With the assumption that the optical variability timescale is dominated by the cooling time of the synchrotron process for BL Lac objects,we estimate time dependent magnetic field strength of the emission region for t...With the assumption that the optical variability timescale is dominated by the cooling time of the synchrotron process for BL Lac objects,we estimate time dependent magnetic field strength of the emission region for two BL Lac objects.The average magnetic field strengths are consistent with those estimated from core shift measurement and spectral energy distribution modelling.Variation of magnetic field strength in the dissipation region is discovered.Variability of flux and magnetic field strength shows no clear correlation,which indicates the variation of magnetic field is not the dominant reason of the variability origin.The evolution of magnetic field strength can provide another approach to constrain the energy dissipation mechanism in jets.展开更多
We monitored BL Lacertae in the B,V,R and I bands for 14 nights during the period of 2016-2018.The source showed significant intra-day variability on 12 nights.We performed color-magnitude analysis and found that the ...We monitored BL Lacertae in the B,V,R and I bands for 14 nights during the period of 2016-2018.The source showed significant intra-day variability on 12 nights.We performed color-magnitude analysis and found that the source exhibited bluer-when-brighter chromatism.This bluer-when-brighter behavior is at least partly caused by the larger variation amplitude at shorter wavelengths.The variations at different wavelengths are correlated well and show no inter-band time lag.展开更多
Hard-Te V BL Lac objects are newly identified populations of active galactic nuclei with the emittedγ-ray photons well above Te V energies.In this paper,we explain the multiwavelength emission of six Hard-Te V BL Lac...Hard-Te V BL Lac objects are newly identified populations of active galactic nuclei with the emittedγ-ray photons well above Te V energies.In this paper,we explain the multiwavelength emission of six Hard-Te V BL Lac objects by using a truncated conical emission region of the jet,where the electron distribution is obtained by numerically solving the evolution equation along the jet self-consistently.For comparison,we also apply the model to Mrk 421and Mrk 501,which are the potential candidates for the hard Te V emissions.We demonstrate that the model can satisfactorily reproduce the spectral energy distributions of eight sources,particularly of six Hard-Te V sources,where no extreme minimum Lorentz factor of the electron population is required.In contrast with Mrk 421 and Mrk 501,six Hard-Te V sources have rather low magnetization in emitting regions and high cutoff energies of the electron distributions.展开更多
We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable ...We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable radio emissions are approximately distributed as a log-normal probability distribution function.The Power Spectral Density for the radio light curves can be well characterized by a power-law model.Using the Weighted Wavelet Z-transform and Lomb-Scargle periodogram methods,significant Quasi-periodic Oscillation(QPO)of∼4.6 yr in the radio light curve has been observed above the 3σconfidence level,which presents an interesting case among blazar QPO phenomena.We explore three plausible physical models to explain the observed QPOs:a supermassive binary black hole system,Lense-Thirring precession of the disk,and helical motion of plasma blobs within the jet.展开更多
3C 66A is one of our first batches of photometric monitoring objects with the 1 m optical telescope at Yunnan University Astronomical Observatory.In the present work,the observational campaign was performed from 2021 ...3C 66A is one of our first batches of photometric monitoring objects with the 1 m optical telescope at Yunnan University Astronomical Observatory.In the present work,the observational campaign was performed from 2021 November 1 to 2022 February 27 in the Johnson-Morgan system V and R bands.The average magnitudes in each band were■=15.52±0.18 mag and■=15.07±0.17 mag.The overall variability amplitudes wereΔV=■,Amp=70.27%andΔR=■,Amp=68.56%,respectively.Most of the intraday variabilities(IDVs)occurred in 2021 December and 2022 February.The minimal rise/decay timescale was about 6 minutes(5.82±2.74 minutes and 6.18±2.81 minutes on 2022 February 11,6.99±3.70 minutes and 6.17±2.91 minutes on 2022 February 12).Durations of these rapid variabilities were from 11.99 to 179.67 minutes.The discrete correlation function analyses between V and R bands showed significantly correlated variability.Color index analysis of ID Vs showed that the spectrums do not change with variabilities.展开更多
