arXiv:1510.03621v1 [astro-ph.IM] 13 Oct 2015
First low frequency all-sky search for continuous gravitat
ional wave signals
J. Aasi,
1
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
,
8
P. Addesso,
9
R. X. Adhikari,
1
V. B. Adya,
10
C. Affeldt,
10
M. Agathos,
11
K. Agatsuma,
11
N. Aggarwal,
12
O. D. Aguiar,
13
A. Ain,
14
P. Ajith,
15
B. Allen,
10
,
16
,
17
A. Allocca,
18
,
19
D. V. Amariutei,
5
M. Andersen,
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
G. Ashton,
24
S. M. Aston,
6
P. Astone,
25
P. Aufmuth,
17
C. Aulbert,
10
S. Babak,
26
P. T. Baker,
27
F. Baldaccini,
28
,
29
G. Ballardin,
30
S. W. Ballmer,
31
J. C. Barayoga,
1
S. E. Barclay,
32
B. C. Barish,
1
D. Barker,
33
F. Barone,
3
,
4
B. Barr,
32
L. Barsotti,
12
M. Barsuglia,
34
J. Bartlett,
33
M. A. Barton,
33
I. Bartos,
35
R. Bassiri,
20
A. Basti,
36
,
19
J. C. Batch,
33
C. Baune,
10
V. Bavigadda,
30
B. Behnke,
26
M. Bejger,
37
C. Belczynski,
38
A. S. Bell,
32
B. K. Berger,
1
J. Bergman,
33
G. Bergmann,
10
C. P. L. Berry,
39
D. Bersanetti,
40
,
41
A. Bertolini,
11
J. Betzwieser,
6
S. Bhagwat,
31
R. Bhandare,
42
I. A. Bilenko,
43
G. Billingsley,
1
J. Birch,
6
R. Birney,
44
S. Biscans,
12
M. Bitossi,
30
C. Biwer,
31
M. A. Bizouard,
23
J. K. Blackburn,
1
C. D. Blair,
45
D. Blair,
45
S. Bloemen,
11
,
46
O. Bock,
10
T. P. Bodiya,
12
M. Boer,
47
G. Bogaert,
47
P. Bojtos,
48
C. Bond,
39
F. Bondu,
49
R. Bonnand,
8
R. Bork,
1
M. Born,
10
V. Boschi,
19
,
36
Sukanta Bose,
14
,
50
C. Bradaschia,
19
P. R. Brady,
16
V. B. Braginsky,
43
M. Branchesi,
51
,
52
V. Branco,
53
J. E. Brau,
54
T. Briant,
55
A. Brillet,
47
M. Brinkmann,
10
V. Brisson,
23
P. Brockill,
16
A. F. Brooks,
1
D. A. Brown,
31
D. Brown,
5
D. D. Brown,
39
N. M. Brown,
12
C. C. Buchanan,
2
A. Buikema,
12
T. Bulik,
38
H. J. Bulten,
56
,
11
A. Buonanno,
57
,
26
D. Buskulic,
8
C. Buy,
34
R. L. Byer,
20
L. Cadonati,
58
G. Cagnoli,
59
J. Calder ́on Bustillo,
60
E. Calloni,
61
,
4
J. B. Camp,
62
K. C. Cannon,
63
J. Cao,
64
C. D. Capano,
10
E. Capocasa,
34
F. Carbognani,
30
S. Caride,
65
J. Casanueva Diaz,
23
C. Casentini,
66
,
67
S. Caudill,
16
M. Cavagli`a,
21
F. Cavalier,
23
R. Cavalieri,
30
C. Celerier,
20
G. Cella,
19
C. Cepeda,
1
L. Cerboni Baiardi,
51
,
52
G. Cerretani,
36
,
19
E. Cesarini,
66
,
67
R. Chakraborty,
1
T. Chalermsongsak,
1
S. J. Chamberlin,
16
S. Chao,
68
P. Charlton,
69
E. Chassande-Mottin,
34
X. Chen,
55
,
45
Y. Chen,
70
C. Cheng,
68
A. Chincarini,
41
A. Chiummo,
30
H. S. Cho,
71
M. Cho,
57
J. H. Chow,
72
N. Christensen,
73
Q. Chu,
45
S. Chua,
55
S. Chung,
45
G. Ciani,
5
F. Clara,
33
J. A. Clark,
58
F. Cleva,
47
E. Coccia,
66
,
74
P.-F. Cohadon,
55
A. Colla,
75
,
25
C. G. Collette,
76
M. Colombini,
29
M. Constancio Jr.,
13
A. Conte,
75
,
25
L. Conti,
77
D. Cook,
33
T. R. Corbitt,
2
N. Cornish,
27
A. Corsi,
78
C. A. Costa,
13
M. W. Coughlin,
73
S. B. Coughlin,
7
J.-P. Coulon,
47
S. T. Countryman,
35
P. Couvares,
31
D. M. Coward,
45
M. J. Cowart,
6
D. C. Coyne,
1
R. Coyne,
78
K. Craig,
32
J. D. E. Creighton,
16
J. Cripe,
2
S. G. Crowder,
79
A. Cumming,
32
L. Cunningham,
32
E. Cuoco,
30
T. Dal Canton,
10
M. D. Damjanic,
10
S. L. Danilishin,
45
S. D’Antonio,
67
K. Danzmann,
17
,
10
N. S. Darman,
80
V. Dattilo,
30
I. Dave,
42
H. P. Daveloza,
81
M. Davier,
23
G. S. Davies,
32
E. J. Daw,
82
R. Day,
30
D. DeBra,
20
G. Debreczeni,
83
J. Degallaix,
59
M. De Laurentis,
61
,
4
S. Del ́eglise,
55
W. Del Pozzo,
39
T. Denker,
10
T. Dent,
10
H. Dereli,
47
V. Dergachev,
1
R. De Rosa,
61
,
4
R. T. DeRosa,
2
R. DeSalvo,
9
S. Dhurandhar,
14
M. C. D ́ıaz,
81
L. Di Fiore,
4
M. Di Giovanni,
75
,
25
A. Di Lieto,
36
,
19
I. Di Palma,
26
A. Di Virgilio,
19
G. Dojcinoski,
84
V. Dolique,
59
E. Dominguez,
85
F. Donovan,
12
K. L. Dooley,
1
,
21
S. Doravari,
6
R. Douglas,
32
T. P. Downes,
16
M. Drago,
86
,
87
R. W. P. Drever,
1
J. C. Driggers,
1
Z. Du,
64
M. Ducrot,
8
S. E. Dwyer,
33
T. B. Edo,
82
M. C. Edwards,
73
M. Edwards,
7
A. Effler,
2
H.-B. Eggenstein,
10
P. Ehrens,
1
J. M. Eichholz,
5
S. S. Eikenberry,
