of 27
Draft version March 12, 2019
Typeset using L
A
T
E
X
twocolumn
style in AASTeX61
LOW-LATENCY GRAVITATIONAL WAVE ALERTS FOR MULTI-MESSENGER ASTRONOMY DURING THE
SECOND ADVANCED LIGO AND VIRGO OBSERVING RUN
B. P. Abbott,
1
R. Abbott,
1
T. D. Abbott,
2
S. Abraham,
3
F. Acernese,
4, 5
K. Ackley,
6
C. Adams,
7
R. X. Adhikari,
1
V. B. Adya,
8, 9
C. Affeldt,
8, 9
M. Agathos,
10
K. Agatsuma,
11
N. Aggarwal,
12
O. D. Aguiar,
13
L. Aiello,
14, 15
A. Ain,
3
P. Ajith,
16
G. Allen,
17
A. Allocca,
18, 19
M. A. Aloy,
20
P. A. Altin,
21
A. Amato,
22
A. Ananyeva,
1
S. B. Anderson,
1
W. G. Anderson,
23
S. V. Angelova,
24
S. Antier,
25
S. Appert,
1
K. Arai,
1
M. C. Araya,
1
J. S. Areeda,
26
M. Ar
`
ene,
27
N. Arnaud,
25, 28
K. G. Arun,
29
S. Ascenzi,
30, 31
G. Ashton,
6
S. M. Aston,
7
P. Astone,
32
F. Aubin,
33
P. Aufmuth,
9
K. AultONeal,
34
C. Austin,
2
V. Avendano,
35
A. Avila-Alvarez,
26
S. Babak,
36, 27
P. Bacon,
27
F. Badaracco,
14, 15
M. K. M. Bader,
37
S. Bae,
38
P. T. Baker,
39
F. Baldaccini,
40, 41
G. Ballardin,
28
S. W. Ballmer,
42
S. Banagiri,
43
J. C. Barayoga,
1
S. E. Barclay,
44
B. C. Barish,
1
D. Barker,
45
K. Barkett,
46
S. Barnum,
12
F. Barone,
4, 5
B. Barr,
44
L. Barsotti,
12
M. Barsuglia,
27
D. Barta,
47
J. Bartlett,
45
I. Bartos,
48
R. Bassiri,
49
A. Basti,
18, 19
M. Bawaj,
50, 41
J. C. Bayley,
44
M. Bazzan,
51, 52
B. B
́
ecsy,
53
M. Bejger,
27, 54
I. Belahcene,
25
A. S. Bell,
44
D. Beniwal,
55
B. K. Berger,
49
G. Bergmann,
8, 9
S. Bernuzzi,
56, 57
J. J. Bero,
58
C. P. L. Berry,
59
D. Bersanetti,
60
A. Bertolini,
37
J. Betzwieser,
7
R. Bhandare,
61
J. Bidler,
26
I. A. Bilenko,
62
S. A. Bilgili,
39
G. Billingsley,
1
J. Birch,
7
R. Birney,
24
O. Birnholtz,
58
S. Biscans,
1, 12
S. Biscoveanu,
6
A. Bisht,
9
M. Bitossi,
28, 19
M. A. Bizouard,
25
J. K. Blackburn,
1
C. D. Blair,
7
D. G. Blair,
63
R. M. Blair,
45
S. Bloemen,
64
N. Bode,
8, 9
M. Boer,
65
Y. Boetzel,
66
G. Bogaert,
65
F. Bondu,
67
E. Bonilla,
49
R. Bonnand,
33
P. Booker,
8, 9
B. A. Boom,
37
C. D. Booth,
68
R. Bork,
1
V. Boschi,
28
S. Bose,
69, 3
K. Bossie,
7
V. Bossilkov,
63
J. Bosveld,
63
Y. Bouffanais,
27
A. Bozzi,
28
C. Bradaschia,
19
P. R. Brady,
23
A. Bramley,
7
M. Branchesi,
14, 15
J. E. Brau,
70
T. Briant,
71
J. H. Briggs,
44
F. Brighenti,
72, 73
A. Brillet,
65
M. Brinkmann,
8, 9
V. Brisson,
25,
P. Brockill,
23
A. F. Brooks,
1
D. D. Brown,
55
S. Brunett,
1
A. Buikema,
12
T. Bulik,
74
H. J. Bulten,
75, 37
A. Buonanno,
36, 76
D. Buskulic,
33
C. Buy,
27
R. L. Byer,
49
M. Cabero,
8, 9
L. Cadonati,
77
G. Cagnoli,
22, 78
C. Cahillane,
1
J. Calder
́
on Bustillo,
6
T. A. Callister,
1
E. Calloni,
79, 5
J. B. Camp,
80
W. A. Campbell,
6
M. Canepa,
81, 60
K. C. Cannon,
82
H. Cao,
55
J. Cao,
83
E. Capocasa,
27
F. Carbognani,
28
S. Caride,
84
M. F. Carney,
59
G. Carullo,
18
J. Casanueva Diaz,
19
C. Casentini,
30, 31
S. Caudill,
37
M. Cavagli
`
a,
85
F. Cavalier,
25
R. Cavalieri,
28
G. Cella,
19
P. Cerd
́
a-Dur
́
an,
20
G. Cerretani,
18, 19
E. Cesarini,
86, 31
O. Chaibi,
65
K. Chakravarti,
3
S. J. Chamberlin,
87
M. Chan,
44
S. Chao,
88
P. Charlton,
89
E. A. Chase,
59
E. Chassande-Mottin,
27
D. Chatterjee,
23
M. Chaturvedi,
61
K. Chatziioannou,
90
B. D. Cheeseboro,
39
H. Y. Chen,
91
X. Chen,
63
Y. Chen,
46
H.-P. Cheng,
48
C. K. Cheong,
92
H. Y. Chia,
48
A. Chincarini,
60
A. Chiummo,
28
G. Cho,
93
H. S. Cho,
94
M. Cho,
76
N. Christensen,
65, 95
Q. Chu,
63
S. Chua,
71
K. W. Chung,
92
S. Chung,
63
G. Ciani,
51, 52
A. A. Ciobanu,
55
R. Ciolfi,
96, 97
F. Cipriano,
65
A. Cirone,
81, 60
F. Clara,
45
J. A. Clark,
77
P. Clearwater,
98
F. Cleva,
65
C. Cocchieri,
85
E. Coccia,
14, 15
P.-F. Cohadon,
71
D. Cohen,
25
R. Colgan,
99
M. Colleoni,
100
C. G. Collette,
101
C. Collins,
11
L. R. Cominsky,
102
M. Constancio Jr.,
13
L. Conti,
52
S. J. Cooper,
11
P. Corban,
7
T. R. Corbitt,
2
I. Cordero-Carri
́
on,
103
K. R. Corley,
99
N. Cornish,
53
A. Corsi,
84
S. Cortese,
28
C. A. Costa,
13
R. Cotesta,
36
M. W. Coughlin,
1
S. B. Coughlin,
68, 59
J.-P. Coulon,
65
S. T. Countryman,
99
P. Couvares,
1
P. B. Covas,
100
E. E. Cowan,
77
D. M. Coward,
63
M. J. Cowart,
7
D. C. Coyne,
1
R. Coyne,
104
J. D. E. Creighton,
23
T. D. Creighton,
105
J. Cripe,
2
M. Croquette,
71
S. G. Crowder,
106
T. J. Cullen,
2
A. Cumming,
44
L. Cunningham,
44
E. Cuoco,
28
T. Dal Canton,
80
G. D
́
alya,
107
S. L. Danilishin,
8, 9
S. D’Antonio,
31
K. Danzmann,
9, 8
A. Dasgupta,
108
C. F. Da Silva Costa,
48
L. E. H. Datrier,
44
V. Dattilo,
28
I. Dave,
61
M. Davier,
25
D. Davis,
42
E. J. Daw,
109
D. DeBra,
49
M. Deenadayalan,
3
J. Degallaix,
22
M. De Laurentis,
79, 5
S. Del
́
eglise,
71
W. Del Pozzo,
18, 19
L. M. DeMarchi,
59
N. Demos,
12
T. Dent,
8, 9, 110
R. De Pietri,
111, 57
J. Derby,
26
R. De Rosa,
79, 5
C. De Rossi,
22, 28
R. DeSalvo,
112
O. de Varona,
8, 9
S. Dhurandhar,
3
M. C. D
́
ıaz,
105
T. Dietrich,
37
L. Di Fiore,
5
M. Di Giovanni,
113, 97
T. Di Girolamo,
79, 5
A. Di Lieto,
18, 19
B. Ding,
101
S. Di Pace,
114, 32
I. Di Palma,
114, 32
F. Di Renzo,
18, 19
A. Dmitriev,
11
Z. Doctor,
91
F. Donovan,
12
K. L. Dooley,
68, 85
