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Journal articles on the topic 'BL Lac objects'

Author: Grafiati

Published: 4 June 2021

Last updated: 20 February 2023

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1

Bondi, M., M. J. M. Marcha, D. Dallacasa, and C. Stanghellini. "Intermediate BL Lac objects." Monthly Notices of the Royal Astronomical Society 325, no. 3 (August 11, 2001): 1109–23. http://dx.doi.org/10.1046/j.1365-8711.2001.04519.x.

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2

Beckmann, V., D. Engels, N. Bade, and O. Wucknitz. "The HRX-BL Lac sample – Evolution of BL Lac objects." Astronomy & Astrophysics 401, no. 3 (April 2003): 927–38. http://dx.doi.org/10.1051/0004-6361:20030184.

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3

Sandrinelli, A., S. Covino, A. Treves, A. M. Holgado, A. Sesana, E. Lindfors, and V. F. Ramazani. "Quasi-periodicities of BL Lacertae objects." Astronomy & Astrophysics 615 (July 2018): A118. http://dx.doi.org/10.1051/0004-6361/201732550.

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We review the reports of possible year-long quasi-periodicities of BL Lac objects in the γ-ray and optical bands, and present a homogeneous time analysis of the light curves of PKS2155−304, PG1553+113, and BL Lac. Based on results from a survey covering the entire Fermi γ-ray sky we have estimated the fraction of possible quasi-periodic BL Lac objects. We compared the cyclical behaviour in BL Lac objects with that derived from the search of possible optical periodicities in quasars, and find that at z ≲ 1 the cosmic density of quasi-periodic BL Lac objects is larger than that of quasi-periodic quasars. If the BL Lac quasi-periodicities were due to a supermassive binary black hole (SBBH) scenario, there could be a tension with the upper limits on the gravitational wave background measured by the pulsar timing array. The argument clearly indicates the difficulties of generally associating quasi-periodicities of BL Lac objects with SBBHs.

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4

Costamante, L., G. Ghisellini, P. Giommi, G. Tagliaferri, A. Celotti, M. Chiaberge, G. Fossati, et al. "Extreme synchrotron BL Lac objects." Astronomy & Astrophysics 371, no. 2 (May 2001): 512–26. http://dx.doi.org/10.1051/0004-6361:20010412.

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5

Costamante, L., and G. Ghisellini. "TeV candidate BL Lac objects." Astronomy & Astrophysics 384, no. 1 (March 2002): 56–71. http://dx.doi.org/10.1051/0004-6361:20011749.

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6

D'Amicis, R., R. Nesci, E. Massaro, M. Maesano, F. Montagni, and F. D'Alessio. "Spectral Variability of BL Lac Objects." Publications of the Astronomical Society of Australia 19, no. 1 (2002): 111–13. http://dx.doi.org/10.1071/as01113.

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AbstractWe present the relation between optical luminosity and spectral slope for eight BL Lac objects (3C66A, PKS 0422+00, S5 0716+71, OJ 287, ON 231, OQ 530, S5 1803+78 and BL Lacertae), derived from B, V, R, and I observations spanning a time interval of about 5 years. Four objects show a marked correlation between spectral slope and luminosity, being bluer when brighter, while for the other four the correlation is weaker or absent. Possible explanations are briefly discussed in the framework of current models of the BL Lac phenomenon.

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7

Day, Charles. "Let’s talk about BL Lac objects!" Physics Today 72, no. 3 (March 2019): 8. http://dx.doi.org/10.1063/pt.3.4152.

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8

Merrifield, Michael R. "Macrolensing, microlensing, and BL Lac objects." Astronomical Journal 104 (October 1992): 1306. http://dx.doi.org/10.1086/116319.

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9

Wurtz, Ronald, Erica Ellingson, John T. Stocke, and H. K. C. Yee. "Clustering environments of BL Lac objects." Astronomical Journal 106 (September 1993): 869. http://dx.doi.org/10.1086/116690.

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10

Pesce, Joseph E., Renato Falomo, and Aldo Treves. "Environmental Properties of BL LAC Objects." Astronomical Journal 110 (October 1995): 1554. http://dx.doi.org/10.1086/117628.

