In this paper: 1. The assumption of the dependence of Doppler factor on the emission frequency (δ v≈δ 0 18logvv o , Fan et al. 1993, ApJ., 415, 113) is used to explain the observational differences between the radi...In this paper: 1. The assumption of the dependence of Doppler factor on the emission frequency (δ v≈δ 0 18logvv o , Fan et al. 1993, ApJ., 415, 113) is used to explain the observational differences between the radio selected BL Lac objects (RBLs) and the X Ray Selected BL lac objects (XBLs): a) Hubble relation; b) different multiwavelength correlations; c) different regions in the effective spectral index (α RO - α OX ) diagram; d) different polarization. The results suggest that RBLs and XBLs are the same. 2. From the analysis of the relation between infrared magnitude and redshift, it is proposed that the parent population of BL Lac objects should be FRI radio galaxies and FRII(G) radio galaxies showing the optical spectra of a galaxy. 3. From the superluminal motion, the assumption (δ v≈δ 0 18+logvv 0 ) is confirmed. 4. Based on the relation between polarization and Doppler factor (Fan et al. 1997a), it is proposed that the f, ratio of the beamed luminosity to the unbeamed luminosity in the source frame of OVVs/HPQs is smaller than that of BL Lac objects: f RBLs ～ 6f FSRQs .展开更多
Ⅰ. INTRODUCTION BL Lac objects were the prototype of a new class of astrophysically interested objects with these peculiar characteristies: (ⅰ) Absence of emission lines in the core source;(ⅱ) rapid variability at ...Ⅰ. INTRODUCTION BL Lac objects were the prototype of a new class of astrophysically interested objects with these peculiar characteristies: (ⅰ) Absence of emission lines in the core source;(ⅱ) rapid variability at radio, IR and visual wavelengths; (ⅲ) non-thermal展开更多
Evidence for the long-term optical curve variability and colour behaviour of the BL Lac object Mkn 421 is presented. Our results show that the amplitude of the optical variations of Mkn 421 is only about △B=4.7 magni...Evidence for the long-term optical curve variability and colour behaviour of the BL Lac object Mkn 421 is presented. Our results show that the amplitude of the optical variations of Mkn 421 is only about △B=4.7 magnitude in the B-band for its photometric history from 1899 to 2002. The results of optical photometric monitoring of the Mkn 421 from April 2000 to Jan 2002 are provided. During our observation, Mkn 421 shows significant rapid variations and exhibits short time variability of 2.42 hours in the B band. A strong correlation between the B - V colour index and the magnitude in the B band is found. Our charge coupled device （CCD） photometry of Mkn 421 shows that the measured results are in good agreement with the predicted optical variability period of about 23 years.展开更多
We present and discuss deep high resolution images taken with the ESO NTT as well as spectra taken with the ESO VLT in the field of the BL Lac object PKS 0537 441. We could neither detect the host galaxy nor a galaxy ...We present and discuss deep high resolution images taken with the ESO NTT as well as spectra taken with the ESO VLT in the field of the BL Lac object PKS 0537 441. We could neither detect the host galaxy nor a galaxy along the line of sight to the BL Lac as claimed from previous observations. We found 4 nearby companion galaxies which could be a splitted and magnified image of a distant background galaxy. Our VLT spectra, however, rule out this possibility. All 4 companions have similar redshifts as the BL Lac and may (at least in part) trigger the enormous activity in this source. PKS 0537 441 might be located in a galaxy cluster as rich as Abell 1. Alternatively, the BL Lac could also be located in the outskirts of a galaxy cluster or even be projected on a large scale structure as indicated by spectra of 30 galaxies in the field. Either lensing hypothesis (lens or being lensed) is considerably weakened by our observations.展开更多
In this paper, we revisit the relationship between the spectral index and the core-dominance parameter using a larger sample of 157 blazars (23 BL Lacertae objects and 134 flat spectrum radio quasars), compiled from t...In this paper, we revisit the relationship between the spectral index and the core-dominance parameter using a larger sample of 157 blazars (23 BL Lacertae objects and 134 flat spectrum radio quasars), compiled from the available literature. From the relevant data, we find the spectral index associated with the core-dominance parameter, for which a relativistic beaming effect is responsible. In addition, we make a comparison of the properties between BL Lacertae objects and flat spectrum radio quasars.展开更多