S. Doravari,
8, 9
I. Dorrington,
68
T. P. Downes,
23
M. Drago,
14, 15
J. C. Driggers,
45
Z. Du,
83
J.-G. Ducoin,
25
P. Dupej,
44
S. E. Dwyer,
45
P. J. Easter,
6
T. B. Edo,
109
M. C. Edwards,
95
A. Effler,
7
P. Ehrens,
1
J. Eichholz,
1
S. S. Eikenberry,
48
M. Eisenmann,
33
R. A. Eisenstein,
12
R. C. Essick,
91
H. Estelles,
100
D. Estevez,
33
Z. B. Etienne,
39
T. Etzel,
1
M. Evans,
12
T. M. Evans,
7
V. Fafone,
30, 31, 14
H. Fair,
42
S. Fairhurst,
68
X. Fan,
83
S. Farinon,
60
B. Farr,
70
W. M. Farr,
11
E. J. Fauchon-Jones,
68
M. Favata,
35
M. Fays,
109
M. Fazio,
115
C. Fee,
116
J. Feicht,
1
M. M. Fejer,
49
F. Feng,
27
A. Fernandez-Galiana,
12
I. Ferrante,
18, 19
E. C. Ferreira,
13
T. A. Ferreira,
13
F. Ferrini,
28
F. Fidecaro,
18, 19
I. Fiori,
28
D. Fiorucci,
27
M. Fishbach,
91
R. P. Fisher,
42, 117
J. M. Fishner,
12
M. Fitz-Axen,
43
R. Flaminio,
33, 118
M. Fletcher,
44
E. Flynn,
26
H. Fong,
90
J. A. Font,
20, 119
P. W. F. Forsyth,
21
J.-D. Fournier,
65
S. Frasca,
114, 32
F. Frasconi,
19
Z. Frei,
107
A. Freise,
11
R. Frey,
70
V. Frey,
25
arXiv:1901.03310v5 [astro-ph.HE] 11 Mar 2019
2
P. Fritschel,
12
V. V. Frolov,
7
P. Fulda,
48
M. Fyffe,
7
H. A. Gabbard,
44
B. U. Gadre,
3
S. M. Gaebel,
11
J. R. Gair,
120
L. Gammaitoni,
40
M. R. Ganija,
55
S. G. Gaonkar,
3
A. Garcia,
26
C. Garc
́
ıa-Quir
́
os,
100
F. Garufi,
79, 5
B. Gateley,
45
S. Gaudio,
34
G. Gaur,
121
V. Gayathri,
122
G. Gemme,
60
E. Genin,
28
A. Gennai,
19
D. George,
17
J. George,
61
L. Gergely,
123
V. Germain,
33
S. Ghonge,
77
Abhirup Ghosh,
16
Archisman Ghosh,
37
S. Ghosh,
23
B. Giacomazzo,
113, 97
J. A. Giaime,
2, 7
K. D. Giardina,
7
A. Giazotto,
19,
K. Gill,
34
G. Giordano,
4, 5
L. Glover,
112
P. Godwin,
87
E. Goetz,
45
R. Goetz,
48
B. Goncharov,
6
G. Gonz
́
alez,
2
J. M. Gonzalez Castro,
18, 19
A. Gopakumar,
124
M. L. Gorodetsky,
62
S. E. Gossan,
1
M. Gosselin,
28
R. Gouaty,
33
A. Grado,
125, 5
C. Graef,
44
M. Granata,
22
A. Grant,
44
S. Gras,
12
P. Grassia,
1
C. Gray,
45
R. Gray,
44
G. Greco,
72, 73
A. C. Green,
11, 48
R. Green,
68
E. M. Gretarsson,
34
P. Groot,
64
H. Grote,
68
S. Grunewald,
36
P. Gruning,
25
G. M. Guidi,
72, 73
H. K. Gulati,
108
Y. Guo,
37
A. Gupta,
87
M. K. Gupta,
108
E. K. Gustafson,
1
R. Gustafson,
126
L. Haegel,
100
O. Halim,
15, 14
B. R. Hall,
69
E. D. Hall,
12
E. Z. Hamilton,
68
G. Hammond,
44
M. Haney,
66
M. M. Hanke,
8, 9
J. Hanks,
45
C. Hanna,
87
M. D. Hannam,
68
O. A. Hannuksela,
92
J. Hanson,
7
T. Hardwick,
2
K. Haris,
16
J. Harms,
14, 15
G. M. Harry,
127
I. W. Harry,
36
C.-J. Haster,
90
K. Haughian,
44
F. J. Hayes,
44
J. Healy,
58
A. Heidmann,
71
M. C. Heintze,
7
H. Heitmann,
65
P. Hello,
25
G. Hemming,
28
M. Hendry,
44
I. S. Heng,
44
J. Hennig,
8, 9
A. W. Heptonstall,
1
Francisco Hernandez Vivanco,
6
M. Heurs,
8, 9
S. Hild,
44
T. Hinderer,
128, 37, 129
D. Hoak,
28
S. Hochheim,
8, 9
D. Hofman,
22
A. M. Holgado,
17
N. A. Holland,
21
K. Holt,
7
D. E. Holz,
91
P. Hopkins,
68
C. Horst,
23
J. Hough,
44
E. J. Howell,
63
C. G. Hoy,
68
A. Hreibi,
65
E. A. Huerta,
17
D. Huet,
25
B. Hughey,
34
M. Hulko,
1
S. Husa,
100
S. H. Huttner,
44
T. Huynh-Dinh,
7
B. Idzkowski,
74
A. Iess,
30, 31
C. Ingram,
55
R. Inta,
84
G. Intini,
114, 32
B. Irwin,
116
H. N. Isa,
44
J.-M. Isac,
71
M. Isi,
1
B. R. Iyer,
16
K. Izumi,
45
T. Jacqmin,
71
S. J. Jadhav,
130
K. Jani,
77
N. N. Janthalur,
130
P. Jaranowski,
131
A. C. Jenkins,
132
J. Jiang,
48
D. S. Johnson,
17
A. W. Jones,
11
D. I. Jones,
133
R. Jones,
44
R. J. G. Jonker,
37
L. Ju,
63
J. Junker,
8, 9
C. V. Kalaghatgi,
68
V. Kalogera,
59
B. Kamai,
1
S. Kandhasamy,
85
G. Kang,
38
J. B. Kanner,
1
S. J. Kapadia,
23
S. Karki,
70
K. S. Karvinen,
8, 9
R. Kashyap,
16
M. Kasprzack,
1
S. Katsanevas,
28
E. Katsavounidis,
12
W. Katzman,
7
S. Kaufer,
9
K. Kawabe,
45
N. V. Keerthana,
3
F. K
́
ef
́
elian,
65
D. Keitel,
44
R. Kennedy,
109
J. S. Key,
134
F. Y. Khalili,
62
H. Khan,
26
I. Khan,
14, 31
S. Khan,
8, 9
Z. Khan,
108
E. A. Khazanov,
135
M. Khursheed,
61
N. Kijbunchoo,
21
Chunglee Kim,
136
J. C. Kim,
137
K. Kim,
92
W. Kim,
55
W. S. Kim,
138
Y.-M. Kim,
139
C. Kimball,
59
E. J. King,
55
P. J. King,
45
M. Kinley-Hanlon,
127
R. Kirchhoff,
8, 9
J. S. Kissel,
45
L. Kleybolte,
140
J. H. Klika,
23
S. Klimenko,
48
T. D. Knowles,
39
P. Koch,
8, 9
S. M. Koehlenbeck,
8, 9
G. Koekoek,
37, 141
S. Koley,
37
V. Kondrashov,
1
A. Kontos,
12
N. Koper,
8, 9
M. Korobko,
140
W. Z. Korth,
1
I. Kowalska,
74
D. B. Kozak,
1
V. Kringel,
8, 9
N. Krishnendu,
29
A. Kr
́
olak,
142, 143
G. Kuehn,
8, 9
A. Kumar,
130
P. Kumar,
144
R. Kumar,
108
S. Kumar,
16
L. Kuo,
88
A. Kutynia,
142
S. Kwang,
23
B. D. Lackey,
36
K. H. Lai,
92
T. L. Lam,
92
M. Landry,
45
B. B. Lane,
12
R. N. Lang,
145
J. Lange,
58
B. Lantz,
49
R. K. Lanza,
12
A. Lartaux-Vollard,
25
P. D. Lasky,
6
M. Laxen,
7
A. Lazzarini,
1
C. Lazzaro,
52
P. Leaci,
114, 32
S. Leavey,
8, 9
Y. K. Lecoeuche,
45
C. H. Lee,
94
H. K. Lee,
146
H. M. Lee,
147
H. W. Lee,
137
J. Lee,
93
K. Lee,
44
J. Lehmann,
8, 9
A. Lenon,
39
N. Leroy,
25
N. Letendre,
33
Y. Levin,
6, 99
J. Li,
83
K. J. L. Li,
92
T. G. F. Li,
92
X. Li,
46
F. Lin,