Fermi-LAT LCR provides continuous and regularly sampled gamma-ray light curves, spanning about 14 yr, for a large sample of blazars. The log-normal flux distribution and linear rms–flux relation of the light curves f...Fermi-LAT LCR provides continuous and regularly sampled gamma-ray light curves, spanning about 14 yr, for a large sample of blazars. The log-normal flux distribution and linear rms–flux relation of the light curves for a few Fermi blazars have been examined in previous studies. However, the probability that blazars exhibit the 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 the distribution of γ-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 365BCUs, and statistically compare their flux distributions with normal and log-normal distributions. The results indicate that the probability of not rejecting log-normal is 42.05% for the large sample, and there is still a 2.05%probability of not rejecting normality, based on the joint of Kolmogorov–Smirnov, Shapiro–Wilk, and Normality tests. We further find that the probability that BL Lacs conform 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 549blazars, which is still a large sample compared to the previous studies, was obtained. Based on dividing the light curves into segments every 20 points(or 40 points, or one year), we fitted the linear rms–flux relation of these three different sets and found that the Pearson correlation coefficients are all close to 1 for most blazars. This result indicates a strong linear correlation between the rms and the flux of these 549 blazars. The log-normal distribution and linear rms–flux relation indicate that the variability of the γ-ray flux for most blazars is a non-linear and multiplicative process.展开更多
We report on our correlation analysis for theγ-ray blazars detected with the Large Area Telescope(LAT)onboard the Fermi Gamma-ray Space Telescope(Fermi),for which we use the Fermi-LAT data and the optical zr and zg b...We report on our correlation analysis for theγ-ray blazars detected with the Large Area Telescope(LAT)onboard the Fermi Gamma-ray Space Telescope(Fermi),for which we use the Fermi-LAT data and the optical zr and zg band data from the Zwicky Transient Facility survey in the time period approximately from 2018 July to 2022February.We start from the full sample of the Fermi-LAT blazars and find~38%of them as significant variables in bothγ-ray and optical bands.Among the variables,which are 705 blazars,95 are selected as our targets based on the requirement for theγ-ray brightnesses.Then 15 out of the 95 blazars are found to show theγ-ray-optical correlations in the~3.7 yr time period.Most of the 15 blazars are classified as low synchrotron peaked(LSP)ones with the time lags between theγ-ray and optical bands in a range from-19 to+25 days.The results generally fit the often-considered emission scenario for the LSP blazars.Two cases of showing~-100 days time lags are discussed,which require farther studies for confirmation.Our analysis results suggest that among the detected significant variables,~23%LSPs can showγ-ray and optical correlations,while their averageγ-ray fluxes are above~4×10^(-8)photon cm^(-2)s^(-1).展开更多
We here report a monitor of the BL Lac object 1 ES 1218+304 in both B-and R-bands by the GWAC-F60 A telescope in eight nights,when it was triggered to be at its highest X-ray flux in history by the VERITAS Observatory...We here report a monitor of the BL Lac object 1 ES 1218+304 in both B-and R-bands by the GWAC-F60 A telescope in eight nights,when it was triggered to be at its highest X-ray flux in history by the VERITAS Observatory and Swift follow-ups.Both ANOVA and χ^(2)-test enable us to clearly reveal an intraday variability in optical wavelengths in seven out of the eight nights.A bluer-when-brighter chromatic relationship has been clearly identified in five out of the eight nights,which can be well explained by the shock-in-jet model.In addition,a quasi-periodic oscillation phenomenon in both bands could be tentatively identified in the first night.A positive delay between the two bands has been revealed in three out of the eight nights,and a negative one in the other nights.The identified minimum time delay enables us to estimate the MBH=2.8 × 10^(7) M_(⊙) that is invalid.展开更多
We examine the scenario that the Doppler factor determines the observational differences of blazars. Significantly negative correlations are found between the observational synchrotron peak frequency and the Doppler f...We examine the scenario that the Doppler factor determines the observational differences of blazars. Significantly negative correlations are found between the observational synchrotron peak frequency and the Doppler factor. After correcting the Doppler boosting, the intrinsic peak frequency has a tight linear relation with the Doppler factor. It is interesting that this relation is consistent with the scenario that the black hole mass governs both the bulk Lorentz factor and the synchrotron peak frequency. In addition, the distinction between the kinetic jet powers of BL Lac objects and flat spectrum radio quasars disappears after the boosting factor δ~2 is considered. The negative correlation between the peak frequency and the observational isotropic luminosity, known as the blazar sequence, also disappears after the Doppler boosting is corrected. We also find that the correlation between the Compton dominance and the Doppler factor exists for all types of blazars. Therefore, this correlation is unsuitable for examining the external Compton emission dominance.展开更多
