We present an analysis of the cross-correlation between optical brightness and polarization degree in different types of blazars.The aim is to identify objects with simultaneous and consistent changes in characteristi...We present an analysis of the cross-correlation between optical brightness and polarization degree in different types of blazars.The aim is to identify objects with simultaneous and consistent changes in characteristics and to determine if this behavior relates to the types of objects studied.The analysis includes 23 objects:11 Flat Spectrum Radio Quasars(FSRQs),11 BL Lacs,and 1 radio galaxy.Dense overlapping observation series in the R band were used,collected over more than 10 yr as part of a monitoring program for bright blazars at St.Petersburg State University.The cross-correlation analysis procedure is detailed,including a method for assessing significance based on Monte Carlo simulations of synthetic light curves modeled using a Damped Random Walk.Significant correlations were found for 5 FSRQs and 1 BL Lac.No significant correlation was detected for 10 BL Lacs and 6 FSRQs.One object did not yield a reliable estimate.Based on the current results,we cannot claim that the observed difference in the behavior of these emission characteristics for different classes of blazars is significant.It is possible that observed correlations may be explained by the contribution of simultaneous flare events to the changes in flux and polarization degree curves,which occur more frequently in FSRQs.展开更多
We present the results of the multi-epoch broadband spectral study of 1ES 2344+514 and study the evolution of physical parameters.We used nearly simultaneous data obtained from 2017 June 6 to 2022 August 6(MJD 57910–...We present the results of the multi-epoch broadband spectral study of 1ES 2344+514 and study the evolution of physical parameters.We used nearly simultaneous data obtained from 2017 June 6 to 2022 August 6(MJD 57910–59797)in optical,UV,X-ray andγ-ray wavebands from various instruments including Swift-UVOT,Swift-XRT,Nuclear Spectroscopic Telescope Array(NuSTAR),AstroSat(SXT and LAXPC),Fermi-LAT,and TeV flux from MAGIC.During 2017 July,1ES 2344+514 appeared to be in the highest flaring state compared to other periods.We used the 0.5–7.0 keV and 3.0–20.0 keV data,respectively,from SXT and LAXPC of AstroSat and also 0.3–8.0 keV and 3.0–79.0 keV data,respectively,from Swift-XRT and NuSTAR.A joint fit between SXT and LAXPC,and between Swift-XRT and NuSTAR has been done for constraining the synchrotron peak.A clear shift in the synchrotron peak has been observed,which included 1ES 2344+514 in the HSP BL Lac family.A“harder-when-brighter”trend is observed in X-rays,and the opposite trend,i.e.,“softer-when-brighter,”is seen in theγ-rays.The multi-epoch broadband spectral energy distributions(SEDs)of this source were built and studied to get an idea of the radiation processes.The SEDs were fitted using a steady-state leptonic one-zone synchrotron+SSC model,and the fitted parameters of the emission region are consistent with those of other TeV BL Lacs.In this study,we found a weak correlation tendency between bolometric luminosity and magnetic field(B),as well as between bolometric luminosity and the break Lorentz factor(γ_(break)).展开更多
Based on the collected multiwavelength data, namely in the radio(NVSS, FIRST, RATAN-600), IR(WISE),optical(Pan-STARRS), UV(GALEX), and X-ray(ROSAT, Swift-XRT) ranges, we have performed a cluster analysis for the blaza...Based on the collected multiwavelength data, namely in the radio(NVSS, FIRST, RATAN-600), IR(WISE),optical(Pan-STARRS), UV(GALEX), and X-ray(ROSAT, Swift-XRT) ranges, we have performed a cluster analysis for the blazars of the Roma-BZCAT catalog. Using two machine learning methods, namely a combination of PCA with k-means clustering and Kohonen's self-organizing maps(SOMs), we have constructed an independent classification of the blazars(five classes) and compared the classes with the known Roma-BZCAT classification(FSRQs, BL Lacs, galaxy-dominated BL Lacs, and blazars of an uncertain type) as well as with the high synchrotron peaked(HSP) blazars from the 3HSP catalog and blazars from the TeVCat catalog. The obtained groups demonstrate concordance with the BL Lac/FSRQ classification along with a continuous character of the change in the properties. The group of HSP blazars stands out against the overall distribution. We examine the characteristics of the five groups and demonstrate distinctions in their spectral energy distribution shapes. The effectiveness of the clustering technique for objective analysis of multiparametric arrays of experimental data is demonstrated.展开更多
