of 20
Observing gravitational-wave transient GW150914 with minimal assumptions
B. P. Abbott,
1
R. Abbott,
1
T. D. Abbott,
2
M. R. Abernathy,
1
F. Acernese,
3
,
4
K. Ackley,
5
C. Adams,
6
T. Adams,
7
P. Addesso,
3
R. X. Adhikari,
1
V. B. Adya,
8
C. Affeldt,
8
M. Agathos,
9
K. Agatsuma,
9
N. Aggarwal,
10
O. D. Aguiar,
11
L. Aiello,
12
,
13
A. Ain,
14
P. Ajith,
15
B. Allen,
8
,
16
,
17
A. Allocca,
18
,
19
P. A. Altin,
20
S. B. Anderson,
1
W. G. Anderson,
16
K. Arai,
1
M. C. Araya,
1
C. C. Arceneaux,
21
J. S. Areeda,
22
N. Arnaud,
23
K. G. Arun,
24
S. Ascenzi,
25
,
13
G. Ashton,
26
M. Ast,
27
S. M. Aston,
6
P. Astone,
28
P. Aufmuth,
8
C. Aulbert,
8
S. Babak,
29
P. Bacon,
30
M. K. M. Bader,
9
P. T. Baker,
31
F. Baldaccini,
32
,
33
G. Ballardin,
34
S. W. Ballmer,
35
J. C. Barayoga,
1
S. E. Barclay,
36
B. C. Barish,
1
D. Barker,
37
F. Barone,
3
,
4
B. Barr,
36
L. Barsotti,
10
M. Barsuglia,
30
D. Barta,
38
J. Bartlett,
37
I. Bartos,
39
R. Bassiri,
40
A. Basti,
18
,
19
J. C. Batch,
37
C. Baune,
8
V. Bavigadda,
34
M. Bazzan,
41
,
42
B. Behnke,
29
M. Bejger,
43
A. S. Bell,
36
C. J. Bell,
36
B. K. Berger,
1
J. Bergman,
37
G. Bergmann,
8
C. P. L. Berry,
44
D. Bersanetti,
45
,
46
A. Bertolini,
9
J. Betzwieser,
6
S. Bhagwat,
35
R. Bhandare,
47
I. A. Bilenko,
48
G. Billingsley,
1
J. Birch,
6
R. Birney,
49
S. Biscans,
10
A. Bisht,
8
,
17
M. Bitossi,
34
C. Biwer,
35
M. A. Bizouard,
23
J. K. Blackburn,
1
L. Blackburn,
10
C. D. Blair,
50
D. G. Blair,
50
R. M. Blair,
37
S. Bloemen,
51
O. Bock,
8
T. P. Bodiya,
10
M. Boer,
52
G. Bogaert,
52
C. Bogan,
8
A. Bohe,
29
P. Bojtos,
53
C. Bond,
44
F. Bondu,
54
R. Bonnand,
7
B. A. Boom,
9
R. Bork,
1
V. Boschi,
18
,
19
S. Bose,
55
,
14
Y. Bouffanais,
30
A. Bozzi,
34
C. Bradaschia,
19
P. R. Brady,
16
V. B. Braginsky,
48
M. Branchesi,
56
,
57
J. E. Brau,
58
T. Briant,
59
A. Brillet,
52
M. Brinkmann,
8
V. Brisson,
23
P. Brockill,
16
A. F. Brooks,
1
D. A. Brown,
35
D. D. Brown,
44
N. M. Brown,
10
C. C. Buchanan,
2
A. Buikema,
10
T. Bulik,
60
H. J. Bulten,
61
,
9
A. Buonanno,
29
,
62
D. Buskulic,
7
C. Buy,
30
R. L. Byer,
40
L. Cadonati,
63
G. Cagnoli,
64
,
65
C. Cahillane,
1
J. Calder ́on Bustillo,
66
,
63
T. Callister,
1
E. Calloni,
67
,
4
J. B. Camp,
68
K. C. Cannon,
69
J. Cao,
70
C. D. Capano,
8
E. Capocasa,
30
F. Carbognani,
34
S. Caride,
71
J. Casanueva Diaz,
23
C. Casentini,
25
,
13
S. Caudill,
16
M. Cavagli`a,
21
F. Cavalier,
23
R. Cavalieri,
34
G. Cella,
19
C. B. Cepeda,
1
L. Cerboni Baiardi,
56
,
57
G. Cerretani,
18
,
19
E. Cesarini,
25
,
13
R. Chakraborty,
1
S. Chatterji,
10
T. Chalermsongsak,
1
S. J. Chamberlin,
72
M. Chan,
36
S. Chao,
73
P. Charlton,
74
E. Chassande-Mottin,
30
H. Y. Chen,
75
Y. Chen,
76
C. Cheng,
73
A. Chincarini,
46
A. Chiummo,
34
H. S. Cho,
77
M. Cho,
62
J. H. Chow,
20
N. Christensen,
78
Q. Chu,
50
S. Chua,
59
S. Chung,
50
G. Ciani,
5
F. Clara,
37
J. A. Clark,
63
F. Cleva,
52
E. Coccia,
25
,
12
,
13
P.-F. Cohadon,
59
A. Colla,
79
,
28
C. G. Collette,
80
L. Cominsky,
81
M. Constancio Jr.,
11
A. Conte,
79
,
28
L. Conti,
42
D. Cook,
37
T. R. Corbitt,
2
N. Cornish,
31
A. Corsi,
71
S. Cortese,
34
C. A. Costa,
11
M. W. Coughlin,
78
S. B. Coughlin,
82
J.-P. Coulon,
52
S. T. Countryman,
39
P. Couvares,
1
E. E. Cowan,
63
D. M. Coward,
50
M. J. Cowart,
6
D. C. Coyne,
1
R. Coyne,
71
K. Craig,
36
J. D. E. Creighton,
16
J. Cripe,
2
S. G. Crowder,
83
A. Cumming,
36
L. Cunningham,
36
E. Cuoco,
34
T. Dal Canton,
8
S. L. Danilishin,
36
S. D’Antonio,
13
K. Danzmann,
17
,
8
N. S. Darman,
84
V. Dattilo,
34
I. Dave,
47
H. P. Daveloza,
85
M. Davier,
23
G. S. Davies,
36
E. J. Daw,
86
R. Day,
34
D. DeBra,
40
G. Debreczeni,
38
J. Degallaix,
65
M. De Laurentis,
67
,
4
S. Del ́eglise,
59
W. Del Pozzo,
44
T. Denker,
8
,
17
T. Dent,
8
H. Dereli,
52
V. Dergachev,
1
R. T. DeRosa,
6
R. De Rosa,
67
,
4
R. DeSalvo,
87
S. Dhurandhar,
14
M. C. D ́ıaz,
85
L. Di Fiore,
4
M. Di Giovanni,
79
,
28
A. Di Lieto,
18
,
19
S. Di Pace,
79
,
28
I. Di Palma,
29
,
8
A. Di Virgilio,
19
G. Dojcinoski,
88
V. Dolique,
65
F. Donovan,
10
K. L. Dooley,
21
S. Doravari,
6
,
8
R. Douglas,
36
T. P. Downes,
16
M. Drago,
8
,
89
,
90
R. W. P. Drever,
1
J. C. Driggers,
37
Z. Du,
70
M. Ducrot,
7
S. E. Dwyer,
37
T. B. Edo,
86
M. C. Edwards,
78
A. Effler,
6
H.-B. Eggenstein,
8
P. Ehrens,
1
J. Eichholz,
5
S. S. Eikenberry,
5
W. Engels,
76
R. C. Essick,
10
T. Etzel,
1
M. Evans,
10