6
F. Linde,
37
S. D. Linker,
112
T. B. Littenberg,
148
J. Liu,
63
X. Liu,
23
R. K. L. Lo,
92, 1
N. A. Lockerbie,
24
L. T. London,
68
A. Longo,
149, 150
M. Lorenzini,
14, 15
V. Loriette,
151
M. Lormand,
7
G. Losurdo,
19
J. D. Lough,
8, 9
C. O. Lousto,
58
G. Lovelace,
26
M. E. Lower,
152
H. L
̈
uck,
9, 8
D. Lumaca,
30, 31
A. P. Lundgren,
153
R. Lynch,
12
Y. Ma,
46
R. Macas,
68
S. Macfoy,
24
M. MacInnis,
12
D. M. Macleod,
68
A. Macquet,
65
F. Maga
̃
na-Sandoval,
42
L. Maga
̃
na Zertuche,
85
R. M. Magee,
87
E. Majorana,
32
I. Maksimovic,
151
A. Malik,
61
N. Man,
65
V. Mandic,
43
V. Mangano,
44
G. L. Mansell,
45, 12
M. Manske,
23, 21
M. Mantovani,
28
F. Marchesoni,
50, 41
F. Marion,
33
S. M
́
arka,
99
Z. M
́
arka,
99
C. Markakis,
10, 17
A. S. Markosyan,
49
A. Markowitz,
1
E. Maros,
1
A. Marquina,
103
S. Marsat,
36
F. Martelli,
72, 73
I. W. Martin,
44
R. M. Martin,
35
D. V. Martynov,
11
K. Mason,
12
E. Massera,
109
A. Masserot,
33
T. J. Massinger,
1
M. Masso-Reid,
44
S. Mastrogiovanni,
114, 32
A. Matas,
43, 36
F. Matichard,
1, 12
L. Matone,
99
N. Mavalvala,
12
N. Mazumder,
69
J. J. McCann,
63
R. McCarthy,
45
D. E. McClelland,
21
S. McCormick,
7
L. McCuller,
12
S. C. McGuire,
154
J. McIver,
1
D. J. McManus,
21
T. McRae,
21
S. T. McWilliams,
39
D. Meacher,
87
G. D. Meadors,
6
M. Mehmet,
8, 9
A. K. Mehta,
16
J. Meidam,
37
A. Melatos,
98
G. Mendell,
45
R. A. Mercer,
23
L. Mereni,
22
E. L. Merilh,
45
M. Merzougui,
65
S. Meshkov,
1
C. Messenger,
44
C. Messick,
87
R. Metzdorff,
71
P. M. Meyers,
98
H. Miao,
11
C. Michel,
22
H. Middleton,
98
E. E. Mikhailov,
155
L. Milano,
79, 5
A. L. Miller,
48
A. Miller,
114, 32
M. Millhouse,
53
J. C. Mills,
68
M. C. Milovich-Goff,
112
O. Minazzoli,
65, 156
Y. Minenkov,
31
A. Mishkin,
48
C. Mishra,
157
T. Mistry,
109
S. Mitra,
3
V. P. Mitrofanov,
62
G. Mitselmakher,
48
R. Mittleman,
12
G. Mo,
95
D. Moffa,
116
K. Mogushi,
85
S. R. P. Mohapatra,
12
M. Montani,
72, 73
C. J. Moore,
10
D. Moraru,
45
G. Moreno,
45
S. Morisaki,
82
B. Mours,
33
C. M. Mow-Lowry,
11
Arunava Mukherjee,
8, 9
D. Mukherjee,
23
S. Mukherjee,
105
N. Mukund,
3
A. Mullavey,
7
J. Munch,
55
E. A. Mu
̃
niz,
42
M. Muratore,
34
P. G. Murray,
44
A. Nagar,
86, 158, 159
I. Nardecchia,
30, 31
L. Naticchioni,
114, 32
R. K. Nayak,
160
J. Neilson,
112
G. Nelemans,
64, 37
T. J. N. Nelson,
7
M. Nery,
8, 9
A. Neunzert,
126
K. Y. Ng,
12
S. Ng,
55
P. Nguyen,
70
D. Nichols,
128, 37
S. Nissanke,
128, 37
A. Nitz,
8
F. Nocera,
28
C. North,
68
L. K. Nuttall,
153
M. Obergaulinger,
20
J. Oberling,
45
B. D. O’Brien,
48
G. D. O’Dea,
112
G. H. Ogin,
161
J. J. Oh,
138
S. H. Oh,
138
F. Ohme,
8, 9
H. Ohta,
82
M. A. Okada,
13
M. Oliver,
100
P. Oppermann,
8, 9
Richard J. Oram,
7
B. O’Reilly,
7
R. G. Ormiston,
43
L. F. Ortega,
48
R. O’Shaughnessy,
58
S. Ossokine,
36
D. J. Ottaway,
55
H. Overmier,
7
B. J. Owen,
84
A. E. Pace,
87
G. Pagano,
18, 19
M. A. Page,
63
A. Pai,
122
3
S. A. Pai,
61
J. R. Palamos,
70
O. Palashov,
135
C. Palomba,
32
A. Pal-Singh,
140
Huang-Wei Pan,
88
B. Pang,
46
P. T. H. Pang,
92
C. Pankow,
59
F. Pannarale,
114, 32
B. C. Pant,
61
F. Paoletti,
19
A. Paoli,
28
A. Parida,
3
W. Parker,
7, 154
D. Pascucci,
44
A. Pasqualetti,
28
R. Passaquieti,
18, 19
D. Passuello,
19
M. Patil,
143
B. Patricelli,
18, 19
B. L. Pearlstone,
44
C. Pedersen,
68
M. Pedraza,
1
R. Pedurand,
22, 162
A. Pele,
7
S. Penn,
163
C. J. Perez,
45
A. Perreca,
113, 97
H. P. Pfeiffer,
36, 90
M. Phelps,
8, 9
K. S. Phukon,
3
O. J. Piccinni,
114, 32
M. Pichot,
65
F. Piergiovanni,
72, 73
G. Pillant,
28
L. Pinard,
22
M. Pirello,
45
M. Pitkin,
44
R. Poggiani,
18, 19
D. Y. T. Pong,
92
S. Ponrathnam,
3
P. Popolizio,
28
E. K. Porter,
27
J. Powell,
152
A. K. Prajapati,
108
J. Prasad,
3
K. Prasai,
49
R. Prasanna,
130
G. Pratten,
100
T. Prestegard,
23
S. Privitera,
36
G. A. Prodi,
113, 97
L. G. Prokhorov,
62
O. Puncken,
8, 9
M. Punturo,
41
P. Puppo,
32
M. P
̈
urrer,
36
H. Qi,
23
V. Quetschke,
105
P. J. Quinonez,
34
E. A. Quintero,
1
R. Quitzow-James,
70
F. J. Raab,
45
H. Radkins,
45
N. Radulescu,
65
P. Raffai,
107
S. Raja,
61
C. Rajan,
61
B. Rajbhandari,
84
M. Rakhmanov,
105
K. E. Ramirez,
105
A. Ramos-Buades,
100
Javed Rana,
3
K. Rao,
59
P. Rapagnani,
114, 32
V. Raymond,
68
M. Razzano,
18, 19
J. Read,
26
T. Regimbau,
33
L. Rei,
60
S. Reid,
24
D. H. Reitze,
1, 48
W. Ren,
17
F. Ricci,
114, 32
C. J. Richardson,
34
J. W. Richardson,
1
P. M. Ricker,
17
K. Riles,
126
M. Rizzo,
59
N. A. Robertson,
1, 44
R. Robie,
44
F. Robinet,
25
A. Rocchi,
31
L. Rolland,
33
J. G. Rollins,
1
V. J. Roma,
70
M. Romanelli,
67
R. Romano,
4, 5
C. L. Romel,
45
J. H. Romie,
7
K. Rose,
116
D. Rosi
́
nska,
164, 54
S. G. Rosofsky,
17
M. P. Ross,
165
S. Rowan,
44
A. R
̈
udiger,
8, 9,
P. Ruggi,
28
G. Rutins,
166
K. Ryan,
45
S. Sachdev,
1
T. Sadecki,
45
M. Sakellariadou,
132
L. Salconi,
28
M. Saleem,
29
A. Samajdar,
37
L. Sammut,
6
E. J. Sanchez,
1
L. E. Sanchez,
1
N. Sanchis-Gual,
20
V. Sandberg,
45
J. R. Sanders,
42
K. A. Santiago,
35
N. Sarin,
6
B. Sassolas,
22
B. S. Sathyaprakash,
87, 68
P. R. Saulson,
42
O. Sauter,
126
R. L. Savage,
45
P. Schale,