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11

Chen, P. S., H. W. Fu, and Y. F. Gao. "2MASS observation of BL Lac objects." New Astronomy 11, no. 1 (October 2005): 27–42. http://dx.doi.org/10.1016/j.newast.2005.05.004.

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12

Bondi, M., D. Dallacasa, C. Stanghellini, and R. Della Ceca. "Extended Emission in BL Lac Objects." Symposium - International Astronomical Union 175 (1996): 53–54. http://dx.doi.org/10.1017/s0074180900079997.

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The study of the extended emission and polarization properties of BL Lacs is an important step for the identification of their parent population. FRI radio sources, the supposed parent population of BL Lacs, have weaker extended radio luminosity and a dominant inferred magnetic field perpendicular to the jet, while FRII radio sources, the supposed parent population of quasars, have stronger extended radio power and an inferred magnetic field parallel to the jet. The only complete sample of radio selected BL Lacs (1 Jy sample, Stickel et al. 1991, ApJ, 374, 431) contains 34 objects. Unfortunately, about half of 1 Jy BL Lacs do not have very high dynamic range images, necessary to detect the low emissivity radio emission surrounding the bright compact source, either because the object was never observed, or because the observation was carried out at the beginning of 1980s with low sensitivity. In 1994 we started a programme using the VLA (A, B, and D configuration, see Table 1) and the WSRT (W in Table 1) to complete the high sensitivity radio imaging of the 1 Jy sample. We aim to investigate morphology and polarization properties, as well as the luminosity of the extended emission. This contribution presents the L band observations. The results are very preliminary, some of the data reduction is still in progress as well as the statistical analysis. The sources in Table 1 have been roughly classified as extended (E), or point-like (P) if no extended feature was detected. Among the 15 sources observed at the highest resolution 13 were classified as extended. In many sources we detect significantly much more extended flux than previously reported from earlier observations. Almost all the BL Lac objects we observed at the highest resolution show some extended features; furthermore, in a few cases, we detected emission on the arcminute scale. The power of the extended luminosity covers 3 orders of magnitude, 3 objects (0537–441, 0820+225, and 2240–260) have values typical of a FRII radio source. These new data will be used for an updated statistical analysis of the properties of the extended emission in the 1 Jy sample of BL Lac objects.

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13

Costamante, L. "TeV-peaked candidate BL Lac objects." Monthly Notices of the Royal Astronomical Society 491, no. 2 (November 13, 2019): 2771–78. http://dx.doi.org/10.1093/mnras/stz3018.

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ABSTRACT BL Lac objects can be extreme in two ways: with their synchrotron emission, peaking beyond 1 keV in their spectral energy distribution, or with their gamma-ray emission, peaking at multi-TeV energies up to and beyond 10–20 TeV, like 1ES 0229+200. This second type of extreme BL Lacs – which we can name TeV-peaked BL Lacs – is not well explained by the usual synchrotron self-Compton scenarios for BL Lacs. These sources are also important as probes for the intergalactic diffuse infrared background and cosmic magnetic fields, as well as possible sites of production of ultra-high-energy cosmic rays and neutrinos. However, all these studies are hindered by their still very limited number. Here I propose a new, simple criterium to select the best candidates for TeV observations, specifically aimed at this peculiar type of BL Lac objects by combining X-ray, gamma-ray, and infrared data. It is based on the observation of a clustering towards a high X-ray to GeV gamma-ray flux ratio, and it does not rely on the radio flux or X-ray spectrum. This makes it suitable to find TeV-peaked sources also with very faint radio emission. Taking advantage of the Fermi all-sky gamma-ray survey applied to the ROMA-BZCAT and Sedentary Survey samples, I produce an initial list of 47 TeV-peaked candidates for observations with present and future air-Cherenkov telescopes.

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14

Xie, G. Z., F. K. Liu, Y. Y. Zhu, J. H. Fan, and R. W. Lu. "Cosmological implications of BL Lac objects." Astrophysics and Space Science 179, no. 2 (1991): 321–29. http://dx.doi.org/10.1007/bf00646952.

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15

Fan, J. H., Z. H. Huang, J. J. Li, G. Z. Xie, and J. Y. Zhang. "BL Lac objects and acceleration model." Astrophysics and Space Science 213, no. 2 (1994): 305–16. http://dx.doi.org/10.1007/bf00658217.