T. M. Evans,
6
R. Everett,
72
M. Factourovich,
39
V. Fafone,
25
,
13
,
12
H. Fair,
35
S. Fairhurst,
91
X. Fan,
70
Q. Fang,
50
S. Farinon,
46
B. Farr,
75
W. M. Farr,
44
M. Favata,
88
M. Fays,
91
H. Fehrmann,
8
M. M. Fejer,
40
I. Ferrante,
18
,
19
E. C. Ferreira,
11
F. Ferrini,
34
F. Fidecaro,
18
,
19
I. Fiori,
34
D. Fiorucci,
30
R. P. Fisher,
35
R. Flaminio,
65
,
92
M. Fletcher,
36
J.-D. Fournier,
52
S. Franco,
23
S. Frasca,
79
,
28
F. Frasconi,
19
Z. Frei,
53
A. Freise,
44
R. Frey,
58
V. Frey,
23
T. T. Fricke,
8
P. Fritschel,
10
V. V. Frolov,
6
P. Fulda,
5
M. Fyffe,
6
H. A. G. Gabbard,
21
J. R. Gair,
93
L. Gammaitoni,
32
,
33
S. G. Gaonkar,
14
F. Garufi,
67
,
4
A. Gatto,
30
G. Gaur,
94
,
95
N. Gehrels,
68
G. Gemme,
46
B. Gendre,
52
E. Genin,
34
A. Gennai,
19
J. George,
47
L. Gergely,
96
V. Germain,
7
Archisman Ghosh,
15
S. Ghosh,
51
,
9
J. A. Giaime,
2
,
6
K. D. Giardina,
6
A. Giazotto,
19
K. Gill,
97
A. Glaefke,
36
E. Goetz,
98
R. Goetz,
5
L. Gondan,
53
G. Gonz ́alez,
2
J. M. Gonzalez Castro,
18
,
19
A. Gopakumar,
99
N. A. Gordon,
36
M. L. Gorodetsky,
48
S. E. Gossan,
1
M. Gosselin,
34
R. Gouaty,
7
C. Graef,
36
P. B. Graff,
62
M. Granata,
65
A. Grant,
36
S. Gras,
10
C. Gray,
37
G. Greco,
56
,
57
A. C. Green,
44
P. Groot,
51
H. Grote,
8
S. Grunewald,
29
G. M. Guidi,
56
,
57
X. Guo,
70
A. Gupta,
14
M. K. Gupta,
95
K. E. Gushwa,
1
E. K. Gustafson,
1
R. Gustafson,
98
J. J. Hacker,
22
B. R. Hall,
55
E. D. Hall,
1
G. Hammond,
36
M. Haney,
99
M. M. Hanke,
8
J. Hanks,
37
C. Hanna,
72
M. D. Hannam,
91
J. Hanson,
6
T. Hardwick,
2
J. Harms,
56
,
57
G. M. Harry,
100
I. W. Harry,
29
M. J. Hart,
36
M. T. Hartman,
5
C.-J. Haster,
44
K. Haughian,
36
A. Heidmann,
59
M. C. Heintze,
5
,
6
H. Heitmann,
52
P. Hello,
23
G. Hemming,
34
M. Hendry,
36
I. S. Heng,
36
J. Hennig,
36
A. W. Heptonstall,
1
M. Heurs,
8
,
17
S. Hild,
36
D. Hoak,
101
K. A. Hodge,
1
D. Hofman,
65
S. E. Hollitt,
102
K. Holt,
6
D. E. Holz,
75
P. Hopkins,
91
D. J. Hosken,
102
arXiv:1602.03843v2 [gr-qc] 22 Aug 2016
2
J. Hough,
36
E. A. Houston,
36
E. J. Howell,
50
Y. M. Hu,
36
S. Huang,
73
E. A. Huerta,
103
,
82
D. Huet,
23
B. Hughey,
97
S. Husa,
66
S. H. Huttner,
36
T. Huynh-Dinh,
6
A. Idrisy,
72
N. Indik,
8
D. R. Ingram,
37
R. Inta,
71
H. N. Isa,
36
J.-M. Isac,
59
M. Isi,
1
G. Islas,
22
T. Isogai,
10
B. R. Iyer,
15
K. Izumi,
37
T. Jacqmin,
59
H. Jang,
77
K. Jani,
63
P. Jaranowski,
104
S. Jawahar,
105
F. Jim ́enez-Forteza,
66
W. W. Johnson,
2
D. I. Jones,
26
R. Jones,
36
R. J. G. Jonker,
9
L. Ju,
50
Haris K,
106
C. V. Kalaghatgi,
24
,
91
V. Kalogera,
82
S. Kandhasamy,
21
G. Kang,
77
J. B. Kanner,
1
S. Karki,
58
M. Kasprzack,
2
,
23
,
34
E. Katsavounidis,
10
W. Katzman,
6
S. Kaufer,
17
T. Kaur,
50
K. Kawabe,
37
F. Kawazoe,
8
,
17
F. K ́ef ́elian,
52
M. S. Kehl,
69
D. Keitel,
8
,
66
D. B. Kelley,
35
W. Kells,
1
R. Kennedy,
86
J. S. Key,
85
A. Khalaidovski,
8
F. Y. Khalili,
48
I. Khan,
12
S. Khan,
91
Z. Khan,
95
E. A. Khazanov,
107
N. Kijbunchoo,
37
C. Kim,
77
J. Kim,
108
K. Kim,
109
Nam-Gyu Kim,
77
Namjun Kim,
40
Y.-M. Kim,
108
E. J. King,
102
P. J. King,
37
D. L. Kinzel,
6
J. S. Kissel,
37
L. Kleybolte,
27
S. Klimenko,
5
S. M. Koehlenbeck,
8
K. Kokeyama,
2
S. Koley,
9
V. Kondrashov,
1
A. Kontos,
10
M. Korobko,
27
W. Z. Korth,
1
I. Kowalska,
60
D. B. Kozak,
1
V. Kringel,
8
A. Kr ́olak,
110
,
111
C. Krueger,
17
G. Kuehn,
8
P. Kumar,
69
L. Kuo,
73
A. Kutynia,
110
B. D. Lackey,
35
M. Landry,
37
J. Lange,
112
B. Lantz,
40
P. D. Lasky,
113
A. Lazzarini,
1
C. Lazzaro,
63
,
42
P. Leaci,
29
,
79
,
28
S. Leavey,
36
E. O. Lebigot,
30
,
70
C. H. Lee,
108
H. K. Lee,
109
H. M. Lee,
114
K. Lee,
36
A. Lenon,
35
M. Leonardi,
89
,
90
J. R. Leong,
8
N. Leroy,
23
N. Letendre,
7
Y. Levin,
113
B. M. Levine,
37
T. G. F. Li,
1
A. Libson,
10
T. B. Littenberg,
115
N. A. Lockerbie,
105
J. Logue,
36
A. L. Lombardi,
101
J. E. Lord,
35
M. Lorenzini,
12
,
13
V. Loriette,
116
M. Lormand,
6
G. Losurdo,
57
J. D. Lough,
8
,
17
H. L
̈
uck,
17
,
8
A. P. Lundgren,
8
J. Luo,
78
R. Lynch,
10
Y. Ma,
50
T. MacDonald,
40
B. Machenschalk,
8
M. MacInnis,
10
D. M. Macleod,
2
F. Maga ̃na-Sandoval,
35
R. M. Magee,
55
M. Mageswaran,
1
E. Majorana,
28
I. Maksimovic,
116
V. Malvezzi,
25
,
13
N. Man,
52
I. Mandel,
44
V. Mandic,
83
V. Mangano,
36
G. L. Mansell,
20
M. Manske,
16
M. Mantovani,
34
F. Marchesoni,
117
,
33
F. Marion,
7
S. M ́arka,
39
Z. M ́arka,
39
