Prospects for Localization of Gravitational Wave Transients by the

Advanced LIGO and Advanced Virgo Observatories

J. Aasi1, J. Abadie1, B. P. Abbott1, R. Abbott1, T. D. Abbott2, M. Abernathy3, T. Accadia4,F. Acernese5ac, C. Adams6, T. Adams7, P. Addesso8, R. X. Adhikari1, C. Affeldt9,10, M. Agathos11a,

O. D. Aguiar12, P. Ajith1, B. Allen9,13,10, A. Allocca14ac, E. Amador Ceron13, D. Amariutei15,S. B. Anderson1, W. G. Anderson13, K. Arai1, M. C. Araya1, C. Arceneaux16, S. Ast9,10, S. M. Aston6,

P. Astone17a, D. Atkinson18, P. Aufmuth10,9, C. Aulbert9,10, L. Austin1, B. E. Aylott19, S. Babak20,P. Baker21, G. Ballardin22, S. Ballmer23, Y. Bao15, J. C. Barayoga1, D. Barker18, F. Barone5ac, B. Barr3,

L. Barsotti24, M. Barsuglia25, M. A. Barton18, I. Bartos26, R. Bassiri3,27, M. Bastarrika3, A. Basti14ab,J. Batch18, J. Bauchrowitz9,10, Th. S. Bauer11a, M. Bebronne4, B. Behnke20, M. Bejger28c, M.G. Beker11a,

A. S. Bell3, C. Bell3, G. Bergmann9,10, J. M. Berliner18, A. Bertolini9,10, J. Betzwieser6, N. Beveridge3,P. T. Beyersdorf29, T. Bhadbade27, I. A. Bilenko30, G. Billingsley1, J. Birch6, S. Biscans24, M. Bitossi14a,

M. A. Bizouard31a, E. Black1, J. K. Blackburn1, L. Blackburn32, D. Blair33, B. Bland18, M. Blom11a,O. Bock9,10, T. P. Bodiya24, C. Bogan9,10, C. Bond19, F. Bondu34b, L. Bonelli14ab, R. Bonnand35,

R. Bork1, M. Born9,10, V. Boschi14a, S. Bose36, L. Bosi37a, B. Bouhou25, J. Bowers2, C. Bradaschia14a,P. R. Brady13, V. B. Braginsky30, M. Branchesi38ab, J. E. Brau39, J. Breyer9,10, T. Briant40,

D. O. Bridges6, A. Brillet34a, M. Brinkmann9,10, V. Brisson31a, M. Britzger9,10, A. F. Brooks1,D. A. Brown23, D. D. Brown19, F. Brueckner19, K. Buckland1, T. Bulik28b, H. J. Bulten11ab,A. Buonanno41, J. Burguet–Castell42, D. Buskulic4, C. Buy25, R. L. Byer27, L. Cadonati43,

G. Cagnoli35,44, E. Calloni5ab, J. B. Camp32, P. Campsie3, K. Cannon45, B. Canuel22, J. Cao46,C. D. Capano41, F. Carbognani22, L. Carbone19, S. Caride47, A. D. Castiglia48, S. Caudill13,

M. Cavaglia16, F. Cavalier31a, R. Cavalieri22, G. Cella14a, C. Cepeda1, E. Cesarini49a, T. Chalermsongsak1,S. Chao101, P. Charlton50, E. Chassande-Mottin25, X. Chen33, Y. Chen51, A. Chincarini52, A. Chiummo22,

H. S. Cho53, J. Chow54, N. Christensen55, Q. Chu33, S. S. Y. Chua54, C. T. Y. Chung56, G. Ciani15,F. Clara18, D. E. Clark27, J. A. Clark43, F. Cleva34a, E. Coccia49ab, P.-F. Cohadon40, C. N. Colacino14ab,

A. Colla17ab, M. Colombini17b, M. Constancio Jr.12, A. Conte17ab, D. Cook18, T. R. Corbitt2, M. Cordier29,N. Cornish21, A. Corsi103, C. A. Costa2,12, M. Coughlin57, J.-P. Coulon34a, S. Countryman26,P. Couvares23, D. M. Coward33, M. Cowart6, D. C. Coyne1, K. Craig3, J. D. E. Creighton13,

T. D. Creighton44, A. Cumming3, L. Cunningham3, E. Cuoco22, K. Dahl9,10, M. Damjanic9,10,S. L. Danilishin33, S. D’Antonio49a, K. Danzmann9,10, V. Dattilo22, B. Daudert1, H. Daveloza44,

M. Davier31a, G. S. Davies3, E. J. Daw58, T. Dayanga36, R. De Rosa5ab, G. Debreczeni59, J. Degallaix35,W. Del Pozzo11a, E. Deleeuw15, T. Denker10, T. Dent9,10, V. Dergachev1, R. DeRosa2, R. DeSalvo8,

S. Dhurandhar60, L. Di Fiore5a, A. Di Lieto14ab, I. Di Palma9,10, A. Di Virgilio14a, M. Dıaz44, A. Dietz4,16,F. Donovan24, K. L. Dooley9,10, S. Doravari1, M. Drago61ab, S. Drasco20, R. W. P. Drever62,

J. C. Driggers1, Z. Du46, J.-C. Dumas33, S. Dwyer24, T. Eberle9,10, M. Edwards7, A. Effler2, P. Ehrens1,S. S. Eikenberry15, G. Endroczi59, R. Engel1, R. Essick24, T. Etzel1, K. Evans3, M. Evans24, T. Evans6,

M. Factourovich26, V. Fafone49ab, S. Fairhurst7, Q. Fang33, B. F. Farr63, W. Farr63, M. Favata13,D. Fazi63, H. Fehrmann9,10, D. Feldbaum15, I. Ferrante14ab, F. Ferrini22, F. Fidecaro14ab, L. S. Finn64,

I. Fiori22, R. P. Fisher23, R. Flaminio35, S. Foley24, E. Forsi6, L. A. Forte5a, N. Fotopoulos1,J.-D. Fournier34a, J. Franc35, S. Franco31a, S. Frasca17ab, F. Frasconi14a, M. Frede9,10, M. A. Frei48,

Z. Frei65, A. Freise19, R. Frey39, T. T. Fricke9,10, D. Friedrich9,10, P. Fritschel24, V. V. Frolov6,M.-K. Fujimoto66, P. J. Fulda15, M. Fyffe6, J. Gair57, M. Galimberti35, L. Gammaitoni37ab, J. Garcia18,

F. Garufi5ab, M. E. Gaspar59, N. Gehrels32, G. Gelencser65, G. Gemme52, E. Genin22, A. Gennai14a,L. A. Gergely67, S. Ghosh36, J. A. Giaime2,6, S. Giampanis13, K. D. Giardina6, A. Giazotto14a,

S. Gil-Casanova42, C. Gill3, J. Gleason15, E. Goetz9,10, G. Gonzalez2, N. Gordon3, M. L. Gorodetsky30,

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S. Gossan51, S. Goßler9,10, R. Gouaty4, C. Graef9,10, P. B. Graff32, M. Granata35, A. Grant3, S. Gras24,C. Gray18, R. J. S. Greenhalgh68, A. M. Gretarsson69, C. Griffo70, H. Grote9,10, K. Grover19,

S. Grunewald20, G. M. Guidi38ab, C. Guido6, E. K. Gustafson1, R. Gustafson47, D. Hammer13,G. Hammond3, J. Hanks18, C. Hanna71, J. Hanson6, K. Haris72, J. Harms62, G. M. Harry73, I. W. Harry23,

E. D. Harstad39, M. T. Hartman15, K. Haughian3, K. Hayama66, J. Heefner1, A. Heidmann40,M. C. Heintze6, H. Heitmann34a, P. Hello31a, G. Hemming22, M. A. Hendry3, I. S. Heng3,

A. W. Heptonstall1, M. Heurs9,10, M. Hewitson9,10, S. Hild3, D. Hoak43, K. A. Hodge1, K. Holt6,M. Holtrop74, T. Hong51, S. Hooper33, J. Hough3, E. J. Howell33, V. Huang101, E. A. Huerta23,

