Abstract
BL Lac objects are active nuclei, hosted in massive elliptical galaxies, the emission of which is dominated by a relativistic jet closely aligned with the line of sight. This implies the existence of a parent population of sources with a misaligned jet that have been identified with low-power radiogalaxies. The spectrum of BL Lacs, dominated by non-thermal emission over the whole electromagnetic range, together with bright compact radio cores, high luminosities, rapid and large amplitude flux variability at all frequencies and strong polarization makes these sources an optimal laboratory for high energy astrophysics. A most distinctive characteristic of the class is the weakness or absence of spectral lines, that historically hindered the identification of their nature and ever thereafter proved to be a hurdle in the determination of their distance. In this paper, we review the main observational facts that contribute to the present basic interpretation of this class of active galaxies. We overview the history of the BL Lac objects research field and their population as it emerged from multi-wavelength surveys. The properties of the flux variability and polarization, compared with those at radio, X-ray and gamma-ray frequencies, are summarized together with the present knowledge of the host galaxies, their environments, and central black hole masses. We focus this review on the optical observations, which played a crucial role in the early phase of BL Lacs studies, and in spite of extensive radio, X-ray, and recently gamma-ray observations, could represent the future major contribution to the unveiling of the origin of these sources. In particular, they could provide a firm conclusion on the long debated issue of the cosmic evolution of this class of active galactic nuclei and on the connection between formation of supermassive black holes and relativistic jets.
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Notes
This term was coined by E. Spiegel during the Conference on BL Lac Objects in Pittsburgh, in April 1978, from a contraction of “BL Lac” and “quasar”.
\(\varGamma \) is defined as \((1 - \beta ^2)^{-0.5}\), where \(\beta = v/c\), with \(v\) representing the plasma velocity.
In general, the luminosity enhancement is a factor \(\delta ^p\), where \( 3 {\mathop {<}\limits _{\sim }}p {\mathop {<}\limits _{\sim }}4\), depending on the geometry of the emitting region and on spectral index.
Fanaroff and Riley (1974) distinguished radiogalaxies into two types: FR I and FR II according to whether their luminosities at 178 MHz were lower or higher than \(2 \times 10^{32}\) erg s\(^{-1}\) Hz\(^{-1}\)sr\(^{-1}\). Their radio morphologies are also different, being core-dominated or lobe-dominated, respectively. The comparison of radio power and morphology and host galaxy luminosity of BLLs and radiogalaxies suggests that the dominant parent population consists of FR I radiogalaxies.
The overlap of several spatial emission components may also make the radio spectrum deviate from a Rayleigh–Jeans shape, so that it appears thin, although the individual components may be self-absorbed.
