A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction...A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.展开更多
Blazars are subclass of AGN （active galactic nuclei） with relativistic jet that is pointing in the general direction of the earth. The energy flux in the jet is about （10^44-10^47） erg/s. The γ-rays in the energy...Blazars are subclass of AGN （active galactic nuclei） with relativistic jet that is pointing in the general direction of the earth. The energy flux in the jet is about （10^44-10^47） erg/s. The γ-rays in the energy range 10 GeV-10 TeV emanating from blazar are examined and their effect on the IGM （intergalactic medium） is studied. The γ-ray emission is considered as due to inverse Compton scattering of relativistic electrons. There appears to be a gamma ray flux from blazar above 10 GeV having a line intensity of 1.5 × 10^-4 cm^-2 s^-1 sr^-1. The IGM is measured to large distances and it is found to be clumpy. It is found that at higher redshifl the density of IGM increases. The cosmological density parameter measured is found to lie within the suggested limit of 0.03 at redshift z = 3 for background intensity of radiation 10^-24 W·m^-2·Hz^-1·sr^-1. The iso-ΩIGM curve shows a kink in its profile which might be significant at the particular value of z equal to 2. Some more detailed studies are required for understanding the distribution of intergalactic medium at the unstable point at z = 2 as shown in inverse Compton radiation.展开更多
In the framework of BLR in AGNs, i.e. large number of small, cold and dense emission-line clouds immerging in an intercloud hot medium, a delicate radiation model for a typical emission cloud is established, in which ...In the framework of BLR in AGNs, i.e. large number of small, cold and dense emission-line clouds immerging in an intercloud hot medium, a delicate radiation model for a typical emission cloud is established, in which the backside photoionization of the cloud against the central continuum source by the scattered diffuse continuum in the hot medium is considered. Under the assumption of the radial kinematics of the BLR clouds, the line profiles for the two important UV emission-lines, Lya and CIV/11549 are computed; and based on these calculations, various physical factors that affect the properties of the emission-line profiles are discussed. It is concluded that: (i) when the BLR clouds is inflow, there exists a confining hot medium with density around 2 x 105 cm-3. In this case, theoretical line profiles agree well with the observational; (ii) both symmetric Lya and nearly symmetric CIV line profiles show blue velocity shifts, the quantities of which are sensitive to the cutoff of the outer radius of the BLR. It is suggested that this cutoff effect is physical background to explain the observations that high ionization lines in the spectra of AGNs have some systematic blue shifts relative to those low ionization lines which usually characterize their source system velocities.展开更多
Since the unknown emission features in the spectrum of quasar 3C 273 have beenfirst identified as the blended Fell multiplets, many papers have contributed to thetheoretical and observation research of Fell emission i...Since the unknown emission features in the spectrum of quasar 3C 273 have beenfirst identified as the blended Fell multiplets, many papers have contributed to thetheoretical and observation research of Fell emission in the spectra of Seyferts andquasars. Usually, optical FeII emission lines are produced by transitions from展开更多
In this paper we give a brief review of the astrophysics of active galactic nuclei （AGNs）. After a general introduction motivating the study of AGNs, we discuss our present understanding of the inner workings of the...In this paper we give a brief review of the astrophysics of active galactic nuclei （AGNs）. After a general introduction motivating the study of AGNs, we discuss our present understanding of the inner workings of the central engines, most likely accreting black holes with masses between 106 and 10^10M. We highlight recent results concerning the jets （collimated outflows） of AGNs derived from X-ray observations （Chandra） of kpc-scale jets and ~/-ray observations of AGNs （Fermi, Cherenkov telescopes） with jets closely aligned with the lines of sight （blazars）, and discuss tile interpretation of these observations. Subsequently, we summarize our knowledge about the cosmic history of AGN formation and evolution. We conclude with a description of upcoming observational opportunities.展开更多