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16

Cheng, F. Z., J. F. Lu, G. Z. Xie, K. H. Li, Z. L. Li, and L. F. Wang. "Optical Short-Term Variability in the X-Ray-Selected BL Lac Object IE 0317+186 and the Radio-Selected BL Lac Object ON231." Symposium - International Astronomical Union 134 (1989): 108–9. http://dx.doi.org/10.1017/s0074180900140513.

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In order to compare X-ray-selected BL Lac objects with radio-selected BL Lac objects, we have carried out optical monitoring of some of these objects for about three years at Yunnan Observatory in China. All observations have been made with a CCD-image system at the f/13.3 Cassegrain focus of the 102-cm RCC telescope. The CCD-image system was developed by Ye et al. in Kitt Peak National Observatory of USA (Ye et al., 1985). The filters used were as follows: B-GG385(2mm)+BG12(1mm)+BG18(1mm), V-GG495(2mm)+BG18(2mm). After observing many times, more complete light curves have obtained for the X-ray-selected BL Lac object IE 0317+186 and the radio-selected BL Lac object ON 231, respectively(Fig 1 and Fig 2). Fig 1 shows that IE 0317+186 has a characteristic timescale of about 4.5hours with an amplitudes of ΔV≃0.65 mag. Fig 2 indicates that a timescale of short-term variability in ON 231 is about 70 min with an amplitudes of ΔB≃0.8 mag.

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17

Anderson, M. W. B., and M. D. Filipovic. "Radio detection of 18 RASS BL Lac objects." Serbian Astronomical Journal, no. 179 (2009): 7–17. http://dx.doi.org/10.2298/saj0979007a.

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We present the radio detection of 18 BL Lac objects from our survey of over 575 deg2 of sky. These 18 objects are located within 20'' of the X-ray position, of which 11 have a measured red-shift. All candidates are radio emitters above ~1 mJy and fall within the range of existing samples on the two colour, ?RO vs ?OX, diagram with a transitional population of three evident. Two unusual sources have been identified, a candidate radio quiet BL Lac, RX J0140.9-4130, and an extreme HBL, RX J0109.9-4020, with log (?peak) ?19:2. The BL Lac log(N)-log(S) relation is consistent with other samples and indicates the ROSAT All Sky Survey (RASS) could contain (2000?400) BL Lac objects.

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18

Stanghellini, C., P. Cassaro, M. Bondi, D. Dallacasa, R. Della Ceca, and R. A. Zappalà. "Arcsecond Scale Polarization of BL Lac Objects." Symposium - International Astronomical Union 175 (1996): 55–56. http://dx.doi.org/10.1017/s0074180900080001.

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BL Lac objects are an enigmatic class of active galactic nuclei. They are characterized by high luminosity, a flat radio spectrum that steepens at higher energies, relatively high optical and radio polarization, rapid variability and an optical continuum with weak or absent emission lines (see Urry and Padovani, 1995 for a recent review).These properties have been interpreted in terms of a relativistic jet closely aligned to the line of sight (Blandford and Rees, 1978, Ghisellini et al., 1993). This model, known as the beaming model, implies that there must be a so called “parent population” of radio sources intrinsically identical to BL Lac objects, but with the jets oriented at large angles to the line of sight. Browne (1983) was the first to propose the low luminosity FR I radio galaxies as the most likely candidates for the “parent population” of the core dominated BL Lac objects. An outcome of the beaming model is that all the properties not depending on orientation should be shared by the BL Lac objects and the FR I radio galaxies.

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19

Kaufmann, S., S. Wagner, and O. Tibolla. "Broadband variability of TeV BL Lac objects." EPJ Web of Conferences 61 (2013): 04016. http://dx.doi.org/10.1051/epjconf/20136104016.

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20

Gabuzda, D. C. "The VLBI Jets of BL Lac Objects." EAS Publications Series 1 (2001): 89–95. http://dx.doi.org/10.1051/eas:2001011.

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21

Mao, L. S. "2MASS observation of BL Lac objects II." New Astronomy 16, no. 8 (December 2011): 503–29. http://dx.doi.org/10.1016/j.newast.2011.05.002.