70
M. Scheel,
46
J. Scheuer,
59
P. Schmidt,
64
R. Schnabel,
140
R. M. S. Schofield,
70
A. Sch
̈
onbeck,
140
E. Schreiber,
8, 9
B. W. Schulte,
8, 9
B. F. Schutz,
68
S. G. Schwalbe,
34
J. Scott,
44
S. M. Scott,
21
E. Seidel,
17
D. Sellers,
7
A. S. Sengupta,
167
N. Sennett,
36
D. Sentenac,
28
V. Sequino,
30, 31, 14
A. Sergeev,
135
Y. Setyawati,
8, 9
D. A. Shaddock,
21
T. Shaffer,
45
M. S. Shahriar,
59
M. B. Shaner,
112
L. Shao,
36
P. Sharma,
61
P. Shawhan,
76
H. Shen,
17
R. Shink,
168
D. H. Shoemaker,
12
D. M. Shoemaker,
77
S. ShyamSundar,
61
K. Siellez,
77
M. Sieniawska,
54
D. Sigg,
45
A. D. Silva,
13
L. P. Singer,
80
N. Singh,
74
A. Singhal,
14, 32
A. M. Sintes,
100
S. Sitmukhambetov,
105
V. Skliris,
68
B. J. J. Slagmolen,
21
T. J. Slaven-Blair,
63
J. R. Smith,
26
R. J. E. Smith,
6
S. Somala,
169
E. J. Son,
138
B. Sorazu,
44
F. Sorrentino,
60
T. Souradeep,
3
E. Sowell,
84
A. P. Spencer,
44
A. K. Srivastava,
108
V. Srivastava,
42
K. Staats,
59
C. Stachie,
65
M. Standke,
8, 9
D. A. Steer,
27
M. Steinke,
8, 9
J. Steinlechner,
140, 44
S. Steinlechner,
140
D. Steinmeyer,
8, 9
S. P. Stevenson,
152
D. Stocks,
49
R. Stone,
105
D. J. Stops,
11
K. A. Strain,
44
G. Stratta,
72, 73
S. E. Strigin,
62
A. Strunk,
45
R. Sturani,
170
A. L. Stuver,
171
V. Sudhir,
12
T. Z. Summerscales,
172
L. Sun,
1
S. Sunil,
108
J. Suresh,
3
P. J. Sutton,
68
B. L. Swinkels,
37
M. J. Szczepa
́
nczyk,
34
M. Tacca,
37
S. C. Tait,
44
C. Talbot,
6
D. Talukder,
70
D. B. Tanner,
48
M. T
́
apai,
123
A. Taracchini,
36
J. D. Tasson,
95
R. Taylor,
1
F. Thies,
8, 9
M. Thomas,
7
P. Thomas,
45
S. R. Thondapu,
61
K. A. Thorne,
7
E. Thrane,
6
Shubhanshu Tiwari,
113, 97
Srishti Tiwari,
124
V. Tiwari,
68
K. Toland,
44
M. Tonelli,
18, 19
Z. Tornasi,
44
A. Torres-Forn
́
e,
173
C. I. Torrie,
1
D. T
̈
oyr
̈
a,
11
F. Travasso,
28, 41
G. Traylor,
7
M. C. Tringali,
74
A. Trovato,
27
L. Trozzo,
174, 19
R. Trudeau,
1
K. W. Tsang,
37
M. Tse,
12
R. Tso,
46
L. Tsukada,
82
D. Tsuna,
82
D. Tuyenbayev,
105
K. Ueno,
82
D. Ugolini,
175
C. S. Unnikrishnan,
124
A. L. Urban,
2
S. A. Usman,
68
H. Vahlbruch,
9
G. Vajente,
1
G. Valdes,
2
N. van Bakel,
37
M. van Beuzekom,
37
J. F. J. van den Brand,
75, 37
C. Van Den Broeck,
37, 176
D. C. Vander-Hyde,
42
J. V. van Heijningen,
63
L. van der Schaaf,
37
A. A. van Veggel,
44
M. Vardaro,
51, 52
V. Varma,
46
S. Vass,
1
M. Vas
́
uth,
47
A. Vecchio,
11
G. Vedovato,
52
J. Veitch,
44
P. J. Veitch,
55
K. Venkateswara,
165
G. Venugopalan,
1
D. Verkindt,
33
F. Vetrano,
72, 73
A. Vicer
́
e,
72, 73
A. D. Viets,
23
D. J. Vine,
166
J.-Y. Vinet,
65
S. Vitale,
12
T. Vo,
42
H. Vocca,
40, 41
C. Vorvick,
45
S. P. Vyatchanin,
62
A. R. Wade,
1
L. E. Wade,
116
M. Wade,
116
R. Walet,
37
M. Walker,
26
L. Wallace,
1
S. Walsh,
23
G. Wang,
14, 19
H. Wang,
11
J. Z. Wang,
126
W. H. Wang,
105
Y. F. Wang,
92
R. L. Ward,
21
Z. A. Warden,
34
J. Warner,
45
M. Was,
33
J. Watchi,
101
B. Weaver,
45
L.-W. Wei,
8, 9
M. Weinert,
8, 9
A. J. Weinstein,
1
R. Weiss,
12
F. Wellmann,
8, 9
L. Wen,
63
E. K. Wessel,
17
P. Weßels,
8, 9
J. W. Westhouse,
34
K. Wette,
21
J. T. Whelan,
58
B. F. Whiting,
48
C. Whittle,
12
D. M. Wilken,
8, 9
D. Williams,
44
A. R. Williamson,
128, 37
J. L. Willis,
1
B. Willke,
8, 9
M. H. Wimmer,
8, 9
W. Winkler,
8, 9
C. C. Wipf,
1
H. Wittel,
8, 9
G. Woan,
44
J. Woehler,
8, 9
J. K. Wofford,
58
J. Worden,
45
J. L. Wright,
44
D. S. Wu,
8, 9
D. M. Wysocki,
58
L. Xiao,
1
H. Yamamoto,
1
C. C. Yancey,
76
L. Yang,
115
M. J. Yap,
21
M. Yazback,
48
D. W. Yeeles,
68
Hang Yu,
12
Haocun Yu,
12
S. H. R. Yuen,
92
M. Yvert,
33
A. K. Zadro
̇
zny,
105, 142
M. Zanolin,
34
T. Zelenova,
28
J.-P. Zendri,
52
M. Zevin,
59
J. Zhang,
63
L. Zhang,
1
T. Zhang,
44
C. Zhao,
63
M. Zhou,
59
Z. Zhou,
59
X. J. Zhu,
6
A. B. Zimmerman,
177, 90
M. E. Zucker,
1, 12
and J. Zweizig
1
The LIGO Scientific Collaboration and the Virgo Collaboration
1
LIGO, California Institute of Technology, Pasadena, CA 91125, USA
2
Louisiana State University, Baton Rouge, LA 70803, USA
3
Inter-University Centre for Astronomy and Astrophysics, Pune 411007, India
4
4
Universit`a di Salerno, Fisciano, I-84084 Salerno, Italy
5
INFN, Sezione di Napoli, Complesso Universitario di Monte S.Angelo, I-80126 Napoli, Italy
6
OzGrav, School of Physics & Astronomy, Monash University, Clayton 3800, Victoria, Australia
7
LIGO Livingston Observatory, Livingston, LA 70754, USA
8
Max Planck Institute for Gravitational Physics (Albert Einstein Institute), D-30167 Hannover, Germany
9
Leibniz Universit ̈at Hannover, D-30167 Hannover, Germany
10
University of Cambridge, Cambridge CB2 1TN, United Kingdom
11
University of Birmingham, Birmingham B15 2TT, United Kingdom
12
LIGO, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
13
Instituto Nacional de Pesquisas Espaciais, 12227-010 S ̃ao Jos ́e dos Campos, S ̃ao Paulo, Brazil
14
Gran Sasso Science Institute (GSSI), I-67100 L’Aquila, Italy
15
INFN, Laboratori Nazionali del Gran Sasso, I-67100 Assergi, Italy
16
International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru 560089, India
17
