LIGO-P1000097-v12Preprint typeset using LATEX style emulateapj v. 5/2/11

IMPLICATIONS FOR THE ORIGIN OF GRB 051103 FROM LIGO OBSERVATIONS

J. Abadie1, B. P. Abbott1, T. D. Abbott60, R. Abbott1, M. Abernathy2, C. Adams3, R. Adhikari1, C. Affeldt4,11,P. Ajith1, B. Allen4,5,11, G. S. Allen6, E. Amador Ceron5, D. Amariutei8, R. S. Amin9, S. B. Anderson1,W. G. Anderson5, K. Arai1, M. A. Arain8, M. C. Araya1, S. M. Aston10, D. Atkinson7, P. Aufmuth4,11,

C. Aulbert4,11, B. E. Aylott10, S. Babak12, P. Baker13, S. Ballmer1, D. Barker7, S. Barnum15, B. Barr2,P. Barriga16, L. Barsotti15, M. A. Barton7, I. Bartos17, R. Bassiri2, M. Bastarrika2, J. Bauchrowitz4,11,

B. Behnke12, A. S. Bell2, I. Belopolski17, M. Benacquista18, A. Bertolini4,11, J. Betzwieser1, N. Beveridge2,P. T. Beyersdorf19, I. A. Bilenko20, G. Billingsley1, J. Birch3, R. Biswas5, E. Black1, J. K. Blackburn1,

L. Blackburn15, D. Blair16, B. Bland7, O. Bock4,11, T. P. Bodiya15, C. Bogan4,11, R. Bondarescu21, R. Bork1,M. Born4,11, S. Bose22, M. Boyle23, P. R. Brady5, V. B. Braginsky20, J. E. Brau24, J. Breyer4,11, D. O. Bridges3,

M. Brinkmann4,11, M. Britzger4,11, A. F. Brooks1, D. A. Brown25, A. Brummitt26, A. Buonanno27,J. Burguet-Castell5, O. Burmeister4,11, R. L. Byer6, L. Cadonati28, J. B. Camp30, P. Campsie2, J. Cannizzo30,

K. Cannon1,a, J. Cao31, C. Capano25, S. Caride32, S. Caudill9, M. Cavaglia29, C. Cepeda1, T. Chalermsongsak1,E. Chalkley10, P. Charlton33, S. Chelkowski10, Y. Chen23, N. Christensen14, S. S. Y. Chua34, S. Chung16,

C. T. Y. Chung35, F. Clara7, D. Clark6, J. Clark36, J. H. Clayton5, R. Conte37, D. Cook7, T. R. C. Corbitt15,N. Cornish13, C. A. Costa9, M. Coughlin14, D. M. Coward16, D. C. Coyne1, J. D. E. Creighton5,

T. D. Creighton18, A. M. Cruise10, A. Cumming2, L. Cunningham2, R. M. Culter10, K. Dahl4,11, S. L. Danilishin20,R. Dannenberg1, K. Danzmann4,11, K. Das8, B. Daudert1, H. Daveloza18, G. Davies36, E. J. Daw38, T. Dayanga22,

D. DeBra6, J. Degallaix4,11, T. Dent36, V. Dergachev1, R. DeRosa9, R. DeSalvo1, S. Dhurandhar39, I. DiPalma4,11, M. Dıaz18, F. Donovan15, K. L. Dooley8, S. Dorsher41, E. S. D. Douglas7, R. W. P. Drever42,

J. C. Driggers1, J. -C. Dumas16, S. Dwyer15, T. Eberle4,11, M. Edgar2, M. Edwards36, A. Effler9, P. Ehrens1,R. Engel1, T. Etzel1, M. Evans15, T. Evans3, M. Factourovich17, S. Fairhurst36, Y. Fan16, B. F. Farr43,

D. Fazi43, H. Fehrmann4,11, D. Feldbaum8, L. S. Finn21, M. Flanigan7, S. Foley15, E. Forsi3, N. Fotopoulos5,M. Frede4,11, M. Frei44, Z. Frei45, A. Freise10, R. Frey24, T. T. Fricke9, D. Friedrich4,11, P. Fritschel15,

V. V. Frolov3, P. Fulda10, M. Fyffe3, J. Garcia7, J. A. Garofoli25, I. Gholami12, S. Ghosh22, J. A. Giaime9,3,S. Giampanis4,11, K. D. Giardina3, C. Gill2, E. Goetz32, L. M. Goggin5, G. Gonzalez9, M. L. Gorodetsky20,S. Goßler4,11, C. Graef4,11, A. Grant2, S. Gras16, C. Gray7, R. J. S. Greenhalgh26, A. M. Gretarsson46,

R. Grosso18, H. Grote4,11, S. Grunewald12, C. Guido3, R. Gupta39, E. K. Gustafson1, R. Gustafson32,B. Hage4,11, J. M. Hallam10, D. Hammer5, G. Hammond2, J. Hanks7, C. Hanna1, J. Hanson3, J. Harms1,

G. M. Harry15, I. W. Harry36, E. D. Harstad24, M. T. Hartman8, K. Haughian2, K. Hayama47, J. Heefner1,M. A. Hendry2, I. S. Heng2, A. W. Heptonstall1, V. Herrera6, M. Hewitson4,11, S. Hild2, D. Hoak28,

K. A. Hodge1, K. Holt 3, T. Hong23, S. Hooper16, D. J. Hosken48, J. Hough2, E. J. Howell16, B. Hughey15,S. Husa49, S. H. Huttner2, D. R. Ingram7, R. Inta34, T. Isogai14, A. Ivanov1, W. W. Johnson9, D. I. Jones50,