Long-term optical,X-ray and γ-ray data of blazar 3 C 279 have been compiled from Swift-XRT,RXTE-PCA,Fermi-LAT,SMARTS and literature.The source exhibits strong variability on long timescales.From the 1980 s until now,...Long-term optical,X-ray and γ-ray data of blazar 3 C 279 have been compiled from Swift-XRT,RXTE-PCA,Fermi-LAT,SMARTS and literature.The source exhibits strong variability on long timescales.From the 1980 s until now,the optical R band light curve spans more than 32 yr,and a possible 5.6-yr-long quasi-periodic variation component has been found in it.The optical spectral behavior has been investigated.In the optical band,the mean spectral index is –1.71.The source exhibits an obvious special spectral behavior.In the low state,the source manifests a clear bluer-when-brighter behavior in the sense that the optical spectrum turns harder(flatter) when the brightness increases.While in the high state,the optical spectrum is stable,which means the source spectral index does not vary with brightness.The correlation analysis has been performed among optical,X-ray and γ-ray energy bands.The result indicates that the variations of γ-ray and X-ray bands are well correlated without time delay on the timescale of days,and their variations exhibit weak correlations with those of the optical band.The variations,especially outbursts,are simultaneous,but the magnitude of variations is disproportionate.The detailed analysis reveals that the main outbursts exhibit strong correlations in different γ-ray,X-ray and optical bands.展开更多
In this work,theγ-ray photon flux,photon spectral index(α_(ph)),variability index(log V.I.),and the synchrotron peak frequency(log v_(p))are compiled for 851 common blazars from the 3 FGL and 4 FGL catalogs and Fan ...In this work,theγ-ray photon flux,photon spectral index(α_(ph)),variability index(log V.I.),and the synchrotron peak frequency(log v_(p))are compiled for 851 common blazars from the 3 FGL and 4 FGL catalogs and Fan et al.to investigate variability properties for Fermi blazars.Our calculations and analyses reach following results:(1)the averaged luminosity,spectral index,and variability index of FSRQs are higher than those of BL Lacs for the whole sample.(2)It is found that the spectral index variation is closely anti-correlated with the luminosity variation implying that the spectrum becomes harder when the source becomes brighter in theγ-ray band.(3)Positive correlations are found between the photon spectral index and bothγ-ray luminosity and variability index(log V.I.)for the whole sample,but anti-correlations are found in the two correlations for FSRQs.For BL Lac subclass,there is a marginal anti-correlation between the photon spectral index and bothγ-ray luminosity,and a positive correlation between the photon spectral index and the variability index(log V.I.).We think those two positive correlations found for the whole sample are apparent.(4)We adopted the SVM machine learning method to separate BL Lacs and FSRQs in theα_(ph)versus log L_(γ)andα_(ph)versus log V.I.plots and proposed that a BCU is an FSRQ candidate if it satisfies log V.I.>-10.119 a+24.855,orα_(ph)>-0.048 log L_(γ)+4.498,otherwise,it is a BL Lac candidate.Our classification results are quite consistent with those by Kang et al(2019).展开更多
Based on the long-term light curves collected from the Catalina Sky Survey(CSS)(from 2005 to 2013)and the All-Sky Automated Survey for Supernovae(ASAS-SN)(from 2014 to 2018),optical quasi-periodic oscillations(QPOs)ab...Based on the long-term light curves collected from the Catalina Sky Survey(CSS)(from 2005 to 2013)and the All-Sky Automated Survey for Supernovae(ASAS-SN)(from 2014 to 2018),optical quasi-periodic oscillations(QPOs)about 300 days can be well determined in the well-known blazar PKS 2155-304 through four different methods:the generalized Lomb-Scargle periodogram(GLSP)method,the weighted wavelet Z-transform technique,the epoch-folded method and the redfit method.The GLSP determined significance level for the periodicity is higher than 99.9999%based on a false alarm probability.The redfit provided confidence level for the periodicity is higher than 99%in the ASAS-SN light curve,after considering the effects of red noise.Based on continuous autoregressive process created artificial light curves,the probability of detecting fake QPOs is lower than 0.8%.The determined optical periodicity of 300 days from the CSS and ASAS-SN light curves is well consistent with the reported optical periodicity in the literature.Moreover,three possible models are discussed to explain the optical QPOs in PKS 2155-304:the relativistic frame-dragging effect,the binary black hole model and the jet precession model.展开更多