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22

Makino, Fumiyoshi. "X-ray variability in BL Lac objects." Advances in Space Research 25, no. 3-4 (January 2000): 723–28. http://dx.doi.org/10.1016/s0273-1177(99)00829-7.

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23

Aller, M. F., H. D. Aller, and P. A. Hughes. "The Radio Properties of BL Lac Objects." International Astronomical Union Colloquium 164 (1998): 107–8. http://dx.doi.org/10.1017/s0252921100044730.

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24

Kuhr, Helmut, and Josef Fried. "A CCD survey of BL Lac objects." Symposium - International Astronomical Union 119 (1986): 125–26. http://dx.doi.org/10.1017/s0074180900152453.

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A long term project was started at the Max-Planck-Institut fur Astronomie, Heidelberg, to study a complete sample of 46 northern and southern BL Lac objects with flux densities exceeding 1 Jy at 5 GHz using optical spectroscopy, optical polarimetry, and direct deep CCD imaging.

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25

Wang, Jian-cheng, Jun Xu, Tong-ling Qian, and Xue-fen Cen. "The spectral properties of BL Lac objects." Chinese Astronomy and Astrophysics 23, no. 3 (July 1999): 288–98. http://dx.doi.org/10.1016/s0275-1062(99)00058-2.

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26

Massaro, F., E. J. Marchesini, R. D’Abrusco, N. Masetti, I. Andruchow, and Howard A. Smith. "RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA." Astrophysical Journal 834, no. 2 (January 6, 2017): 113. http://dx.doi.org/10.3847/1538-4357/834/2/113.

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27

Cassaro, P., C. Stanghellini, M. Bondi, D. Dallacasa, R. Della Ceca, and R. A. Zappalà. "Extended radio emission in BL Lac objects." Astronomy and Astrophysics Supplement Series 139, no. 3 (November 1999): 601–16. http://dx.doi.org/10.1051/aas:1999511.

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28

Makino, F. "X-ray variability in BL Lac objects." Astronomische Nachrichten 320, no. 4-5 (August 1999): 228–29. http://dx.doi.org/10.1002/1521-3994(199908)320:4/5<228::aid-asna228>3.0.co;2-s.

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29

Yuan, YuHai, JunHui Fan, and XiaoLi Long. "Radio spectral index of BL Lac objects." Science China Physics, Mechanics and Astronomy 56, no. 5 (April 19, 2013): 1035–40. http://dx.doi.org/10.1007/s11433-013-5058-9.

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30

Bi, X. W., B. Z. Wang, Z. Q. Ni, Q. Cai, and J. J. Tian. "Optical Spectra Evolution of BL Lac Objects." Journal of Astrophysics and Astronomy 32, no. 1-2 (June 2011): 109–12. http://dx.doi.org/10.1007/s12036-011-9029-0.

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31

Marchã, M. J. M. "Can BL Lac Nuclei and Broad Line Regions Coexist? or When is an Object a BL Lac?" Symposium - International Astronomical Union 175 (1996): 244–45. http://dx.doi.org/10.1017/s0074180900080669.

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The problem of BL Lac classification is a long standing one and it is mainly due to the subjectiveness of selection criteria used in the definition of BL Lac samples. For instance, an object will undoubtedly be classified as a BL Lac if it shows flat radio spectrum, high optical and radio polarization, featureless optical continuum with weak or absent emission lines, and variable flux and polarization. However, the problem arises when the object shows some but not all of these properties. In face of this difficulty, different authors (Stickel et al. 1991, Stocke et al. 1991) have tried to make a systematic analysis of the data and it has been common to classify as BL Lacs those objects whose strongest emission lines have equivalent width (EW) ≤ 5 Å. Another common criterion is to require the 4000 Å break contrast to be ≤ 0.25. Nevertheless, both of these criteria are rather arbitrary and more directly related to practical observational considerations, than they are to any physical distinction between objects. What is proposed here is a slightly different approach; it is proposed that we take a step back from common classification and that instead of imposing strict selection criteria, we create a multi-observational parameter space to investigate any breaks in the distribution of observed properties that will help clarify the distinction between BL Lacs and other flat radio spectrum sources.