B. Hughey69, S. H. Huttner3, M. Huynh13, T. Huynh–Dinh6, D. R. Ingram18, R. Inta54, T. Isogai24,A. Ivanov1, B. R. Iyer75, K. Izumi66, M. Jacobson1, E. James1, H. Jang76, Y. J. Jang63, P. Jaranowski28d,E. Jesse69, W. W. Johnson2, D. Jones18, D. I. Jones77, R. Jones3, R.J.G. Jonker11a, L. Ju33, P. Kalmus1,

V. Kalogera63, S. Kandhasamy78, G. Kang76, J. B. Kanner32, M. Kasprzack22,31a, R. Kasturi79,E. Katsavounidis24, W. Katzman6, H. Kaufer9,10, K. Kawabe18, S. Kawamura66, F. Kawazoe9,10,

D. Keitel9,10, D. Kelley23, W. Kells1, D. G. Keppel9,10, A. Khalaidovski9,10, F. Y. Khalili30,E. A. Khazanov80, B. K. Kim76, C. Kim76, K. Kim81, N. Kim27, Y. M. Kim53, P. J. King1, D. L. Kinzel6,

J. S. Kissel24, S. Klimenko15, J. Kline13, K. Kokeyama2, V. Kondrashov1, S. Koranda13, W. Z. Korth1,I. Kowalska28b, D. Kozak1, C. Kozameh82, A. Kremin78, V. Kringel9,10, B. Krishnan10,9, A. Krolak28ae,C. Kucharczyk27, G. Kuehn9,10, P. Kumar23, R. Kumar3, B. J. Kuper70, R. Kurdyumov27, P. Kwee24,

M. Landry18, B. Lantz27, P. D. Lasky56, C. Lawrie3, A. Lazzarini1, A. Le Roux6, P. Leaci20, C. H. Lee53,H. K. Lee81, H. M. Lee83, J. Lee70, J. R. Leong9,10, N. Leroy31a, N. Letendre4, B. Levine18, V. Lhuillier18,

T. G. F. Li11a, A. C. Lin27, V. Litvine1, Y. Liu46, Z. Liu15, N. A. Lockerbie84, D. Lodhia19, K. Loew69,J. Logue3, A. L. Lombardi41, M. Lorenzini49ab, V. Loriette31b, M. Lormand6, G. Losurdo38a, J. Lough23,

M. Lubinski18, H. Luck9,10, A. P. Lundgren9,10, J. Macarthur3, E. Macdonald7, B. Machenschalk9,10,M. MacInnis24, D. M. Macleod7, F. Magana-Sandoval70, M. Mageswaran1, K. Mailand1, E. Majorana17a,I. Maksimovic31b, V. Malvezzi49a, N. Man34a, G. Manca20, I. Mandel19, V. Mandic78, M. Mantovani14a,

F. Marchesoni37ac, F. Marion4, S. Marka26, Z. Marka26, A. Markosyan27, E. Maros1, J. Marque22,F. Martelli38ab, I. W. Martin3, R. M. Martin15, D. Martonov1, J. N. Marx1, K. Mason24, A. Masserot4,

F. Matichard24, L. Matone26, R. A. Matzner85, N. Mavalvala24, G. May15, G. Mazzolo9,10, K. McAuley29,R. McCarthy18, D. E. McClelland54, S. C. McGuire86, G. McIntyre1, J. McIver43, G. D. Meadors47,

M. Mehmet9,10, J. Meidam11a, T. Meier10,9, A. Melatos56, G. Mendell18, R. A. Mercer13, S. Meshkov1,C. Messenger7, M. S. Meyer6, H. Miao51, C. Michel35, L. Milano5ab, J. Miller54, Y. Minenkov49a,

C. M. F. Mingarelli19, S. Mitra60, V. P. Mitrofanov30, G. Mitselmakher15, R. Mittleman24, B. Moe13,M. Mohan22, S. R. P. Mohapatra23,48, F. Mokler10,9, D. Moraru18, G. Moreno18, N. Morgado35, T. Mori66,

S. R. Morriss44, K. Mossavi9,10, B. Mours4, C. M. Mow–Lowry9,10, C. L. Mueller15, G. Mueller15,S. Mukherjee44, A. Mullavey2,54, J. Munch87, D. Murphy26, P. G. Murray3, A. Mytidis15,

D. Nanda Kumar15, T. Nash1, L. Naticchioni17ab, R. Nayak88, V. Necula15, I. Neri37ab, G. Newton3,T. Nguyen54, E. Nishida66, A. Nishizawa66, A. Nitz23, F. Nocera22, D. Nolting6, M. E. Normandin44,L. Nuttall7, E. Ochsner13, J. O’Dell68, E. Oelker24, G. H. Ogin1, J. J. Oh89, S. H. Oh89, F. Ohme7,P. Oppermann9,10, B. O’Reilly6, R. O’Shaughnessy13, C. Osthelder1, C. D. Ott51, D. J. Ottaway87,

R. S. Ottens15, J. Ou101, H. Overmier6, B. J. Owen64, C. Padilla70, A. Page19, A. Pai72, L. Palladino49ac,C. Palomba17a, Y. Pan41, C. Pankow13, F. Paoletti14a,22, R. Paoletti14ac, M. A. Papa20,13, H. Paris18,

M. Parisi5ab, W. Parkinson90, A. Pasqualetti22, R. Passaquieti14ab, D. Passuello14a, M. Pedraza1,S. Penn79, C. Peralta20, A. Perreca23, M. Phelps1, M. Pichot34a, M. Pickenpack9,10, F. Piergiovanni38ab,

V. Pierro8, L. Pinard35, I. M. Pinto8, M. Pitkin3, H. J. Pletsch9,10, R. Poggiani14ab, J. Pold9,10,F. Postiglione91, C. Poux1, V. Predoi7, T. Prestegard78, L. R. Price1, M. Prijatelj9,10, S. Privitera1,

G. A. Prodi61ab, L. G. Prokhorov30, O. Puncken44, M. Punturo37a, P. Puppo17a, V. Quetschke44,E. Quintero1, R. Quitzow-James39, F. J. Raab18, D. S. Rabeling11ab, I. Racz59, H. Radkins18, P. Raffai26,

S. Raja92, M. Rakhmanov44, C. Ramet6, P. Rapagnani17ab, V. Raymond1, V. Re49ab, C. M. Reed18,T. Reed93, T. Regimbau34a, S. Reid94, D. H. Reitze1, F. Ricci17ab, R. Riesen6, K. Riles47, M. Roberts27,

N. A. Robertson1,3, F. Robinet31a, E. L. Robinson20, A. Rocchi49a, S. Roddy6, C. Rodriguez63,L. Rodriguez85, M. Rodruck18, L. Rolland4, J. G. Rollins1, J. D. Romano44, R. Romano5ac, J. H. Romie6,

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D. Rosinska28cf , C. Rover9,10, S. Rowan3, A. Rudiger9,10, P. Ruggi22, K. Ryan18, F. Salemi9,10,L. Sammut56, V. Sandberg18, J. Sanders47, S. Sankar24, V. Sannibale1, L. Santamarıa1, I. Santiago-Prieto3,

E. Saracco35, B. Sassolas35, B. S. Sathyaprakash7, P. R. Saulson23, R. L. Savage18, R. Schilling9,10,R. Schnabel9,10, R. M. S. Schofield39, D. Schuette9,10, B. Schulz9,10, B. F. Schutz20,7, P. Schwinberg18,

J. Scott3, S. M. Scott54, F. Seifert1, D. Sellers6, A. S. Sengupta95, D. Sentenac22, A. Sergeev80,D. A. Shaddock54, S. Shah96, M. Shaltev9,10, Z. Shao1, B. Shapiro27, P. Shawhan41, D. H. Shoemaker24,