5
R. C. Essick,
12
T. Etzel,
1
M. Evans,
12
T. M. Evans,
6
R. Everett,
88
M. Factourovich,
35
V. Fafone,
66
,
67
,
74
S. Fairhurst,
7
Q. Fang,
45
S. Farinon,
41
B. Farr,
89
W. M. Farr,
39
M. Favata,
84
M. Fays,
7
H. Fehrmann,
10
M. M. Fejer,
20
D. Feldbaum,
5
,
6
I. Ferrante,
36
,
19
E. C. Ferreira,
13
F. Ferrini,
30
F. Fidecaro,
36
,
19
I. Fiori,
30
R. P. Fisher,
31
R. Flaminio,
59
J.-D. Fournier,
47
S. Franco,
23
S. Frasca,
75
,
25
F. Frasconi,
19
M. Frede,
10
Z. Frei,
48
A. Freise,
39
R. Frey,
54
T. T. Fricke,
10
P. Fritschel,
12
V. V. Frolov,
6
P. Fulda,
5
M. Fyffe,
6
H. A. G. Gabbard,
21
J. R. Gair,
90
L. Gammaitoni,
28
,
29
S. G. Gaonkar,
14
F. Garufi,
61
,
4
A. Gatto,
34
N. Gehrels,
62
G. Gemme,
41
B. Gendre,
47
E. Genin,
30
A. Gennai,
19
L.
́
A. Gergely,
91
V. Germain,
8
A. Ghosh,
15
S. Ghosh,
11
,
46
J. A. Giaime,
2
,
6
K. D. Giardina,
6
A. Giazotto,
19
J. R. Gleason,
5
E. Goetz,
10
,
65
R. Goetz,
5
L. Gondan,
48
G. Gonz ́alez,
2
J. Gonzalez,
36
,
19
A. Gopakumar,
92
N. A. Gordon,
32
M. L. Gorodetsky,
43
S. E. Gossan,
70
M. Gosselin,
30
S. Goßler,
10
R. Gouaty,
8
C. Graef,
32
P. B. Graff,
62
,
57
M. Granata,
59
A. Grant,
32
S. Gras,
12
C. Gray,
33
G. Greco,
51
,
52
P. Groot,
46
H. Grote,
10
K. Grover,
39
S. Grunewald,
26
G. M. Guidi,
51
,
52
C. J. Guido,
6
X. Guo,
64
A. Gupta,
14
M. K. Gupta,
93
K. E. Gushwa,
1
E. K. Gustafson,
1
R. Gustafson,
65
J. J. Hacker,
22
B. R. Hall,
50
E. D. Hall,
1
D. Hammer,
16
G. Hammond,
32
M. Haney,
92
M. M. Hanke,
10
J. Hanks,
33
C. Hanna,
88
M. D. Hannam,
7
J. Hanson,
6
T. Hardwick,
2
J. Harms,
51
,
52
G. M. Harry,
94
I. W. Harry,
26
M. J. Hart,
32
M. T. Hartman,
5
C.-J. Haster,
39
K. Haughian,
32
A. Heidmann,
55
M. C. Heintze,
5
,
6
H. Heitmann,
47
P. Hello,
23
G. Hemming,
30
M. Hendry,
32
I. S. Heng,
32
J. Hennig,
32
A. W. Heptonstall,
1
M. Heurs,
10
S. Hild,
32
D. Hoak,
95
K. A. Hodge,
1
J. Hoelscher-Obermaier,
17
D. Hofman,
59
S. E. Hollitt,
96
K. Holt,
6
P. Hopkins,
7
D. J. Hosken,
96
J. Hough,
32
E. A. Houston,
32
E. J. Howell,
45
Y. M. Hu,
32
S. Huang,
68
E. A. Huerta,
97
D. Huet,
23
B. Hughey,
53
S. Husa,
60
S. H. Huttner,
32
M. Huynh,
16
T. Huynh-Dinh,
6
A. Idrisy,
88
N. Indik,
10
D. R. Ingram,
33
R. Inta,
78
G. Islas,
22
2
J. C. Isler,
31
T. Isogai,
12
B. R. Iyer,
15
K. Izumi,
33
M. B. Jacobson,
1
H. Jang,
98
P. Jaranowski,
99
S. Jawahar,
100
Y. Ji,
64
F. Jim ́enez-Forteza,
60
W. W. Johnson,
2
D. I. Jones,
24
R. Jones,
32
R.J.G. Jonker,
11
L. Ju,
45
Haris K,
101
V. Kalogera,
102
S. Kandhasamy,
21
G. Kang,
98
J. B. Kanner,
1
S. Karki,
54
J. L. Karlen,
95
M. Kasprzack,
23
,
30
E. Katsavounidis,
12
W. Katzman,
6
S. Kaufer,
17
T. Kaur,
45
K. Kawabe,
33
F. Kawazoe,
10
F. K ́ef ́elian,
47
M. S. Kehl,
63
D. Keitel,
10
D. B. Kelley,
31
W. Kells,
1
J. Kerrigan,
95
J. S. Key,
81
F. Y. Khalili,
43
Z. Khan,
93
E. A. Khazanov,
103
N. Kijbunchoo,
33
C. Kim,
98
K. Kim,
104
N. G. Kim,
98
N. Kim,
20
Y.-M. Kim,
71
E. J. King,
96
P. J. King,
33
D. L. Kinzel,
6
J. S. Kissel,
33
S. Klimenko,
5
J. T. Kline,
16
S. M. Koehlenbeck,
10
K. Kokeyama,
2
S. Koley,
11
V. Kondrashov,
1
M. Korobko,
10
W. Z. Korth,
1
I. Kowalska,
38
D. B. Kozak,
1
V. Kringel,
10
B. Krishnan,
10
A. Kr ́olak,
105
,
106
C. Krueger,
17
G. Kuehn,
10
A. Kumar,
93
P. Kumar,
63
L. Kuo,
68
A. Kutynia,
105
B. D. Lackey,
31
M. Landry,
33
B. Lantz,
20
P. D. Lasky,
80
,
107
A. Lazzarini,
1
C. Lazzaro,
58
,
77
P. Leaci,
26
,
75
S. Leavey,
32
E. O. Lebigot,
34
,
64
C. H. Lee,
71
H. K. Lee,
104
H. M. Lee,
108
J. Lee,
104
J. P. Lee,
12
M. Leonardi,
86
,
87
J. R. Leong,
10
N. Leroy,
23
N. Letendre,
8
Y. Levin,
107
B. M. Levine,
33
J. B. Lewis,
1
T. G. F. Li,
1
A. Libson,
12
A. C. Lin,
20
T. B. Littenberg,
102
N. A. Lockerbie,
100
V. Lockett,
22
D. Lodhia,
39
J. Logue,
32
A. L. Lombardi,
95
M. Lorenzini,
74
V. Loriette,
109
M. Lormand,
6
G. Losurdo,
52
J. D. Lough,
31
,
10
M. J. Lubinski(Ski),
33
H. L ̈uck,
17
,
10
A. P. Lundgren,
10
J. Luo,
73
R. Lynch,
12
Y. Ma,
45
J. Macarthur,
32
E. P. Macdonald,
7
T. MacDonald,
20
B. Machenschalk,