A. S. Markosyan,
40
E. Maros,
1
F. Martelli,
56
,
57
L. Martellini,
52
I. W. Martin,
36
R. M. Martin,
5
D. V. Martynov,
1
J. N. Marx,
1
K. Mason,
10
A. Masserot,
7
T. J. Massinger,
35
M. Masso-Reid,
36
F. Matichard,
10
L. Matone,
39
N. Mavalvala,
10
N. Mazumder,
55
G. Mazzolo,
8
R. McCarthy,
37
D. E. McClelland,
20
S. McCormick,
6
S. C. McGuire,
118
G. McIntyre,
1
J. McIver,
1
D. J. McManus,
20
S. T. McWilliams,
103
D. Meacher,
72
G. D. Meadors,
29
,
8
J. Meidam,
9
A. Melatos,
84
G. Mendell,
37
D. Mendoza-Gandara,
8
R. A. Mercer,
16
E. Merilh,
37
M. Merzougui,
52
S. Meshkov,
1
C. Messenger,
36
C. Messick,
72
P. M. Meyers,
83
F. Mezzani,
28
,
79
H. Miao,
44
C. Michel,
65
H. Middleton,
44
E. E. Mikhailov,
119
L. Milano,
67
,
4
J. Miller,
10
M. Millhouse,
31
Y. Minenkov,
13
J. Ming,
29
,
8
S. Mirshekari,
120
C. Mishra,
15
S. Mitra,
14
V. P. Mitrofanov,
48
G. Mitselmakher,
5
R. Mittleman,
10
A. Moggi,
19
M. Mohan,
34
S. R. P. Mohapatra,
10
M. Montani,
56
,
57
B. C. Moore,
88
C. J. Moore,
121
D. Moraru,
37
G. Moreno,
37
S. R. Morriss,
85
K. Mossavi,
8
B. Mours,
7
C. M. Mow-Lowry,
44
C. L. Mueller,
5
G. Mueller,
5
A. W. Muir,
91
Arunava Mukherjee,
15
D. Mukherjee,
16
S. Mukherjee,
85
N. Mukund,
14
A. Mullavey,
6
J. Munch,
102
D. J. Murphy,
39
P. G. Murray,
36
A. Mytidis,
5
I. Nardecchia,
25
,
13
L. Naticchioni,
79
,
28
R. K. Nayak,
122
V. Necula,
5
K. Nedkova,
101
G. Nelemans,
51
,
9
M. Neri,
45
,
46
A. Neunzert,
98
G. Newton,
36
T. T. Nguyen,
20
A. B. Nielsen,
8
S. Nissanke,
51
,
9
A. Nitz,
8
F. Nocera,
34
D. Nolting,
6
M. E. Normandin,
85
L. K. Nuttall,
35
J. Oberling,
37
E. Ochsner,
16
J. O’Dell,
123
E. Oelker,
10
G. H. Ogin,
124
J. J. Oh,
125
S. H. Oh,
125
F. Ohme,
91
M. Oliver,
66
P. Oppermann,
8
Richard J. Oram,
6
B. O’Reilly,
6
R. O’Shaughnessy,
112
C. D. Ott,
76
D. J. Ottaway,
102
R. S. Ottens,
5
H. Overmier,
6
B. J. Owen,
71
A. Pai,
106
S. A. Pai,
47
J. R. Palamos,
58
O. Palashov,
107
C. Palomba,
28
A. Pal-Singh,
27
H. Pan,
73
C. Pankow,
82
F. Pannarale,
91
B. C. Pant,
47
F. Paoletti,
34
,
19
A. Paoli,
34
M. A. Papa,
29
,
16
,
8
J. Page,
115
H. R. Paris,
40
W. Parker,
6
D. Pascucci,
36
A. Pasqualetti,
34
R. Passaquieti,
18
,
19
D. Passuello,
19
B. Patricelli,
18
,
19
Z. Patrick,
40
B. L. Pearlstone,
36
M. Pedraza,
1
R. Pedurand,
65
L. Pekowsky,
35
A. Pele,
6
S. Penn,
126
A. Perreca,
1
M. Phelps,
36
O. Piccinni,
79
,
28
M. Pichot,
52
F. Piergiovanni,
56
,
57
V. Pierro,
87
G. Pillant,
34
L. Pinard,
65
I. M. Pinto,
87
M. Pitkin,
36
R. Poggiani,
18
,
19
P. Popolizio,
34
A. Post,
8
J. Powell,
36
J. Prasad,
14
V. Predoi,
91
S. S. Premachandra,
113
T. Prestegard,
83
L. R. Price,
1
M. Prijatelj,
34
M. Principe,
87
S. Privitera,
29
G. A. Prodi,
89
,
90
L. Prokhorov,
48
O. Puncken,
8
M. Punturo,
33
P. Puppo,
28
M. P
̈
urrer,
29
H. Qi,
16
J. Qin,
50
V. Quetschke,
85
E. A. Quintero,
1
R. Quitzow-James,
58
F. J. Raab,
37
D. S. Rabeling,
20
H. Radkins,
37
P. Raffai,
53
S. Raja,
47
M. Rakhmanov,
85
P. Rapagnani,
79
,
28
V. Raymond,
29
M. Razzano,
18
,
19
V. Re,
25
J. Read,
22
C. M. Reed,
37
T. Regimbau,
52
L. Rei,
46
S. Reid,
49
D. H. Reitze,
1
,
5
H. Rew,
119
S. D. Reyes,
35
F. Ricci,
79
,
28
K. Riles,
98
N. A. Robertson,
1
,
36
R. Robie,
36
F. Robinet,
23
A. Rocchi,
13
L. Rolland,
7
J. G. Rollins,
1
V. J. Roma,
58
R. Romano,
3
,
4
G. Romanov,
119
J. H. Romie,
6
D. Rosi ́nska,
127
,
43
S. Rowan,
36
A. R
̈
udiger,
8
P. Ruggi,
34
K. Ryan,
37
S. Sachdev,
1
T. Sadecki,
37
L. Sadeghian,
16
L. Salconi,
34
M. Saleem,
106
F. Salemi,
8
A. Samajdar,
122
L. Sammut,
84
,
113
E. J. Sanchez,
1
V. Sandberg,
37
B. Sandeen,
82
J. R. Sanders,
98
,
35
B. Sassolas,
65
B. S. Sathyaprakash,
91
P. R. Saulson,
35
O. Sauter,
98
R. L. Savage,
37
A. Sawadsky,
17
P. Schale,
58
R. Schilling
,
8
J. Schmidt,
8
P. Schmidt,
1
,
76
R. Schnabel,
27
R. M. S. Schofield,
58
A. Sch
̈
onbeck,
27
E. Schreiber,
8
D. Schuette,
8
,
17
B. F. Schutz,
91
,
29
J. Scott,
36
S. M. Scott,
20
D. Sellers,
6
A. S. Sengupta,
94
D. Sentenac,
34
3
V. Sequino,
25
,
13
A. Sergeev,
107
G. Serna,
22
Y. Setyawati,
51
,
9
A. Sevigny,
37
D. A. Shaddock,
20
S. Shah,
51
,
9
M. S. Shahriar,
82
M. Shaltev,
8
Z. Shao,
1
B. Shapiro,
40
P. Shawhan,
62
A. Sheperd,
16
D. H. Shoemaker,
10
D. M. Shoemaker,
63
K. Siellez,
52
,
63
X. Siemens,
16
D. Sigg,
37
A. D. Silva,
11
D. Simakov,
8
A. Singer,
1
L. P. Singer,
68
A. Singh,
29
,
8
R. Singh,