We present a one-zone homogeneous lepton-hadronic model and obtain steady-state spectra by solving the time-dependent equations to study a plausible origin of hard TeV spectra in PKS 2155-304.In this model,we assume a...We present a one-zone homogeneous lepton-hadronic model and obtain steady-state spectra by solving the time-dependent equations to study a plausible origin of hard TeV spectra in PKS 2155-304.In this model,we assume a steady electron and proton injection rate in the source and solve the non-linear time-dependent kinematic equations that self-consistently consist of proton-photon interaction,synchrotron radiation of electron/positron pairs and proton,inverse Compton scattering,and synchrotron self-absorption.We employ this model to reproduce the multi-wavelength spectrum of PKS 2155-304,then find that the possible bump located at E~1 TeV which may originate from the synchrotron radiation of secondary electrons produced by Bethe-Heitler pair production,resulting in the hard TeV spectrum.展开更多
It is surprising to find an instance of migration in the peak positions of synchrotron spectral energy distribution components during the activity epochs of Markarian 421(Mrk 421),accompanying an orphan flare at the X...It is surprising to find an instance of migration in the peak positions of synchrotron spectral energy distribution components during the activity epochs of Markarian 421(Mrk 421),accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands.A geometric interpretation and standard shock or stochastic acceleration models of blazar emission have difficulty reproducing these observed behaviors.The present paper introduces a linear acceleration by integrating the reconnection electric field into the particle transport model for the observed behaviors of Mrk 421.We note that strong evidence for evolution in characteristic of multi-wavelength spectral energy distribution including shifting the peak frequency,accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands provides an important electrostatic acceleration diagnostic in a blazar jet.Assuming suitable model parameters,we apply the results of the simulation to the 13-day flaring event in March 2010 of Mrk 421,concentrating on the evolution of multiwavelength spectral energy distribution characteristic by shifting the peak frequency.It is clear that the ratio of the electric field and magnetic field strength plays an important role in temporal evolution of the peak frequency of synchrotron spectral energy distribution component.We suggest it is reasonable that the electrostatic acceleration is responsible for the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency.Based on the model results,we assert that the peak frequency of the synchrotron spectral energy distribution component may signify a temporary characteristic of blazars,rather than a permanent one.展开更多
High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars...High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s)follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ0)of GRBs.It is shown that the AGN sample does not agree with the Lp-Ep,z-Γ0 relation of GRBs.In addition,we obtain a tight relation of Lsyn∝Е0.45±0.15δ3.50±0.25 syn,p for FSRQs and NLS1 galaxies,where Lsyn is the luminosity at peak photon energy Esyn,p of the synchrotron radiations.This relation is different from the Lp-Ep,z-Γ0 relation of GRB s.The dependence of Lsyn toδis consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue thatΓ0 may be a representative of the kinetic power of the radiating region and the tight Lp-Ep,z-Γ0 relation is shaped by the radiation physics and the jet power together.展开更多
BL Lac object S5 0716+714 is a well-studied object.In this paper,the available optical(BVRI) data of this source are compiled,and the B-,V-,R-and I-band light curves are constructed.Each of them is analyzed by means o...BL Lac object S5 0716+714 is a well-studied object.In this paper,the available optical(BVRI) data of this source are compiled,and the B-,V-,R-and I-band light curves are constructed.Each of them is analyzed by means of the discrete correlation function(DCF) method,the structure function(SF) method and the z-transformed discrete correlation function(ZDCF) method.The results imply that there is a possible periodic variation of 1211 days in each passband light curve.The source varies violently and complicatedly,and exhibits a brightening trend in the light curves.展开更多
基金supported by the National Natural Science Foundation of China(NSFCGrant Nos.11803081,11947099,U1931203,and 12003014)supported by the CAS Youth Innovation Promotion Association and Basic Research Program of Yunnan Province(202001AW070013)。
文摘With the assumption that the optical variability timescale is dominated by the cooling time of the synchrotron process for BL Lac objects,we estimate time dependent magnetic field strength of the emission region for two BL Lac objects.The average magnetic field strengths are consistent with those estimated from core shift measurement and spectral energy distribution modelling.Variation of magnetic field strength in the dissipation region is discovered.Variability of flux and magnetic field strength shows no clear correlation,which indicates the variation of magnetic field is not the dominant reason of the variability origin.The evolution of magnetic field strength can provide another approach to constrain the energy dissipation mechanism in jets.