10
M. MacInnis,
12
D. M. Macleod,
2
D. X. Madden-Fong,
20
F. Maga ̃na-Sandoval,
31
R. M. Magee,
50
M. Mageswaran,
1
E. Majorana,
25
I. Maksimovic,
109
V. Malvezzi,
66
,
67
N. Man,
47
I. Mandel,
39
V. Mandic,
79
V. Mangano,
75
,
25
,
32
N. M. Mangini,
95
G. L. Mansell,
72
M. Manske,
16
M. Mantovani,
30
F. Marchesoni,
110
,
29
F. Marion,
8
S. M ́arka,
35
Z. M ́arka,
35
A. S. Markosyan,
20
E. Maros,
1
F. Martelli,
51
,
52
L. Martellini,
47
I. W. Martin,
32
R. M. Martin,
5
D. V. Martynov,
1
J. N. Marx,
1
K. Mason,
12
A. Masserot,
8
T. J. Massinger,
31
S. Mastrogiovanni,
75
,
25
F. Matichard,
12
L. Matone,
35
N. Mavalvala,
12
N. Mazumder,
50
G. Mazzolo,
10
R. McCarthy,
33
D. E. McClelland,
72
S. McCormick,
6
S. C. McGuire,
111
G. McIntyre,
1
J. McIver,
95
S. T. McWilliams,
97
D. Meacher,
47
G. D. Meadors,
10
M. Mehmet,
10
J. Meidam,
11
M. Meinders,
10
A. Melatos,
80
G. Mendell,
33
R. A. Mercer,
16
M. Merzougui,
47
S. Meshkov,
1
C. Messenger,
32
C. Messick,
88
P. M. Meyers,
79
F. Mezzani,
25
,
75
H. Miao,
39
C. Michel,
59
H. Middleton,
39
E. E. Mikhailov,
112
L. Milano,
61
,
4
J. Miller,
12
M. Millhouse,
27
Y. Minenkov,
67
J. Ming,
26
S. Mirshekari,
113
C. Mishra,
15
S. Mitra,
14
V. P. Mitrofanov,
43
G. Mitselmakher,
5
R. Mittleman,
12
B. Moe,
16
A. Moggi,
19
M. Mohan,
30
S. R. P. Mohapatra,
12
M. Montani,
51
,
52
B. C. Moore,
84
D. Moraru,
33
G. Moreno,
33
S. R. Morriss,
81
K. Mossavi,
10
B. Mours,
8
C. M. Mow-Lowry,
39
C. L. Mueller,
5
G. Mueller,
5
A. Mukherjee,
15
S. Mukherjee,
81
A. Mullavey,
6
J. Munch,
96
D. J. Murphy IV,
35
P. G. Murray,
32
A. Mytidis,
5
M. F. Nagy,
83
I. Nardecchia,
66
,
67
L. Naticchioni,
75
,
25
R. K. Nayak,
114
V. Necula,
5
K. Nedkova,
95
G. Nelemans,
11
,
46
M. Neri,
40
,
41
G. Newton,
32
T. T. Nguyen,
72
A. B. Nielsen,
10
A. Nitz,
31
F. Nocera,
30
D. Nolting,
6
M. E. N. Normandin,
81
L. K. Nuttall,
16
E. Ochsner,
16
J. O’Dell,
115
E. Oelker,
12
G. H. Ogin,
116
J. J. Oh,
117
S. H. Oh,
117
F. Ohme,
7
M. Okounkova,
70
P. Oppermann,
10
R. Oram,
6
B. O’Reilly,
6
W. E. Ortega,
85
R. O’Shaughnessy,
118
C. D. Ott,
70
D. J. Ottaway,
96
R. S. Ottens,
5
H. Overmier,
6
B. J. Owen,
78
C. T. Padilla,
22
A. Pai,
101
S. A. Pai,
42
J. R. Palamos,
54
O. Palashov,
103
C. Palomba,
25
A. Pal-Singh,
10
H. Pan,
68
Y. Pan,
57
C. Pankow,
16
F. Pannarale,
7
B. C. Pant,
42
F. Paoletti,
30
,
19
M. A. Papa,
26
,
16
H. R. Paris,
20
A. Pasqualetti,
30
R. Passaquieti,
36
,
19
D. Passuello,
19
Z. Patrick,
20
M. Pedraza,
1
L. Pekowsky,
31
A. Pele,
6
S. Penn,
119
A. Perreca,
31
M. Phelps,
32
O. Piccinni,
75
,
25
M. Pichot,
47
M. Pickenpack,
10
F. Piergiovanni,
51
,
52
V. Pierro,
9
G. Pillant,
30
L. Pinard,
59
I. M. Pinto,
9
M. Pitkin,
32
J. H. Poeld,
10
R. Poggiani,
36
,
19
A. Post,
10
J. Powell,
32
J. Prasad,
14
V. Predoi,
7
S. S. Premachandra,
107
T. Prestegard,
79
L. R. Price,
1
M. Prijatelj,
30
M. Principe,
9
S. Privitera,
26
R. Prix,
10
G. A. Prodi,
86
,
87
L. Prokhorov,
43
O. Puncken,
81
,
10
M. Punturo,
29
P. Puppo,
25
M. P ̈urrer,
7
J. Qin,
45
V. Quetschke,
81
E. A. Quintero,
1
R. Quitzow-James,
54
F. J. Raab,
33
D. S. Rabeling,
72
I. R ́acz,
83
H. Radkins,
33
P. Raffai,
48
S. Raja,
42
M. Rakhmanov,
81
P. Rapagnani,
75
,
25
V. Raymond,
26
M. Razzano,
36
,
19
V. Re,
66
,
67
C. M. Reed,
33
T. Regimbau,
47
L. Rei,
41
S. Reid,
44
D. H. Reitze,
1
,
5
F. Ricci,
75
,
25
K. Riles,
65
N. A. Robertson,
1
,
32
R. Robie,
32
F. Robinet,
23
A. Rocchi,
67
A. S. Rodger,
32
L. Rolland,
8
J. G. Rollins,
1
V. J. Roma,
54
J. D. Romano,
81
R. Romano,
3
,
4
G. Romanov,
112
J. H. Romie,
6
D. Rosi ́nska,
120
,
37
S. Rowan,
32
A. R ̈udiger,
10
P. Ruggi,
30
K. Ryan,
33
S. Sachdev,
1
T. Sadecki,
33
L. Sadeghian,
16
M. Saleem,
101
F. Salemi,
10
L. Sammut,
80
E. Sanchez,
1
V. Sandberg,
33
J. R. Sanders,
65
I. Santiago-Prieto,
32
B. Sassolas,
59
B. S. Sathyaprakash,
7
P. R. Saulson,
31
R. Savage,
33
A. Sawadsky,
17
P. Schale,
54
R. Schilling,
10
P. Schmidt,
1
R. Schnabel,
10
R. M. S. Schofield,
54
A. Sch ̈onbeck,
10
E. Schreiber,
10
D. Schuette,
