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Artigos de revistas sobre o assunto "BL Lacertae objects":
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Britzen, S., A. Witzel, B. P. Gong, J. W. Zhang, G. Krishna, A. Goyal, M. F. Aller, H. D. Aller e J. A. Zensus. "Understanding BL Lacertae objects". Astronomy and Astrophysics 515 (junho de 2010): A105. http://dx.doi.org/10.1051/0004-6361/200913685.
Sandrinelli, A., S. Covino, A. Treves, A. M. Holgado, A. Sesana, E. Lindfors e V. F. Ramazani. "Quasi-periodicities of BL Lacertae objects". Astronomy & Astrophysics 615 (julho de 2018): A118. http://dx.doi.org/10.1051/0004-6361/201732550.
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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Stocke, John T. "New Observations of BL Lacertae Objects". Symposium - International Astronomical Union 175 (1996): 385–88. http://dx.doi.org/10.1017/s0074180900081171.
This contribution is divided into three parts: 1. A summary of mostly published work that describes the new type of BL Lac Objects discovered with X-ray satellites, “X-ray Bright BL Lacs (XBLs)”, and their relationship to the previously known “radio bright BL Lacs (RBLs).” Most (but not all?) of the differences between XBLs and RBLs are explicable using a “viewing angle” model in which the soft X-ray emission emanates into a much wider cone (23-30°) than the radio emission (8-10°). 2. New ROSAT PSPC soft X-ray observations are presented for complete samples of XBLs and RBLs which may explain the absence of luminous optical emission lines in BL Lacs. 3. A deep, subarcsec optical imaging survey of a large (50) sample of both XBLs and RBLs conducted at the Canada-France-Hawaii 3.6m Telescope (CFHT), whose purpose was to characterize the host galaxies and clustering environment of BL Lacs. This work defines more precisely the “parent population” of BL Lacs and identifies a small number of discrepant objects which may not be “beamed FR 1s”.
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Paggi, A., A. Cavaliere, V. Vittorini e M. Tavani. "Power for dry BL Lacertae objects". Astronomy & Astrophysics 508, n.º 3 (dezembro de 2009): L31—L34. http://dx.doi.org/10.1051/0004-6361/200913566.
Fan, Jun-Hui, Tong-Xu Hua, Yu-Hai Yuan, Yong-Xiang Wang, Yi Liu, Jiang-Bo Su, Yong-Wei Zhang, Jiang-He Yang e Yong Huang. "Radio Polarization of BL Lacertae Objects". Publications of the Astronomical Society of Japan 58, n.º 6 (25 de dezembro de 2006): 945–49. http://dx.doi.org/10.1093/pasj/58.6.945.
Andruchow, I., G. E. Romero e S. A. Cellone. "Polarization microvariability of BL Lacertae objects". Astronomy & Astrophysics 442, n.º 1 (30 de setembro de 2005): 97–107. http://dx.doi.org/10.1051/0004-6361:20053325.
Sbarufatti, B., R. Falomo, A. Treves e J. Kotilainen. "Optical spectroscopy of BL Lacertae objects". Astronomy & Astrophysics 457, n.º 1 (12 de setembro de 2006): 35–43. http://dx.doi.org/10.1051/0004-6361:20065455.
Moles, M., J. M. Garcia-Pelayo, J. Masegosa e A. Aparicio. "UBVRI observations of BL Lacertae objects". Astrophysical Journal Supplement Series 58 (junho de 1985): 255. http://dx.doi.org/10.1086/191040.
Sbarufatti, B., A. Treves e R. Falomo. "Imaging Redshifts of BL Lacertae Objects". Astrophysical Journal 635, n.º 1 (10 de dezembro de 2005): 173–79. http://dx.doi.org/10.1086/497022.
Teses / dissertações sobre o assunto "BL Lacertae objects":
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Abraham, Roberto G. "Imaging of BL Lac objects". Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:8af2b188-06a4-4412-bd2a-6ee27b0bf781.