We report a candidate tidal disruption event(TDE) found in the Zwicky Transient Facility survey data.This candidate,with its transient name AT2021acak,showed brightness increases of ~1 mag around MJD 59500 and subsequ...We report a candidate tidal disruption event(TDE) found in the Zwicky Transient Facility survey data.This candidate,with its transient name AT2021acak,showed brightness increases of ~1 mag around MJD 59500 and subsequent power-law–like brightness declines.We have conducted multiple optical spectroscopic observations with the 2.4 m Lijiang telescope and one observation at X-ray and ultraviolet(UV) bands with the Neil Gehrels Swift Observatory(Swift).The optical spectra of the source show broad H and He emission lines and Fe emission features.Possible 0.3–2 ke V X-ray and bright UV emission of the source was detected.We analyze the declines of the optical light curves,the emission features of the optical spectra,and the constructed broad-band UV and optical spectra.The properties derived from the analyses are consistent with those of reported(candidate) TDEs,and in particular very similar to those of ASASSN-18jd.The identification is complicated by the host being likely an AGN,and thus further observations of the event and quiescent host are required in order to have a clear understanding of the nature of this transient event.展开更多
By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central （R ≤ 10 h^-171 kpc） gas entropy excess （AK0）, which cor...By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central （R ≤ 10 h^-171 kpc） gas entropy excess （AK0）, which corresponds to = 0.1 - 0.5 keV per gas particle, beyond the power-law model that best fits the radial entropy profile of the outer regions. We also find a distinct correlation between the central entropy excess △K0 and K-band luminosity LK of the central dominating galaxies （CDGs）, which is scaled as △K0 ∝ L K 1.6±04, where LK is tightly associated with the mass of the supermassive black hole hosted in the CDG. In fact, if an effective mass-to-energy conversionefficiency of 0.02 is assumed for the accretion process, the cumulative AGN feedback E AGN feedack=ηMBHc2 yields an extra heating of = 0.5 - 17.0keV per particle, which feedback is sufficient to explain the central entropy excess. In most cases, the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius （= 0.002 - 2.2 keV per particle）, and apparently exceeds the energy required to cause the scaling relations to deviate from the self-similar predictions （=0.2 - 1.0 keV per particle）. In contrast to the AGN feedback, the extra heating provided by supernova explosions accounts for = 0.01 - 0.08 keV per particle in groups and is almost negligible in clusters. Therefore, the observed correlation between △K0 and Lx can be considered as direct evidence for AGN feedback in galaxy groups and clusters.展开更多
This paper presents an adaptive Under Frequency Load Shedding scheme based on Wide Area Measurement System. Due to the lack of enough adaptability to the operation state of the system, the traditional successive appro...This paper presents an adaptive Under Frequency Load Shedding scheme based on Wide Area Measurement System. Due to the lack of enough adaptability to the operation state of the system, the traditional successive approximation under frequency load shedding method will cause excessive cut or undercut problems inevitably. This method consists first in a comprehensive weight index including load characteristics and inertias of generators. Then active-power deficit calculation based on the Low-order Frequency Response Model, concerning the effect of voltage was put forward. Finally, a dynamic correction of the load shedding amount was proposed to modify the scheme. This approach was applied to IEEE-39 system and the simulation results indicated that the proposed method was effective in reducing the load shedding amount as well as the frequency recovery time.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
Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGN...Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGNs）. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 〈 z 〈 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.展开更多
基金the National Science Foundation grant AST-2108622several NASA Fermi vip Investigator grants,the latest is 80NSSC23K1507supported by Fermi vip Investigator grants NNX08AW56G,NNX09AU10G,NNX12AO93G,and NNX15AU81G.