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32

Sillanpää, A., L. Takalo, K. Nilsson, T. Pursimo, P. Teerikorpi, J. Heidt, D. Dultzin-Hacyan, and E. Benítez. "The Environment of OJ 287: Nearby Galaxies and a Long Optical Jet?" Symposium - International Astronomical Union 175 (1996): 47–48. http://dx.doi.org/10.1017/s0074180900079961.

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A widely accepted model for BL Lac objects is that they are radio galaxies with a relativistic jet pointing almost directly towards us. But we need a clear trigger mechanism for these jets. One possibility is the close interaction between the BL Lac host and the closeby galaxies (e.g. Heckman et al. 1986). This interaction has been seen many times in the case of quasars (Hutchings et al. 1989) but not so much is known about the close surroundings of the BL Lac objects although there has been some pioneer work like Stickel et al. (1993). The problem has usually been that the images are not deep enough and that the seeing has not been so good. To clarify the situation we have started an observing program to get very deep images in the sub-arcsecond seeing conditions from the whole 1 Jy sample (Stickel et al. 1991) of BL Lac objects. The aims of this study are: 1. to search for very close companions to the BL Lacs, 2. to study the large scale galaxy clustering around the BL Lacs and 3. to study the BL Lac hosts themselves.

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33

Xie, G. Z., W. Brinkmann, G. W. Cha, S. Laurent-Muehleisen, Y. H. Zhang, K. H. Li, J. M. Bai, and F. K. Liu. "Discovery of Five New X-ray–Selected BL Lacertae Objects and Three New Quasars." International Astronomical Union Colloquium 159 (1997): 423–24. http://dx.doi.org/10.1017/s025292110004063x.

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Through combined ROSAT and VLA observations, we have identified 19 BL Lac/quasar candidates. In 1994 December, 1995 January and October, and 1996 January 1996, we obtained spectra of all 19 candidates using the 2.16-m telescope of Beijing Astronomical Observatory. The dispersion used is 195 Å mm−1, which yields a dispersion of about 4.65 Å pixel−1, and the wavelength coverage is 3500–7800 Å. Five of these objects are uniformly featureless, and we identify them as BL Lac objects. Three new quasars are also identified. Table 1 presents VLA positions and redshifts for the 5 new BL Lac objects and three new quasars. By checking them in the NASA/IPAC Extragalactic Database (NED) and Véron-Cetty & Véron’s (1993) Catalogue of Quasars and AGNs, and other recent reports about discovery of new BL Lac objects and quasars, we find that these sources are previously unreported.

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34

Lipovetsky, V. A., B. E. Markarian, and J. A. Stepanian. "The First Byurakan Survey (FBS) and Search Problems for AGN." Symposium - International Astronomical Union 121 (1987): 17–23. http://dx.doi.org/10.1017/s0074180900154853.

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The history of the First Byurakan Survey carried out to search for AGN is shortly described. The sample completeness for different classes of objects: Sy1, Sy2, QSO, BL Lac objects is estimated as 0.6, 0.4, 0.4 and 0.6, respectively. The lack of radioquiet BL Lac objects as a whole class is shown. Different search procedures of AGN are compared, their perspectives are evaluated.

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35

González, Josefa Becerra. "VHE BL Lacs through the MAGIC glasses." Proceedings of the International Astronomical Union 10, S313 (September 2014): 64–69. http://dx.doi.org/10.1017/s174392131500188x.

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AbstractIn this contribution an overview of the latest results on the study of BL Lac objects with the MAGIC telescopes at the very high energy (VHE, E>100 GeV) gamma-rays is presented. Three new VHE sources were detected during 2014, two BL Lac objects and the gravitational lensed blazar S3 0218+357. MAGIC detected very fast intra-night variability from IC 310. This detection points to smaller emitting regions than the event horizon, this is hard to be explained in the framework of the current theoretical models. The long term multi wavelength (MWL) study of the BL Lac PKS 1424+240 shows correlation between the radio and optical emission, pointing to a common origin. The MWL SED is not well fitted by a one-zone synchrotron-self Compton (SSC) model, but a two-zone SSC model can explain both, the MWL light curve and the SED. Spectral curvature has been found in the observed VHE spectrum from PG 1553+113. This is the first time that spectral curvature compatible with the EBL absorption is found in an individual object.