Large-amplitude X-ray variation is a special feature of AGN, reflecting possible extreme change in the central engine or the ab- sorption along the line of sight. Till now there are only a few relevant studies on indi...Large-amplitude X-ray variation is a special feature of AGN, reflecting possible extreme change in the central engine or the ab- sorption along the line of sight. Till now there are only a few relevant studies on individual sources or rather small samples. In this work we aim to perform a systematic study of AGNs with strong soft X-ray variations at timescale of 〉 10 years. To build the sample, we compare the soft X-ray fluxes of AGNs measured in ROSAT All-Sky Survey （RASS） during 1990-1991 with those measured by XMM-Newton during 2000-2009. This investigation bings forth to a sample of 13 AGNs, which appeared bright in RASS era, and went into low states （flux dropped by a factor of 〉 10） when they were caught by XMM-Newton. Most of the 13 sources are type I Seyfert galaxies. 5 of them are noticed to have strong X-ray vai＇iation for the first time. We study the nature of their variations through performing XMM-Newton spectral analyses and by collecting reports from the existing literature. We find the sample could be divided into three categories according to the possible causes of the strong X-ray variations. The variations in MRK 0478 and 1H 0419-557 are consistent with strong light-bending effect, i.e., the observed X-ray flux drops significantly as the X-ray emitting corona gets much closer to the central black hole. The variations in ESO 140-G043 and NGC 7158 are caused by absorption changes along the line of sight. For one special case MRK 0335, the variation can be explained by either light-bending or absorption variation. In the rest 8 sources （- 60%）, the strong soft X-ray variations are likely to exist due to intrinsic changes in the activities of the corona, although in some of them without high quality X-ray spectra we are unable to rule out alternative models. This sample provides good targets for future monitoring campaigns with more extensive studies.展开更多
With the support by the National Natural Science Foundation of China,a collaboration led by Prof.Wang Jianmin(王建民)from the Institute of High Energy Physics,Chinese Academy of Sciences proposes a new mechanism for t...With the support by the National Natural Science Foundation of China,a collaboration led by Prof.Wang Jianmin(王建民)from the Institute of High Energy Physics,Chinese Academy of Sciences proposes a new mechanism for the origin of the broad-line region in Active Galactic Nuclei,which was published展开更多
In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN)...In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN).The emission lines around Hαand around Hβare well described by different model functions,considering broad Balmer lines to be described by Gaussian or Lorentz functions.Different model functions lead to different determined narrow emission line fiuxes,but the different narrow emission line fiux ratios lead SDSS J1042-0018 as an H II galaxy in the BPT diagram.In order to explain the unique properties of the misclassified broad line AGN SDSS J1042-0018,two methods are proposed,the star-forming contributions and the compressed narrow emission line regions with high electron densities near to critical densities of forbidden emission lines.Fortunately,the strong star-forming contributions can be preferred in SDSS J1042-0018.The misclassified broad line AGN SDSS J1042-0018,well explained by star-forming contributions,could provide further clues on the applications of BPT diagrams to the normal broad line AGNs.展开更多
Studies have proposed that there is evidence for cosmological coupling of black holes(BHs)with an index of k≈3;hence,BHs serve as the astrophysical source of dark energy.However,the data sample is limited for the red...Studies have proposed that there is evidence for cosmological coupling of black holes(BHs)with an index of k≈3;hence,BHs serve as the astrophysical source of dark energy.However,the data sample is limited for the redshifts of≤2.5.In recent years,the James Webb Space Telescope(JWST)has detected many high-redshift active galactic nuclei(AGNs)and quasars.Among the JWST NIRSpec-/NIRCam-resolved AGNs,three are determined to be in early-type host galaxies with a redshift of z~4.5-7.However,their M_(*)and MBH are in tension with the predicted cosmological coupling of black holes with k=3 at a confidence level of~2σ,which challenges the hypothesis that BHs serve as the origin of dark energy.Future work on high-redshift AGNs using the JWST will further assess such a hypothesis by identifying more early-type host galaxies in the higher mass range.展开更多
基金supported by the National Natural Science Foundation of China(12033006,12192221,123B2042).
文摘A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.