文摘We present an analysis of the cross-correlation between optical brightness and polarization degree in different types of blazars.The aim is to identify objects with simultaneous and consistent changes in characteristics and to determine if this behavior relates to the types of objects studied.The analysis includes 23 objects:11 Flat Spectrum Radio Quasars(FSRQs),11 BL Lacs,and 1 radio galaxy.Dense overlapping observation series in the R band were used,collected over more than 10 yr as part of a monitoring program for bright blazars at St.Petersburg State University.The cross-correlation analysis procedure is detailed,including a method for assessing significance based on Monte Carlo simulations of synthetic light curves modeled using a Damped Random Walk.Significant correlations were found for 5 FSRQs and 1 BL Lac.No significant correlation was detected for 10 BL Lacs and 6 FSRQs.One object did not yield a reliable estimate.Based on the current results,we cannot claim that the observed difference in the behavior of these emission characteristics for different classes of blazars is significant.It is possible that observed correlations may be explained by the contribution of simultaneous flare events to the changes in flux and polarization degree curves,which occur more frequently in FSRQs.
基金support of the Department of Atomic Energy,Government of India,under project identification No.RT4002supported by Fermi vip Investigator grants NNX08AN56G,NNX08AN56G,NNX09AV10G,and NNX15AU81G。
文摘We present the results of the multi-epoch broadband spectral study of 1ES 2344+514 and study the evolution of physical parameters.We used nearly simultaneous data obtained from 2017 June 6 to 2022 August 6(MJD 57910–59797)in optical,UV,X-ray andγ-ray wavebands from various instruments including Swift-UVOT,Swift-XRT,Nuclear Spectroscopic Telescope Array(NuSTAR),AstroSat(SXT and LAXPC),Fermi-LAT,and TeV flux from MAGIC.During 2017 July,1ES 2344+514 appeared to be in the highest flaring state compared to other periods.We used the 0.5–7.0 keV and 3.0–20.0 keV data,respectively,from SXT and LAXPC of AstroSat and also 0.3–8.0 keV and 3.0–79.0 keV data,respectively,from Swift-XRT and NuSTAR.A joint fit between SXT and LAXPC,and between Swift-XRT and NuSTAR has been done for constraining the synchrotron peak.A clear shift in the synchrotron peak has been observed,which included 1ES 2344+514 in the HSP BL Lac family.A“harder-when-brighter”trend is observed in X-rays,and the opposite trend,i.e.,“softer-when-brighter,”is seen in theγ-rays.The multi-epoch broadband spectral energy distributions(SEDs)of this source were built and studied to get an idea of the radiation processes.The SEDs were fitted using a steady-state leptonic one-zone synchrotron+SSC model,and the fitted parameters of the emission region are consistent with those of other TeV BL Lacs.In this study,we found a weak correlation tendency between bolometric luminosity and magnetic field(B),as well as between bolometric luminosity and the break Lorentz factor(γ_(break)).
文摘Based on the collected multiwavelength data, namely in the radio(NVSS, FIRST, RATAN-600), IR(WISE),optical(Pan-STARRS), UV(GALEX), and X-ray(ROSAT, Swift-XRT) ranges, we have performed a cluster analysis for the blazars of the Roma-BZCAT catalog. Using two machine learning methods, namely a combination of PCA with k-means clustering and Kohonen's self-organizing maps(SOMs), we have constructed an independent classification of the blazars(five classes) and compared the classes with the known Roma-BZCAT classification(FSRQs, BL Lacs, galaxy-dominated BL Lacs, and blazars of an uncertain type) as well as with the high synchrotron peaked(HSP) blazars from the 3HSP catalog and blazars from the TeVCat catalog. The obtained groups demonstrate concordance with the BL Lac/FSRQ classification along with a continuous character of the change in the properties. The group of HSP blazars stands out against the overall distribution. We examine the characteristics of the five groups and demonstrate distinctions in their spectral energy distribution shapes. The effectiveness of the clustering technique for objective analysis of multiparametric arrays of experimental data is demonstrated.