see list at http://tevcat.uchicago.edu.
GASP/WEBT, http://www.oato.inaf.it/blazars/webt/.
The only other known sources showing similar polarization are optical counterparts of GRBs, at least during the first seconds to minutes after explosion, and indeed have in common with blazars the non-thermal origin of their continuum.
References
Abazajian KN, Adelman-McCarthy JK, Agüeros MA et al (2009) Ap J Suppl 182:543
Abdo AA, Ackermann M, Ajello M et al (2010a) Ap J 715:429
Abdo AA, Ackermann M, Agudo I et al (2010b) Ap J 716:30
Abraham RG, Crawford CS, McHardy IM (1991) MNRAS 252:482
Acciari VA, Aliu E, Arlen T et al (2011) Ap J 738:169
Ackermann M, Ajello M, Allafort A et al (2011) Ap J 743:171
Ackermann M, Ajello M, Ballet J et al (2012) Ap J 751:159
Agudo I, Marscher AP, Jorstad SG et al (2011) Ap J Lett 735:L10
Aharonian FA (2000) New Astron 5:377
Aharonian F, Akhperjanian AG, Anton G et al (2009) A&A 502:749
Ajello M, Shaw MS, Romani RW et al (2012) Ap J 751:108
Ajello M, Romani RW, Gasparrini D et al (2014) Ap J 780:73
Aleksić J, Antonelli LA, Antoranz P et al (2011) A&A 530:A4
Aleksić J, Alvarez EA, Antonelli LA et al (2012) A&A 542:A100
Aliu E, Aune T, Beilicke M et al (2011) Ap. J. 742:127
Aliu E, Archambault S, Arlen T et al (2013) Ap J 775:3
Allen RG, Smith PS, Angel JRP et al (1993) Ap J 403:610
Andruchow I, Cellone SA, Romero GE (2008) MNRAS 388:1766
Angel JRP, Stockman HS (1980) Ann Rev A A 18:321
Asano K, Takahara F, Kusunose M, Toma K, Kakuwa J (2014) Ap J 780:64
Barres de Almeida U, Ward MJ, Dominici TP et al (2010) MNRAS 408:1778
Barth AJ, Ho LC, Sargent WLW (2003) Ap J 583:134
Bauer A, Baltay C, Coppi P et al (2009) Ap J 699:1732
Beckmann V, Engels D, Bade N, Wucknitz O (2003) A&A 401:927
Begelman MC, Blandford RD, Rees MJ (1984) Rev Modern Phys 56:255
Begelman MC, Fabian AC, Rees MJ (2008) MNRAS 384:L19
Bersanelli M, Bouchet P, Falomo R, Tanzi EG (1992) A J 104:28
Birkinshaw M, Worrall DM, Hardcastle MJ (2002) MNRAS 335:142
Blandford RD, Znajek RL (1977) MNRAS 179:433
Blandford RD, Rees MJ (1978). In: Pittsburgh conference on BL Lac Objects, Pittsburgh, Pa, April 24–26, 1978, Proceedings. (A79–30026 11–90) Pittsburgh, Pa., University of Pittsburgh, pp. 328–341
Błażejowski M, Sikora M, Moderski R, Madejski GM (2000) Ap J 545:107
Böttcher M, Reimer A, Sweeney K, Prakash A (2013) Ap J 768:54
Bonning E, Urry CM, Bailyn C et al (2012) Ap J 756:13
Bressan A, Falomo R, Valdés JR, Rampazzo R (2006) Ap J Lett 645:L101
Butcher HR, Oemler A Jr, Tapia S, Tarenghi M (1976) Ap J Lett 209:L11
Caccianiga A, Maccacaro T, Wolter A, Della Ceca R, Gioia IM (2002) Ap J 566:181
Caccianiga A, Severgnini P, Della Ceca R et al (2008) A&A 477:735
Cagnoni I, Nicastro F, Maraschi L, Treves A, Tavecchio F (2004) Ap J 603:449
Camenzind M, Krockenberger M (1992) A&A 255:59
Capetti A, Celotti A, Chiaberge M et al (2002) A&A 383:104
Carini MT, Barnaby D, Mattox JR et al (2004) Astronomische Nachrichten 325:646
Celotti A, Ghisellini G, Chiaberge M (2001) MNRAS 321:L1
Chen PS, Fu HW, Gao YF (2005) Nature 11:27
Chen PS, Shan HG (2011) Ap J 732:22