The investigation of the host galaxies of BL Lac objects (BL Lacs) is a promising new field made practical in recent years by advances in detector technology and improved telescope siting. By better understanding the nature of these host galaxies we can test the standard beaming and lensing models for BL Lacs. This thesis describes the techniques that we have developed for studying the host galaxies of BL Lac objects, and presents the results of a survey of BL Lac host galaxies that we have undertaken with the 4.2m William Herschel Telescope. This survey successfully resolved many new host galaxies, determined the morphology of three BL Lac host galaxies for the first time, and confirmed the morphology of an additional three objects. One BL Lac object, PKS1413+135, displayed a number of surprising properties, and was consequently studied in greater detail at multiple wavelengths. These observations are also presented in this thesis. We conclude with a description of Monte-Carlo simulations that we have undertaken in order to better determine the uncertainty in the results from our survey, and to assess the promise of future telescope/instrumentation combinations for host galaxy imaging.
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Jannuzi, Buell Tomasson. "The optical polarization of BL Lacertae objects". Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185256.
We have used the optical polarization properties of BL Lacertae objects to gain insights into the range and physical causes of their extreme and spectacular observed properties. This dissertation consists of three parts. In Part I we provide an introduction to BL Lacs and other active galactic nuclei. In Part II we present the result of an extensive monitoring program of the optical polarization of x-ray selected BL Lacs (XSBLs). In Part III we present the results of the most extensive optical polarization survey so far undertaken. Our study of the optical polarization properties of XSBLs confirms that the BL Lac candidates found in x-ray surveys like the Einstein Extended Medium Sensitivity Survey meet the requirements for membership in the class of BL Lacs. In addition to having featureless optical spectra, the majority of the XSBLs are also variable in their flux output and have intrinsic and variable polarized emission. Although x-ray selected BL Lac candidates have proven to be BL Lacs, the characteristics of their optical polarized emission are different from those of the classical radio selected BL Lacs. The XSBLs have lower maximum percent polarizations, a lower duty cycle, smaller variations in flux, and a greater tendency to have preferred angles of polarization than radio selected BL Lacs (RSBLs). We discuss the consequences of these differences and their consistency with the "beaming" model first proposed by Blandford and Rees (1978). Our optical polarization survey is the most extensive survey of its kind ever undertaken. The survey is complete to a B magnitude of 20 and covers 560 square degrees. Our sensitivity to polarized objects is a function of survey field. We did not find any confirmed BL Lacs or highly polarized quasars, but we are able to constrain the surface density of the various populations of polarized objects. For example we are able to rule out at the 90.0% confidence level the presence of a population of radio quiet BL Lacs or highly polarized quasars (with optical flux and polarization properties similar to radio selected BL Lacs) that would have a cumulative surface density of 0.03 per square degree down to a B magnitude of 20.
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Londish, Diana. "Properties of BL Lac objects from the 2dF QSO Redshift Survey". University of Sydney. Physics, 2003. http://hdl.handle.net/2123/600.
This thesis is an analysis of the X-ray, optical, infrared and radio properties of a sample of candidate BL Lac objects, identified from two catalogues of colour-selected point sources, the 2QZ and 6QZ. The importance of the sample lies in the fact that it is the first BL Lac sample in which initial selection has been made from optical spectra, independent of the objects' flux levels at X-ray and radio frequencies. These optically selected candidate BL Lac objects thus provide an unbiased sample (in terms of radio flux density) with which to study the proportion of radio- dominant and X-ray-dominant BL Lac objects in the global population. The observed number counts and redshift distribution of the 2BL are consistent with theoretical predictions based on the QSO evolutionary model. Given the small number statistics we are not, however, able to show that this distribution is significantly different to that of the 2QZ/6QZ white dwarfs. A median redshift of z=1.25 was computed for these candidate BL Lacs, a value supported by redshift information obtained for ~25% of the sample. This median redshift is much higher than redshifts found for X-ray selected BL Lac objects and suggests that in the past high redshift, low luminosity, radio-weak BL Lacs may have been missed in radio- and X-ray-selected samples. From results of the above studies it appears that this sample of optically selected candidate BL Lac objects is different to that of hitherto known radio-loud BL Lacs. We explore mechanisms that might produce such radio-weak/radio-quiet continuum objects, and also demonstrate that such radio-quiet BL Lac objects could exist at low redshift. Failure to include these radio-quiet BL Lacs in X-ray selected samples could explain the negative evolution found for this class of object.