基金supported by the National Natural Science Foundation of China(Grant No.11973017)。
文摘We monitored BL Lacertae in the B,V,R and I bands for 14 nights during the period of 2016-2018.The source showed significant intra-day variability on 12 nights.We performed color-magnitude analysis and found that the source exhibited bluer-when-brighter chromatism.This bluer-when-brighter behavior is at least partly caused by the larger variation amplitude at shorter wavelengths.The variations at different wavelengths are correlated well and show no inter-band time lag.
基金the financial supports from the growth project of young scientific and technological talents in colleges and universities in Guizhou Province(Qianjiaohe-KY-Zi[2020]221)Scientific Research Foundation for Doctoral Program of Xingyi Normal University for Nationalities(20XYBS16)。
文摘Hard-Te V BL Lac objects are newly identified populations of active galactic nuclei with the emittedγ-ray photons well above Te V energies.In this paper,we explain the multiwavelength emission of six Hard-Te V BL Lac objects by using a truncated conical emission region of the jet,where the electron distribution is obtained by numerically solving the evolution equation along the jet self-consistently.For comparison,we also apply the model to Mrk 421and Mrk 501,which are the potential candidates for the hard Te V emissions.We demonstrate that the model can satisfactorily reproduce the spectral energy distributions of eight sources,particularly of six Hard-Te V sources,where no extreme minimum Lorentz factor of the electron population is required.In contrast with Mrk 421 and Mrk 501,six Hard-Te V sources have rather low magnetization in emitting regions and high cutoff energies of the electron distributions.
基金funded by the National Natural Science Foundation of China (NSFC) under No.11903028the support from the “Yunnan Revitalization Talent Support Program” of Yunnan province, China+2 种基金the University of Michigan Radio Astronomy Observatory, which is supported by the University of Michiganby a series of grants from the National Science Foundation, most recently AST-0607523NASA Fermi grants NNX09AU16G, NNX10AP16G, and NNX11AO13G.
文摘We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable radio emissions are approximately distributed as a log-normal probability distribution function.The Power Spectral Density for the radio light curves can be well characterized by a power-law model.Using the Weighted Wavelet Z-transform and Lomb-Scargle periodogram methods,significant Quasi-periodic Oscillation(QPO)of∼4.6 yr in the radio light curve has been observed above the 3σconfidence level,which presents an interesting case among blazar QPO phenomena.We explore three plausible physical models to explain the observed QPOs:a supermassive binary black hole system,Lense-Thirring precession of the disk,and helical motion of plasma blobs within the jet.
基金supported by the fund for the Youth Project of Basic Research Program of Yunnan Province (202001BB050012)the Joint Foundation of Department of Science and Technology of Yunnan Province and Yunnan University (202201BF070001-020)funded by the“Yunnan University Development Plan for World-Class Astronomy Discipline”。
文摘3C 66A is one of our first batches of photometric monitoring objects with the 1 m optical telescope at Yunnan University Astronomical Observatory.In the present work,the observational campaign was performed from 2021 November 1 to 2022 February 27 in the Johnson-Morgan system V and R bands.The average magnitudes in each band were■=15.52±0.18 mag and■=15.07±0.17 mag.The overall variability amplitudes wereΔV=■,Amp=70.27%andΔR=■,Amp=68.56%,respectively.Most of the intraday variabilities(IDVs)occurred in 2021 December and 2022 February.The minimal rise/decay timescale was about 6 minutes(5.82±2.74 minutes and 6.18±2.81 minutes on 2022 February 11,6.99±3.70 minutes and 6.17±2.91 minutes on 2022 February 12).Durations of these rapid variabilities were from 11.99 to 179.67 minutes.The discrete correlation function analyses between V and R bands showed significantly correlated variability.Color index analysis of ID Vs showed that the spectrums do not change with variabilities.