Chiaberge M, Celotti A, Capetti A, Ghisellini G (2000) A&A 358:104
Chiaberge M, Capetti A, Celotti A (2001) MNRAS 324:L33
Ciprini S, Tosti G, Raiteri CM et al (2003) A&A 400:487
Corbett EA, Robinson A, Axon DJ et al (1996) MNRAS 281:737
Costamante L, Ghisellini G, Giommi P et al (2001) A&A 371:512
Costamante L (2013) Int J Modern Phys D 22:30025
Cusumano G, La Parola V, Segreto A et al (2010) A&A 524:A64
D’Abrusco R, Massaro F, Paggi A et al (2013) Ap J Suppl 206:12
Danforth CW, Keeney BA, Stocke JT, Shull JM, Yao Y (2010) Ap J 720:976
Disney MJ (1974) Ap J Lett 193:L103
Disney MJ, Peterson BA, Rodgers AW (1974) Ap J Lett 194:L79
Dolan JF, Clark LL (2004) Ap J 607:84
Dolcini A, Farfanelli F, Ciprini S et al (2007) A&A 469:503
Edelson RA, Saken J, Pike G et al (1991) Ap J Lett 372:L9
Edelson R, Mushotzky R, Vaughan S et al (2013) Ap J 766:16
Elvis M, Plummer D, Schachter J, Fabbiano G (1992) Ap J Suppl 80:257
Emmanoulopoulos D, McHardy IM, Uttley P (2010) MNRAS 404:931
Falomo R, Treves A, Chiappetti L et al (1993) Ap J 402:532
Falomo R, Pesce JE, Treves A (1993) Ap J Lett 411:L63
Falomo R, Pesce JE, Treves A (1993) A J 105:2031
Falomo R, Bersanelli M, Bouchet P, Tanzi EG (1993) A J 106:11
Falomo R, Pesce JE, Treves A (1995) Ap J Lett 438:L9
Falomo R (1996) MNRAS 283:241
Falomo R, Kotilainen J, Pursimo T et al (1997) A&A 321:374
Falomo R, Urry CM, Pesce JE et al (1997) Ap J 476:113
Falomo R, Kotilainen JK (1999) A&A 352:85
Falomo R, Scarpa R, Treves A, Urry CM (2000) Ap J 542:731
Falomo R, Kotilainen JK, Treves A (2002) Ap J Lett 569:L35
Falomo R, Kotilainen JK, Carangelo N, Treves A (2003a) Ap J 595:624
Falomo R, Carangelo N, Treves A (2003b) MNRAS 343:505
Falomo R, Pian E, Treves A et al (2009) A&A 501:907
Fanaroff BL, Riley JM (1974) MNRAS 167:31P
Finke JD, Dermer CD, Boettcher M (2008) Ap J 686:181
Fleming TA, Green RF, Jannuzi BT et al (1993) A J 106:1729
Fosbury RAE, Disney MJ (1976) Ap J Lett 207:L75
Foschini L, Ghisellini G, Tavecchio F et al (2007) Ap J Lett 657:L81
Fossati G, Maraschi L, Celotti A, Comastri A, Ghisellini G (1998) MNRAS 299:433
Fossati G, Celotti A, Chiaberge M et al (2000) Ap J 541:166
Fried JW, Stickel M, Kühr H (1993) A&A 268:53
Fujiwara M, Matsuoka Y, Ienaka N (2012) A J 144:112
Gabuzda DC, Cawthorne TV, Roberts DH, Wardle JFC (1989) Ap J 347:701
Gaur H, Gupta AC, Wiita PJ et al (2014) Ap J Lett 781:L4
Ghisellini G, Maraschi L, Treves A (1985) A&A 146:204
Ghisellini G, Padovani P, Celotti A, Maraschi L (1993) Ap J 407:65
Ghisellini G, Villata M, Raiteri CM et al (1997) A&A 327:61
Ghisellini G, Celotti A, Fossati G, Maraschi L, Comastri A (1998) MNRAS 301:451
Ghisellini G, Tavecchio F (2008) MNRAS 387:1669
Ghisellini G, Tavecchio F, Foschini L et al (2010) MNRAS 402:497
Ghisellini G (2013) Lecture notes in physics. Springer, Berlin
Gioia IM, Maccacaro T, Schild RE et al (1990) Ap J Suppl 72:567
Giommi P, Menna MT, Padovani P (1999) MNRAS 310:465
Giommi P, Piranomonte S, Perri M, Padovani P (2005) A&A 434:385
Giovannini G, Falomo R, Scarpa R, Treves A, Urry CM (2004) Ap J 613:747
Giroletti M, Giovannini G, Taylor GB, Falomo R (2004) Ap J 613:752