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D'Arcangelo, Francesca D. "Correlated multiwavelength polarization in blazars". [S.l. :] Boston University, 2010. https://staff.nrao.edu/library/00000000009785.pdf.
George, Ian Michael. "X-ray and ultra-violet observations of BL Lacertae type objects". Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35891.
We present the results from EXOSAT and IUE observations of five BL Lac type objects, Mrk 421, Mrk 501, 1218+304, Mrk 180 and 0414+009. We find that at least for the relatively well studied sources Mrk 421 and Mrk 501, the behaviour in the X-ray and ultra-violet differs significantly. In the majority of cases, the X-ray spectra are well represented by a simple power-law model over the 1-6 keV band. In the case of the high state observations of Mrk 421, however, a marked downward curvature of the spectrum is required above ~3 keV, which can be modelled as an exponential decrease. Similar convex spectra are also suggested, although not statistically required, in a number of other cases. We found no evidence in any of the observations for a hardening of the X-ray spectra above a few keV as has been previously reported. In all cases we find low energy cut-offs in the X-ray spectra consistent with absorption in the line-of-sight gas column density through out own galaxy implying that the intrinsic column density of cold gas in these objects is small (< 1 X 1020 cm-2). All five sources exhibit significant X-ray variability with minimum variability timescales in the range ~3 hr to ~7 days. Furthermore, the X-ray flux and spectral index for each object appears to be correlated in the sense that the X-ray spectrum hardens as the source brightens. In contrast, the ultra-violet spectra are generally consistent with a simple power-law of index ~1, and exhibit only slow drifts in flux on a timescale ~weeks. The ultra-violet to X-ray continuum can therefore be modelled as a power-law of index ~1 below about 0.1 keV, above which the source steepens. The spectral variability in the X-ray band can then be described in terms of a 'pivoting' of the high-energy continuum about the break-point. We have investigated two specific SSC models for the continuum emission. It was found that whilst a simplistic homogeneous disk-shaped emission region can provide an acceptable explanation of single epoch snap-shots of the multi-waveband spectrum, it experiences some difficulty accounting for the high energy spectral variability. In contrast, by allowing a variable radial dependence in the upper cut-off in the synchrotron emitting electron population in an inhomogeneous relativistic jet model, we have demonstrated that the multi-waveband spectrum of the most demanding source, Mrk 421, at all epochs can be reproduced. Thus we conclude that a jet model, broadly following the current paradigm for BL Lac type objects can give an acceptable explanation of present multi-waveband measurements.
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Ma, Feng. "Discovery of hidden blazars inside quasars /". Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
Londish, Diana. "Properties of BL Lac objects from the 2dF QSO Redshift Survey". Thesis, The University of Sydney, 2003. http://hdl.handle.net/2123/600.
This thesis is an analysis of the X-ray, optical, infrared and radio properties of a sample of candidate BL Lac objects, identified from two catalogues of colour-selected point sources, the 2QZ and 6QZ. The importance of the sample lies in the fact that it is the first BL Lac sample in which initial selection has been made from optical spectra, independent of the objects' flux levels at X-ray and radio frequencies. These optically selected candidate BL Lac objects thus provide an unbiased sample (in terms of radio flux density) with which to study the proportion of radio- dominant and X-ray-dominant BL Lac objects in the global population. The observed number counts and redshift distribution of the 2BL are consistent with theoretical predictions based on the QSO evolutionary model. Given the small number statistics we are not, however, able to show that this distribution is significantly different to that of the 2QZ/6QZ white dwarfs. A median redshift of z=1.25 was computed for these candidate BL Lacs, a value supported by redshift information obtained for ~25% of the sample. This median redshift is much higher than redshifts found for X-ray selected BL Lac objects and suggests that in the past high redshift, low luminosity, radio-weak BL Lacs may have been missed in radio- and X-ray-selected samples. From results of the above studies it appears that this sample of optically selected candidate BL Lac objects is different to that of hitherto known radio-loud BL Lacs. We explore mechanisms that might produce such radio-weak/radio-quiet continuum objects, and also demonstrate that such radio-quiet BL Lac objects could exist at low redshift. Failure to include these radio-quiet BL Lacs in X-ray selected samples could explain the negative evolution found for this class of object.