T. L Sidery19, X. Siemens13, D. Sigg18, D. Simakov9,10, A. Singer1, L. Singer1, A. M. Sintes42,G. R. Skelton13, B. J. J. Slagmolen54, J. Slutsky9,10, J. R. Smith70, M. R. Smith1, R. J. E. Smith19,

N. D. Smith-Lefebvre1, E. J. Son89, B. Sorazu3, T. Souradeep60, L. Sperandio49ab, M. Stefszky54,E. Steinert18, J. Steinlechner9,10, S. Steinlechner9,10, S. Steplewski36, D. Stevens63, A. Stochino54,

R. Stone44, K. A. Strain3, S. E. Strigin30, A. S. Stroeer44, R. Sturani38ab, A. L. Stuver6,T. Z. Summerscales97, S. Susmithan33, P. J. Sutton7, B. Swinkels22, G. Szeifert65, M. Tacca22,

L. Taffarello61c, D. Talukder39, D. B. Tanner15, S. P. Tarabrin9,10, R. Taylor1, A. P. M. ter Braack11a,M. Thomas6, P. Thomas18, K. A. Thorne6, K. S. Thorne51, E. Thrane1, V. Tiwari15, K. V. Tokmakov84,

C. Tomlinson58, A. Toncelli14ab, M. Tonelli14ab, O. Torre14ac, C. V. Torres44, C. I. Torrie1,3, E. Tournefier4,F. Travasso37ab, G. Traylor6, M. Tse26, D. Ugolini98, C. S. Unnikrishnan99, H. Vahlbruch10,9,

G. Vajente14ab, M. Vallisneri51, J. F. J. van den Brand11ab, C. Van Den Broeck11a, S. van der Putten11a,M. V. van der Sluys63, A. A. van Veggel3, S. Vass1, M. Vasuth59, R. Vaulin24, M. Vavoulidis31a,

A. Vecchio19, G. Vedovato61c, J. Veitch7, K. Venkateswara100, D. Verkindt4, S. Verma33, F. Vetrano38ab,A. Vicere38ab, R. Vincent-Finley86, J.-Y. Vinet34a, S. Vitale24, S. Vitale11a, T. Vo18, H. Vocca37a,

C. Vorvick18, W. D. Vousden19, S. P. Vyatchanin30, A. Wade54, L. Wade13, M. Wade13, S. J. Waldman24,L. Wallace1, Y. Wan46, J. Wang101, M. Wang19, X. Wang46, A. Wanner9,10, R. L. Ward25,54,

M. Was9,10,31a, M. Weinert9,10, A. J. Weinstein1, R. Weiss24, T. Welborn6, L. Wen33, P. Wessels9,10,M. West23, T. Westphal9,10, K. Wette9,10, J. T. Whelan48, D. J. White58, B. F. Whiting15, K. Wiesner9,10,C. Wilkinson18, P. A. Willems1, L. Williams15, R. Williams1, T. Williams90, J. L. Willis102, B. Willke9,10,

M. Wimmer9,10, L. Winkelmann9,10, W. Winkler9,10, C. C. Wipf24, A. G. Wiseman13, H. Wittel9,10,G. Woan3, R. Wooley6, J. Worden18, J. Yablon63, I. Yakushin6, H. Yamamoto1, C. C. Yancey41, H. Yang51,

D. Yeaton-Massey1, S. Yoshida90, H. Yum63, M. Yvert4, A. Zadrozny28e, M. Zanolin69, J.-P. Zendri61c,F. Zhang24, L. Zhang1, C. Zhao33, H. Zhu64, X. J. Zhu33, N. Zotov93, M. E. Zucker24, J. Zweizig1

(The LIGO Scientific Collaboration and the Virgo Collaboration)1LIGO - California Institute of Technology, Pasadena, CA 91125, USA

2Louisiana State University, Baton Rouge, LA 70803, USA3SUPA, University of Glasgow, Glasgow, G12 8QQ, United Kingdom

4Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Universite de Savoie, CNRS/IN2P3,F-74941 Annecy-Le-Vieux, France

5INFN, Sezione di Napoli a; Universita di Napoli ’Federico II’b, Complesso Universitario di MonteS.Angelo, I-80126 Napoli; Universita di Salerno, Fisciano, I-84084 Salernoc, Italy

6LIGO - Livingston Observatory, Livingston, LA 70754, USA7Cardiff University, Cardiff, CF24 3AA, United Kingdom

8University of Sannio at Benevento, I-82100 Benevento, Italy and INFN (Sezione di Napoli), Italy9Albert-Einstein-Institut, Max-Planck-Institut fur Gravitationsphysik, D-30167 Hannover, Germany

10Leibniz Universitat Hannover, D-30167 Hannover, Germany11Nikhef, Science Park, Amsterdam, The Netherlandsa; VU University Amsterdam, De Boelelaan 1081,

1081 HV Amsterdam, The Netherlandsb

12Instituto Nacional de Pesquisas Espaciais, 12227-010 - Sao Jose dos Campos, SP, Brazil13University of Wisconsin–Milwaukee, Milwaukee, WI 53201, USA

14INFN, Sezione di Pisaa; Universita di Pisab; I-56127 Pisa; Universita di Siena, I-53100 Sienac, Italy15University of Florida, Gainesville, FL 32611, USA

16The University of Mississippi, University, MS 38677, USA17INFN, Sezione di Romaa; Universita ’La Sapienza’b, I-00185 Roma, Italy

3

18LIGO - Hanford Observatory, Richland, WA 99352, USA19University of Birmingham, Birmingham, B15 2TT, United Kingdom

20Albert-Einstein-Institut, Max-Planck-Institut fur Gravitationsphysik, D-14476 Golm, Germany21Montana State University, Bozeman, MT 59717, USA

22European Gravitational Observatory (EGO), I-56021 Cascina (PI), Italy23Syracuse University, Syracuse, NY 13244, USA

24LIGO - Massachusetts Institute of Technology, Cambridge, MA 02139, USA25APC, AstroParticule et Cosmologie, Universite Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de

Paris, Sorbonne Paris Cite, 10, rue Alice Domon et Leonie Duquet, F-75205 Paris Cedex 13, France26Columbia University, New York, NY 10027, USA27Stanford University, Stanford, CA 94305, USA

28IM-PAN 00-956 Warsawa; Astronomical Observatory Warsaw University 00-478 Warsawb; CAMK-PAN00-716 Warsawc; Bia lystok University 15-424 Bia lystokd; NCBJ 05-400 Swierk-Otwocke; Institute of

Astronomy 65-265 Zielona Goraf , Poland29San Jose State University, San Jose, CA 95192, USA

30Moscow State University, Moscow, 119992, Russia31LAL, Universite Paris-Sud, IN2P3/CNRS, F-91898 Orsaya; ESPCI, CNRS, F-75005 Parisb, France

32NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA33University of Western Australia, Crawley, WA 6009, Australia

34Universite Nice-Sophia-Antipolis, CNRS, Observatoire de la Cote d’Azur, F-06304 Nicea; Institut dePhysique de Rennes, CNRS, Universite de Rennes 1, F-35042 Rennesb, France

35Laboratoire des Materiaux Avances (LMA), IN2P3/CNRS, Universite de Lyon, F-69622 Villeurbanne,Lyon, France

36Washington State University, Pullman, WA 99164, USA37INFN, Sezione di Perugiaa; Universita di Perugiab, I-06123 Perugia; Universita’ di Camerino,

Dipartimento di Fisicac, I-62032 Camerino, Italy38INFN, Sezione di Firenze, I-50019 Sesto Fiorentinoa; Universita degli Studi di Urbino ’Carlo Bo’,

I-61029 Urbinob, Italy39University of Oregon, Eugene, OR 97403, USA

40Laboratoire Kastler Brossel, ENS, CNRS, UPMC, Universite Pierre et Marie Curie, 4 Place Jussieu,F-75005 Paris, France

41University of Maryland, College Park, MD 20742 USA42Universitat de les Illes Balears, E-07122 Palma de Mallorca, Spain43University of Massachusetts - Amherst, Amherst, MA 01003, USA