2
A. Singhal,
12
A. M. Sintes,
66
B. J. J. Slagmolen,
20
J. R. Smith,
22
N. D. Smith,
1
R. J. E. Smith,
1
E. J. Son,
125
B. Sorazu,
36
F. Sorrentino,
46
T. Souradeep,
14
A. K. Srivastava,
95
A. Staley,
39
M. Steinke,
8
J. Steinlechner,
36
S. Steinlechner,
36
D. Steinmeyer,
8
,
17
B. C. Stephens,
16
R. Stone,
85
K. A. Strain,
36
N. Straniero,
65
G. Stratta,
56
,
57
N. A. Strauss,
78
S. Strigin,
48
R. Sturani,
120
A. L. Stuver,
6
T. Z. Summerscales,
128
L. Sun,
84
P. J. Sutton,
91
B. L. Swinkels,
34
M. J. Szczepa ́nczyk,
97
M. Tacca,
30
D. Talukder,
58
D. B. Tanner,
5
M. T ́apai,
96
S. P. Tarabrin,
8
A. Taracchini,
29
R. Taylor,
1
T. Theeg,
8
M. P. Thirugnanasambandam,
1
E. G. Thomas,
44
M. Thomas,
6
P. Thomas,
37
K. A. Thorne,
6
K. S. Thorne,
76
E. Thrane,
113
S. Tiwari,
12
V. Tiwari,
91
K. V. Tokmakov,
105
C. Tomlinson,
86
M. Tonelli,
18
,
19
C. V. Torres
,
85
C. I. Torrie,
1
D. T
̈
oyr
̈
a,
44
F. Travasso,
32
,
33
G. Traylor,
6
D. Trifir`o,
21
M. C. Tringali,
89
,
90
L. Trozzo,
129
,
19
M. Tse,
10
M. Turconi,
52
D. Tuyenbayev,
85
D. Ugolini,
130
C. S. Unnikrishnan,
99
A. L. Urban,
16
S. A. Usman,
35
H. Vahlbruch,
17
G. Vajente,
1
G. Valdes,
85
N. van Bakel,
9
M. van Beuzekom,
9
J. F. J. van den Brand,
61
,
9
C. Van Den Broeck,
9
D. C. Vander-Hyde,
35
,
22
L. van der Schaaf,
9
J. V. van Heijningen,
9
A. A. van Veggel,
36
M. Vardaro,
41
,
42
S. Vass,
1
M. Vas ́uth,
38
R. Vaulin,
10
A. Vecchio,
44
G. Vedovato,
42
J. Veitch,
44
P. J. Veitch,
102
K. Venkateswara,
131
D. Verkindt,
7
F. Vetrano,
56
,
57
A. Vicer ́e,
56
,
57
S. Vinciguerra,
44
D. J. Vine,
49
J.-Y. Vinet,
52
S. Vitale,
10
T. Vo,
35
H. Vocca,
32
,
33
C. Vorvick,
37
D. Voss,
5
W. D. Vousden,
44
S. P. Vyatchanin,
48
A. R. Wade,
20
L. E. Wade,
132
M. Wade,
132
M. Walker,
2
L. Wallace,
1
S. Walsh,
16
,
8
,
29
G. Wang,
12
H. Wang,
44
M. Wang,
44
X. Wang,
70
Y. Wang,
50
R. L. Ward,
20
J. Warner,
37
M. Was,
7
B. Weaver,
37
L.-W. Wei,
52
M. Weinert,
8
A. J. Weinstein,
1
R. Weiss,
10
T. Welborn,
6
L. Wen,
50
P. Weßels,
8
T. Westphal,
8
K. Wette,
8
J. T. Whelan,
112
,
8
D. J. White,
86
B. F. Whiting,
5
D. Williams,
36
R. D. Williams,
1
A. R. Williamson,
91
J. L. Willis,
133
B. Willke,
17
,
8
M. H. Wimmer,
8
,
17
W. Winkler,
8
C. C. Wipf,
1
H. Wittel,
8
,
17
G. Woan,
36
J. Worden,
37
J. L. Wright,
36
G. Wu,
6
J. Yablon,
82
W. Yam,
10
H. Yamamoto,
1
C. C. Yancey,
62
M. J. Yap,
20
H. Yu,
10
M. Yvert,
7
A. Zadro ̇zny,
110
L. Zangrando,
42
M. Zanolin,
97
J.-P. Zendri,
42
M. Zevin,
82
F. Zhang,
10
L. Zhang,
1
M. Zhang,
119
Y. Zhang,
112
C. Zhao,
50
M. Zhou,
82
Z. Zhou,
82
X. J. Zhu,
50
M. E. Zucker,
1
,
10
S. E. Zuraw,
101
and J. Zweizig
1
(LIGO Scientific Collaboration and Virgo Collaboration)
M. Clark,
63
R. Haas,
29
J. Healy,
112
I. Hinder,
29
M. Kinsey,
63
P. Laguna
63
Deceased, May 2015.
Deceased, March 2015.
1
LIGO, California Institute of Technology, Pasadena, CA 91125, USA
2
Louisiana State University, Baton Rouge, LA 70803, USA
3
Universit`a di Salerno, Fisciano, I-84084 Salerno, Italy
4
INFN, Sezione di Napoli, Complesso Universitario di Monte S.Angelo, I-80126 Napoli, Italy
5
University of Florida, Gainesville, FL 32611, USA
6
LIGO Livingston Observatory, Livingston, LA 70754, USA
7
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP),
Universit ́e Savoie Mont Blanc, CNRS/IN2P3, F-74941 Annecy-le-Vieux, France
8
Albert-Einstein-Institut, Max-Planck-Institut f
̈
ur Gravitationsphysik, D-30167 Hannover, Germany
9
Nikhef, Science Park, 1098 XG Amsterdam, Netherlands
10
LIGO, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
11
Instituto Nacional de Pesquisas Espaciais, 12227-010 S ̃ao Jos ́e dos Campos, S ̃ao Paulo, Brazil
12
INFN, Gran Sasso Science Institute, I-67100 L’Aquila, Italy
13
INFN, Sezione di Roma Tor Vergata, I-00133 Roma, Italy
14
Inter-University Centre for Astronomy and Astrophysics, Pune 411007, India
15
International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore 560012, India
16
University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
17
Leibniz Universit
̈
at Hannover, D-30167 Hannover, Germany
18
Universit`a di Pisa, I-56127 Pisa, Italy
19
INFN, Sezione di Pisa, I-56127 Pisa, Italy
20
Australian National University, Canberra, Australian Capital Territory 0200, Australia
21
The University of Mississippi, University, MS 38677, USA
22