文摘Blazars are subclass of AGN （active galactic nuclei） with relativistic jet that is pointing in the general direction of the earth. The energy flux in the jet is about （10^44-10^47） erg/s. The γ-rays in the energy range 10 GeV-10 TeV emanating from blazar are examined and their effect on the IGM （intergalactic medium） is studied. The γ-ray emission is considered as due to inverse Compton scattering of relativistic electrons. There appears to be a gamma ray flux from blazar above 10 GeV having a line intensity of 1.5 × 10^-4 cm^-2 s^-1 sr^-1. The IGM is measured to large distances and it is found to be clumpy. It is found that at higher redshifl the density of IGM increases. The cosmological density parameter measured is found to lie within the suggested limit of 0.03 at redshift z = 3 for background intensity of radiation 10^-24 W·m^-2·Hz^-1·sr^-1. The iso-ΩIGM curve shows a kink in its profile which might be significant at the particular value of z equal to 2. Some more detailed studies are required for understanding the distribution of intergalactic medium at the unstable point at z = 2 as shown in inverse Compton radiation.
基金Project supported by Pangden Project FoundationNational Natural Science Foundation of China.
文摘In the framework of BLR in AGNs, i.e. large number of small, cold and dense emission-line clouds immerging in an intercloud hot medium, a delicate radiation model for a typical emission cloud is established, in which the backside photoionization of the cloud against the central continuum source by the scattered diffuse continuum in the hot medium is considered. Under the assumption of the radial kinematics of the BLR clouds, the line profiles for the two important UV emission-lines, Lya and CIV/11549 are computed; and based on these calculations, various physical factors that affect the properties of the emission-line profiles are discussed. It is concluded that: (i) when the BLR clouds is inflow, there exists a confining hot medium with density around 2 x 105 cm-3. In this case, theoretical line profiles agree well with the observational; (ii) both symmetric Lya and nearly symmetric CIV line profiles show blue velocity shifts, the quantities of which are sensitive to the cutoff of the outer radius of the BLR. It is suggested that this cutoff effect is physical background to explain the observations that high ionization lines in the spectra of AGNs have some systematic blue shifts relative to those low ionization lines which usually characterize their source system velocities.
文摘Since the unknown emission features in the spectrum of quasar 3C 273 have beenfirst identified as the blended Fell multiplets, many papers have contributed to thetheoretical and observation research of Fell emission in the spectra of Seyferts andquasars. Usually, optical FeII emission lines are produced by transitions from
文摘In this paper we give a brief review of the astrophysics of active galactic nuclei （AGNs）. After a general introduction motivating the study of AGNs, we discuss our present understanding of the inner workings of the central engines, most likely accreting black holes with masses between 106 and 10^10M. We highlight recent results concerning the jets （collimated outflows） of AGNs derived from X-ray observations （Chandra） of kpc-scale jets and ~/-ray observations of AGNs （Fermi, Cherenkov telescopes） with jets closely aligned with the lines of sight （blazars）, and discuss tile interpretation of these observations. Subsequently, we summarize our knowledge about the cosmic history of AGN formation and evolution. We conclude with a description of upcoming observational opportunities.
基金supported by the National Natural Science Foundation of China(Grant No.11233002)the Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences(Grant No.XDB09000000)support from Chinese Top-notch Young Talents Program
文摘Large-amplitude X-ray variation is a special feature of AGN, reflecting possible extreme change in the central engine or the ab- sorption along the line of sight. Till now there are only a few relevant studies on individual sources or rather small samples. In this work we aim to perform a systematic study of AGNs with strong soft X-ray variations at timescale of 〉 10 years. To build the sample, we compare the soft X-ray fluxes of AGNs measured in ROSAT All-Sky Survey （RASS） during 1990-1991 with those measured by XMM-Newton during 2000-2009. This investigation bings forth to a sample of 13 AGNs, which appeared bright in RASS era, and went into low states （flux dropped by a factor of 〉 10） when they were caught by XMM-Newton. Most of the 13 sources are type I Seyfert galaxies. 5 of them are noticed to have strong X-ray vai＇iation for the first time. We study the nature of their variations through performing XMM-Newton spectral analyses and by collecting reports from the existing literature. We find the sample could be divided into three categories according to the possible causes of the strong X-ray variations. The variations in MRK 0478 and 1H 0419-557 are consistent with strong light-bending effect, i.e., the observed X-ray flux drops significantly as the X-ray emitting corona gets much closer to the central black hole. The variations in ESO 140-G043 and NGC 7158 are caused by absorption changes along the line of sight. For one special case MRK 0335, the variation can be explained by either light-bending or absorption variation. In the rest 8 sources （- 60%）, the strong soft X-ray variations are likely to exist due to intrinsic changes in the activities of the corona, although in some of them without high quality X-ray spectra we are unable to rule out alternative models. This sample provides good targets for future monitoring campaigns with more extensive studies.