Gladders MD, Abraham RG, McHardy IM et al (1997) MNRAS 284:27
Green RF, Schmidt M, Liebert J (1986) Ap J Suppl 61:305
Green JC, Froning CS, Osterman S et al (2012) Ap J 744:60
Gu MF, Lee C-U, Pak S, Yim HS, Fletcher AB (2006) A&A 450:39
Guilbert PW, Fabian AC, Rees MJ (1983) MNRAS 205:593
Gupta AC, Krichbaum TP, Wiita PJ et al (2012) MNRAS 425:1357
Hagen-Thorn VA, Larionov VM, Jorstad SG et al (2008) Ap J 672:40
Halpern JP, Impey CD, Bothun GD et al (1986) Ap J 302:711
Hanson CG, Coe MJ (1985) MNRAS 217:831
Hartman RC, Bertsch DL, Bloom SD et al (1999) Ap J Suppl 123:79
Heidt J, Wagner SJ, Wilhelm-Erkens U (1997) A&A 325:27
Heidt J, Wagner SJ (1998) A&A 329:853
Heidt J, Nilsson K, Fried JW, Takalo LO, Sillanpää A (1999) A&A 348:113
Heidt J, Nilsson K (2011) A&A 529:A162
H.E.S.S. Collaboration, Abramowski A, Acero F, et al. (2012) A&A 539:A149
H.E.S.S. Collaboration, Abramowski A, Acero F, et al. (2013) A&A 552:A118
Hoffmeister C (1929) Astronomische Nachrichten 236:233
Hoyle F, Burbidge GR, Sargent WLW (1966) Nature 209:751
Hudec R, Bašta M, Pihajoki P, Valtonen M (2013) A&A 559:A20
Hutsemékers D, Borguet B, Sluse D, Cabanac R, Lamy H (2010) A&A 520:L7
Impey CD, Tapia S (1988) Ap J 333:666
Impey CD, Lawrence CR, Tapia S (1991) Ap J 375:46
Impey CD, Bychkov V, Tapia S, Gnedin Y, Pustilnik S (2000) A J 119:1542
Itoh R, Fukazawa Y, Chiang J et al (2013) PASJ 65:18
Jannuzi BT, Yanny B, Impey C (1997) Ap J 491:146
Jorstad SG, Marscher AP, Larionov VM et al (2010) Ap J 715:362
Kastendieck MA, Ashley MCB, Horns D (2011) A&A 531:A123
Kato T, Uemura M, Ishioka R et al (2004) PASJ 56:1
Kellermann KI, Pauliny-Toth IIK (1969) Ap J Lett 155:L71
Kinman TD (1975) Ap J Lett 197:L49
Kirk JG, Rieger FM, Mastichiadis A (1998) A&A 333:452
Kotilainen JK, Falomo R, Scarpa R (1998) A&A 336:479
Kühr H, Pauliny-Toth IIK, Witzel A, Schmidt J (1981) A J 86:854
Lamer G, Newsam AM, McHardy IM (1999) MNRAS 309:1085
Landoni M, Falomo R, Treves A et al (2012) A&A 543:A116
Landoni M, Falomo R, Treves A et al (2013) A J 145:114
Landoni M, Falomo R, Treves A, Sbarufatti B (2014) A&A. arXiv:1407.3085 (in press)
Larionov VM, Villata M, Raiteri CM (2010) A&A 510:A93
Larionov VM, Jorstad SG, Marscher AP et al (2013) Ap J 768:40
Laurent-Muehleisen SA, Kollgaard RI, Moellenbrock GA, Feigelson ED (1993) A J 106:875
Laurent-Muehleisen SA, Kollgaard RI, Ciardullo R et al (1998) Ap J Suppl 118:127
Laurent-Muehleisen SA, Kollgaard RI, Feigelson ED, Brinkmann W, Siebert J (1999) Ap J 525:127
Maccacaro T, Gioia IM, Maccagni D, Stocke JT (1984) Ap J Lett 284:L23
Maccacaro T, Caccianiga A, della Ceca A, Wolter A, Gioia IM (1998) Astronomische Nachrichten 319:15
MacLeod JM, Andrew BH (1968) Ap Lett 1:243
MAGIC Collaboration, Albert J, Aliu E, et al. (2008) Science 320:1752
Mannheim K, Biermann PL (1992) A&A 253:L21
Mannheim K (1998) Science 279:684
Maraschi L, Ghisellini G, Tanzi EG, Treves A (1986) Ap J 310:325
Maraschi L, Ghisellini G, Celotti A (1992) Ap J Lett 397:L5
Maraschi L, Rovetti F (1994) Ap J 436:79
Maraschi L, Tavecchio F (2003) Ap J 593:667
Marchã MJM, Caccianiga A (2013) MNRAS 430:2464