44The University of Texas at Brownsville, Brownsville, TX 78520, USA45Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario, M5S 3H8,

Canada46Tsinghua University, Beijing 100084 China

47University of Michigan, Ann Arbor, MI 48109, USA48Rochester Institute of Technology, Rochester, NY 14623, USA

49INFN, Sezione di Roma Tor Vergataa; Universita di Roma Tor Vergata, I-00133 Romab; Universitadell’Aquila, I-67100 L’Aquilac, Italy

50Charles Sturt University, Wagga Wagga, NSW 2678, Australia51Caltech-CaRT, Pasadena, CA 91125, USA

52INFN, Sezione di Genova; I-16146 Genova, Italy53Pusan National University, Busan 609-735, Korea

54Australian National University, Canberra, ACT 0200, Australia55Carleton College, Northfield, MN 55057, USA

4

56The University of Melbourne, Parkville, VIC 3010, Australia57University of Cambridge, Cambridge, CB2 1TN, United Kingdom58The University of Sheffield, Sheffield S10 2TN, United Kingdom

59Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Miklos ut 29-33, Hungary60Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India

61INFN, Gruppo Collegato di Trentoa and Universita di Trentob, I-38050 Povo, Trento, Italy; INFN,Sezione di Padovac and Universita di Padovad, I-35131 Padova, Italy

62California Institute of Technology, Pasadena, CA 91125, USA63Northwestern University, Evanston, IL 60208, USA

64The Pennsylvania State University, University Park, PA 16802, USA65Eotvos Lorand University, Budapest, 1117 Hungary

66National Astronomical Observatory of Japan, Tokyo 181-8588, Japan67University of Szeged, 6720 Szeged, Dom ter 9, Hungary

68Rutherford Appleton Laboratory, HSIC, Chilton, Didcot, Oxon OX11 0QX United Kingdom69Embry-Riddle Aeronautical University, Prescott, AZ 86301 USA70California State University Fullerton, Fullerton CA 92831 USA

71Perimeter Institute for Theoretical Physics, Ontario, N2L 2Y5, Canada72IISER-TVM, CET Campus, Trivandrum Kerala 695016, India

73American University, Washington, DC 20016, USA74University of New Hampshire, Durham, NH 03824, USA

75Raman Research Institute, Bangalore, Karnataka 560080, India76Korea Institute of Science and Technology Information, Daejeon 305-806, Korea

77University of Southampton, Southampton, SO17 1BJ, United Kingdom78University of Minnesota, Minneapolis, MN 55455, USA

79Hobart and William Smith Colleges, Geneva, NY 14456, USA80Institute of Applied Physics, Nizhny Novgorod, 603950, Russia

81Hanyang University, Seoul 133-791, Korea82Universidad Nacional de Cordoba, Cordoba 5000, Argentina

83Seoul National University, Seoul 151-742, Korea84University of Strathclyde, Glasgow, G1 1XQ, United Kingdom85The University of Texas at Austin, Austin, TX 78712, USA

86Southern University and A&M College, Baton Rouge, LA 70813, USA87University of Adelaide, Adelaide, SA 5005, Australia

88IISER-Kolkata, Mohanpur West. Bengal 741252, India89National Institute for Mathematical Sciences, Daejeon 305-390, Korea

90Southeastern Louisiana University, Hammond, LA 70402, USA91University of Salerno, I-84084 Fisciano (Salerno), Italy

92RRCAT, Indore MP 452013, India93Louisiana Tech University, Ruston, LA 71272, USA

94SUPA, University of the West of Scotland, Paisley, PA1 2BE, United Kingdom95Indian Institute of Technology, Gandhinagar Ahmedabad Gujarat 382424, India

96Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen,The Netherlands; Nikhef, Science Park, Amsterdam, The Netherlands

97Andrews University, Berrien Springs, MI 49104 USA98Trinity University, San Antonio, TX 78212, USA

99Tata Institute for Fundamental Research, Mumbai 400005, India100University of Washington, Seattle, WA, 98195-4290, USA

5

101National Tsing Hua University, Hsinchu Taiwan 300, Province of China102Abilene Christian University, Abilene TX 79699, USA

103The George Washington University, Washington, DC 20052, USA

March 23, 2019

Abstract

We present a possible observing scenario for the Advanced LIGO and Advanced Virgo gravi-tational wave detectors over the next decade, with the intention of providing information to theastronomy community to facilitate planning for multi-messenger astronomy with gravitationalwaves. We determine the expected sensitivity of the network to transient gravitational-wavesignals, and study the capability of the network to determine the sky location of the source.For concreteness, we focus primarily on gravitational-wave signals from the inspiral of binaryneutron star (BNS) systems, as the source considered likely to be the most common for detectionand also promising for multimessenger astronomy. We find that confident detections will likelyrequire at least 2 detectors operating with BNS sensitive ranges of at least 100 Mpc, while rangesapproaching 200 Mpc should give at least ∼1 BNS detection per year even under pessimisticpredictions of signal rates. The ability to localize the source of the detected signals dependson the geographical distribution of the detectors and their relative sensitivity, and can be aslarge as thousands of square degrees with only 2 sensitive detectors operating. Determiningthe sky position of a significant fraction of detected signals to areas of 5 deg2 to 20 deg2 willrequire at least 3 detectors of sensitivity within a factor of ∼ 2 of each other and with a broadfrequency bandwidth. Should one of the LIGO detectors be relocated in India as expected,many gravitational-wave signals will be localized to a few square degrees by gravitational-waveobservations alone.

1 Introduction

Advanced LIGO (aLIGO) [1] and Advanced Virgo (AdV) [2, 3] are kilometer-scale gravitationalwave (GW) detectors that are expected to yield direct observations of gravitational waves. In thisdocument we describe the currently projected schedule, sensitivity, and sky localization accuracy forthe GW detector network. The purpose of this document is to provide information to the astronomycommunity to assist in the formulation of plans for the upcoming era of GW observations. Inparticular, we intend this document to provide the information required for assessing the featuresof programs for joint observation of GW events using electromagnetic, neutrino, or other observingfacilities.

The full science of aLIGO and AdV is broad [4], and is not covered in this document. We con-centrate solely on candidate GW transient signals. We place particular emphasis on the coalescenceof neutron-star binary systems, which are the GW source with the most reliable predictions on theprospects of detection.

Although our collaborations have amassed a great deal of experience with GW detectors andanalysis, it is still very difficult to make predictions for both improvements in search methods andfor the rate of progress for detectors which are not yet fully installed or operational. We stressthat the scenarios of LIGO and Virgo detector sensitivity evolution and observing times given hererepresent our best estimates at present. They should not be considered as fixed or firm commitments.As the detectors’ construction and commissioning progresses, we intend to release updates versionsof this document.

6

2 Commissioning and Observing Phases

We divide the roadmap for the aLIGO and AdV observatories into three phases:

1. Construction includes the installation and testing of the detectors. This phase ends withacceptance of the detectors. Acceptance means that the interferometers can lock for periods ofhours: light is resonant in the arms of the interferometer with no guaranteed gravitational-wavesensitivity. Construction will likely involve several short engineering runs with no expectedastrophysical output as the detectors progress towards acceptance.

2. Commissioning will take the detectors from their configuration at acceptance through pro-gressively better sensitivity to the ultimate second-generation detector sensitivity. Engineer-ing and science runs in the commissioning phase will allow us to understand our detectors andanalyses in an observational mode. It is expected that science runs will produce astrophysicalresults, including upper limits on the rate of sources and quite possibly the first detectionsof GWs. During this phase, exchange of GW candidates with partners outside the LSC andVirgo collaborations will be governed by memoranda of understanding (MOUs) [5].

3. Observing runs begin when the detectors are at a sensitivity which makes detections likely.We anticipate that there will be a gradual transition from the commissioning to the observingphases. If it has not happened previously, the first few GW signals will be observed and theLSC and Virgo will be engaged in a long-term campaign to observe the GW sky. After thefirst four detections [5] we expect free exchange of GW event candidates with the astronomicalcommunity and the maturation of GW astronomy.