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36

Ye, Xu-Hong, and Jun-Hui Fan. "Unification of BL Lac objects and FR I and FR II(G) radio galaxies, and Doppler factor estimation for BL Lac objects." Publications of the Astronomical Society of Japan 73, no. 4 (May 20, 2021): 775–85. http://dx.doi.org/10.1093/pasj/psab039.

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Abstract In this work, we collected a sample of BL Lacs and FR I and FR II(G) radio galaxies with available core and extended emissions from published works to discuss the unified schemes and estimate the Doppler factor for BL Lacs. A Wilcoxon rank-sum test and a Kolmogorov–Smirnov test both suggest that the probabilities of the distribution of the extended luminosity of BL Lacs and that of FR I and FR II(G) radio galaxies being from the same parent distribution are pWRS = 0.779 and pK-S = 0.326, suggesting they are unified. Based on this unified scheme, we propose to estimate the Doppler factors for BL Lacs. Comparing the Doppler factor estimated by the fitting/regression method with those for the common sources in the literature, we found a good linear correlation for common sources.

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37

Barr, P., P. Giommi, A. Pollock, G. Tagliaferri, D. Maccagni, and B. Garilli. "An X-ray Spectral Survey of BL Lac Objects." Symposium - International Astronomical Union 134 (1989): 191–93. http://dx.doi.org/10.1017/s0074180900140793.

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A wide variety of X-ray spectral forms has been reported in BL Lac objects. Concave spectra, i.e. a steep soft X-ray spectrum with a flat high energy tail, have been reported in a few of the brightest BL Lacs (e.g Urry 1986). Conversely, convex spectra (steep hard X-rays, flat soft X-ray spectrum) have also been reported, sometimes in the same objects (Madejski 1985, Barr et al 1988, George et al 1988). The high energy tails have usually been invoked as a signature of synchrotron-self-Compton emission. Two conflicting interpretations of the convex spectra have been made. Urry et al (1986) suggest absorption by a partially ionised medium, probably intrinsic to the BL Lac object, following the identification of an Oxygen absorption trough in the Einstein OGS spectrum of PKS 2155-304 by Canizares and Kruper (1984). Conversely, Barr et al (1988) attribute the hard X-ray steepening to energy loss mechanisms operating on a synchrotron source.

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38

Landoni, M., S. Paiano, R. Falomo, R. Scarpa, and A. Treves. "High-redshift BL Lac Objects: Spectroscopy of Candidates." Astrophysical Journal 861, no. 2 (July 12, 2018): 130. http://dx.doi.org/10.3847/1538-4357/aac77c.

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39

Gear, W. K. "Are there two populations of BL Lac objects?" Monthly Notices of the Royal Astronomical Society 264, no. 4 (October 15, 1993): 919–28. http://dx.doi.org/10.1093/mnras/264.4.919.

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40

Dai, Ben-Zhong, Guang-Zhong Xie, and Ze-Jun Jiang. "Properties of BL Lac Objects with Redshift ⩽ 0.2." Chinese Journal of Astronomy and Astrophysics 2, no. 1 (February 2002): 8–16. http://dx.doi.org/10.1088/1009-9271/2/1/8.

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41

Kuehr, H., and Gary D. Schmidt. "Complete samples of radio-selected BL Lac objects." Astronomical Journal 99 (January 1990): 1. http://dx.doi.org/10.1086/115305.

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42

Wagner, S. J., and A. Witzel. "Intraday Variability in Quasars and BL LAC Objects." Annual Review of Astronomy and Astrophysics 33, no. 1 (September 1995): 163–97. http://dx.doi.org/10.1146/annurev.aa.33.090195.001115.

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43

Paiano, Simona, Renato Falomo, Aldo Treves, and Riccardo Scarpa. "Optical spectroscopy of BL Lac objects: TeV candidates." Monthly Notices of the Royal Astronomical Society 497, no. 1 (June 27, 2020): 94–108. http://dx.doi.org/10.1093/mnras/staa1840.