10
B. F. Schutz,
7
J. Scott,
32
S. M. Scott,
72
D. Sellers,
6
D. Sentenac,
30
V. Sequino,
66
,
67
A. Sergeev,
103
G. Serna,
22
A. Sevigny,
33
D. A. Shaddock,
72
P. Shaffery,
108
S. Shah,
11
,
46
M. S. Shahriar,
102
M. Shaltev,
10
Z. Shao,
1
B. Shapiro,
20
P. Shawhan,
57
D. H. Shoemaker,
12
T. L. Sidery,
39
K. Siellez,
47
X. Siemens,
16
D. Sigg,
33
A. D. Silva,
13
D. Simakov,
10
A. Singer,
1
L. P. Singer,
62
R. Singh,
2
3
A. M. Sintes,
60
B. J. J. Slagmolen,
72
J. R. Smith,
22
N. D. Smith,
1
R. J. E. Smith,
1
E. J. Son,
117
B. Sorazu,
32
T. Souradeep,
14
A. K. Srivastava,
93
A. Staley,
35
M. Steinke,
10
J. Steinlechner,
32
S. Steinlechner,
32
D. Steinmeyer,
10
B. C. Stephens,
16
S. Steplewski,
50
S. P. Stevenson,
39
R. Stone,
81
K. A. Strain,
32
N. Straniero,
59
N. A. Strauss,
73
S. Strigin,
43
R. Sturani,
113
A. L. Stuver,
6
T. Z. Summerscales,
121
L. Sun,
80
P. J. Sutton,
7
B. L. Swinkels,
30
M. J. Szczepanczyk,
53
M. Tacca,
34
D. Talukder,
54
D. B. Tanner,
5
M. T ́apai,
91
S. P. Tarabrin,
10
A. Taracchini,
26
R. Taylor,
1
T. Theeg,
10
M. P. Thirugnanasambandam,
1
M. Thomas,
6
P. Thomas,
33
K. A. Thorne,
6
K. S. Thorne,
70
E. Thrane,
107
S. Tiwari,
74
V. Tiwari,
5
K. V. Tokmakov,
100
C. Tomlinson,
82
M. Tonelli,
36
,
19
C. V. Torres,
81
C. I. Torrie,
1
F. Travasso,
28
,
29
G. Traylor,
6
D. Trifir`o,
21
M. C. Tringali,
86
,
87
M. Tse,
12
M. Turconi,
47
D. Ugolini,
122
C. S. Unnikrishnan,
92
A. L. Urban,
16
S. A. Usman,
31
H. Vahlbruch,
10
G. Vajente,
1
G. Valdes,
81
M. Vallisneri,
70
N. van Bakel,
11
M. van Beuzekom,
11
J. F. J. van den Brand,
56
,
11
C. van den Broeck,
11
L. van der Schaaf,
11
M. V. van der Sluys,
11
,
46
J. van Heijningen,
11
A. A. van Veggel,
32
M. Vardaro,
123
,
77
S. Vass,
1
M. Vas ́uth,
83
R. Vaulin,
12
A. Vecchio,
39
G. Vedovato,
77
J. Veitch,
39
P. J. Veitch,
96
K. Venkateswara,
124
D. Verkindt,
8
F. Vetrano,
51
,
52
A. Vicer ́e,
51
,
52
J.-Y. Vinet,
47
S. Vitale,
12
T. Vo,
31
H. Vocca,
28
,
29
C. Vorvick,
33
W. D. Vousden,
39
S. P. Vyatchanin,
43
A. R. Wade,
72
M. Wade,
16
L. E. Wade IV,
16
M. Walker,
2
L. Wallace,
1
S. Walsh,
16
G. Wang,
74
H. Wang,
39
M. Wang,
39
X. Wang,
64
R. L. Ward,
72
J. Warner,
33
M. Was,
8
B. Weaver,
33
L.-W. Wei,
47
M. Weinert,
10
A. J. Weinstein,
1
R. Weiss,
12
T. Welborn,
6
L. Wen,
45
P. Weßels,
10
T. Westphal,
10
K. Wette,
10
J. T. Whelan,
118
,
10
S. E. Whitcomb,
1
D. J. White,
82
B. F. Whiting,
5
K. J. Williams,
111
L. Williams,
5
R. D. Williams,
1
A. R. Williamson,
7
J. L. Willis,
125
B. Willke,
17
,
10
M. H. Wimmer,
10
W. Winkler,
10
C. C. Wipf,
1
H. Wittel,
10
G. Woan,
32
J. Worden,
33
J. Yablon,
102
I. Yakushin,
6
W. Yam,
12
H. Yamamoto,
1
C. C. Yancey,
57
M. Yvert,
8
A. Zadro ̇zny,
105
L. Zangrando,
77
M. Zanolin,
53
J.-P. Zendri,
77
Fan Zhang,
12
L. Zhang,
1
M. Zhang,
112
Y. Zhang,
118
C. Zhao,
45
M. Zhou,
102
X. J. Zhu,
45
M. E. Zucker,
12
S. E. Zuraw,
95
and J. Zweizig
1
1
LIGO—California Institute of Technology, Pasadena, CA 911
25, 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
Cardiff University, Cardiff CF24 3AA, United Kingdom
8
Laboratoire d’Annecy-le-Vieux de Physique des Particules
(LAPP),
Universit ́e Savoie Mont Blanc, CNRS/IN2P3, F-74941 Annecy
-le-Vieux, France
9
University of Sannio at Benevento, I-82100 Benevento,
Italy and INFN, Sezione di Napoli, I-80100 Napoli, Italy
10
Albert-Einstein-Institut, Max-Planck-Institut f ̈ur Gra
vitationsphysik, D-30167 Hannover, Germany
11
Nikhef, Science Park, 1098 XG Amsterdam, The Netherlands
12
LIGO—Massachusetts Institute of Technology, Cambridge, M
A 02139, USA
13
Instituto Nacional de Pesquisas Espaciais, 12227-010 S ̃ao
Jos ́e dos Campos, SP, Brazil
14
Inter-University Centre for Astronomy and Astrophysics, P
une 411007, India
15
International Centre for Theoretical Sciences, Tata Insti
tute of Fundamental Research, Bangalore 560012, India
16
University of Wisconsin-Milwaukee, Milwaukee, WI 53201, U
SA
17
Leibniz Universit ̈at Hannover, D-30167 Hannover, Germany
18
Universit`a di Siena, I-53100 Siena, Italy