The progress in sensitivity as a function of time will affect the duration of the runs that weplan at any stage, as we strive to minimize the time to the first gravitational wave detection.Commissioning is a complex process which involves both scheduled improvements to the detec-tors and tackling unexpected new problems. While our experience makes us cautiously optimisticregarding the schedule for the advanced detectors, we note that we are targeting an order of magni-tude improvement in sensitivity relative to the previous generation of detectors over a much widerfrequency band. Consequently it is not possible to make concrete predictions for sensitivity as afunction of time. We can, however, use our previous experience as a guide to plausible scenariosfor the detector operational states that will allow us to reach the desired sensitivity. Unexpectedproblems could slow down the commissioning, but there is also the possibility that progress mayhappen faster than predicted here. As the detectors begin to be commissioned, information onthe cost in time and benefit in sensitivity will become more apparent and drive the schedule ofruns. More information on event rates, including the first detection, will also very likely change theschedule and duration of runs. In section 2.1 we present the commissioning plans for the aLIGOand AdV detectors. A summary of expected science runs is in section 2.2.

2.1 Commissioning and Observing Roadmap

The anticipated strain sensitivity evolution for aLIGO and AdV is shown in Fig. 1. A standardfigure of merit for the sensitivity of an interferometer is the binary neutron star (BNS) range: thevolume- and orientation-averaged distance at which a compact binary coalescence consisting of two1.4 M� neutron stars gives a matched filter signal-to-noise ratio of 8 in a single detector [6]1. The

1 Another often quoted number is the BNS horizon—the distance at which an optimally oriented and located BNSsystem would be observed with a signal to noise ratio of 8. The horizon is a factor of 2.26 larger than the range.

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Early (2016−17, 20 − 60 Mpc)Mid (2017−18, 60 − 85 Mpc)Late (2018−20, 65 − 115 Mpc)Design (2021, 130 Mpc)BNS−optimized (145 Mpc)

Figure 1: aLIGO (left) and AdV (right) target strain sensitivity as a function of frequency. Theaverage distance to which binary neutron star (BNS) signals could be seen is given in Mpc. Currentnotions of the progression of sensitivity are given for early, middle, and late commissioning phases,as well as the final design sensitivity target and the BNS-optimized sensitivity. While both datesand sensitivity curves are subject to change, the overall progression represents our best currentestimates.

BNS ranges for the various stages of aLIGO and AdV expected evolution are also provided in Fig. 1.The installation of aLIGO is well underway. The plan calls for three identical 4 km interfer-

ometers, referred to as H1, H2, and L1. In 2011, the LIGO Lab and IndIGO consortium in Indiaproposed installing one of the aLIGO Hanford detectors, H2, at a new observatory in India (LIGO-India). As of early 2013 LIGO Laboratory has begun preparing the H2 interferometer for shipmentto India. Funding for the Indian portion of LIGO-India is in the final stages of consideration bythe Indian government.

The first aLIGO science run is expected in 2015. It will be of order three months in duration,and will involve the H1 and L1 detectors (assuming H2 is placed in storage for LIGO-India). Thedetectors will not be at full design sensitivity; we anticipate a possible BNS range of 40 – 80 Mpc.Subsequent science runs will have increasing duration and sensitivity. We aim for a BNS range of80 – 170 Mpc over 2016–18, with science runs of several months. Assuming that no unexpectedobstacles are encountered, the aLIGO detectors are expected to achieve a 200 Mpc BNS range circa2019. After the first observing runs, circa 2020, it might be desirable to optimize the detectorsensitivity for a specific class of astrophysical signals, such as BNSs. The BNS range may thenbecome 215 Mpc. The sensitivity for each of these stages is shown in Fig. 1.

Because of the planning for the installation of one of the LIGO detectors in India, the installationof the H2 detector has been deferred. This detector will be reconfigured to be identical to H1 andL1 and will be installed in India once the LIGO-India Observatory is complete. The final schedulewill be adopted once final funding approvals are granted. It is expected that the site developmentwould start in 2014, with installation of the detector beginning in 2018. Assuming no unexpectedproblems, first runs are anticipated circa 2020 and design sensitivity at the same level as the H1and L1 detectors is anticipated for no earlier than 2022.

The commissioning timeline for AdV [3] is still being defined, but it is anticipated that in

8

2015 AdV might join the LIGO detectors in their first science run depending on the sensitivityattained. Following an early step with sensitivity corresponding to a BNS range of 20 – 60 Mpc,commissioning is expected to bring AdV to a 60 – 85 Mpc in 2017–18. A configuration upgradeat this point will allow the range to increase to approximately 65 – 115 Mpc in 2018–20. Thefinal design sensitivity, with a BNS range of 130 Mpc, is anticipated circa 2021. The correspondingBNS-optimised range would be 145 Mpc. The sensitivity curves for the various AdV configurationsare shown in Fig. 1.

The GEO600 [7] detector will likely be operational in the early to middle phase of the AdV andaLIGO science runs, i.e. from 2015–2017. The sensitivity that potentially can be achieved by GEOin this timeframe is similar to the AdV sensitivity of the early and mid scenarios at frequenciesaround 1 kHz and above. Around 100 Hz GEO will be at least 10 times less sensitive than theearly AdV and aLIGO detectors.

Japan has recently begun the construction of an advanced detector, KAGRA [8]. KAGRA isdesigned to have a BNS range comparable to AdV at final sensitivity. While we do not considerKAGRA in this document, we note that the addition of KAGRA to the worldwide GW detectornetwork will improve both sky coverage and localization capabilities beyond those envisioned here.

2.2 Estimated observing schedule

Keeping in mind the mentioned important caveats about commissioning affecting the schedulingand length of science runs, the following is a plausible scenario for the operation of the LIGO-Virgonetwork over the next decade:

• 2015: A 3 month run with the two-detector H1L1 network at early aLIGO sensitivity (40 –80 Mpc BNS range). Virgo in commissioning at ∼ 20 Mpc with a chance to join the run.

• 2016–17: A 6 month run with H1L1 at 80 – 120 Mpc and Virgo at 20 – 60 Mpc.

• 2017–18: A 9 month run with H1L1 at 120 – 170 Mpc and Virgo at 60 – 85 Mpc.

• 2019+: Three-detector network with H1L1 at full sensitivity of 200 Mpc and V1 at 65 –130 Mpc.

• 2022+: Four-detector H1L1V1+LIGO-India network at full sensitivity (aLIGO at 200 Mpc,AdV at 130 Mpc).

The observational implications of this scenario are discussed in section 4.

3 Searches for gravitational-wave transients

Data from gravitational wave detectors are searched for many types of possible signals [4]. Here wefocus on signals from compact binary coalescences (CBC), including BNS systems, and on generictransient or burst signals. See [9, 10, 11] for recent observational results from LIGO and Virgo forsuch systems.

The gravitational waveform from a binary neutron star coalescence is well modelled and matchedfiltering can be used to search for signals and measure the system parameters. For systems con-taining black holes, or in which the component spin is significant, uncertainties in the waveformmodel can reduce the sensitivity of the search. Searches for bursts make few assumptions on thesignal morphology, using time-frequency decompositions to identify statistically significant excesspower transients in the data. Burst searches generally perform best for short-duration signals

9

(.1 s); their astrophysical targets include core-collapse supernovae, magnetar flares, black holebinary coalescence, cosmic string cusps, and possibly as-yet-unknown systems.

In the era of advanced detectors, the LSC and Virgo will search in near real-time for CBC andburst signals for the purpose of rapidly identifying event candidates. A prompt notice of a potentialGW transient by LIGO-Virgo might enable followup observations in the electromagnetic spectrum.A first followup program including low-latency analysis, event candidate selection, position recon-struction and the sending of alerts to several observing partners (optical, X-ray, and radio) wasimplemented and exercised during the 2009–2010 LIGO-Virgo science run [12, 13, 14]. Latenciesof less than 1 hour were achieved and we expect to improve this in the advanced detector era.Increased detection confidence, improved sky localization, and identification of host galaxy andredshift are just some of the benefits of joint GW-electromagnetic observations. With this in mind,we focus on two points of particular relevance for followup of GW events: the source localizationafforded by a GW network and the relationship between signal significance (or false alarm rate)and localization.