基金funded by the National Natural Science Foundation of China (grants 12063007 and 11863007)。
文摘Fermi-LAT LCR provides continuous and regularly sampled gamma-ray light curves, spanning about 14 yr, for a large sample of blazars. The log-normal flux distribution and linear rms–flux relation of the light curves for a few Fermi blazars have been examined in previous studies. However, the probability that blazars exhibit the 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 the distribution of γ-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 365BCUs, and statistically compare their flux distributions with normal and log-normal distributions. The results indicate that the probability of not rejecting log-normal is 42.05% for the large sample, and there is still a 2.05%probability of not rejecting normality, based on the joint of Kolmogorov–Smirnov, Shapiro–Wilk, and Normality tests. We further find that the probability that BL Lacs conform 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 549blazars, which is still a large sample compared to the previous studies, was obtained. Based on dividing the light curves into segments every 20 points(or 40 points, or one year), we fitted the linear rms–flux relation of these three different sets and found that the Pearson correlation coefficients are all close to 1 for most blazars. This result indicates a strong linear correlation between the rms and the flux of these 549 blazars. The log-normal distribution and linear rms–flux relation indicate that the variability of the γ-ray flux for most blazars is a non-linear and multiplicative process.
基金supported by Basic Research Program of Yunnan Province(No.202201AS070005)the National Natural Science Foundation of China(12273033)the Original Innovation Program of the Chinese Academy of Sciences(E085021002)。
文摘We report on our correlation analysis for theγ-ray blazars detected with the Large Area Telescope(LAT)onboard the Fermi Gamma-ray Space Telescope(Fermi),for which we use the Fermi-LAT data and the optical zr and zg band data from the Zwicky Transient Facility survey in the time period approximately from 2018 July to 2022February.We start from the full sample of the Fermi-LAT blazars and find~38%of them as significant variables in bothγ-ray and optical bands.Among the variables,which are 705 blazars,95 are selected as our targets based on the requirement for theγ-ray brightnesses.Then 15 out of the 95 blazars are found to show theγ-ray-optical correlations in the~3.7 yr time period.Most of the 15 blazars are classified as low synchrotron peaked(LSP)ones with the time lags between theγ-ray and optical bands in a range from-19 to+25 days.The results generally fit the often-considered emission scenario for the LSP blazars.Two cases of showing~-100 days time lags are discussed,which require farther studies for confirmation.Our analysis results suggest that among the detected significant variables,~23%LSPs can showγ-ray and optical correlations,while their averageγ-ray fluxes are above~4×10^(-8)photon cm^(-2)s^(-1).
基金support from the National Key R & D Program of China (Grant No.2020YFE0202100)supported by the National Natural Science Foundation of China (Grant 11773036)+2 种基金by the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences (Grant Nos.XDA15052600 and XDA15016500)supported by the Natural Science Foundation of Guangxi (2018GXUSFGA281007 & 2020GXNSFDA238018)by the Bagui Young Scholars Program。
文摘We here report a monitor of the BL Lac object 1 ES 1218+304 in both B-and R-bands by the GWAC-F60 A telescope in eight nights,when it was triggered to be at its highest X-ray flux in history by the VERITAS Observatory and Swift follow-ups.Both ANOVA and χ^(2)-test enable us to clearly reveal an intraday variability in optical wavelengths in seven out of the eight nights.A bluer-when-brighter chromatic relationship has been clearly identified in five out of the eight nights,which can be well explained by the shock-in-jet model.In addition,a quasi-periodic oscillation phenomenon in both bands could be tentatively identified in the first night.A positive delay between the two bands has been revealed in three out of the eight nights,and a negative one in the other nights.The identified minimum time delay enables us to estimate the MBH=2.8 × 10^(7) M_(⊙) that is invalid.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences - The Emergence of Cosmological Structures (grant No. XDB09000000)the Key Research Program of the Chinese Academy of Sciences (grant No. KJZD-EW-M06)+1 种基金the National Natural Science Foundation of China (NSFC) through NSFC-11133006 and 11361140347supported by the Hundred-Talent Program of Chinese Academy of Sciences
文摘We examine the scenario that the Doppler factor determines the observational differences of blazars. Significantly negative correlations are found between the observational synchrotron peak frequency and the Doppler factor. After correcting the Doppler boosting, the intrinsic peak frequency has a tight linear relation with the Doppler factor. It is interesting that this relation is consistent with the scenario that the black hole mass governs both the bulk Lorentz factor and the synchrotron peak frequency. In addition, the distinction between the kinetic jet powers of BL Lac objects and flat spectrum radio quasars disappears after the boosting factor δ~2 is considered. The negative correlation between the peak frequency and the observational isotropic luminosity, known as the blazar sequence, also disappears after the Doppler boosting is corrected. We also find that the correlation between the Compton dominance and the Doppler factor exists for all types of blazars. Therefore, this correlation is unsuitable for examining the external Compton emission dominance.