NCSA, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
18
Universit`a di Pisa, I-56127 Pisa, Italy
19
INFN, Sezione di Pisa, I-56127 Pisa, Italy
20
Departamento de Astronom ́ıa y Astrof ́ısica, Universitat de Val`encia, E-46100 Burjassot, Val`encia, Spain
21
OzGrav, Australian National University, Canberra, Australian Capital Territory 0200, Australia
22
Laboratoire des Mat ́eriaux Avanc ́es (LMA), CNRS/IN2P3, F-69622 Villeurbanne, France
23
University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
24
SUPA, University of Strathclyde, Glasgow G1 1XQ, United Kingdom
25
LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit ́e Paris-Saclay, F-91898 Orsay, France
26
California State University Fullerton, Fullerton, CA 92831, USA
27
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
28
European Gravitational Observatory (EGO), I-56021 Cascina, Pisa, Italy
29
Chennai Mathematical Institute, Chennai 603103, India
30
Universit`a di Roma Tor Vergata, I-00133 Roma, Italy
31
INFN, Sezione di Roma Tor Vergata, I-00133 Roma, Italy
32
INFN, Sezione di Roma, I-00185 Roma, Italy
33
Laboratoire d’Annecy de Physique des Particules (LAPP), Univ. Grenoble Alpes, Universit ́e Savoie Mont Blanc, CNRS/IN2P3, F-74941
Annecy, France
34
Embry-Riddle Aeronautical University, Prescott, AZ 86301, USA
35
Montclair State University, Montclair, NJ 07043, USA
36
Max Planck Institute for Gravitational Physics (Albert Einstein Institute), D-14476 Potsdam-Golm, Germany
37
Nikhef, Science Park 105, 1098 XG Amsterdam, The Netherlands
38
Korea Institute of Science and Technology Information, Daejeon 34141, South Korea
39
West Virginia University, Morgantown, WV 26506, USA
40
Universit`a di Perugia, I-06123 Perugia, Italy
41
INFN, Sezione di Perugia, I-06123 Perugia, Italy
42
Syracuse University, Syracuse, NY 13244, USA
43
University of Minnesota, Minneapolis, MN 55455, USA
44
SUPA, University of Glasgow, Glasgow G12 8QQ, United Kingdom
45
LIGO Hanford Observatory, Richland, WA 99352, USA
46
Caltech CaRT, Pasadena, CA 91125, USA
47
Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Mikl ́os ́ut 29-33, Hungary
48
University of Florida, Gainesville, FL 32611, USA
49
Stanford University, Stanford, CA 94305, USA
50
Universit`a di Camerino, Dipartimento di Fisica, I-62032 Camerino, Italy
51
Universit`a di Padova, Dipartimento di Fisica e Astronomia, I-35131 Padova, Italy
52
INFN, Sezione di Padova, I-35131 Padova, Italy
53
Montana State University, Bozeman, MT 59717, USA
54
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, 00-716, Warsaw, Poland
55
OzGrav, University of Adelaide, Adelaide, South Australia 5005, Australia
5
56
Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universit ̈at Jena, D-07743 Jena, Germany
57
INFN, Sezione di Milano Bicocca, Gruppo Collegato di Parma, I-43124 Parma, Italy
58
Rochester Institute of Technology, Rochester, NY 14623, USA
59
Center for Interdisciplinary Exploration & Research in Astrophysics (CIERA), Northwestern University, Evanston, IL 60208, USA
60
INFN, Sezione di Genova, I-16146 Genova, Italy
61
RRCAT, Indore, Madhya Pradesh 452013, India
62
Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
63
OzGrav, University of Western Australia, Crawley, Western Australia 6009, Australia
64
Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
65
Artemis, Universit ́e Cˆote d’Azur, Observatoire Cˆote d’Azur, CNRS, CS 34229, F-06304 Nice Cedex 4, France
66
Physik-Institut, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
67
Univ Rennes, CNRS, Institut FOTON - UMR6082, F-3500 Rennes, France
68
Cardiff University, Cardiff CF24 3AA, United Kingdom
69
Washington State University, Pullman, WA 99164, USA
70
University of Oregon, Eugene, OR 97403, USA
71
Laboratoire Kastler Brossel, Sorbonne Universit ́e, CNRS, ENS-Universit ́e PSL, Coll`ege de France, F-75005 Paris, France
72
Universit`a degli Studi di Urbino ’Carlo Bo,’ I-61029 Urbino, Italy
73
INFN, Sezione di Firenze, I-50019 Sesto Fiorentino, Firenze, Italy
74
Astronomical Observatory Warsaw University, 00-478 Warsaw, Poland
75
VU University Amsterdam, 1081 HV Amsterdam, The Netherlands
76
University of Maryland, College Park, MD 20742, USA
77
School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
78
Universit ́e Claude Bernard Lyon 1, F-69622 Villeurbanne, France
79
Universit`a di Napoli ’Federico II,’ Complesso Universitario di Monte S.Angelo, I-80126 Napoli, Italy
80
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
81
Dipartimento di Fisica, Universit`a degli Studi di Genova, I-16146 Genova, Italy
82
RESCEU, University of Tokyo, Tokyo, 113-0033, Japan.
83
Tsinghua University, Beijing 100084, China
84
Texas Tech University, Lubbock, TX 79409, USA
85
The University of Mississippi, University, MS 38677, USA
86
Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, I-00184 Roma, Italyrico Fermi, I-00184 Roma, Italy
87
The Pennsylvania State University, University Park, PA 16802, USA
88
National Tsing Hua University, Hsinchu City, 30013 Taiwan, Republic of China
89
Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia
90
Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario M5S 3H8, Canada
91
University of Chicago, Chicago, IL 60637, USA
92
The Chinese University of Hong Kong, Shatin, NT, Hong Kong
93
Seoul National University, Seoul 08826, South Korea
94
Pusan National University, Busan 46241, South Korea
95
Carleton College, Northfield, MN 55057, USA
96
INAF, Osservatorio Astronomico di Padova, I-35122 Padova, Italy
97
INFN, Trento Institute for Fundamental Physics and Applications, I-38123 Povo, Trento, Italy
98
OzGrav, University of Melbourne, Parkville, Victoria 3010, Australia
99
Columbia University, New York, NY 10027, USA
100
Universitat de les Illes Balears, IAC3—IEEC, E-07122 Palma de Mallorca, Spain
101
Universit ́e Libre de Bruxelles, Brussels 1050, Belgium
102
Sonoma State University, Rohnert Park, CA 94928, USA
103
Departamento de Matem ́aticas, Universitat de Val`encia, E-46100 Burjassot, Val`encia, Spain
104
University of Rhode Island, Kingston, RI 02881, USA
105
The University of Texas Rio Grande Valley, Brownsville, TX 78520, USA
106
Bellevue College, Bellevue, WA 98007, USA
107
MTA-ELTE Astrophysics Research Group, Institute of Physics, E ̈otv ̈os University, Budapest 1117, Hungary
108
Institute for Plasma Research, Bhat, Gandhinagar 382428, India
109
The University of Sheffield, Sheffield S10 2TN, United Kingdom
6
110
IGFAE, Campus Sur, Universidade de Santiago de Compostela, 15782 Spain
111
Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Universit`a di Parma, I-43124 Parma, Italy
112
California State University, Los Angeles, 5151 State University Dr, Los Angeles, CA 90032, USA
113
Universit`a di Trento, Dipartimento di Fisica, I-38123 Povo, Trento, Italy
114
Universit`a di Roma ’La Sapienza,’ I-00185 Roma, Italy
115
Colorado State University, Fort Collins, CO 80523, USA
116
Kenyon College, Gambier, OH 43022, USA
117
Christopher Newport University, Newport News, VA 23606, USA
118
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
119
Observatori Astron`omic, Universitat de Val`encia, E-46980 Paterna, Val`encia, Spain
120
School of Mathematics, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
121
Institute Of Advanced Research, Gandhinagar 382426, India
122
Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
123
University of Szeged, D ́om t ́er 9, Szeged 6720, Hungary
124
Tata Institute of Fundamental Research, Mumbai 400005, India
125
INAF, Osservatorio Astronomico di Capodimonte, I-80131, Napoli, Italy
126
University of Michigan, Ann Arbor, MI 48109, USA
127
American University, Washington, D.C. 20016, USA
128
GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam, Science Park
904, 1098 XH Amsterdam, The Netherlands
129
Delta Institute for Theoretical Physics, Science Park 904, 1090 GL Amsterdam, The Netherlands
130
Directorate of Construction, Services & Estate Management, Mumbai 400094 India
131
University of Bia lystok, 15-424 Bia lystok, Poland
132
King’s College London, University of London, London WC2R 2LS, United Kingdom
133
University of Southampton, Southampton SO17 1BJ, United Kingdom
134
University of Washington Bothell, Bothell, WA 98011, USA
135
Institute of Applied Physics, Nizhny Novgorod, 603950, Russia
136
Ewha Womans University, Seoul 03760, South Korea
137
Inje University Gimhae, South Gyeongsang 50834, South Korea
138
National Institute for Mathematical Sciences, Daejeon 34047, South Korea
139
Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
140
Universit ̈at Hamburg, D-22761 Hamburg, Germany
141
Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands
142
NCBJ, 05-400
́
Swierk-Otwock, Poland
143
Institute of Mathematics, Polish Academy of Sciences, 00656 Warsaw, Poland
144
Cornell University, Ithaca, NY 14850, USA
145
Hillsdale College, Hillsdale, MI 49242, USA
146
Hanyang University, Seoul 04763, South Korea
147
Korea Astronomy and Space Science Institute, Daejeon 34055, South Korea
148
NASA Marshall Space Flight Center, Huntsville, AL 35811, USA
149
Dipartimento di Matematica e Fisica, Universit`a degli Studi Roma Tre, I-00146 Roma, Italy
150
INFN, Sezione di Roma Tre, I-00146 Roma, Italy
151
ESPCI, CNRS, F-75005 Paris, France
152
OzGrav, Swinburne University of Technology, Hawthorn VIC 3122, Australia
153
University of Portsmouth, Portsmouth, PO1 3FX, United Kingdom
154
Southern University and A&M College, Baton Rouge, LA 70813, USA
155
College of William and Mary, Williamsburg, VA 23187, USA
156
Centre Scientifique de Monaco, 8 quai Antoine Ier, MC-98000, Monaco
157
Indian Institute of Technology Madras, Chennai 600036, India
158
INFN Sezione di Torino, Via P. Giuria 1, I-10125 Torino, Italy
159
Institut des Hautes Etudes Scientifiques, F-91440 Bures-sur-Yvette, France
160
IISER-Kolkata, Mohanpur, West Bengal 741252, India
161
Whitman College, 345 Boyer Avenue, Walla Walla, WA 99362 USA
162
Universit ́e de Lyon, F-69361 Lyon, France
7
163
Hobart and William Smith Colleges, Geneva, NY 14456, USA
164