3.1 Localization

The aLIGO-AdV network will determine the sky position of a GW transient source mainly bytriangulation using the observed time delays between sites [15, 16]. The effective single-site timingaccuracy is approximately

σt =1

2πρσf, (1)

where ρ is the signal-to-noise ratio in the given detector and σf is the effective bandwidth of thesignal in the detector, typically of order 100 Hz. Thus a typical timing accuracy is on the orderof 10−4 s (about 1/100 of the light travel time between sites). This sets the localization scale.Equation (1) ignores many other relevant issues such as uncertainty in the emitted gravitationalwaveform, instrumental calibration accuracies, and correlation of sky location with other binaryparameters [15, 17, 18, 19, 20, 21]. While many of these will affect the measurement of the timeof arrival in individual detectors, such factors are largely common between two similar detectors,so the time difference between the two detectors is relatively uncorrelated with these “nuisance”parameters. The triangulation approach therefore provides a good leading order estimate to local-izations.

Source localization using only timing for a 2-site network yields an annulus on the sky; seeFig. 2. Additional information such as signal amplitude, spin, and precessional effects can sometimesresolve this to only parts of the annulus, but even then sources will only be localized to regions ofhundreds to thousands of square degrees. For three detectors, the time delays restrict the source totwo sky regions whose locations are mirror images in the plane formed by the three detectors. It isoften possible to eliminate one of these regions by requiring consistent amplitudes in all detectors.For signals just above the detection threshold, this typically yields regions with areas of several tensof square degrees. If there is significant difference in sensitivity between detectors, the source is lesswell localized and we may be left with the majority of the annulus on the sky determined by thetwo most sensitive detectors. With four or more detectors, timing information alone is sufficientto localize to a single sky region, and the additional baselines help to limit the region to under 10square degrees for some signals.

From (1), it follows that the linear size of the localization ellipse scales inversely with thesignal to noise ratio (SNR) of the signal and the frequency bandwidth of the signal in the detector.For GWs that sweep across the band of the detector, such as binary merger signals, the effective

10

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Figure 2: Source localization by triangulation for the aLIGO-AdV network. The locus of constanttime delay (with associated timing uncertainty) between two detectors forms an annulus on thesky concentric about the baseline between the two sites. For three detectors, these annuli mayintersect in two locations. One is centered on the true source direction, S, while the other (S′) isits mirror image with respect to the geometrical plane passing through the three sites. For four ormore detectors there is a unique intersection region of all of the annuli. Figure adapted from [22].

bandwidth is ∼ 100 Hz, determined by the most sensitive frequencies of the detector. For shortertransients the bandwidth σf depends on the specific signal. For example, GWs emitted by variousprocesses in core-collapse supernovae are anticipated to have relatively large bandwidths, between150-500 Hz [23, 24, 25, 26], largely independent of detector configuration. By contrast, the skylocalization region for narrowband burst signals may consist of multiple disconnected regions; seefor example [27, 12].

Finally, we note that some GW searches are triggered by electromagnetic observations, and inthese cases localization information is known a priori. For example, in GW searches triggered bygamma-ray bursts [10] the triggering satellite provides the localization. The rapid identification ofa GW counterpart to such a trigger could prompt further followups by other observatories. Thisis of particular relevance to binary mergers, which are considered the likely progenitors of mostshort gamma-ray bursts. It is therefore important to have high-energy satellites operating duringthe advanced detector era.

Finally, it is also worth noting that all GW data are stored permanently, so that it is possibleto perform retroactive analyses at any time.

3.2 Detection and False Alarm Rates

The rate of BNS coalescences is uncertain, but is currently predicted to lie between 10−8 −10−5 Mpc−3 yr−1 [28]. This corresponds to between 0.4 and 400 signals above SNR 8 per yearof observation for a single aLIGO detector at final sensitivity [28]. The predicted observable ratesfor NS-BH and BBH are similar. Expected rates for other transient sources are lower and/or lesswell constrained.

The rate of false alarm triggers above a given SNR will depend critically upon the data quality of

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Figure 3: False alarm rate versus detection statistic for CBC and burst searches on 2009-2010LIGO-Virgo data. Left: Cumulative rate of background events for the CBC search, as a functionof the threshold ranking statistic ρc [9]. Right: Cumulative rate of background events for the burstsearch, as a function of the coherent network amplitude η [11]. In the large-amplitude limit η isrelated to the combined SNR by ρc ∼

√2Kη, where K is the number of detectors. The burst events

are divided into two sets based on their central frequency.

the advanced detectors; non-stationary transients or glitches will produce an elevated backgroundof loud triggers. For low-mass binary coalescence searches, the waveforms are well modelled andsignal consistency tests reduce the background significantly. For burst sources which are not wellmodelled, or which spend only a short time in the detectors’ sensitive band, it is more difficult todistinguish between the signal and a glitch, and so a reduction of the false alarm rate comes at ahigher cost in terms of reduced detection efficiency.

Figure 3 shows the noise background as a function of detection statistic for the low-mass binarycoalescence and burst searches with the 2009–2010 LIGO-Virgo data [9, 11]. For binary mergers,the background rate decreases by a factor of ∼100 for every unit increase in combined SNR ρc,with no evidence of a tail even at low false alarm rates. Here, ρc is a combined, re-weighted SNR.The re-weighting is designed to reduce the SNR of glitches while leaving signals largely unaffected.Consequently, for a signal ρc is essentially the root-sum-square of the SNRs in the individualdetectors.

We conservatively estimate a ρc threshold of 12 is required for a false rate below ∼ 10−2 yr−1

in aLIGO-AdV, where we have taken into account trials factors due to the increase in the numberof template waveforms required to search the advanced detector data. In future sections, we quoteresults for this threshold. A combined SNR of 12 corresponds to a single detector SNR of 8.5 ineach of two detectors or 7 in three detectors. At this threshold we estimate approximately a quarterof detected signals can be localized with 90% containment to areas of 20 deg2 or less by the H1L1V1network at design sensitivity; see the 2019+ epoch in Table 1 for details. For a background rateof 1 yr−1 (100 yr−1) the threshold ρc decreases by about 10% (20%), the number of signals abovethreshold increases by about 30% (90%), and the area localization for these low-threshold signalsis degraded by approximately 20% (60%).

Imperfections in the data can have a greater effect on the burst search. At frequencies above

12

200 Hz the rate of background events falls off steeply as a function of amplitude. At lower fre-quencies, however, the data often exhibit a significant tail of loud background events that arenot removed by multi-detector consistency tests. While the extent of these tails varies, whenpresent they typically begin at rates of approximately 1 yr−1, hindering the confident detection oflow-frequency gravitational-wave transients. Although the advanced detectors are designed withmany technical improvements, we must anticipate that burst searches will likely still have to dealwith such tails in some cases, particularly at low frequencies. The unambiguous observation of anelectromagnetic counterpart could increase the detection confidence in these cases.

A study [27] of the localization capability of the burst search for the aLIGO-AdV network usinga variety of waveform morphologies finds that at an SNR of ρc ' 17 (false rate of . 0.1 yr−1 fromFig. 3) the typical error box area for 50% (90%) containment is approximately 40 deg2 (400 deg2).The median 50% containment area increases to 100 deg2 at ρc ' 12, and drops to approximately16 deg2 at ρc ' 25. These results are broadly consistent with a study of two burst detectionalgorithms using real LIGO-Virgo data from 2009 [12], which shows that for signals near thenominal search threshold (coherent network amplitude η & 6, corresponding ρc & 15 [11]) mediancontainment regions are typically between 30 deg2 and 200 deg2, dropping to approximately 10 deg2

at large amplitudes. See Fig. 4 for an example.