基金the support from National Natural Science Foundation of China (NSFC,Nos.U1831124 and 11273008)the Natural Science Foundation of Anhui Province of China (Grant No.1908085MA28)。
文摘Long-term optical,X-ray and γ-ray data of blazar 3 C 279 have been compiled from Swift-XRT,RXTE-PCA,Fermi-LAT,SMARTS and literature.The source exhibits strong variability on long timescales.From the 1980 s until now,the optical R band light curve spans more than 32 yr,and a possible 5.6-yr-long quasi-periodic variation component has been found in it.The optical spectral behavior has been investigated.In the optical band,the mean spectral index is –1.71.The source exhibits an obvious special spectral behavior.In the low state,the source manifests a clear bluer-when-brighter behavior in the sense that the optical spectrum turns harder(flatter) when the brightness increases.While in the high state,the optical spectrum is stable,which means the source spectral index does not vary with brightness.The correlation analysis has been performed among optical,X-ray and γ-ray energy bands.The result indicates that the variations of γ-ray and X-ray bands are well correlated without time delay on the timescale of days,and their variations exhibit weak correlations with those of the optical band.The variations,especially outbursts,are simultaneous,but the magnitude of variations is disproportionate.The detailed analysis reveals that the main outbursts exhibit strong correlations in different γ-ray,X-ray and optical bands.
基金the National Natural Science Foundation of China(NSFC U2031201,11733001,U2031112,12133004 and 12103012)Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)+2 种基金the science research grants from the China Manned Space Project with NO.CMSCSST-2021-A06the supports for Astrophysics Key Subjects of Guangdong Province and Guangzhou Citysupported by Guangzhou University(YM2020001)。
文摘In this work,theγ-ray photon flux,photon spectral index(α_(ph)),variability index(log V.I.),and the synchrotron peak frequency(log v_(p))are compiled for 851 common blazars from the 3 FGL and 4 FGL catalogs and Fan et al.to investigate variability properties for Fermi blazars.Our calculations and analyses reach following results:(1)the averaged luminosity,spectral index,and variability index of FSRQs are higher than those of BL Lacs for the whole sample.(2)It is found that the spectral index variation is closely anti-correlated with the luminosity variation implying that the spectrum becomes harder when the source becomes brighter in theγ-ray band.(3)Positive correlations are found between the photon spectral index and bothγ-ray luminosity and variability index(log V.I.)for the whole sample,but anti-correlations are found in the two correlations for FSRQs.For BL Lac subclass,there is a marginal anti-correlation between the photon spectral index and bothγ-ray luminosity,and a positive correlation between the photon spectral index and the variability index(log V.I.).We think those two positive correlations found for the whole sample are apparent.(4)We adopted the SVM machine learning method to separate BL Lacs and FSRQs in theα_(ph)versus log L_(γ)andα_(ph)versus log V.I.plots and proposed that a BCU is an FSRQ candidate if it satisfies log V.I.>-10.119 a+24.855,orα_(ph)>-0.048 log L_(γ)+4.498,otherwise,it is a BL Lac candidate.Our classification results are quite consistent with those by Kang et al(2019).
基金the National Natural Science Foundation of China(Grant Nos.11873032 and 12173020)。
文摘Based on the long-term light curves collected from the Catalina Sky Survey(CSS)(from 2005 to 2013)and the All-Sky Automated Survey for Supernovae(ASAS-SN)(from 2014 to 2018),optical quasi-periodic oscillations(QPOs)about 300 days can be well determined in the well-known blazar PKS 2155-304 through four different methods:the generalized Lomb-Scargle periodogram(GLSP)method,the weighted wavelet Z-transform technique,the epoch-folded method and the redfit method.The GLSP determined significance level for the periodicity is higher than 99.9999%based on a false alarm probability.The redfit provided confidence level for the periodicity is higher than 99%in the ASAS-SN light curve,after considering the effects of red noise.Based on continuous autoregressive process created artificial light curves,the probability of detecting fake QPOs is lower than 0.8%.The determined optical periodicity of 300 days from the CSS and ASAS-SN light curves is well consistent with the reported optical periodicity in the literature.Moreover,three possible models are discussed to explain the optical QPOs in PKS 2155-304:the relativistic frame-dragging effect,the binary black hole model and the jet precession model.