文摘In this paper: 1. The assumption of the dependence of Doppler factor on the emission frequency (δ v≈δ 0 18logvv o , Fan et al. 1993, ApJ., 415, 113) is used to explain the observational differences between the radio selected BL Lac objects (RBLs) and the X Ray Selected BL lac objects (XBLs): a) Hubble relation; b) different multiwavelength correlations; c) different regions in the effective spectral index (α RO - α OX ) diagram; d) different polarization. The results suggest that RBLs and XBLs are the same. 2. From the analysis of the relation between infrared magnitude and redshift, it is proposed that the parent population of BL Lac objects should be FRI radio galaxies and FRII(G) radio galaxies showing the optical spectra of a galaxy. 3. From the superluminal motion, the assumption (δ v≈δ 0 18+logvv 0 ) is confirmed. 4. Based on the relation between polarization and Doppler factor (Fan et al. 1997a), it is proposed that the f, ratio of the beamed luminosity to the unbeamed luminosity in the source frame of OVVs/HPQs is smaller than that of BL Lac objects: f RBLs ～ 6f FSRQs .
文摘Ⅰ. INTRODUCTION BL Lac objects were the prototype of a new class of astrophysically interested objects with these peculiar characteristies: (ⅰ) Absence of emission lines in the core source;(ⅱ) rapid variability at radio, IR and visual wavelengths; (ⅲ) non-thermal
基金Project supported by an CRCG grant of the University of Hong Kong, Yunnan Provincial Foundation of Science of China （Grant No 2004A0027M） and the National Natural Science Foundation of China（Grant No 10363002）, and the Natural Science Foundation of China Education Department（Grant No 02142）.
文摘Evidence for the long-term optical curve variability and colour behaviour of the BL Lac object Mkn 421 is presented. Our results show that the amplitude of the optical variations of Mkn 421 is only about △B=4.7 magnitude in the B-band for its photometric history from 1899 to 2002. The results of optical photometric monitoring of the Mkn 421 from April 2000 to Jan 2002 are provided. During our observation, Mkn 421 shows significant rapid variations and exhibits short time variability of 2.42 hours in the B band. A strong correlation between the B - V colour index and the magnitude in the B band is found. Our charge coupled device （CCD） photometry of Mkn 421 shows that the measured results are in good agreement with the predicted optical variability period of about 23 years.
文摘We present and discuss deep high resolution images taken with the ESO NTT as well as spectra taken with the ESO VLT in the field of the BL Lac object PKS 0537 441. We could neither detect the host galaxy nor a galaxy along the line of sight to the BL Lac as claimed from previous observations. We found 4 nearby companion galaxies which could be a splitted and magnified image of a distant background galaxy. Our VLT spectra, however, rule out this possibility. All 4 companions have similar redshifts as the BL Lac and may (at least in part) trigger the enormous activity in this source. PKS 0537 441 might be located in a galaxy cluster as rich as Abell 1. Alternatively, the BL Lac could also be located in the outskirts of a galaxy cluster or even be projected on a large scale structure as indicated by spectra of 30 galaxies in the field. Either lensing hypothesis (lens or being lensed) is considerably weakened by our observations.
基金supported by the National Natural Science Foundation of China (Grant Nos.10633010 and 11173009)the National Basic Research Program of China (Grant No.2007CB815405)+2 种基金the Bureau of Education of Guangzhou Municipality (Grant No.11 Sui-Jiao-Ke [2009])Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme-GDUPS (2009)the Yangcheng Scholar Funded Scheme (Grant No.10A027S)
文摘In this paper, we revisit the relationship between the spectral index and the core-dominance parameter using a larger sample of 157 blazars (23 BL Lacertae objects and 134 flat spectrum radio quasars), compiled from the available literature. From the relevant data, we find the spectral index associated with the core-dominance parameter, for which a relativistic beaming effect is responsible. In addition, we make a comparison of the properties between BL Lacertae objects and flat spectrum radio quasars.