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Carnerero, M. I., C. M. Raiteri, M. Villata, J. A. Acosta-Pulido, V. M. Larionov, P. S. Smith, F. D'Ammando et al. "Dissecting the long-term emission behaviour of the BL Lac object Mrk 421". OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/626278.
We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by several extreme flares. The ratio between the optical, X-ray and gamma-ray fluxes is very variable. The gamma-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of similar to 50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.
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Carnerero, Maria, Claudia Raiteri, Massimo Villata, Pulido Jose Acosta, Paul Smith e Valeri Larionov. "Investigating the Puzzling Synchrotron Behaviour of Mrk 421". MDPI AG, 2016. http://hdl.handle.net/10150/622694.
We investigate the multiwavelength behaviour of the high-energy peaked BL Lac object (HBL) Mrk 421 at redshift z = 0.031 in the period 2007-2015. We use optical photometric, spectroscopic, and polarimetric data and near-infrared data obtained by 35 observatories participating in the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as by the Steward Observatory Support of the Fermi Mission. We also employ high-energy data from the Swift (UV and X-rays) satellite to study correlations among emission in different bands.
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Wright, Susan Clare. "Blazar host galaxies". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243088.
Meeting, OJ-94 Annual. Blazar monitoring: Towards the third millennium : proceedings of the OJ-94 Annual Meeting 1999 : Torino, Italy, May 19-21, 1999. Pino Torinese, Italy: Osservatorio astronomico di Torino, 1999.
Heidelberg Workshop on Gamma-ray Emitting AGN (1996 Heidelberg, Germany). Proceedings of the Heidelberg Workshop on Gamma-ray Emitting AGN: Held at the Landessternwarte, Heidelberg-Königstuhl, 16th to 18th October 1996. Editado por Kirk J. G e Max-Planck-Institut für Kernphysik. Heidelberg, Germany: Max-Planck-Institut für Kernphysik, 1996.
Blazar Variability Workshop (2nd 2005 Florida International University). Blazar Variability Workshop II: Entering the GLAST era : proceedings of a workshop held at Florida International University, Miami, Florida, USA, 10-12 April 2005. San Francisco, Calif: Astronomical Society of the Pacific, 2006.
Urry, Claudia Megan. Coordinated observations of X-ray bright BL Lacertae objects: Semi-annual status report #2, NASA grant NAG 5-495. [Washington, DC: National Aeronautics and Space Administration, 1986.
Urry, Claudia Megan. Final status report, testing the pairs-reflection model with X-ray spectral variability and X-ray properties of complete samples of radio-selected BL lacertae objects: NASA grant NAG5-2510 : period covered: February 1994 through May 1997. [Washington, D.C: National Aeronautics and Space Administration, 1997.
United States. National Aeronautics and Space Administration., ed. Hot absorbers and the X-ray spectra of BL Lac objects: Final report for NASA grant, NAG5-1671. Baltimore, MD: Space Telescope Science Institute, 1994.
Urry, Claudia Megan. Hot absorbers and the X-ray spectra of BL Lac objects: Final report for NASA grant, NAG5-1671. Baltimore, MD: Space Telescope Science Institute, 1994.
1891-1971, Väisälä Yrjö, Valtaoja Esko e Valtonen M. J. 1945-, eds. Variability of blazars: Proceedings of a conference in honour of the 100th anniversary of the birth of Academician Yrjö Väisälä, held at Tuorla Obervatory, University of Turku, Finland, January 6-10, 1991. Cambridge: Cambridge University Press, 1992.
Capítulos de livros sobre o assunto "BL Lacertae objects":
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Stocke, John T. "New Observations of BL Lacertae Objects". In Extragalactic Radio Sources, 385–88. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0295-4_136.
Nilsson, K., L. Takalo, T. Pursimo, A. Sillanpää e J. Heidt. "Host Galaxies of RGB BL Lacertae Objects". In QSO Hosts and Their Environments, 51–54. Boston, MA: Springer US, 2001. http://dx.doi.org/10.1007/978-1-4615-0695-9_8.