California State University Fullerton, Fullerton, CA 92831, USA
23
LAL, Universit ́e Paris-Sud, CNRS/IN2P3, Universit ́e Paris-Saclay, 91400 Orsay, France
24
Chennai Mathematical Institute, Chennai 603103, India
25
Universit`a di Roma Tor Vergata, I-00133 Roma, Italy
26
University of Southampton, Southampton SO17 1BJ, United Kingdom
4
27
Universit
̈
at Hamburg, D-22761 Hamburg, Germany
28
INFN, Sezione di Roma, I-00185 Roma, Italy
29
Albert-Einstein-Institut, Max-Planck-Institut f
̈
ur Gravitationsphysik, D-14476 Potsdam-Golm, Germany
30
APC, AstroParticule et Cosmologie, Universit ́e Paris Diderot,
CNRS/IN2P3, CEA/Irfu, Observatoire de Paris,
Sorbonne Paris Cit ́e, F-75205 Paris Cedex 13, France
31
Montana State University, Bozeman, MT 59717, USA
32
Universit`a di Perugia, I-06123 Perugia, Italy
33
INFN, Sezione di Perugia, I-06123 Perugia, Italy
34
European Gravitational Observatory (EGO), I-56021 Cascina, Pisa, Italy
35
Syracuse University, Syracuse, NY 13244, USA
36
SUPA, University of Glasgow, Glasgow G12 8QQ, United Kingdom
37
LIGO Hanford Observatory, Richland, WA 99352, USA
38
Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Mikl ́os ́ut 29-33, Hungary
39
Columbia University, New York, NY 10027, USA
40
Stanford University, Stanford, CA 94305, USA
41
Universit`a di Padova, Dipartimento di Fisica e Astronomia, I-35131 Padova, Italy
42
INFN, Sezione di Padova, I-35131 Padova, Italy
43
CAMK-PAN, 00-716 Warsaw, Poland
44
University of Birmingham, Birmingham B15 2TT, United Kingdom
45
Universit`a degli Studi di Genova, I-16146 Genova, Italy
46
INFN, Sezione di Genova, I-16146 Genova, Italy
47
RRCAT, Indore MP 452013, India
48
Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
49
SUPA, University of the West of Scotland, Paisley PA1 2BE, United Kingdom
50
University of Western Australia, Crawley, Western Australia 6009, Australia
51
Department of Astrophysics/IMAPP, Radboud University Nijmegen, 6500 GL Nijmegen, Netherlands
52
Artemis, Universit ́e Cˆote d’Azur, CNRS, Observatoire Cˆote d’Azur, CS 34229, Nice cedex 4, France
53
MTA E
̈
otv
̈
os University, “Lendulet” Astrophysics Research Group, Budapest 1117, Hungary
54
Institut de Physique de Rennes, CNRS, Universit ́e de Rennes 1, F-35042 Rennes, France
55
Washington State University, Pullman, WA 99164, USA
56
Universit`a degli Studi di Urbino “Carlo Bo,” I-61029 Urbino, Italy
57
INFN, Sezione di Firenze, I-50019 Sesto Fiorentino, Firenze, Italy
58
University of Oregon, Eugene, OR 97403, USA
59
Laboratoire Kastler Brossel, UPMC-Sorbonne Universit ́es, CNRS,
ENS-PSL Research University, Coll`ege de France, F-75005 Paris, France
60
Astronomical Observatory Warsaw University, 00-478 Warsaw, Poland
61
VU University Amsterdam, 1081 HV Amsterdam, Netherlands
62
University of Maryland, College Park, MD 20742, USA
63
Center for Relativistic Astrophysics and School of Physics,
Georgia Institute of Technology, Atlanta, GA 30332, USA
64
Institut Lumi`ere Mati`ere, Universit ́e de Lyon, Universit ́e Claude
Bernard Lyon 1, UMR CNRS 5306, 69622 Villeurbanne, France
65
Laboratoire des Mat ́eriaux Avanc ́es (LMA), IN2P3/CNRS,
Universit ́e de Lyon, F-69622 Villeurbanne, Lyon, France
66
Universitat de les Illes Balears, IAC3—IEEC, E-07122 Palma de Mallorca, Spain
67
Universit`a di Napoli “Federico II,” Complesso Universitario di Monte S.Angelo, I-80126 Napoli, Italy
68
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
69
Canadian Institute for Theoretical Astrophysics,
University of Toronto, Toronto, Ontario M5S 3H8, Canada
70
Tsinghua University, Beijing 100084, China
71
Texas Tech University, Lubbock, TX 79409, USA
72
The Pennsylvania State University, University Park, PA 16802, USA
73
National Tsing Hua University, Hsinchu City, 30013 Taiwan, Republic of China
74
Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia
75
University of Chicago, Chicago, IL 60637, USA
76
Caltech CaRT, Pasadena, CA 91125, USA
77
Korea Institute of Science and Technology Information, Daejeon 305-806, Korea
78
Carleton College, Northfield, MN 55057, USA
79
Universit`a di Roma “La Sapienza,” I-00185 Roma, Italy
80
University of Brussels, Brussels 1050, Belgium
81
Sonoma State University, Rohnert Park, CA 94928, USA
82
Northwestern University, Evanston, IL 60208, USA
83
University of Minnesota, Minneapolis, MN 55455, USA
5
84