基金supported by the National Science Foundation under grant No.AST-2034437supported by the National SKA program of China(No.2022SKA0130101)+2 种基金Basic Research Program of Yunnan Province(No.202201AS070005)the National Natural Science Foundation of China(12273033)the support by the Original Innovation Program of the Chinese Academy of Sciences(E085021002)。
文摘We report a candidate tidal disruption event(TDE) found in the Zwicky Transient Facility survey data.This candidate,with its transient name AT2021acak,showed brightness increases of ~1 mag around MJD 59500 and subsequent power-law–like brightness declines.We have conducted multiple optical spectroscopic observations with the 2.4 m Lijiang telescope and one observation at X-ray and ultraviolet(UV) bands with the Neil Gehrels Swift Observatory(Swift).The optical spectra of the source show broad H and He emission lines and Fe emission features.Possible 0.3–2 ke V X-ray and bright UV emission of the source was detected.We analyze the declines of the optical light curves,the emission features of the optical spectra,and the constructed broad-band UV and optical spectra.The properties derived from the analyses are consistent with those of reported(candidate) TDEs,and in particular very similar to those of ASASSN-18jd.The identification is complicated by the host being likely an AGN,and thus further observations of the event and quiescent host are required in order to have a clear understanding of the nature of this transient event.
基金Supported by the National Natural Science Foundation of China(Grant Nos.10673008,10878001 and 10973010)the Ministry of Science and Technology of China(Grant No.2009CB824900/2009CB24904)the Ministry of Education of China(the NCET Program)
文摘By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central （R ≤ 10 h^-171 kpc） gas entropy excess （AK0）, which corresponds to = 0.1 - 0.5 keV per gas particle, beyond the power-law model that best fits the radial entropy profile of the outer regions. We also find a distinct correlation between the central entropy excess △K0 and K-band luminosity LK of the central dominating galaxies （CDGs）, which is scaled as △K0 ∝ L K 1.6±04, where LK is tightly associated with the mass of the supermassive black hole hosted in the CDG. In fact, if an effective mass-to-energy conversionefficiency of 0.02 is assumed for the accretion process, the cumulative AGN feedback E AGN feedack=ηMBHc2 yields an extra heating of = 0.5 - 17.0keV per particle, which feedback is sufficient to explain the central entropy excess. In most cases, the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius （= 0.002 - 2.2 keV per particle）, and apparently exceeds the energy required to cause the scaling relations to deviate from the self-similar predictions （=0.2 - 1.0 keV per particle）. In contrast to the AGN feedback, the extra heating provided by supernova explosions accounts for = 0.01 - 0.08 keV per particle in groups and is almost negligible in clusters. Therefore, the observed correlation between △K0 and Lx can be considered as direct evidence for AGN feedback in galaxy groups and clusters.
文摘This paper presents an adaptive Under Frequency Load Shedding scheme based on Wide Area Measurement System. Due to the lack of enough adaptability to the operation state of the system, the traditional successive approximation under frequency load shedding method will cause excessive cut or undercut problems inevitably. This method consists first in a comprehensive weight index including load characteristics and inertias of generators. Then active-power deficit calculation based on the Low-order Frequency Response Model, concerning the effect of voltage was put forward. Finally, a dynamic correction of the load shedding amount was proposed to modify the scheme. This approach was applied to IEEE-39 system and the simulation results indicated that the proposed method was effective in reducing the load shedding amount as well as the frequency recovery time.
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 National Natural Science Foundation of China
文摘Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGNs）. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 〈 z 〈 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.