19
INFN, Sezione di Pisa, I-56127 Pisa, Italy
20
Stanford University, Stanford, CA 94305, USA
21
The University of Mississippi, University, MS 38677, USA
22
California State University Fullerton, Fullerton, CA 9283
1, USA
23
LAL, Universit ́e Paris-Sud, IN2P3/CNRS, F-91898 Orsay, Fr
ance
24
University of Southampton, Southampton SO17 1BJ, United Ki
ngdom
25
INFN, Sezione di Roma, I-00185 Roma, Italy
26
Albert-Einstein-Institut, Max-Planck-Institut f ̈ur Gra
vitationsphysik, D-14476 Golm, Germany
27
Montana State University, Bozeman, MT 59717, USA
28
Universit`a di Perugia, I-06123 Perugia, Italy
29
INFN, Sezione di Perugia, I-06123 Perugia, Italy
30
European Gravitational Observatory (EGO), I-56021 Cascin
a, Pisa, Italy
31
Syracuse University, Syracuse, NY 13244, USA
32
SUPA, University of Glasgow, Glasgow G12 8QQ, United Kingdo
m
33
LIGO Hanford Observatory, Richland, WA 99352, USA
34
APC, AstroParticule et Cosmologie, Universit ́e Paris Dide
rot,
CNRS/IN2P3, CEA/Irfu, Observatoire de Paris,
Sorbonne Paris Cit ́e, F-75205 Paris Cedex 13, France
35
Columbia University, New York, NY 10027, USA
4
36
Universit`a di Pisa, I-56127 Pisa, Italy
37
CAMK-PAN, 00-716 Warsaw, Poland
38
Astronomical Observatory Warsaw University, 00-478 Warsa
w, Poland
39
University of Birmingham, Birmingham B15 2TT, United Kingd
om
40
Universit`a degli Studi di Genova, I-16146 Genova, Italy
41
INFN, Sezione di Genova, I-16146 Genova, Italy
42
RRCAT, Indore MP 452013, India
43
Faculty of Physics, Lomonosov Moscow State University, Mos
cow 119991, Russia
44
SUPA, University of the West of Scotland, Paisley PA1 2BE, Un
ited Kingdom
45
University of Western Australia, Crawley, Western Austral
ia 6009, Australia
46
Department of Astrophysics/IMAPP, Radboud University Nij
megen,
P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
47
ARTEMIS, Universit ́e Nice-Sophia-Antipolis, CNRS and Obs
ervatoire de la Cˆote d’Azur, F-06304 Nice, France
48
MTA E ̈otv ̈os University, “Lendulet” Astrophysics Researc
h Group, Budapest 1117, Hungary
49
Institut de Physique de Rennes, CNRS, Universit ́e de Rennes
1, F-35042 Rennes, France
50
Washington State University, Pullman, WA 99164, USA
51
Universit`a degli Studi di Urbino ’Carlo Bo’, I-61029 Urbin
o, Italy
52
INFN, Sezione di Firenze, I-50019 Sesto Fiorentino, Firenz
e, Italy
53
Embry-Riddle Aeronautical University, Prescott, AZ 86301
, USA
54
University of Oregon, Eugene, OR 97403, USA
55
Laboratoire Kastler Brossel, UPMC-Sorbonne Universit ́es
, CNRS,
ENS-PSL Research University, Coll`ege de France, F-75005 P
aris, France
56
VU University Amsterdam, 1081 HV Amsterdam, The Netherland
s
57
University of Maryland, College Park, MD 20742, USA
58
Center for Relativistic Astrophysics and School of Physics
,
Georgia Institute of Technology, Atlanta, GA 30332, USA
59
Laboratoire des Mat ́eriaux Avanc ́es (LMA), IN2P3/CNRS,
Universit ́e de Lyon, F-69622 Villeurbanne, Lyon, France
60
Universitat de les Illes Balears—IEEC, E-07122 Palma de Mal
lorca, Spain
61
Universit`a di Napoli ’Federico II’, Complesso Universita
rio di Monte S.Angelo, I-80126 Napoli, Italy
62
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
63
Canadian Institute for Theoretical Astrophysics,
University of Toronto, Toronto, Ontario M5S 3H8, Canada
64
Tsinghua University, Beijing 100084, China
65
University of Michigan, Ann Arbor, MI 48109, USA
66
Universit`a di Roma Tor Vergata, I-00133 Roma, Italy
67
INFN, Sezione di Roma Tor Vergata, I-00133 Roma, Italy
68
National Tsing Hua University, Hsinchu Taiwan 300
69
Charles Sturt University, Wagga Wagga, New South Wales 2678
, Australia
70
Caltech—CaRT, Pasadena, CA 91125, USA
71
Pusan National University, Busan 609-735, Korea
72
Australian National University, Canberra, Australian Cap
ital Territory 0200, Australia
73
Carleton College, Northfield, MN 55057, USA
74
INFN, Gran Sasso Science Institute, I-67100 L’Aquila, Ital
y
75
Universit`a di Roma ’La Sapienza’, I-00185 Roma, Italy