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ABSTRACT We investigate the spectroscopic optical properties of gamma-ray sources detected with high significance above 50 GeV in the Third Catalog of Hard Fermi-LAT Sources and that are good candidates as TeV emitters. We focus on the 91 sources that are labelled by the Fermi team as BL Lac (BLL) objects or blazar candidates of uncertain type (BCUs), are in the Northern hemisphere, and are with unknown or uncertain redshift. We report here on GTC (Gran Telescopio Canarias) spectra (in the spectral range 4100–7750 Å) of 13 BCUs and 42 BLL objects. We are able to classify the observed targets as BLL objects and each source is briefly discussed. The spectra allowed us to determine the redshift of 25 objects on the basis of emission and/or absorption lines, finding 0.05 < z < 0.91. Most of the emission lines detected are due to forbidden transition of [O iii] and [N ii]. The observed line luminosity is found to be lower than that of quasi-stellar objects (QSOs) at similar continuum and could be reconciled with the line–continuum luminosity relationship of QSOs if a significant beaming factor is assumed. Moreover, for five sources we found intervening absorption lines that allow to set a spectroscopic lower limit of the redshift. For the remaining 25 sources, for which the spectra are lineless, a lower limit to z is given, assuming that the host galaxies are giant ellipticals.

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44

Ding, N., X. Zhang, D. R. Xiong, and H. J. Zhang. "The physical properties ofFermiTeV BL Lac objects’ jets." Monthly Notices of the Royal Astronomical Society 464, no. 1 (September 15, 2016): 599–612. http://dx.doi.org/10.1093/mnras/stw2347.

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45

Kikuchi, S. "Long-Term Optical Behavior of BL Lac Objects." Symposium - International Astronomical Union 159 (1994): 394. http://dx.doi.org/10.1017/s0074180900175837.

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On the basis of results of optical photometry and polarimetry of OJ287 and Mrk421 since 1981, we find two states of activities for both objects. In OJ287, a color-magnitude relation which is consistent with the standard jet-shock model is seen after the outburst in 1983, while before 1982 the optical colors were almost constant. In Mrk421, the colors became redder in 1985–87, and the change of the preferred direction of polarization was associated on smaller time scale in 1987.

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BÖTTCHER, MARKUS. "MODELING INTERMEDIATE BL LAC OBJECTS DETECTED BY VERITAS." International Journal of Modern Physics D 19, no. 06 (June 2010): 873–78. http://dx.doi.org/10.1142/s0218271810017135.

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Modeling implications of recent VERITAS discoveries of Intermediate BL Lac Objects (IBLs) are presented. Leptonic jet models for the IBLs W Comae (z = 0.102) and 3C 66A (z = 0.444) are, in principle, viable with only synchrotron and synchrotron self-Compton (SSC) components, but more plausible parameters can be achieved including an external infrared radiation field as source for Compton upscattering to produce the observed VHE gamma-ray emission. The unknown redshift of PKS 1424+240 makes a theoretical interpretation difficult. A pure SSC model seems to be sufficient to represent its SED, and modeling results favor a low redshift of z ≲ 0.1.

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Pushkarev, A. B., and D. C. Gabuzda. "Global VLBI polarisation observations of BL Lac objects." New Astronomy Reviews 43, no. 8-10 (November 1999): 695–98. http://dx.doi.org/10.1016/s1387-6473(99)00080-9.

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48

Vats, Hari Om, S. S. Degaonkar, P. K. Manoharan, and S. Ananthakrishnan. "Monitoring of BL Lac objects at 327 MHz." Symposium - International Astronomical Union 119 (1986): 171–72. http://dx.doi.org/10.1017/s0074180900152581.

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The variable BL Lac objects OJ 287 and B2 (1308+326) have been observed using the Ooty Synthesis Radio Telescope (OSRT) at 327 MHz. Preliminary analysis of one of them, namely OJ 287 indicates that flux variations of ∼ 20% on a time scale of few hours to few days could be present, but this needs to be confirmed by a larger data base.

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Paiano, Simona, Marco Landoni, Renato Falomo, Aldo Treves, Riccardo Scarpa, and Chiara Righi. "On the Redshift of TeV BL Lac Objects." Astrophysical Journal 837, no. 2 (March 13, 2017): 144. http://dx.doi.org/10.3847/1538-4357/837/2/144.

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Zeng, Houdun, Dahai Yan, and Li Zhang. "Gamma-ray luminosity function of BL Lac objects." Monthly Notices of the Royal Astronomical Society 441, no. 2 (May 12, 2014): 1760–68. http://dx.doi.org/10.1093/mnras/stu644.

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