The University of Melbourne, Parkville, Victoria 3010, Australia
85
The University of Texas Rio Grande Valley, Brownsville, TX 78520, USA
86
The University of Sheffield, Sheffield S10 2TN, United Kingdom
87
University of Sannio at Benevento, I-82100 Benevento,
Italy and INFN, Sezione di Napoli, I-80100 Napoli, Italy
88
Montclair State University, Montclair, NJ 07043, USA
89
Universit`a di Trento, Dipartimento di Fisica, I-38123 Povo, Trento, Italy
90
INFN, Trento Institute for Fundamental Physics and Applications, I-38123 Povo, Trento, Italy
91
Cardiff University, Cardiff CF24 3AA, United Kingdom
92
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
93
School of Mathematics, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
94
Indian Institute of Technology, Gandhinagar Ahmedabad Gujarat 382424, India
95
Institute for Plasma Research, Bhat, Gandhinagar 382428, India
96
University of Szeged, D ́om t ́er 9, Szeged 6720, Hungary
97
Embry-Riddle Aeronautical University, Prescott, AZ 86301, USA
98
University of Michigan, Ann Arbor, MI 48109, USA
99
Tata Institute of Fundamental Research, Mumbai 400005, India
100
American University, Washington, D.C. 20016, USA
101
University of Massachusetts-Amherst, Amherst, MA 01003, USA
102
University of Adelaide, Adelaide, South Australia 5005, Australia
103
West Virginia University, Morgantown, WV 26506, USA
104
University of Bia lystok, 15-424 Bia lystok, Poland
105
SUPA, University of Strathclyde, Glasgow G1 1XQ, United Kingdom
106
IISER-TVM, CET Campus, Trivandrum Kerala 695016, India
107
Institute of Applied Physics, Nizhny Novgorod, 603950, Russia
108
Pusan National University, Busan 609-735, Korea
109
Hanyang University, Seoul 133-791, Korea
110
NCBJ, 05-400
́
Swierk-Otwock, Poland
111
IM-PAN, 00-956 Warsaw, Poland
112
Rochester Institute of Technology, Rochester, NY 14623, USA
113
Monash University, Victoria 3800, Australia
114
Seoul National University, Seoul 151-742, Korea
115
University of Alabama in Huntsville, Huntsville, AL 35899, USA
116
ESPCI, CNRS, F-75005 Paris, France
117
Universit`a di Camerino, Dipartimento di Fisica, I-62032 Camerino, Italy
118
Southern University and A&M College, Baton Rouge, LA 70813, USA
119
College of William and Mary, Williamsburg, VA 23187, USA
120
Instituto de F ́ısica Te ́orica, University Estadual Paulista/ICTP South
American Institute for Fundamental Research, S ̃ao Paulo SP 01140-070, Brazil
121
University of Cambridge, Cambridge CB2 1TN, United Kingdom
122
IISER-Kolkata, Mohanpur, West Bengal 741252, India
123
Rutherford Appleton Laboratory, HSIC, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
124
Whitman College, 345 Boyer Avenue, Walla Walla, WA 99362 USA
125
National Institute for Mathematical Sciences, Daejeon 305-390, Korea
126
Hobart and William Smith Colleges, Geneva, NY 14456, USA
127
Janusz Gil Institute of Astronomy, University of Zielona G ́ora, 65-265 Zielona G ́ora, Poland
128
Andrews University, Berrien Springs, MI 49104, USA
129
Universit`a di Siena, I-53100 Siena, Italy
130
Trinity University, San Antonio, TX 78212, USA
131
University of Washington, Seattle, WA 98195, USA
132
Kenyon College, Gambier, OH 43022, USA
133
Abilene Christian University, Abilene, TX 79699, USA
The gravitational-wave signal GW150914 was first identified on Sept 14 2015 by searches for
short-duration gravitational-wave transients. These searches identify time-correlated transients in
multiple detectors with minimal assumptions about the signal morphology, allowing them to be
sensitive to gravitational waves emitted by a wide range of sources including binary black-hole
mergers. Over the observational period from September 12th to October 20th 2015, these transient
searches were sensitive to binary black-hole mergers similar to GW150914 to an average distance
of
600 Mpc. In this paper, we describe the analyses that first detected GW150914 as well as the
parameter estimation and waveform reconstruction techniques that initially identified GW150914 as
the merger of two black holes. We find that the reconstructed waveform is consistent with the signal
from a binary black-hole merger with a chirp mass of
30 M
and a total mass before merger of
70 M
in the detector frame.
6
I. INTRODUCTION
The newly upgraded Advanced LIGO observatories
[1, 2], with sites near Hanford, WA (H1) and Livingston,