文摘With the support by the National Natural Science Foundation of China,a collaboration led by Prof.Wang Jianmin(王建民)from the Institute of High Energy Physics,Chinese Academy of Sciences proposes a new mechanism for the origin of the broad-line region in Active Galactic Nuclei,which was published
基金the kind support of Starting Research Fund of Nanjing Normal Universitythe kind support of NSFC-12173020the kind support of Da Chuang project of Nanjing Normal University for undergraduate students。
文摘In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN).The emission lines around Hαand around Hβare well described by different model functions,considering broad Balmer lines to be described by Gaussian or Lorentz functions.Different model functions lead to different determined narrow emission line fiuxes,but the different narrow emission line fiux ratios lead SDSS J1042-0018 as an H II galaxy in the BPT diagram.In order to explain the unique properties of the misclassified broad line AGN SDSS J1042-0018,two methods are proposed,the star-forming contributions and the compressed narrow emission line regions with high electron densities near to critical densities of forbidden emission lines.Fortunately,the strong star-forming contributions can be preferred in SDSS J1042-0018.The misclassified broad line AGN SDSS J1042-0018,well explained by star-forming contributions,could provide further clues on the applications of BPT diagrams to the normal broad line AGNs.
文摘HADAR(High Altitude Detection of Astronomical Radiation)是一个基于大气切伦科夫成像技术的地面望远镜阵列,其采用大口径折射式水透镜系统来收集大气切伦科夫光,以实现对10 GeV—10 TeV能量段的伽马射线和宇宙线的探测.HADAR具有低阈能和大视场的优势,因此可以对天区进行连续扫描和观测,在观测活动星系核(Active Galactic Nuclei,AGN)等银河系外伽马射线源方面具有明显优势.本文研究了HADAR实验对AGN的探测能力.基于费米望远镜(Fermi Large Area Telescope,Fermi-LAT)的AGN源能谱信息,将观测能量外推至甚高能能段,同时加入河外背景光的吸收效应,以计算HADAR对AGN源观测的统计显著性.研究结果显示,HADAR运行一年时间,预计将有31个Fermi-LAT AGN源以高于5倍显著性被观测到,其中大部分为蝎虎状天体类型.
基金support of Cyrus Chun Ying Tang Foundationssupported by the National Natural Science Foundation of China(Grant Nos.11921003,and 12233011)the Chinese Academy of Sciences via the Key Research Program of Frontier Sciences(Grant No.QYZDJ-SSWSYS024)。
文摘Studies have proposed that there is evidence for cosmological coupling of black holes(BHs)with an index of k≈3;hence,BHs serve as the astrophysical source of dark energy.However,the data sample is limited for the redshifts of≤2.5.In recent years,the James Webb Space Telescope(JWST)has detected many high-redshift active galactic nuclei(AGNs)and quasars.Among the JWST NIRSpec-/NIRCam-resolved AGNs,three are determined to be in early-type host galaxies with a redshift of z~4.5-7.However,their M_(*)and MBH are in tension with the predicted cosmological coupling of black holes with k=3 at a confidence level of~2σ,which challenges the hypothesis that BHs serve as the origin of dark energy.Future work on high-redshift AGNs using the JWST will further assess such a hypothesis by identifying more early-type host galaxies in the higher mass range.