76
University of Brussels, Brussels 1050, Belgium
77
INFN, Sezione di Padova, I-35131 Padova, Italy
78
Texas Tech University, Lubbock, TX 79409, USA
79
University of Minnesota, Minneapolis, MN 55455, USA
80
The University of Melbourne, Parkville, Victoria 3010, Aus
tralia
81
The University of Texas at Brownsville, Brownsville, TX 785
20, USA
82
The University of Sheffield, Sheffield S10 2TN, United Kingdom
83
Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Mikl ́os ́u
t 29-33, Hungary
84
Montclair State University, Montclair, NJ 07043, USA
85
Argentinian Gravitational Wave Group, Cordoba Cordoba 500
0, Argentina
86
Universit`a di Trento, Dipartimento di Fisica, I-38123 Pov
o, Trento, Italy
87
INFN, Trento Institute for Fundamental Physics and Applica
tions, I-38123 Povo, Trento, Italy
88
The Pennsylvania State University, University Park, PA 168
02, USA
89
University of Chicago, Chicago, IL 60637, USA
90
University of Cambridge, Cambridge CB2 1TN, United Kingdom
91
University of Szeged, D ́om t ́er 9, Szeged 6720, Hungary
92
Tata Institute for Fundamental Research, Mumbai 400005, In
dia
93
Institute for Plasma Research, Bhat, Gandhinagar 382428, I
ndia
94
American University, Washington, D.C. 20016, USA
5
95
University of Massachusetts-Amherst, Amherst, MA 01003, U
SA
96
University of Adelaide, Adelaide, South Australia 5005, Au
stralia
97
West Virginia University, Morgantown, WV 26506, USA
98
Korea Institute of Science and Technology Information, Dae
jeon 305-806, Korea
99
University of Bia Lystok, 15-424 Bia Lystok, Poland
100
SUPA, University of Strathclyde, Glasgow G1 1XQ, United Kin
gdom
101
IISER-TVM, CET Campus, Trivandrum Kerala 695016, India
102
Northwestern University, Evanston, IL 60208, USA
103
Institute of Applied Physics, Nizhny Novgorod, 603950, Rus
sia
104
Hanyang University, Seoul 133-791, Korea
105
NCBJ, 05-400
́
Swierk-Otwock, Poland
106
IM-PAN, 00-956 Warsaw, Poland
107
Monash University, Victoria 3800, Australia
108
Seoul National University, Seoul 151-742, Korea
109
ESPCI, CNRS, F-75005 Paris, France
110
Universit`a di Camerino, Dipartimento di Fisica, I-62032 C
amerino, Italy
111
Southern University and A&M College, Baton Rouge, LA 70813,
USA
112
College of William and Mary, Williamsburg, VA 23187, USA
113
Instituto de F ́ısica Te ́orica, University Estadual Paulis
ta/ICTP South
American Institute for Fundamental Research, S ̃ao Paulo SP
01140-070, Brazil
114
IISER-Kolkata, Mohanpur, West Bengal 741252, India
115
Rutherford Appleton Laboratory, HSIC, Chilton, Didcot, Ox
on OX11 0QX, United Kingdom
116
Whitman College, 280 Boyer Ave, Walla Walla, WA 9936, USA
117
National Institute for Mathematical Sciences, Daejeon 305
-390, Korea
118
Rochester Institute of Technology, Rochester, NY 14623, US
A
119
Hobart and William Smith Colleges, Geneva, NY 14456, USA
120
Institute of Astronomy, 65-265 Zielona G ́ora, Poland
121
Andrews University, Berrien Springs, MI 49104, USA
122
Trinity University, San Antonio, TX 78212, USA
123
Universit`a di Padova, Dipartimento di Fisica e Astronomia
, I-35131 Padova, Italy
124
University of Washington, Seattle, WA 98195, USA and
125
Abilene Christian University, Abilene, TX 79699, USA
In this paper we present the results of the first low frequency
all-sky search of continuous gravi-
tational wave signals conducted on Virgo VSR2 and VSR4 data.
The search covered the full sky, a
frequency range between 20 Hz and 128 Hz with a range of spin-d
own between
−
1
.
0
×
10
−
10
Hz/s
and +1
.
5
×
10
−
11
Hz/s, and was based on a hierarchical approach. The starting
point was a set
of short Fast Fourier Transforms (FFT), of length 8192 secon
ds, built from the calibrated strain
data. Aggressive data cleaning, both in the time and frequen
cy domains, has been done in order to
remove, as much as possible, the effect of disturbances of ins
trumental origin. On each dataset a
number of candidates has been selected, using the Frequency
Hough transform in an incoherent step.
