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: 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
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
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
BL Lac object S5 2007+777 has been classified as a HYMOR(Hybrid Morphology radio source) for its hybrid FR I and FR II radio morphology.It is one of four BL Lac objects with a kpc scale extended X-ray jet.In this pape...BL Lac object S5 2007+777 has been classified as a HYMOR(Hybrid Morphology radio source) for its hybrid FR I and FR II radio morphology.It is one of four BL Lac objects with a kpc scale extended X-ray jet.In this paper,we searched the unpublished European VLBI Network(EVN) archived high resolution data for this source,and present the high resolution radio structure.The EVN images all show a core-jet structure in 1.6,5 and 8 GHz.In combination with the VLA data in the literature,we found position angle differences(△PA) of about 10°-20° between pc and kpc scale jet structures.The brightness temperature estimated from multi-band EVN images are around 1011.2-1011.8 K,from which the Doppler factor ranges from 3.2 to 12.0.We found significant flux variations of the radio core in 1.6 and 5 GHz,from which we derived the variability in brightness temperature Tvar to be 1013.6 K and 1014.0 K,corresponding to the Doppler factors of 9.3 and 12.4,respectively.展开更多
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.
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 .
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supported by the National Natural Science Foundation of China (Grant Nos. 10633010, 10703009, 10833002 and 10821302)the National Basic Research Program of China (Grant No. 2009CB824800)+2 种基金the Study Abroad Fund from the Ministry of Education of China (Grant No. O922571001)the Science Foundation of Guizhou Province (Grant No. 20092064)the Science Foundation of Guizhou University (Grant No. 2008035)
文摘BL Lac object S5 2007+777 has been classified as a HYMOR(Hybrid Morphology radio source) for its hybrid FR I and FR II radio morphology.It is one of four BL Lac objects with a kpc scale extended X-ray jet.In this paper,we searched the unpublished European VLBI Network(EVN) archived high resolution data for this source,and present the high resolution radio structure.The EVN images all show a core-jet structure in 1.6,5 and 8 GHz.In combination with the VLA data in the literature,we found position angle differences(△PA) of about 10°-20° between pc and kpc scale jet structures.The brightness temperature estimated from multi-band EVN images are around 1011.2-1011.8 K,from which the Doppler factor ranges from 3.2 to 12.0.We found significant flux variations of the radio core in 1.6 and 5 GHz,from which we derived the variability in brightness temperature Tvar to be 1013.6 K and 1014.0 K,corresponding to the Doppler factors of 9.3 and 12.4,respectively.
