal is 42.05% for the large sample, and there is still 2.05% probability of not reject normality, based on the joint of Kolmogorov-Smirnov, Shapiro-Wilk and Normality tests. We further find that the probability that BL Lacs conforms to the log-normal distribution is higher than that of FSRQs. Besides, after removing sources with less than 200 data points from this large sample, a sample of 549 blazars, which is still a large sample comparing to the previous studies, was obtained. Basing on dividing the light curves into segments every 20 points (or 40 points, or one year), we fitted the linear RMS-Flux relation of this three different sets, and found that the Pearson correlation coefficients are all close to 1 of the most blazars. This result indicates a strong linear correlation between the RMS and the flux of this 549 blazars. The log-normal distribution and linear RMS-Flux relation indicate that the variability of gamma-ray flux for most blazars is non-linear and multiplicative process.

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arXiv2022

GRB 211227A as a peculiar long gamma-ray burst from compact star merger

Long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe) are believed to originate from massive star core-collapse events, whereas short-duration GRBs that are related to compact star mergers are expected to be accompanied by kilonovae. GRB 211227A, which lasted about 84 s, had an initial short/hard spike followed by a series of soft gamma-ray extended emission at redshift $z=$0.228. We performed follow-up observations of the optical emission using BOOTES, LCOGT, and the Lijiang 2.4m telescope, but we detected no associated supernova signature, even down to very stringent limits at such a low redshift. We observed the host galaxy within a large error-circle and roughly estimate the physical offset of GRB 211227A as $20.47\pm14.47$ kpc from the galaxy center. These properties are similar to those of GRB 060614, and suggest that the progenitor of GRB 211227A is not favored to be associated with the death of massive stars. Hence, we propose that GRB 211227A originates from a compact star merger. Calculating pseudo-kilonova emission for this case by adopting the typical parameters, we find that any associated pseudo-kilonova is too faint to be detected. If this is the case, it explains naturally the characteristics of the prompt emission, the lack of SN and kilonova emission, and the large physical offset from the galaxy center.

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arXiv2021

Highly Variable $γ$-Ray Emission of CTD 135 and Implications for its Compact Symmetric Structure

The $γ$-ray emission properties of CTD 135, a typical compact symmetric object (CSO), are investigated with $\sim$11-year Fermi/LAT observations. We show that it has bright and significantly variable GeV emission, with the $γ$-ray luminosity of $L_γ\sim10^{47}$ erg s$^{-1}$ and a variation index of TS$_{\rm var}=1002$. A quasi-periodic oscillation (QPO) with a periodicity of $\sim$460 days is detected in the global 95\% false-alarm level. These $γ$-ray emission features are similar to that of blazars. Its broadband spectral energy distribution (SED) can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region. The SED modeling shows that the $γ$-rays are from the core region, which has a Doppler boosting factor of $δ\sim10.8$ and relativistically moves with a small viewing angle, being similar to blazar jets. On the base of the analysis results, we propose that the episodic activity of the central engine in CTD 135 results in a blazar-like jet and the bubble-like lobes as the Fermi bubbles in the Galaxy. The strong $γ$-ray emission with obvious variability is from the jet radiations and the symmetric radio structure is attributed to the bubbles. The jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio galaxies, indicating that its jet radiation may be also driven by the Eddington ratio.

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arXiv2020

Jet Properties of Compact Steep-Spectrum Sources and an Eddington-Ratio-Driven Unification Scheme of Jet Radiation in Active Galactic Nuclei

Compact steep-spectrum sources (CSSs) likely represent a population of young radio-loud active galactic nuclei (AGNs) and have been identified as gamma-ray emitting sources. We present a comprehensive analysis of their gamma-ray emission observed with Fermi/LAT and establish their broadband spectral energy distributions (SEDs). We derive their jet properties by the SED fits with a two-zone leptonic model for radiations from the compact core and large-scale extended region, and explore the possible signature of a unification picture of jet radiation among subclasses of AGNs. We show that the observed gamma-rays of CSSs with significant variability are contributed by the radiation of their compact cores via the inverse Compton process of the torus photons. The derived power-law distribution index of the radiating electrons is p_1~1.5-1.8, magnetic field strength is B~0.15-0.6 G, and Doppler boosting factor is δ~2.8-8.9. Assuming that the jet is composed of electron-positron pairs, the compact cores of CSSs are magnetized and have a high radiation efficiency, similar to that of flat spectrum radio quasars. The six CSSs on average have higher Eddington ratio and black hole mass than those non-GeV-detected CSSs, and they follow the correlation between the jet power in units of Eddington luminosity (P_jet/L_Edd) and Eddington ratio (R_Edd) with other sub-classes of AGNs, P_jet/L_Edd~R_Edd^0.52, indicating that R_Edd would be a key physical driver for the unification scheme of AGN jet radiation.