LA (L1), host the most sensitive gravitational-wave de-
tectors ever built. The observatories use kilometer-scale
Michelson interferometers that are designed to detect
small, traveling perturbations in space-time predicted by
Einstein [3, 4], and thought to radiate from a variety of
astrophysical processes. Advanced LIGO recently com-
pleted its first observing period, from September, 2015
to January, 2016. Advanced LIGO is among a genera-
tion of planned instruments that includes GEO 600, Ad-
vanced Virgo, and KAGRA; the capabilities of this global
gravitational-wave network should quickly grow over the
next few years [5–8].
An important class of sources for gravitational-wave
detectors are short duration transients, known collec-
tively as gravitational-wave bursts [9]. To search broadly
for a wide range of astrophysical phenomena, we employ
unmodelled searches for gravitational-wave bursts of du-
rations
10
3
10 s, with minimal assumptions about
the expected signal waveform. Bursts may originate from
a range of astrophysical sources, including core-collapse
supernovae of massive stars [10] and cosmic string cusps
[11]. An important source of gravitational-wave tran-
sients are the mergers of binary black holes (BBH) [12–
14]. Burst searches in data from the initial generation
of interferometer detectors were sensitive to distant BBH
signals from mergers with total masses in the range
20
– 400 M
[15, 16]. Since burst methods do not require
precise waveform models, the unmodelled search space
may include BBH mergers with mis-aligned spins, large
mass ratios, or eccentric orbits. A number of all-sky, all-
time burst searches have been performed on data from
initial LIGO and Virgo [17–19]. Recent work has fo-
cussed on improving detection confidence in unmodelled
searches, and the last year has seen several improvements
in the ability to distinguish astrophysical signals from
noise transients [20–24]. As a result, burst searches are
now able to make high confidence detections across a wide
parameter space.
On September 14, 2015, an online burst search [25] re-
ported a transient that clearly stood above the expected
background from detector noise [26]. The alert came
only three minutes after the event time-stamp of 09:50:45
UTC. A second online burst search independently iden-
tified the event with a latency of a few hours, providing
a rapid confirmation of the signal [23]. The initial wave-
form reconstruction showed a frequency evolution that
rises in time, suggesting binary coalescence as the likely
progenitor, and a best fit model provided a chirp mass
around 28
M
, indicating the presence of a BBH signal.
Within days of the event, many follow-up investigations
began, including detailed checks of the observatory state
to check for any possible anomalies [27]. Two days af-
ter the signal was found, a notice with the estimated
source position was sent to a consortium of astronomers
to search for possible counterparts [28]. Investigations
continued over the next several months to validate the ob-
servation, estimate its statistical significance, and char-
acterize the astrophysical source [29, 30].
In this article, we present details of the burst searches
that made the first detection of the gravitational-wave
transient, GW150914 announced in [26]. We describe re-
sults reported in this announcement that are based on the
coherent Waveburst algorithm, along with those obtained
by two other analyses using omicron-LALInference-
Bursts and BayesWave [23, 25, 31]. In Section II, we
present a brief overview of the quality of the acquired
data and detector performance, before moving on, in Sec-
tion III, to present the three analyses employed. Using
each pipeline, we assess the statistical significance of the
event. Section IV characterizes each search sensitivity us-
ing simulated signals from BBH mergers. In Section V,
we demonstrate how a range of source properties may be
estimated using these same tools – including sky position
and masses of the black holes. The reconstructed signal
waveform is directly compared to results from numerical
relativity simulations (numerical relativity (NR)), giving
further evidence that this signal is consistent with expec-
tations from general relativity. Finally, the paper con-
cludes with a discussion about the implications of this
work.