Only coincident candidates among VSR2 and VSR4 have been exa
mined in order to strongly reduce
the false alarm probability, and the most significant candid
ates have been selected. The criteria we
have used for candidate selection and for the coincidence st
ep greatly reduce the harmful effect of
large instrumental artifacts. Selected candidates have be
en subject to a follow-up by constructing a
new set of longer FFTs followed by a further incoherent analy
sis, still based on the FrequencyHough
transform. No evidence for continuous gravitational wave s
ignals was found, therefore we have set a
population-based joint VSR2-VSR4 90% confidence level uppe
r limit on the dimensionless gravita-
tional wave strain in the frequency range between 20 Hz and 12
8 Hz. This is the first all-sky search
for continuous gravitational waves conducted at frequenci
es below 50 Hz. We set upper limits in
the range between about 10
−
24
and 2
×
10
−
23
at most frequencies. Our upper limits on signal strain
show an improvement of up to a factor of
∼
2 with respect to the results of previous all-sky searches
at frequencies below 80 Hz.
PACS numbers: 04.80Nn,95.55Ym, 97.60Gb, 07.05Kf
I. INTRODUCTION
Continuous gravitational wave signals (CW) emitted
by asymmetric spinning neutron stars are among the
sources currently sought in the data of interferometric
gravitational wave detectors. The search for signals emit-
ted by spinning neutron stars with no electromagnetic
counterpart requires the exploration of a large portion
of the source parameter space, consisting of the source
position, signal frequency and signal frequency time-
derivative (spin-down). This kind of search, called all-
sky, cannot be based on fully coherent methods, as in
6
targeted searches for known pulsars, see e.g. [1, 2], be-
cause of the huge computational resources that would be
required.
For this reason various hierachical analysis pipelines,
based on the alternation of coherent and incoherent steps,
have been developed [3], [4], [5], [6], [7]. They allow us
to dramatically reduce the computational burden of the
analysis, at the cost of a small sensitivity loss. In this
paper we present the results of the first all-sky search for
CW signals using the data of Virgo science runs VSR2
and VSR4 (discussed in Sec. III). The analysis has been
carried out on the frequency band 20-128 Hz, using an
efficient hierarchical analysis pipeline, based on the Fre-
quencyHough transform [7]. No detection was made, so
we established upper limits on signal strain amplitude
as a function of the frequency. The rationale for the
chosen frequency band is twofold. First, frequencies be-
low 50 Hz have never been considered in all-sky searches
for CW signals, and the estimated joint sensitivity of
Virgo VSR2 and VSR4 data is better than that of data
from LIGO science runs S5 and S6 below about 60-70
Hz. Second, lower frequencies potentially offer promising
sources. Higher frequency signals would be in principle
easier to detect because of their high signal amplitudes
at fixed distance and ellipticity (see Eq. 5). On the other
hand, based on the electromagnetically observed pulsar
population and the results of population synthesis mod-
elling, e.g. [8], [9], we expect that a substantial fraction of
the galactic neutron star population emits gravitational
waves at frequencies below
∼
100 Hz. This is particu-
larly true when considering young, unrecycled, neutron
stars, which could be more distorted than older objects.
A search at low frequency, as described below, could de-
tect signals from a potentially significant population of
nearby neutron stars.
The plan of the paper is as follows. In Sec. II we de-
scribe the kind of gravitational wave (GW) signal we are
searching for. In Sec. III we discuss the Virgo detec-
tor performance during VSR2 and VSR4 runs. In Sec.
IV we briefly recap the analysis procedure, referring the
reader to [7] for more details. Section V is focused on
the cleaning steps applied at different stages of the anal-
ysis. Section VI is dedicated to candidate selection, and
Sec. VII to their clustering and coincidences. Section
VIII deals with the follow-up of candidates surviving the
coincidence step. Section IX is dedicated to validation
tests of the analysis pipeline, by using hardware-injected
signals in VSR2 and VSR4 data. In Sec. X a joint upper
limit on signal strain amplitude is derived as a function of
the search frequency. Conclusions and future prospects
are presented in Sec. XI. Appendix A contains a list
of the 108 candidates for which the follow-up has been
done, along with their main parameters. Appendix B is
devoted to a deeper analysis of the three outliers found.
Appendix C contains the list of frequency intervals ex-
cluded from the computation of the upper limits.
II. THE SIGNAL
The expected quadrupolar GW signal from a non-
axisymmetric neutron star steadily spinning around one
of its principal axes has a frequency
f
0
twice the rotation
frequency
f
rot
, with a strain at the detector of [7, 10]
h
(
t
) =
H
0
(
H
+
A
+
+
H
×
A
×
)
e
(
ω
(
t
)
t
+Φ
0
)
,
(1)
where taking the real part is understood and where Φ
0
is an initial phase. The signal’s time-dependent angular
frequency
ω
(
t
) will be discussed below. The two complex
amplitudes
H
+
and
H
×
are given respectively by
H
+
=
cos 2
ψ
−
η
sin 2
ψ
√
1 +
η
2
,
(2)
H
×
=
sin 2
ψ
+
η
cos 2
ψ
√
1 +
η
2
,
(3)
in which
η
is the ratio of the polarization ellipse semi-
minor to semi-major axis, and the polarization angle
ψ
defines the direction of the major axis with respect to the
celestial parallel of the source (counterclockwise). The
parameter
η
varies in the range [
−
1
,
1], where
η
= 0 for
a linearly polarized wave, while
η
=
±
1 for a circularly
polarized wave (
η
= 1 if the circular rotation is coun-
terclockwise). The functions
A
+
,
×
describe the detector
response as a function of time, with a periodicity of one
and two sidereal periods, and depend on the source posi-
tion, detector position and orientation on the Earth [10].
As discussed in [1], the strain described by Eq.(1) is
equivalent to the standard expression (see e.g. [11])
h
(
t
) =
1
2
F
+
(
t,ψ
)
h
0
(1 + cos
2
ι
) cos Φ(
t
)
(4)
+
F
×
(
t,ψ
)
h
0
cos
ι
sin Φ(
t
)
Here
F
+
, F
×
are the standard beam-pattern functions
and
ι
is the angle between the star’s rotation axis and
the line of sight. The amplitude parameter
h
0
=
4
π
2
G
c
4
I
zz
εf
2
0
d
(5)
depends on the signal frequency
f
0
and on the source dis-
tance
d
; on
I
zz
, the star’s moment of inertia with respect
to the principal axis aligned with the rotation axis; and
on
ε
, which is the fiducial equatorial ellipticity expressed
in terms of principal moments of inertia as
ε
=
I
xx
−
I
yy
I
zz
.