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Figure 4: (left) Plot of typical uncertainty region sizes for the burst search, as a function of GWstrain amplitude at Earth, for a mix of ad hoc Gaussian, sine-Gaussian, and broadband white-noise burst waveforms [12]. The “searched area” is the area of the skymap with a likelihoodvalue greater than the likelihood value at the true source location. The solid line represents themedian (50%) performance, while the upper and lower limits of the shaded area show the 75%and 25% quartile values. The detection threshold of η ' 6 corresponds to signal root-sum-squareamplitudes (h2rss =

∫[h2+ +h2×]dt) of approximately hrss ∼ 0.5× 10−21 Hz−1/2 to ∼ 2× 10−21 Hz−1/2

[11], depending on signal frequency. Median uncertainty regions at these amplitudes are typicallybetween 30 deg2 and 200 deg2. (right) Typical uncertainty region sizes for two specific signal models:short-duration Gaussian-modulated sinusoids (sine-Gaussians) with central frequency 153 Hz or1053 Hz and bandwidths of 17 Hz or 117 Hz. The larger-bandwidth signal is more precisely localized,as expected from the discussion in Sect. 3.1. See [12] for more details.

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4 Observing Scenario

In this section we estimate the sensitivity, possible number of detections, and localization capabilityfor each of the observing scenarios laid out in section 2.2. We discuss each future science run inturn and also summarize the results in Table 1.

We estimate the expected number of binary neutron star coalescence detections using both thelower and upper estimates on the BNS source rate density, 10−8 − 10−5 Mpc−3 yr−1 [28]. Similarestimates may be made for neutron star – black hole (NS-BH) binaries using the fact that theNS-BH range is approximately a factor of 2 larger2 than the BNS range, though the uncertainty inthe NS-BH source rate density is slightly larger [28]. We assume a nominal ρc threshold of 12, atwhich the expected false alarm rate is 10−2 yr−1. However, such a stringent threshold may not beappropriate for selecting candidates triggers for electromagnetic followup. For example, selectingCBC candidates at thresholds corresponding to a higher background rate of 1 yr−1 (100 yr−1) wouldincrease the number of true signals subject to electromagnetic followup by about 30% (90%). Thearea localization for these low-threshold signals is only fractionally worse than for the high-thresholdpopulation – by approximately 20% (60%). The localization of NS-BH signals is expected to besimilar to that of BNS signals.

For typical burst sources the GW waveform is not well known. However, the performance ofburst searches is largely independent of the detailed waveform morphology [11], allowing us toquote an approximate sensitive range determined by the total energy EGW emitted in GWs, thecentral frequency f0 of the burst, the detector noise spectrum S(f0), and the single-detector SNRthreshold ρdet [29]:

D '(

G

2π2c3EGW

S(f0)f20ρ2det

) 12

.

In this document we quote ranges using EGW = 10−2M�c2 and f0 = 150 Hz. We note that

EGW = 10−2M�c2 is an optimistic value for GW emission by various processes (see e.g. [10]);

for other values the distance reach scales as E1/2GW. We use a single-detector SNR threshold of 8,

corresponding to a typical ρc ' 12 and false alarm rates of ∼0.3 yr−1. Due to the tail of the low-frequency background-rate-vs.-amplitude distribution in Fig. 3, we see that varying the selectionthreshold from a background of 0.1 yr−1 (ρc & 15) to even 3 yr−1 (ρc & 10) would increase thenumber of true signals selected for electromagnetic followup by a factor (15/10)3 ∼ 3, though thearea localization for low-SNR bursts may be particularly challenging.

The run durations discussed below are in calendar time. Based on prior experience, we canreasonably expect a duty cycle of ∼80% for each instrument after a few science runs. Assumingdowntime periods are uncorrelated among detectors, this means 50% coincidence time in a 3-detector network. Our estimates of expected number of detections account for these duty cycles.They also account for the uncertainty in the detector sensitive ranges as indicated in Fig. 1.

4.1 2015 run: aLIGO 40 – 80Mpc, AdV 20Mpc

This is envisioned as the first advanced detector science run, lasting three months. The aLIGOsensitivity is expected to be similar to the “early” curve in Fig. 1, with a BNS range of 40 – 80 Mpcand a burst range of 40 – 60 Mpc. The Virgo detector will be in commissioning, but may join therun with a ∼ 20 Mpc BNS range.

2This assumes a black hole mass of 10M�.

14

A three month run gives a BNS search volume3 of (0.4 − 3) × 105 Mpc3 yr at the confidentdetection threshold of ρc = 12. We therefore expect 0.0004 − 3 BNS detections. A detection islikely only if the most optimistic astrophysical rates hold.

With the 2-detector H1-L1 network any detected events would not be well localized, and evenif AdV joins the run this will continue to be the case due to its lower sensitivity. Follow-up obser-vations of a GW signal would therefore likely rely on localizations provided by another instrument,such as a gamma-ray burst satellite.

4.2 2016–17 run: aLIGO 80 – 120Mpc, AdV 20 – 60Mpc

This is envisioned to be a six month run with three detectors. The aLIGO performance is expectedto be similar to the “mid” curve in Fig. 1, with a BNS range of 80 – 120 Mpc and a burst range of60 – 75 Mpc. The AdV range may be similar to the “early” curve, approximately 20 – 60 Mpc forBNS and 20 – 40 Mpc for bursts. This gives a BNS search volume of (0.6− 2)× 106 Mpc3 yr, andan expected number of 0.006− 20 BNS detections. Source localization for various points in the skyfor CBC signals for the 3-detector network is illustrated in Fig. 5.

4.3 2017–18 run: aLIGO 120 – 170Mpc, AdV 60 – 85Mpc

This is envisioned to be a nine month run with three detectors. The aLIGO (AdV) sensitivity willbe similar to the “late” (“mid”) curve of Fig. 1, with BNS ranges of 120 – 170 Mpc and 60 – 85 Mpcrespectively and burst ranges of 75 – 90 Mpc and 40 – 50 Mpc respectively. This gives a BNS searchvolume of (3− 10)× 106 Mpc3 yr, and an expected 0.04− 100 BNS detections. Source localizationfor CBC signals is illustrated in Fig. 5. While the greater range compared to the 2016–17 runincreases the expected number of detections, the detector bandwidths are marginally smaller. Thisslightly degrades the localization capability for a source at a fixed signal-to-noise ratio.

4.4 2019+ run: aLIGO 200Mpc, AdV 65 – 130Mpc

At this point we anticipate extended runs with the detectors at or near design sensitivity. TheaLIGO detectors are expected to have a sensitivity curve similar to the “design (2019)” curve ofFig. 1. AdV may be operating similarly to the “late” curve, eventually reaching the “design”sensitivity c.2021. This gives a per-year BNS search volume of 2× 107 Mpc3 yr, giving an expected(0.2 - 200) confident BNS detections annually. Source localization for CBC signals is illustrated inFig. 5. The fraction of signals localized to areas of a few tens of square degrees is greatly increasedcompared to previous runs. This is due to the much larger detector bandwidths, particularly forAdV; see Fig. 1.

4.5 2022+ run: aLIGO (including India) 200Mpc, AdV 130Mpc

The four-site network incorporating LIGO-India at design sensitivity will have both improvedsensitivity and better localization capabilities. The per-year BNS search volume increases to 4 ×107 Mpc3 yr, giving an expected 0.4−400 BNS detections annually. Source localization is illustratedin Fig. 5. The addition of a fourth detector site allows for good source localization over the wholesky.

5 Conclusions

We have presented a possible observing scenario for the Advanced LIGO and Advanced Virgonetwork of gravitational wave detectors, with emphasis on the expected sensitivities and sky local-

3 The search volume is 43πR3 × T , where R is the range and T the observing time.

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Figure 5: Network sensitivity and localization accuracy for face-on BNS systems with advanceddetector networks. The ellipses show 90% confidence localization areas, and the red crosses showregions of the sky where the signal would not be confidently detected. The top two plots show thelocalization expected for a BNS system at 80 Mpc by the HLV network in the 2016–17 run (left)and 2017–18 run (right). The bottom two plots show the localization expected for a BNS systemat 160 Mpc by the HLV network in the 2019+ run (left) and by the HILV network in 2022+ withall detectors at final design sensitivity (right). The inclusion of a fourth site in India provides goodlocalization over the whole sky.