Janusz Gil Institute of Astronomy, University of Zielona G ́ora, 65-265 Zielona G ́ora, Poland
165
University of Washington, Seattle, WA 98195, USA
166
SUPA, University of the West of Scotland, Paisley PA1 2BE, United Kingdom
167
Indian Institute of Technology, Gandhinagar Ahmedabad Gujarat 382424, India
168
Universit ́e de Montr ́eal/Polytechnique, Montreal, Quebec H3T 1J4, Canada
169
Indian Institute of Technology Hyderabad, Sangareddy, Khandi, Telangana 502285, India
170
International Institute of Physics, Universidade Federal do Rio Grande do Norte, Natal RN 59078-970, Brazil
171
Villanova University, 800 Lancaster Ave, Villanova, PA 19085, USA
172
Andrews University, Berrien Springs, MI 49104, USA
173
Max Planck Institute for Gravitationalphysik (Albert Einstein Institute), D-14476 Potsdam-Golm, Germany
174
Universit`a di Siena, I-53100 Siena, Italy
175
Trinity University, San Antonio, TX 78212, USA
176
Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
177
Department of Physics, University of Texas, Austin, TX 78712, USA
(Dated: March 12, 2019)
ABSTRACT
Advanced LIGO’s second observing run (O2), conducted from November 30, 2016 to August 25, 2017, combined
with Advanced Virgo’s first observations in August 2017 witnessed the birth of gravitational-wave multi-messenger
astronomy. The first ever gravitational-wave detection from the coalescence of two neutron stars, GW170817, and its
gamma-ray counterpart, GRB 170817A, led to an electromagnetic follow-up of the event at an unprecedented scale.
Several teams from across the world searched for EM/neutrino counterparts to GW170817, paving the way for the
discovery of optical, X-ray, and radio counterparts. In this article, we describe the online identification of gravitational-
wave transients and the distribution of gravitational-wave alerts by the LIGO and Virgo collaborations during O2. We
also describe the gravitational-wave observables which were sent in the alerts to enable searches for their counterparts.
Finally, we give an overview of the online candidate alerts shared with observing partners during O2. Alerts were
issued for 14 candidates, six of which have been confirmed as gravitational-wave events associated with the merger of
black holes or neutron stars. Eight of the 14 alerts were issued less than an hour after data acquisition.
Deceased, February 2018.
Deceased, November 2017.
Deceased, July 2018.
8
1.
INTRODUCTION
Gravitational-wave (GW) multi-messenger astronomy
provides a unique view of the cosmos. In this paper, we
explain the procedures used during the second observing
run of the advanced ground-based gravitational-wave-
detector network to issue alerts for multi-messenger
follow-up. We also include a summary of all alerts is-
sued to observing partners and an update on the status
of candidate events.
The Advanced Laser Interferometer Gravitational-
wave Observatory (LIGO) detectors (Abbott et al. 2015)
are installed in the US at Hanford, WA and Livingston,
LA while the Advanced Virgo detector (Acernese et al.
2015) is located in Cascina, Italy near Pisa. The detec-
tors use a modified Michelson laser interferometer de-
sign to measure GW strain. A passing GW causes a
differential length change in the detector arms, produc-
ing interference of the laser beams at the beam splitter,
and giving an optical readout proportional to the GW
strain.
In September 2015 the two Advanced LIGO detec-
tors began their first observing run (O1), lasting four
months.
The first direct detection of gravitational
waves, GW150914, from the coalescence of binary black
holes (BBH; Abbott et al. 2016b) marked the beginning
of gravitational-wave (GW) astronomy. Two additional
BBH merger signals, GW151012
1
(Abbott et al. 2016c)
and GW151226 (Abbott et al. 2016d), were identified
before the end of O1. Following hardware and soft-
ware upgrades, the second Advanced LIGO observing
run (O2) began on 30 November 2016. Advanced Virgo
joined the network in August 2017 for the last month of
data acquisition.
A number of additional BBH coalescences were de-
tected in O2 (see Abbott et al. 2017a,b,c, 2018a). Fur-
thermore, on August 17, 2017, at 12:41:04 UTC a bi-
nary neutron star (BNS) inspiral signal (GW170817)
was observed (Abbott et al. 2017d). Less than two sec-
onds later, the short gamma-ray burst (sGRB) GRB
170817A was detected by two space-based instruments:
the Gamma-ray Burst Monitor (GBM) onboard
Fermi
(Goldstein et al. 2017), and the spectrometer anti-
coincidence shield (SPI-ACS) onboard
INTEGRAL
(Savchenko et al. 2017). This joint observation pro-
vided the first direct evidence that at least a fraction of
sGRBs have a BNS system as progenitor, as predicted
by Eichler et al. 1989; Paczynski 1986, 1991. Short
1
The candidate LVT151012 has been confirmed as a
gravitational-wave event, now called, GW151012 (Abbott et al.
2018a).
GRBs are typically expected to result in a long lasting,
multi-wavelength afterglow emission in X-ray, optical,
and radio bands (for a review see Nakar 2007; Berger
2014; D’Avanzo 2015).