Marscher AP, Jorstad SG, Mattox JR, Wehrle AE (2002) Ap J 577:85
Marscher AP, Jorstad SG, D’Arcangelo FD et al (2008) Nature 452:966
Maselli A, Massaro E, Nesci R et al (2010) A&A 512:A74
Massaro E, Giommi P, Leto C et al (2009) A&A 495:691
Massaro E, Nesci R, Piranomonte S (2012a) MNRAS 422:2322
Massaro F, Paggi A, Errando M et al (2013) Ap J Suppl 207:16
McBreen B (1979) A&A 71:L19
McHardy IM, Koerding E, Knigge C, Uttley P, Fender RP (2006) Nature 444:730
Miller JS, Hawley SA (1977) Ap J Lett 212:L47
Miller JS, French HB, Hawley SA (1978a) Optical spectra of BL Lacertae objects. In: Pittsburgh Conference on BL Lac Objects, Pittsburgh, PA, April 24-26, Proceedings (A79-30026 11-90). University of Pittsburgh, Pittsburgh, PA, pp 176–187
Miller JS, French HB, Hawley SA (1978b) Ap J Lett 219:L85
Miller HR, McGimsey BQ (1978) Ap J 220:19
Miller HR, Carini MT, Goodrich BD (1989) Nature 337:627
Moderski R, Sikora M, Coppi PS, Aharonian F (2005) MNRAS 363:954
Moore RL, Stockman HS (1981) Ap J 243:60
Morris SL, Stocke JT, Gioia IM et al (1991) Ap J 380:49
Mücke A, Protheroe RJ (2001) Astropart Phys 15:121
Mücke A, Protheroe RJ, Engel R, Rachen JP, Stanev T (2003) Astropart Phys 18:593
Nesci R, Tosti G, Pursimo T, Ojha R, Kadler M (2013) A&A 555:A2
Nicastro F, Zezas A, Drake J et al (2002) Ap J 573:157
Ojha R, Kadler M, Böck M et al (2010) A&A 519:A45
Osone S (2006) Astropart Phys 26:209
Ostorero L, Villata M, Raiteri CM (2004) A&A 419:913
Ostriker JP, Vietri M (1985) Nature 318:446
Ostriker JP, Vietri M (1990) Nature 344:45
Padovani P, Giommi P (1995) Ap J 444:567
Padovani P, Giommi P, Landt H, Perlman ES (2007) Ap J 662:182
Padovani P, Giommi P, Rau A (2012) MNRAS 422:L48
Paggi A, Massaro F, D’Abrusco R, Smith HA, Masetti N, Giroletti M, Tosti G, Funk S (2013) Ap J Suppl 209:9
Paltani S, Courvoisier TJ-L (1994) A&A 291:74
Pavlidou V, Angelakis E, Myserlis I, et al. (2013). arXiv:1311.3304
Perlman ES, Stocke JT, Schachter JF et al (1996) Ap J Suppl 104:251
Perri M, Maselli A, Giommi P et al (2007) A&A 462:889
Persic M, de Angelis A (2008) A&A 483:1
Pesce JE, Falomo R, Treves A (1994) A J 107:494
Pesce JE, Falomo R, Treves A (1995) A J 110:1554
Peterson BM (1997) An introduction to active galactic nuclei. Cambridge University Press, New York
Pian E, Falomo R, Scarpa R, Treves A (1994) ApJ 432:547
Pian E, Urry CM, Treves A et al (1997) Ap J 486:784
Pian E, Vacanti G, Tagliaferri G et al (1998) Ap J Lett 492:L17
Pian E, Romano P, Treves A et al (2007) Ap J 664:106
Pietilä H, Takalo LO, Tosti G et al (1999) A&A 345:760
Pihajoki P, Valtonen M, Zola S et al (2013a) Ap J 764:5
Pihajoki P, Valtonen M, Ciprini S (2013b) MNRAS 434:3122
Piner BG, Pant N, Edwards PG (2010) Ap J 723:1150
Plotkin RM, Anderson SF, Brandt WN et al (2010) A J 139:390
Plotkin RM, Markoff S, Trager SC, Anderson SF (2011) MNRAS 413:805
Pollock JT, Webb JR, Azarnia G (2007) A J 133:487
Potter WJ, Cotter G (2013) MNRAS 436:304
Punch M, Akerlof CW, Cawley MF et al (1992) Nature 358:477
Raiteri CM, Villata M, Capetti A et al (2007) A&A 464:871
Raiteri CM, Villata M, Capetti A et al (2009) A&A 507:769