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arXiv2020

Diversity of gamma-ray and Radio Variabilities of Bright Blazars and Implications for gamma-ray Emission Location

Violent multi-wavelength variabilities are observed in gamma-ray-selected blazars. We present an analysis of long-term light curves for eight bright blazars to explore the co-variation pattern in the gamma-ray and radio bands. We extract their gamma-ray light curves and spectra with data observed by the Fermi/LAT since 2008. We find diverse co-variation patterns between the gamma-ray and radio (at 43 GHz) fluxes in these sources. The gamma-ray and radio fluxes of 3C 454.3 and PKS 1633+382 are correlated without any time-lag, suggesting that they are from the same radiation region. Similar correlation is also observed in 3C 273 and PKS 1222+216, but the radio flux is lag behind the gamma-ray flux approximately ~160 days and ~290 days, respectively. This likely suggests that their gamma-ray emission regions are located at the upstream of their radio cores at 43 GHz. The gamma-ray and radio fluxes of the other four blazars are not correlated, implying that the gamma-ray and radio emission may be from different regions in their jets. The gamma-ray light curves of the eight blazars can be decomposed into some long timescale variability components and fast spike flares. We propose that they may be attributed to the central engine activity and the magnetic reconnection process or turbulence in the local emission region, respectively.

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arXiv2017

Flux and Spectral Variation Characteristics of 3C 454.3 at the GeV Band

We analyze the long-term lightcurve of 3C 454.3 observed with Fermi/LAT and investigate its relation to the flux in the radio, optical, and X-ray bands. By fitting the 1-day binned GeV lightcurve with multiple Gaussian function (MGF), we propose that the typical variability timescale in the GeV band is 1--10 days. The GeV flux variation is accompanied by the spectral variation characterized as flux-tracking, i.e., "harder when brighter". The GeV flux is correlated with the optical and X-ray fluxes, and a weak correlation between gamma-ray flux and radio flux is also observed. The gamma-ray flux is not correlated with the optical linear polarization degree for the global lightcurves, but they show a correlation for the lightcurves before MJD 56000. The power density spectrum of the global lightcurve shows an obvious turnover at ~7.7 days, which may indicate a typical variability timescale of 3C 454.3 in the gamma-ray band. This is also consistent with the derived timescales by fitting the global lightcurve with MGF. The spectral evolution and an increase of the optical linear polarization degree along with the increase of the gamma-ray flux may indicate that the radiation particles are accelerated and the magnetic field is ordered by the shock processes during the outbursts. In addition, the nature of 3C 454.3 may be consistent with the self-organized criticality system, similar to Sagittarius A, and thus the outbursts are from plasmoid ejections driven by magnetic reconnection. This may further support the idea that the jet radiation regions are magnetized.

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arXiv2017

Multiple Wavelength Variability and Quasi-Periodic Oscillation of PMN J0948+0022

We present a comprehensive analysis of multiple wavelength observational data of the first GeV-selected narrow-line Seyfert 1 galaxy PMN J0948+0022. We derive its lightcurves in the γ-ray and X-ray bands from the data observed with Fermi/LAT and Swift/XRT, and make the optical and radio lightcurves by collecting the data from the literature. These lightcurves show significant flux variations. With the LAT data we show that this source is analogue to typical flat spectrum radio quasars in the $L_γ-Γ_γ$ plane, where $L_γ$ and $Γ_γ$ are the luminosity and spectral index in the LAT energy band. The gamma-ray flux is correlated with the V-band flux with a lag of ~44 days, and a moderate quasi-periodic oscillation (QPO) with a periodicity of ~490 days observed in the LAT lightcurve. A similar QPO signature is also found in the V-band lightcurve. The gamma-ray flux is not correlated with the radio flux in 15 GHz, and no similar QPO signature is found in a confidence level of 95%. Possible mechanisms of the QPO are discussed. We propose that gravitational wave observations in the future may clarify the current plausible models for the QPO.