Sol, Hélène, e Lourdes Vicente. "A Tentative Sketch for BL Lacertae Objects". In Multi-Wavelength Continuum Emission of AGN, 473. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-010-9537-2_177.
Lamer, G., H. Brunner e R. Staubert. "ROSAT Observations of Bright BL Lacertae Objects". In Multi-Wavelength Continuum Emission of AGN, 377. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-010-9537-2_94.
Cavaliere, A., E. Giallongo e F. Vagnetti. "BL Lacertae Objects as an Evolutionary Population". In Quasars, 491–92. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_110.
Gabuzda, D. C., D. H. Roberts, J. F. C. Wardle e L. F. Brown. "Milliarcsecond Polarization Properties of Several BL Lacertae Objects". In The Impact of VLBI on Astrophysics and Geophysics, 167–68. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2949-4_64.
Padovani, Paolo, e Paolo Giommi. "The Rosat X-Ray Spectra of BL Lacertae Objects". In Extragalactic Radio Sources, 267–68. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0295-4_97.
Gabuzda, D. C. "New Results from VLBI Polarization Observations of BL Lacertae Objects". In Extragalactic Radio Sources, 49–50. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0295-4_19.
Falomo, R., E. Pian, R. Scarpa e A. Treves. "The UV-Optical-Near-IR Emission of BL Lacertae Objects". In Multi-Wavelength Continuum Emission of AGN, 17–20. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-010-9537-2_2.
Giommi, P., S. G. Ansari e A. Micol. "Radio to X-ray Energy Distribution of BL Lacertae Objects". In Multi-Wavelength Continuum Emission of AGN, 506–7. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-010-9537-2_204.
Trabalhos de conferências sobre o assunto "BL Lacertae objects":
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PURSIMO, T., T. RECTOR, M. TORNIKOSKI e D. LONDISH. "SEARCH FOR RADIO QUIET BL LACERTAE OBJECTS". In Proceedings of the Guillermo Haro Conference 2003. WORLD SCIENTIFIC, 2004. http://dx.doi.org/10.1142/9789812702432_0076.
Kollgaard, R. I., G. A. Moellenbrock, S. A. Laurent-Muehleisen e E. D. Feigelson. "VLA studies of X-ray selected BL Lacertae objects". In Testing the AGN paradigm diagnostics. AIP, 1992. http://dx.doi.org/10.1063/1.42273.
Randall, Jill M., Eric S. Perlman, Sebastian Heinz e Eric Wilcots. "X-ray Emission of Low-Energy-Peaked BL Lacertae Objects". In THE MONSTER’S FIERY BREATH: FEEDBACK IN GALAXIES, GROUPS, AND CLUSTERS. AIP, 2009. http://dx.doi.org/10.1063/1.3293025.
Kollgaard, R. I., E. D. Feigelson, D. C. Gabuzda, R. M. Sambruna e C. M. Urry. "X-rays and relativistic beaming in radio-selected BL Lacertae objects". In The soft x-ray cosmos: ROSAT science symposium and data analysis workshop. AIP, 1994. http://dx.doi.org/10.1063/1.46659.
Abeysekara, Anushka. "VERITAS Long Term Monitoring of Gamma-Ray Emission from the BL Lacertae Object". In 35th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2017. http://dx.doi.org/10.22323/1.301.0610.
Schultz, C., K. Berger, E. Lindfors, R. Reinthal, A. Stamerra, MAGIC Collaboration, S. Buson, Fermi Collaboration, T. Hovatta e OVRO Collaboration. "Spectral variability and multiwavelength studies of the high-frequency-peaked BL Lacertae object 1ES 0806+524 with the MAGIC telescopes". In HIGH ENERGY GAMMA-RAY ASTRONOMY: 5th International Meeting on High Energy Gamma-Ray Astronomy. AIP, 2012. http://dx.doi.org/10.1063/1.4772315.
Relatórios de organizações sobre o assunto "BL Lacertae objects":
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Perlman, E. Intrinsic Curvature in the X-Ray Spectra of BL Lacertae Objects. Office of Scientific and Technical Information (OSTI), fevereiro de 2005. http://dx.doi.org/10.2172/839750.