基金partially supported by the National Natural Science Foundation of China(Grant Nos.12063006,11803027and 11863007)Yunnan Local Colleges Applied Basic Research Projects(Grant Nos.202001BA070001-031,2017FH001-102,2018FH001-015,2019FH001-012 and2019FH001-076)+1 种基金Science Research Foundation of Yunnan Education Department of China(Grant Nos.2017ZZX177,2018JS422 and 2019J0733)the financial support from the Hundred Talents Program of Yuxi(Grant Nos.2019)。
文摘We present a one-zone homogeneous lepton-hadronic model and obtain steady-state spectra by solving the time-dependent equations to study a plausible origin of hard TeV spectra in PKS 2155-304.In this model,we assume a steady electron and proton injection rate in the source and solve the non-linear time-dependent kinematic equations that self-consistently consist of proton-photon interaction,synchrotron radiation of electron/positron pairs and proton,inverse Compton scattering,and synchrotron self-absorption.We employ this model to reproduce the multi-wavelength spectrum of PKS 2155-304,then find that the possible bump located at E~1 TeV which may originate from the synchrotron radiation of secondary electrons produced by Bethe-Heitler pair production,resulting in the hard TeV spectrum.
基金the National Natural Science Foundation of China(Grant Nos.11673060,11763005,11873043 and 11991051)the Specialized Research Fund for Shandong Provincial Key Laboratory(Grant No.KLWH201804)the Research Foundation for Scientific Elitists of the Department of Education of Guizhou Province(Grant No.QJHKYZ[2018]068)。
文摘It is surprising to find an instance of migration in the peak positions of synchrotron spectral energy distribution components during the activity epochs of Markarian 421(Mrk 421),accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands.A geometric interpretation and standard shock or stochastic acceleration models of blazar emission have difficulty reproducing these observed behaviors.The present paper introduces a linear acceleration by integrating the reconnection electric field into the particle transport model for the observed behaviors of Mrk 421.We note that strong evidence for evolution in characteristic of multi-wavelength spectral energy distribution including shifting the peak frequency,accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands provides an important electrostatic acceleration diagnostic in a blazar jet.Assuming suitable model parameters,we apply the results of the simulation to the 13-day flaring event in March 2010 of Mrk 421,concentrating on the evolution of multiwavelength spectral energy distribution characteristic by shifting the peak frequency.It is clear that the ratio of the electric field and magnetic field strength plays an important role in temporal evolution of the peak frequency of synchrotron spectral energy distribution component.We suggest it is reasonable that the electrostatic acceleration is responsible for the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency.Based on the model results,we assert that the peak frequency of the synchrotron spectral energy distribution component may signify a temporary characteristic of blazars,rather than a permanent one.
基金the National Natural Science Foundation of China(Grant Nos.11533003,11851304 and U1731239)Guangxi Science Foundation and special funding for Guangxi distinguished professors(2017AD22006)。
文摘High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s)follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ0)of GRBs.It is shown that the AGN sample does not agree with the Lp-Ep,z-Γ0 relation of GRBs.In addition,we obtain a tight relation of Lsyn∝Е0.45±0.15δ3.50±0.25 syn,p for FSRQs and NLS1 galaxies,where Lsyn is the luminosity at peak photon energy Esyn,p of the synchrotron radiations.This relation is different from the Lp-Ep,z-Γ0 relation of GRB s.The dependence of Lsyn toδis consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue thatΓ0 may be a representative of the kinetic power of the radiating region and the tight Lp-Ep,z-Γ0 relation is shaped by the radiation physics and the jet power together.
基金supported by the Scientific Research Foundation of Fuyang Normal Collegethe National Natural Science Foundation of China (Grant No. 10975145)partially by Natural Science Foundation of Yunnan Province (Grant No.2007A026M)
文摘BL Lac object S5 0716+714 is a well-studied object.In this paper,the available optical(BVRI) data of this source are compiled,and the B-,V-,R-and I-band light curves are constructed.Each of them is analyzed by means of the discrete correlation function(DCF) method,the structure function(SF) method and the z-transformed discrete correlation function(ZDCF) method.The results imply that there is a possible periodic variation of 1211 days in each passband light curve.The source varies violently and complicatedly,and exhibits a brightening trend in the light curves.