II. DATA QUALITY AND BACKGROUND
ESTIMATION
We identify 39 calendar days of Advanced LIGO data,
from September 12th to October 20th, 2015, as a data set
to measure the sensitivity of the searches and the impact
of background noise events, known as glitches.
As in previous LIGO, Virgo and GEO transient
searches [17–19], a range of monitors tracking environ-
mental noise and the state of the instruments are used to
discard periods of poor quality data. Numerous studies
are performed to identify efficient veto criteria to remove
non-Gaussian noise features, while having the smallest
possible impact on detector livetime [27].
However, it is not possible to remove all noise glitches
based on monitors. This leaves a background residual
that has to be estimated from the data. To calculate the
background rate of noise events arising from glitches oc-
curring simultaneously at the two LIGO sites by chance
[17–19], the analyses are repeated on
O
(10
6
) independent
time-shifted data sets. Those data sets are generated by
translating the time of data in one interferometer by a
delay of some integer number of seconds, much larger
than the maximum GW travel time
'
10 ms between
the Livingston and Hanford facilities. By considering
the whole coincident livetime resulting from each arti-
ficial time shift, we obtain thousands of years of effective
background based on the available data. With this ap-
proach, we estimate a false alarm rate (FAR) expected
from background for each pipeline.
7
The “time-shift” method is effective to estimate the
background due to uncorrelated noise sources at the
two LIGO sites.
For the time immediately around
GW150914, we also examined potential sources of cor-
related noise between the detectors, and concluded that
all possible sources were too weak to have produced the
observed signal [27].
III. SEARCHES FOR GRAVITATIONAL WAVE
BURSTS
Strain data are searched by gravitational wave burst
search algorithms without assuming any particular signal
morphology, origin, direction or time. Burst searches are
performed in two operational modes; on-line and off-line.
On-line, low-latency searches provide alerts within
minutes of a GW signal passing the detectors to facil-
itate follow-up analyses such as searching for electro-
magnetic counterparts. In the days and weeks follow-
ing the data collection, burst analyses are refined using
updated information on the data quality and detector
calibration to perform off-line searches. These off-line
searches provide improved detection confidence estimates
for GW candidates, measure search sensitivity, and add
to waveform reconstruction and astrophysical interpreta-
tion. For short-duration, narrowband signals, coherent
burst searches have sensitivities approaching that of op-
timal matched filters [16, 32].
In the following subsections, we describe the burst
analysis of GW150914. This includes two independent
end-to-end pipelines, coherent Waveburst (cWB) and
omicron-LALInference-Bursts (oLIB), and BayesWave,
which performed a follow-up analysis at trigger times
identified by cWB. These three algorithms employ dif-
ferent strategies (and implementations) to search for un-
modelled GW transients, hence, they could perform quite
differently for specific classes of GW signals. Given the
very broad character of burst signals, the use of multi-
ple search algorithms is then beneficial, both to validate
results and to improve coverage of the wide signal pa-
rameter space.
A summary of the results from cWB has been pre-
sented in [26]. Here, we provide more details regarding
the cWB search pertaining the discovery of GW150914
and present its results with respect to the other burst
searches. In this paper, we focus our characterizations of
our pipelines on BBH sources only.
A. Coherent WaveBurst
The cWB algorithm has been used to perform all-sky
searches for gravitational wave transients in LIGO, Virgo
and GEO data since 2004. The most recent cWB results
from the initial detectors are [17, 19, 33]. The cWB al-
gorithm has since been upgraded to conduct transient
searches with the advanced detectors [24]. The cWB
pipeline was used in the low-latency transient search that
initially detected GW150914, reporting the event three
minutes after the data was collected. This search aims
at rapid alerts for the LIGO/Virgo electromagnetic fol-
lowup program [28] and provides a first estimation of the
event parameters and sky location. A slightly different
configuration of the same pipeline was used in the of-
fline search to measure the statistical significance of the
GW150914 event which is reported in [26]. The low-
latency search was performed in the frequency range of
16-2048 Hz, while the offline search covered the band of
the best detector sensitivity between 16 and 1024 Hz.
1. cWB pipeline overview
The cWB pipeline searches for a broad range of grav-
itational wave transients in the LIGO frequency band
without prior knowledge of the signal waveforms [25].
The pipeline identifies coincident events in data from the
two LIGO detectors and reconstructs the gravitational-
wave signal associated with these events using a likeli-
hood analysis.
First, the data are whitened and converted to the time-
frequency domain using the Wilson-Daubechies-Meyer
wavelet transform [34]. Data from both detectors are
then combined to obtain a time-frequency power map. A
transient event is identified as a cluster of time-frequency
data samples with power above the baseline detector
noise. To obtain a good time-frequency coverage for a
broad range of signal morphologies, the analysis is re-
peated with seven frequency resolutions ∆
f
ranging from
1 Hz to 64 Hz in steps of powers of two, corresponding to
time resolutions ∆
t
= 1
/
(2∆
f
) from 500 ms to 7
.
8 ms.
The clusters at different resolutions overlapping in time
and frequency are combined into a trigger that provides a
multi-resolution representation of the excess power event
recorded by the detectors.
The data associated with each trigger are analyzed co-
herently [24] to estimate the signal waveforms, the wave
polarization, and the source sky location. The signal
waveforms in both detectors are reconstructed with the
constrained likelihood method [35]. The constraint used
in this analysis is model independent and requires the
reconstructed waveforms to be similar in both detectors,
as expected from the close alignment of the H1 and L1
detector arms.
The waveforms are reconstructed over a uniform grid
of sky locations with 0
.
4
×
0
.
4
resolution. We select the
best fit waveforms that correspond to the maximum of
the likelihood statistic
L
=
c
c
E
s
, where
E
s
is the total
energy of the reconstructed waveforms
1
and
c
c
measures
the similarity of the waveforms in the two detectors. The
coefficient
c
c
is defined as
c
c
=
E
c
/
(
E
c
+
E
n
), where
E
c
1
E
s
is the network signal-to-noise ratio [24]