The extensive electromagnetic (EM) observational
campaign using the well-constrained, three-detector
skymap from the detection of GW170817 led to the
discovery of an optical transient (SSS17a/AT 2017gfo)
in the host galaxy NGC 4993 (Coulter et al. 2017); the
counterpart was also detected in ultraviolet and infrared
wavelengths (Abbott et al. 2017e). Photometric and
spectroscopic observations of the counterpart support
the hypothesis that BNS mergers are sites of r-process
nucleosynthesis of heavy elements that decay, thus pow-
ering so-called kilonova emission in UV/optical/NIR
(see, e.g., Li & Paczy ́nski 1998; Kulkarni 2005; Tanaka
2016; Metzger 2017; Kasen et al. 2017; Villar et al. 2017;
Evans et al. 2017; Pian et al. 2017). Several days after
the BNS merger, X-ray (Troja et al. 2017) and radio
(Hallinan et al. 2017a) emissions were also discovered
at the transient’s position (see also Abbott et al. 2017e
and references therein). These observations are consis-
tent with the expected interaction of merger ejecta with
the interstellar medium on timescales up to years (see,
e.g., Nakar & Piran 2011; Hotokezaka & Piran 2015;
Hotokezaka et al. 2016). Data from exhaustive followup
in X-ray, radio and optical covering almost one year
allowed detailed modeling of emission mechanisms, such
as an off-axis structured jet (see, e.g., D’Avanzo et al.
2018; Dobie et al. 2018; Margutti et al. 2018; Mooley
et al. 2018a; Ruan et al. 2018). The degeneracy among
the various models has been broken with late-time radio
observations that support the emergence of a relativistic
jet from the BNS merger (Ghirlanda et al. 2018; Mooley
et al. 2018b).
Besides compact binary mergers, other transient GW
sources that may be observed by ground-based interfer-
ometers include the core-collapse of massive stars, which
are expected to emit GWs if some asymmetry is present
(see Kotake et al. 2006; Ott 2009; Gossan et al. 2016 for
an overview). The core-collapse of a massive star is ac-
companied by supernova (SN) emissions, starting in the
ultraviolet and soft X-ray bands from the shock break-
out of the stellar surface (see, e.g., Falk & Arnett 1977;
Klein & Chevalier 1978; Andreoni et al. 2016; Ensman &
Burrows 1992), and followed by emissions at optical and
radio frequencies that typically start from days to weeks
after the collapse and last for weeks up to years. Neu-
trinos are also emitted during core-collapse supernovae
as confirmed on February 23, 1987 when MeV neutrinos
were detected from SN 1987A in the Large Magellanic
Cloud (at a distance of
50 kpc) by the Kamiokande-II
9
(Hirata et al. 1987) and the Irvine-Michigan-Brookhaven
(Bionta et al. 1987) neutrino detectors, a few hours be-
fore its optical counterpart was discovered. In addition,
GRBs and SNe are expected to produce relativistic out-
flows in which particles (protons and nuclei) can be ac-
celerated and produce high-energy neutrinos by inter-
acting with the surrounding medium and radiation (see,
e.g., Murase 2018).
One further class of transient GW sources are magne-
tars, i.e., rotating NSs with very intense magnetic fields
(
10
15
G). Theoretical models predict that when these
stars undergo starquakes, asymmetric strains can tem-
porarily alter the geometry of the star and GWs could
be emitted (see, e.g., Corsi & Owen 2011). Electro-
magnetic phenomena possibly associated with magnetar
starquakes include Soft Gamma Repeaters (SGRs) and
Anomalous X-ray Pulsars (AXPs), sources that sporad-
ically emit short bursts of gamma-rays and X-rays (see
Mereghetti 2008 for a review). Starquakes can also cause
radio/X-ray pulsar glitches: sudden increases in the ro-
tational frequency of a highly magnetized, rotating NS
(pulsar) followed by exponential decays, which bring the
pulsar rotational frequency back down to its initial value
(see, e.g., Espinoza et al. 2011).
During O1 and O2, extensive EM observing cam-
paigns searched for counterparts to GW candidates iden-
tified in low-latency.
Significant improvements were
made between these two observing runs regarding the
data analysis software and source modeling, allowing
important additional information to be distributed in
low-latency during O2. For CBC events, 3D sky local-
ization maps were released, providing information about
the direction and the luminosity distance of the source
(Singer et al. 2016a), while in O1, only 2D sky local-
ization maps were provided, without distance informa-
tion. During O2, probabilities that at least one low-
mass object was present in the coalescing binary system
and that tidally disrupted material formed a massive
accretion disk around the merged object were reported.
This information is useful in assessing the likelihood that
a merger could power an EM transient (Foucart 2012;
Pannarale & Ohme 2014).
During O1 and the first part of O2, with the GW
network formed only by the two Advanced LIGO inter-
ferometers, sources were typically localized in sky areas
ranging from a few hundreds to several thousands of
square degrees (see, e.g., Abbott et al. 2016e,d, 2017a).
Improvements in localization areas were made since Ad-
vanced Virgo joined the gravitational-wave detector net-
work starting August 1, 2017. For instance, GW170814
and GW170817 were localized by the three detector net-
work within a few tens of square degrees, see Abbott
et al. 2017b,d.
Jointly observing the same event in both gravitational
waves and electromagnetic radiation provides comple-
mentary insights into the progenitor and its local envi-
ronment. The GW signal is key to determining several
physical properties of the source such as the masses and
system properties (inclination, orientation, spin, etc.).
The EM counterpart provides information about ra-
dioactive decay, shocks, the emission mechanism of the
central engine, magnetic fields, beaming and also probes
the surrounding environment of the source (see for in-
stance Berger 2014). The detection of an EM counter-
part also can give precise localization and lead to the
identification of the host galaxy of the source. The
distance estimated from the GW data combined with
the measured redshift of the host galaxy enables mea-
surement of the Hubble constant (Schutz 1986; Holz &
Hughes 2005; Nissanke et al. 2010, 2013a; Abbott et al.
2017f; Seto & Kyutoku 2018; Hotokezaka et al. 2018;
Vitale & Chen 2018). Precise measurements of the host
galaxy distance and the binary inclination given by the
EM observations can be used to reduce the degeneracy in
the GW parameter estimation (see, e.g., Guidorzi et al.
2017; Cantiello et al. 2018; Mandel 2018; Chen et al.
2018). Furthermore, the detection of an EM counterpart
may increase the confidence in the astrophysical origin
of a weak GW signal (Kochanek & Piran 1993). It also
provides constraints on the relative merger rates of the
two classes of compact binaries (BNS and NS-BH), on
the beaming angle of sGRBs, and the NS equation of
state (Abadie et al. 2010; Chen & Holz 2013; Pannarale
& Ohme 2014; Clark et al. 2015; Dominik et al. 2015;
Regimbau et al. 2015; Siellez et al. 2016; Radice et al.
2018). Finally, joint GW and EM observations can pro-
vide constraints on fundamental physics (Abbott et al.
2017g).
In this paper, we describe the identification of GW
transients and the distribution of GW alerts performed
during O2 by the LIGO and Virgo collaborations. We
also detail the GW event information shared with the
astronomy community and give an overview of the EM
follow-up strategies.
In section 2 we present an overview of the online GW
analysis, with a description of the online analysis detec-
tion pipelines, the vetting and the approval processes
for potential GW events. In section 3 we summarize
the GW alerts that were distributed during O2 and
the properties of the gravitational wave candidates af-
ter the offline analysis. We describe the information
that was shared with astronomers including how this
was used during the electromagnetic/neutrino follow-up