Raiteri CM, Villata M, Bruschini L et al (2010) A&A 524:A43
Raiteri CM, Villata M, D’Ammando F et al (2013) MNRAS 436:1530
Rani B, Krichbaum TP, Fuhrmann L et al (2013) A&A 552:A11
Rector TA, Stocke JT, Perlman ES, Morris SL, Gioia IM (2000) A J 120:1626
Rector TA, Stocke JT (2003) AJ 125:2447
Rieger FM (2004) Ap J Lett 615:L5
Romanishin W (1987) Ap J 320:586
Salpeter EE (1964) Ap J 140:796
Sambruna RM, Maraschi L, Urry CM (1996) Ap J 463:444
Sambruna RM, Donato D, Tavecchio F et al (2007) Ap J 670:74
Sandrinelli A, Treves A, Falomo R, Farina EP, Foschini L, Landoni M, Sbarufatti B (2013) A J 146:163
Sandrinelli A, Covino S, Treves A (2014) A&A 562:A79
Sasada M, Uemura M, Arai A et al (2008) PASJ 60:L37
Sbarrato T, Ghisellini G, Nardini M et al (2013) MNRAS 433:2182
Sbarufatti B, Treves A, Falomo R (2005) Ap J 635:173
Sbarufatti B, Falomo R, Treves A, Kotilainen J (2006a) A&A 457:35
Sbarufatti B, Treves A, Falomo R et al (2006b) A J 132:1
Scarpa R, Falomo R (1997) A&A 325:109
Scarpa R, Urry CM, Falomo R, Treves A (1999) ApJ 526:643
Scarpa R, Urry CM, Falomo R, Pesce JE, Treves A (2000) Ap J 532:740
Schmidt M (1963) Nature 197:1040
Schmitt JL (1968) Nature 218:663
Schwartz DA, Ku WH-M (1983) Ap J 266:459
Schwartz DA, Marshall HL, Lovell JEJ et al (2000) Ap J Lett 540:L69
Şentürk GD, Errando M, Böttcher M, Mukherjee R (2013) Ap J 764:119
Shakura NI, Sunyaev RA (1973) A&A 24:337
Shaw MS, Romani RW, Cotter G et al (2013) Ap J 764:135
Shen Y, Richards GT, Strauss MA et al (2011) Ap J Suppl 194:45
Sikora M, Begelman MC, Rees MJ (1994) Ap J 421:153
Sillanpää A, Haarala S, Korhonen T (1988a) A&A Suppl 72:347
Sillanpää A, Haarala S, Valtonen MJ, Sundelius B, Byrd GG (1988b) Ap J 325:628
Sillanpää A, Takalo LO, Pursimo T et al (1996) A&A 305:L17
Smith PS, Allen RG, Angel JRP (1993) Ap J Lett 415:L83
Smith EP, O’Dea CP, Baum SA (1995) Ap J 441:113
Smith PS, Williams GG, Schmidt GD, Diamond-Stanic AM, Means DL (2007) Ap J 663:118
Sorcia M, Benítez E, Hiriart D et al (2013) Ap J Suppl 206:11
Stalin CS, Gopal-Krishna, Sagar R et al (2006) MNRAS 366:1337
Stein WA, Odell SL, Strittmatter PA (1976) Ann Rev A A 14:173
Stickel M, Padovani P, Urry CM, Fried JW, Kühr H (1991) Ap J 374:431
Stickel M, Fried JW, Kühr H (1993) A&A Suppl 98:393
Stocke JT, Morris SL, Gioia I et al (1990) Ap J 348:141
Stocke JT, Wurtz R, Wang Q, Elston R, Jannuzi BT (1992) Ap J Lett 400:L17
Strittmatter PA, Serkowski K, Carswell R et al (1972) Ap J Lett 175:L7
Takahashi T, Tashiro M, Madejski G et al (1996) Ap J Lett 470:L89
Takalo LO, Sillanpaa A, Nilsson K et al (1992) A&A Suppl 94:37
Takalo LO, Sillanpaa A (1993) Ap&SS 206:191
Takalo LO (1994) Vistas Astron 38:77
Tavecchio F, Maraschi L, Sambruna RM, Urry CM (2000) Ap J Lett 544:L23
Tommasi L, Palazzi E, Pian E et al (2001a) A&A 376:51
Tommasi L, Díaz R, Palazzi E et al (2001b) Ap J Suppl 132:73
Tosti G, Pascolini S, Fiorucci M (1996) PASP 108:706
Tosti G, Fiorucci M, Luciani M et al (1998) A&A 339:41
Tosti G, Massaro E, Nesci R et al (2002) A&A 395:11
Tramacere A, Giommi P, Massaro E et al (2007) A&A 467:501
Treves A, Falomo R, Uslenghi M (2007) A&A 473:L17