Estimated EGW = 10−2M�c2 Number % BNS Localized

Run Burst Range (Mpc) BNS Range (Mpc) of BNS within

Epoch Duration LIGO Virgo LIGO Virgo Detections 5 deg2 20 deg2

2015 3 months 40 – 60 – 40 – 80 – 0.0004 – 3 – –2016–17 6 months 60 – 75 20 – 40 80 – 120 20 – 60 0.006 – 20 2 5 – 122017–18 9 months 75 – 90 40 – 50 120 – 170 60 – 85 0.04 – 100 1 – 2 10 – 122019+ (per year) 105 40 – 80 200 65 – 130 0.2 – 200 3 – 8 8 – 28

2022+ (India) (per year) 105 80 200 130 0.4 – 400 17 48

Table 1: Summary of a plausible observing schedule, expected sensitivities, and source localizationwith the advanced LIGO and Virgo detectors, which will be strongly dependent on the detectors’commissioning progress. The burst ranges assume standard-candle emission of 10−2M�c

2 in GWs

at 150 Hz and scale as E1/2GW. The burst and binary neutron star (BNS) ranges and the BNS

localizations reflect the uncertainty in the detector noise spectra shown in Fig. 1. The BNS detectionnumbers also account for the uncertainty in the BNS source rate density [28], and are computedassuming a false alarm rate of 10−2 yr−1. Burst localizations are expected to be broadly similarto those for BNS systems, but will vary depending on the signal bandwidth. Localization anddetection numbers assume an 80% duty cycle for each instrument.

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ization accuracies. This network is expected to begin operations in 2015. Unless the most optimisticastrophysical rates hold, two or more detectors with an average range of at least 100 Mpc and witha run of several months will be required for detection.

Electromagnetic followup of GW candidates may help confirm GW candidates that would notbe confidently identified from GW observations alone. However, such follow-ups would need todeal with large position uncertainties, with areas of many tens to thousands of square degrees.This is likely to remain the situation until late in the decade. Optimizing the EM follow-up andsource identification is an outstanding research topic. Triggering of focused searches in GW databy EM-detected events can also help in recovering otherwise hidden GW signals.

Networks with at least 2 detectors with sensitivities of the order of 200 Mpc are expected to yielddetections with a year of observation based purely on GW data even under pessimistic predictionsof signal rates. Sky localization will continue to be poor until a third detector reaches a sensitivitywithin a factor of ∼ 2 of the others and with a broad frequency bandwidth. With a four-sitedetector network at final design sensitivity, we may expect a significant fraction of GW signals tobe localized to as well as a few square degrees by GW observations alone.

The purpose of this document is to provide information to the astronomy community to facil-itate planning for multi-messenger astronomy with advanced gravitational-wave detectors. Whilethe scenarios described here are our best current projections, they will likely evolve as detectorinstallation and commissioning progresses. We will therefore update this document regularly.

The authors gratefully acknowledge the support of the United States National Science Foun-dation for the construction and operation of the LIGO Laboratory, the Science and TechnologyFacilities Council of the United Kingdom, the Max-Planck-Society, and the State of Niedersach-sen/Germany for support of the construction and operation of the GEO600 detector, and the ItalianIstituto Nazionale di Fisica Nucleare and the French Centre National de la Recherche Scientifiquefor the construction and operation of the Virgo detector. The authors also gratefully acknowledgethe support of the research by these agencies and by the Australian Research Council, the Inter-national Science Linkages program of the Commonwealth of Australia, the Council of Scientificand Industrial Research of India, the Istituto Nazionale di Fisica Nucleare of Italy, the SpanishMinisterio de Educacion y Ciencia, the Conselleria d’Economia Hisenda i Innovacio of the Governde les Illes Balears, the Foundation for Fundamental Research on Matter supported by the Nether-lands Organisation for Scientific Research, the Polish Ministry of Science and Higher Education,the FOCUS Programme of Foundation for Polish Science, the Royal Society, the Scottish FundingCouncil, the Scottish Universities Physics Alliance, The National Aeronautics and Space Admin-istration, the Carnegie Trust, the Leverhulme Trust, the David and Lucile Packard Foundation,the Research Corporation, and the Alfred P. Sloan Foundation. This document has been assignedLIGO Document number P1200087, Virgo Document number VIR-0288A-12.

References

[1] Harry, G. M. for the LIGO Scientific Collaboration. Classical and Quantum Gravity 27, 084006(2010).

[2] Acernese, F. et al. Virgo Technical Report VIR-0027A-09 (2009), https://tds.ego-gw.it/ql/?c=6589.

[3] Accadia, T. et al. Virgo Document VIR-0128A-12 (2012), https://tds.ego-gw.it/ql/?c=8940.

17

[4] Abadie, J. et al. LIGO Document number T1200286-v3 (2012), https://dcc.ligo.org/LIGO-T1200286-v3/public.

[5] Abadie, J. et al. LIGO Document number M1200055-v2, Virgo Document number VIR-0173A-12 (2012), https://dcc.ligo.org/LIGO-M1200055-v2/public.

[6] Finn, L. S. and Chernoff, D. F. Phys. Rev. D 47 2198–2219 (1993), arXiv:9301003 [gr-qc].

[7] Luck, H. et al. J. Phys.: Conf. Ser. 228 012012 (2010), arXiv:1004.0339.

[8] Somiya, K. Classical and Quantum Gravity 29 124007 (2012), arXiv:1111.7185.

[9] Abadie, J. et al. Phys. Rev. D 85 082002 (2012), arXiv:1111.7314.

[10] Abadie, J. et al. Astrophys.J. 760 12 (2012), arXiv:1205.2216.

[11] Abadie, J. et al. Phys. Rev. D 85 122007 (2012), arXiv:1202.2788.

[12] Abadie, J. et al. Astronomy & Astrophysics 539 A124 (2012), arXiv:1109.3498.

[13] Abadie, J. et al. Astronomy & Astrophysics 541 A155 (2012), arXiv:1112.6005.

[14] Evans, P. A. et al. Astrophys.J. Supplements 203 28 (2012), arXiv:1205.1124.

[15] Fairhurst, S. New J.Phys. 11 123006 (2009), arXiv:0908.2356.

[16] Fairhurst, S. Class.Quant.Grav. 28 105021 (2011), arXiv:1010.6192.

[17] Vitale, S. and Zanolin, M. Phys. Rev. D 84 104020 (2011), arXiv:1108.2410.

[18] Vitale, S. et al. Phys.Rev. D85 064034 (2012), arXiv:1111.3044.

[19] Nissanke, S., Sievers, J., Dalal, N., and Holz, D. Astrophys.J. 739 99 (2011), arXiv:1105.3184.

[20] Veitch, J. et al. Phys. Rev. D 85 104045 (2012), arXiv:1201.1195.

[21] Nissanke, S., Kasliwal, M., and Georgieva, A. arXiv:1210.6362.

[22] Chatterji, S. et al. Phys.Rev. D74 082005 (2006), arXiv:0605002 [gr-qc].

[23] Dimmelmeier, H., Ott, C. D., Marek, A., and Janka, H.-T. Phys. Rev. D 78 064056 (2008).

[24] Ott, C. D. Class. Quantum Grav. 26 063001 (2009), arXiv:0809.0695.

[25] Yakunin, K. N. et al. Classical and Quantum Gravity 27 194005 (2010), arXiv:1005.0779.

[26] Ott, C. D. et al. Physical Review Letters 106 161103 (2011), arXiv:1012.1853.

[27] Klimenko, S. et al. Physical Review D 83 102001 (2011), arXiv:1101.5408.

[28] Abadie, J. et al. Classical and Quantum Gravity 27 173001 (2010), arXiv:1003.2480.

[29] Sutton, P. J. arXiv:1304.0210.

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