(6)
It must be stressed that it is not the fiducial ellipticity
but the quadrupole moment
Q
22
∝
I
zz
ε
that, in case
of detection, can be measured independently of any as-
sumption about the star’s equation of state and moment
7
of inertia (assuming the source distance can be also es-
timated). There exist estimates of the maximum ellip-
ticity a neutron star can sustain from both elastic and
magnetic deformations. In the elastic case, these max-
ima depend strongly on the breaking strain of the solid
portion sustaining the deformation (see, e.g., [12], [13]
for calculations for the crust) as well as on the star’s
structure and equation of state, and the possible pres-
ence of exotic phases in the stars interior (like in hybrid
or strange quark stars, see, e.g., [14]). In the magnetic
case, the deformation depends on the strength and con-
figuration of the star’s internal magnetic field (see, e.g.,
[15]). However, the actual ellipticity of a given neutron
star is unknown—the best we have are observational up-
per limits. The relations between
H
0
, η
and
h
0
, ι
are
given, e.g., in [10]. In Eq. 1 the signal angular frequency
ω
(
t
) is a function of time, therefore the signal phase
Φ(
t
) =
∫
t
t
0
ω
(
t
′
)
dt
′
(7)
is not that of a simple monochromatic signal. It depends
on the rotational frequency and frequency derivatives of
the neutron star, as well as on Doppler and propaga-
tion effects. In particular, the received Doppler-shifted
frequency
f
(
t
) is related to the emitted frequency
f
0
(
t
)
by the well-known relation (valid in the non-relativistic
approximation)
f
(
t
) =
1
2
π
d
Φ(
t
)
dt
=
f
0
(
t
)
(
1 +
~v
(
t
)
·
ˆ
n
c
)
,
(8)
where
~v
is the detector velocity with respect to the So-
lar System barycenter (SSB), ˆ
n
is the unit vector in the
direction to the source from the SSB and
c
is the light
speed. Smaller relativistic effects, namely the
Einstein
delay
and the
Shapiro delay
are not relevant for the search
described in this paper, due to the use of short length
FFTs, and are therfore neglected.
The intrinsic signal frequency
f
0
(
t
) slowly decreases in
time due to the source’s spin-down, associated with the
rotational energy loss following emission of electromag-
netic and/or gravitational radiation. The spin-down can
be described through a series expansion
f
0
(
t
) =
f
0
+
̇
f
0
(
t
−
t
0
) +
̈
f
0
2
(
t
−
t
0
)
2
+
...
(9)
In general, the frequency evolution of a CW depends on
3+
s
parameters: position, frequency and
s
spin-down
parameters. In the all-sky search described in this paper
we need to take into account only the first spin-down
(
s
= 1) parameter (see Sec. IV).
III. INSTRUMENTAL PERFORMANCE
DURING VSR2 AND VSR4 RUNS
Interferometric GW detectors, such as LIGO [16],
Virgo [17], and GEO [18], have collected years of data,
from 2002 to 2011. For the analysis described in this pa-
per we have used calibrated data from the Virgo VSR2
and VSR4 science runs. The VSR3 run was character-
ized by a diminished sensitivity level and poor data qual-
ity (highly non-stationary data, large glitch rate), and so
was not included in this analysis. The VSR2 run began
on July 7th, 2009 (21:00 UTC) and ended on January
8th, 2010 (22:00 UTC). The duty cycle was 80
.
4%, re-
sulting in a total of
∼
149 days of
science mode
data,
divided among 361 segments. The data used in the anal-
ysis have been produced using the most up-to-date cal-
ibration parameters and reconstruction procedure. The
associated systematic error amounts to 5
.
5% in ampli-
tude and
∼
50 mrad in phase [19].
The VSR4 run extended from June 3rd, 2011 (10:27
UTC) to September 5th, 2011 (13:26 UTC), with a duty
factor of about 81%, corresponding to an effective dura-
tion of 76 days. Calibration uncertainties amounted to
7.5% in amplitude and (40 + 50
f
kHz
) mrad in phase up
to 500 Hz, where
f
kHz
is the frequency in kilohertz [20].
The uncertainty on the amplitude contributes to the un-
certainty on the upper limit on signal amplitude, together
with that coming from the finite size of the Monte Carlo
simulation used to compute it (see Sec. X). A calibra-
tion error on the phase of this size can be shown to have a
negligible impact on the analysis [1]. The low-frequency
sensitivity of VSR4 was significantly better, up to a fac-
tor of 2, than that of previous Virgo runs, primarily due
to the use of monolithic mirror suspensions, and nearly in
agreement with the design sensitivity of the initial Virgo
interferometer [17]. We show in Fig. 1 the average exper-
imental strain amplitude spectral density for VSR2 and
VSR4, in the frequency range 20-128 Hz, obtained by
making an average of the periodograms (squared modu-
lus of the FFTs) stored in the short FFT database (see
next section).
IV. THE ANALYSIS PROCEDURE
All-sky searches are intractable using completely co-
herent methods because of the huge size of the parameter
space, which poses challenging computational problems
[21], [22]. Moreover, a completely coherent search would
not be robust against unpredictable phase variations of
the signal during the observation time.
For these reasons hierarchical schemes have been devel-
oped. The hierarchical scheme we have used for this anal-
ysis has been described in detail in [7]. In this section we
briefly recall the main steps. The analysis starts from the
detector calibrated data, sampled at 4096 Hz. The first
step consists of constructing a database of
short Discrete
Fourier Transforms
(SFDB) [23], computed through the
FFT algorithm (the FFT is just an efficient algorithm
to compute Discrete Fourier Transforms (DFT), but for
historical reasons and for consistency with previous pa-
pers we will use the term FFT instead of DFT). Each
FFT covers the frequency range from 20 to 128Hz and