Trussoni E, Capetti A, Celotti A, Chiaberge M, Feretti L (2003) A&A 403:889
Ulrich M-H (1978) Ap J Lett 222:L3
Ulrich MH, Hackney KRH, Hackney RL, Kondo Y (1984) Ap J 276:466
Ulrich MH (1989) BL Lac Objects 334:45
Ulvestad JS, Antonucci RRJ (1986) A J 92:6
Urry CM, Shafer RA (1984) Ap J 280:569
Urry CM, Padovani P (1991) Ap J 371:60
Urry CM, Maraschi L, Edelson R et al (1993) Ap J 411:614
Urry CM, Padovani P (1995) PASP 107:803
Urry CM, Treves A, Maraschi L et al (1997) Ap J 486:799
Urry CM, Falomo R, Scarpa R et al (1999) Ap J 512:88
Urry CM, Scarpa R, O’Dowd M et al (2000) Ap J 532:816
Valtonen MJ, Lehto HJ, Nilsson K et al (2008) Nature 452:851
Vercellone S, Striani E, Vittorini V et al (2011) Ap J Lett 736:L38
Vermeulen RC, Ogle PM, Tran HD, Browne IWA, Cohen MH, Readhead ACS, Taylor GB, Goodrich RW (1995) ApJ 452:L5
Véron P, Véron MP (1976) A&A 47:319
Véron-Cetty M-P, Véron P (2010) A&A 518:A10
Villata M, Raiteri CM, Kurtanidze OM et al (2002) A&A 390:407
Villata M, Raiteri CM, Kurtanidze OM et al (2004a) A&A 421:103
Villata M, Raiteri CM, Aller HD et al (2004b) A&A 424:497
Visvanathan N, Griersmith D (1977) Ap J 215:759
Visvanathan N, Wills BJ (1998) A J 116:2119
Voges W, Aschenbach B, Boller T et al (1999) A&A 349:389
Wagner SJ, Witzel A (1995) Ann Rev A A 33:163
Watson D, Hanlon L, McBreen B et al (1999) A&A 345:414
Weistrop D (1973) Nature 241:157
Weistrop D, Smith BA, Reitsema HJ (1979) Ap J 233:504
Weistrop D, Reitsema HJ, Smith BA, Shaffer DB (1983) Ap J 271:471
Westerlund BE, Wlerick G, Garnier R (1982) A&A 105:284
Westfold KC (1959) Ap J 130:241
Wolter A, Comastri A, Ghisellini G et al (1998) A&A 335:899
Woltjer L (1966) Ap J 146:597
Woo J-H, Urry CM (2002) Ap J 579:530
Wright SC, McHardy IM, Abraham RG, Crawford CS (1998) MNRAS 296:961
Wurtz R, Ellingson E, Stocke JT, Yee HKC (1993) A J 106:869
Wurtz R, Stocke JT, Yee HKC (1996) Ap J Suppl 103:109
Wurtz R, Stocke JT, Ellingson E, Yee HKC (1997) Ap J 480:547
Zel’dovich YB (1964) Sov Phys Dokl 9:195
Zhang X, Zheng YG, Zhang HJ et al (2008) A J 136:1846
Zhang B-K, Wang S, Zhao X-Y, Dai B-Z, Zha M (2013a) MNRAS 428:3630
Zhang Y-H, Bian F-Y, Li J-Z, Shang R-C (2013b) MNRAS 432:1189
Zhang H, Chen X, Boettcher M (2014). arXiv:1401.7138
Acknowledgments
We are grateful to Catherine Boisson, Alessandro Caccianiga, Stefano Covino, Luigi Foschini, Gabriele Ghisellini, Oliver King, Alan Marscher, Claudia Raiteri, Kenji Toma, Massimo Villata, Andreas Zech for inputs in the preparation of this work. In particular, we thank Gabriele Giovannini and Massimo Persic for useful suggestions, comments and discussions on this review. We are also very grateful to Angela Sandrinelli and Marco Landoni for a careful reading of the manuscript and for fruitful comments. We acknowledge support from ASI/INAF Grant I/088/06/0 and PRIN MIUR 2010/2011.
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Falomo, R., Pian, E. & Treves, A. An optical view of BL Lacertae objects. Astron Astrophys Rev 22, 73 (2014). https://doi.org/10.1007/s00159-014-0073-z
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DOI: https://doi.org/10.1007/s00159-014-0073-z