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arXiv2017

Evaluating Optical Classification for {\em Fermi} Blazar Candidates with a Statistical method using Broadband Spectral Indices

We aim to test if a blazar candidate of uncertain-type (BCU) in the third Fermi active galactic nuclei catalog (3LAC) can be potentially classified as a BL Lac object or a flat spectrum radio quasar (FSRQ) by performing a statistical analysis of its broadband spectral properties. We find that 34% of the radio-selected BCUs (583 BCUs) are BL Lac-like and 20% of them are FSRQ-like, which maybe within 90% level of confidence. Similarly, 77.3% of the X-ray selected BCUs (176 BCUs) are evaluated as BL Lac-like and 6.8% of them may be FSRQ-like sources. And 88.7% of the BL Lac-like BCUs that have synchrotron peak frequencies available are high synchrotron peaked BL Lacs in the X-ray selected BCUs. The percentages are accordingly 62% and 7.3% in the sample of 124 optical-selected BCUs. The high ratio of source numbers of the BL Lac-like to the FSRQ-like BCUs in the X-ray and optically selected BCU samples is due to the selection effect. Examining the consistency between our evaluation and spectroscopic identification case by case with a sample of 78 radio-selected BCUs, it is found that the statistical analysis and its resulting classifications agree with the results of the optical follow-up spectroscopic observations. Our observation campaign for high-|ρ_{s}| BCUs , i.e., |ρ_{s}|>0.8, selected with our method is ongoing.

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arXiv2005

Method of determining cosmological parameter ranges with samples of candles with an intrinsic distribution

In this paper, the effect of the intrinsic distribution of cosmological candles is investigated. We find that, in the case of a narrow distribution, the deviation of the observed modulus of sources from the expected central value could be estimated within a ceratin range. We thus introduce a lower and upper limits of $χ^{2}$, $χ_{\min}^{2}$ and $ χ_{\max}^{2}$, to estimate cosmological parameters by applying the conventional minimizing $χ^{2}$ method. We apply this method to a gamma-ray burst (GRB) sample as well as to a combined sample including this GRB sample and an SN Ia sample. Our analysis shows that: a) in the case of assuming an intrinsic distribution of candles of the GRB sample, the effect of the distribution is obvious and should not be neglected; b) taking into account this effect would lead to a poorer constraint of the cosmological parameter ranges. The analysis suggests that in the attempt of constraining the cosmological model with current GRB samples, the results tend to be worse than what previously thought if the mentioned intrinsic distribution does exist.

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arXiv2005

Relationship between the rise width and the full width of gamma-ray burst pulses and its implications in terms of the fireball model

Kocevski et al. (2003) found that there is a linear relation between the rise width and the full width of gamma-ray burst pulses detected by the BATSE instrument based on their empirical functions. Motivated by this, we investigate the relationship based on Qin et al. (2004) model. Theoretical analysis shows that each of the two quantities, the rise width and the full width of observed pulse, is proportional to $Γ^{-2}Δτ_{θ,\rm FWHM}\frac{R_c}{c}$, where $Γ$ is the Lorentz factor for the bulk motion, $Δτ_{θ,\rm FWHM}$ is a local pulse's width, $R_{c}$ is the radius of fireballs and c is the velocity of light. We employ the observed pulses coming from four samples to study the relationship and find that: (1) Merely the curvature effect could produce the relationship with the same slope as those derived from Qin et al. (2004) model in the rise width vs. the full width panel. (2) Gamma-ray burst pulses, long or short ones (selected from the short and long GRBs), follow the same sequence in the rise width vs. the full width panel, with the shorter pulses at the end of this sequence. (3) All GRBs may intrinsically result from local Gaussian pulses. These features place constraints on the physical mechanism(s) for producing long and short GRBs.

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