G. Jones36, R. Jones2, L. Ju16, P. Kalmus1, V. Kalogera43, S. Kandhasamy41, J. B. Kanner27, E. Katsavounidis15,W. Katzman3, K. Kawabe7, S. Kawamura47, F. Kawazoe4,11, W. Kells1, M. Kelner43, D. G. Keppel4,11,A. Khalaidovski4,11, F. Y. Khalili20, E. A. Khazanov51, N. Kim6, H. Kim4,11, P. J. King1, D. L. Kinzel3,J. S. Kissel9, S. Klimenko8, V. Kondrashov1, R. Kopparapu21, S. Koranda5, W. Z. Korth1, D. Kozak1,V. Kringel4,11, S. Krishnamurthy43, B. Krishnan12, G. Kuehn4,11, R. Kumar2, P. Kwee4,11, M. Landry7,B. Lantz6, N. Lastzka4,11, A. Lazzarini1, P. Leaci12, J. Leong4,11, I. Leonor24, J. Li18, P. E. Lindquist1,

N. A. Lockerbie52, D. Lodhia10, M. Lormand3, P. Lu6, J. Luan23, M. Lubinski7, H. Luck4,11, A. P. Lundgren25,E. Macdonald2, B. Machenschalk4,11,, M. MacInnis15, M. Mageswaran1, K. Mailand1, I. Mandel43, V. Mandic41,

A. Marandi6, S. Marka17, Z. Marka17, E. Maros1, I. W. Martin2, R. M. Martin8, J. N. Marx1, K. Mason15,F. Matichard15, L. Matone17, R. A. Matzner44, N. Mavalvala15, R. McCarthy7, D. E. McClelland34,

S. C. McGuire40, G. McIntyre1, J. McIver28, D. J. A. McKechan36, G. Meadors32, M. Mehmet4,11, T. Meier4,11,A. Melatos35, A. C. Melissinos53, G. Mendell7, R. A. Mercer5, S. Meshkov1, C. Messenger4,11, M. S. Meyer3,

H. Miao16, J. Miller2, Y. Mino23, V. P. Mitrofanov20, G. Mitselmakher8, R. Mittleman15, O. Miyakawa47,B. Moe5, P. Moesta12, S. D. Mohanty18, D. Moraru7, G. Moreno7, K. Mossavi4,11, C. M. Mow-Lowry34,

G. Mueller8, S. Mukherjee18, A. Mullavey34, H. Muller-Ebhardt4,11, J. Munch48, D. Murphy17, P. G. Murray2,T. Nash1, R. Nawrodt2, J. Nelson2, G. Newton2, A. Nishizawa47, D. Nolting3, L. Nuttall36, B. O’Reilly3,

R. O’Shaughnessy21, E. Ochsner27, J. O’Dell26, G. H. Ogin1, R. G. Oldenburg5, C. Osthelder1, C. D. Ott23,D. J. Ottaway48, R. S. Ottens8, H. Overmier3, B. J. Owen21, A. Page10, Y. Pan27, C. Pankow8, M. A. Papa12,5,

P. Patel1, M. Pedraza1, L. Pekowsky25, S. Penn54, C. Peralta12, A. Perreca10,b, M. Phelps1, M. Pickenpack4,11,I. M. Pinto55, M. Pitkin2, H. J. Pletsch4,11, M. V. Plissi2, J. Podkaminer54, J. Pold4,11, F. Postiglione37,

V. Predoi36, L. R. Price5, M. Prijatelj4,11, M. Principe55, S. Privitera1, R. Prix4,11, L. Prokhorov20,O. Puncken4,11, V. Quetschke18, F. J. Raab7, H. Radkins7, P. Raffai45, M. Rakhmanov18, C. R. Ramet3,

B. Rankins29, S. R. P. Mohapatra28, V. Raymond43, K. Redwine17, C. M. Reed7, T. Reed56, S. Reid2,D. H. Reitze8, R. Riesen3, K. Riles32, P. Roberts57, N. A. Robertson1,2, C. Robinson36, E. L. Robinson12,S. Roddy3, J. Rollins17, J. D. Romano18, J. H. Romie3, C. Rover4,11, S. Rowan2, A. Rudiger4,11, K. Ryan7,

S. Sakata47, M. Sakosky7, F. Salemi4,11, M. Salit43, L. Sammut35, L. Sancho de la Jordana49, V. Sandberg7,V. Sannibale1, L. Santamara12, I. Santiago-Prieto2, G. Santostasi58, S. Saraf59, B. S. Sathyaprakash36,

S. Sato47, P. R. Saulson25, R. Savage7, R. Schilling4,11, S. Schlamminger5, R. Schnabel4,11, R. M. S. Schofield24,B. Schulz4,11, B. F. Schutz12,36, P. Schwinberg7, J. Scott2, S. M. Scott34, A. C. Searle1, F. Seifert1,

D. Sellers3, A. S. Sengupta1,c, A. Sergeev51, D. A. Shaddock34, M. Shaltev4,11, B. Shapiro15, P. Shawhan27,T. Shihan Weerathunga18, D. H. Shoemaker15, A. Sibley3, X. Siemens5, D. Sigg7, A. Singer1, L. Singer1,A. M. Sintes49, G. Skelton5, B. J. J. Slagmolen34, J. Slutsky9, R. Smith10, J. R. Smith60, M. R. Smith1,

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N. D. Smith15, K. Somiya23, B. Sorazu2, J. Soto15, F. C. Speirits2, A. J. Stein15, J. Steinlechner4,11,S. Steinlechner4,11, S. Steplewski22, M. Stefszky34, A. Stochino1, R. Stone18, K. A. Strain2, S. Strigin20,

A. S. Stroeer30, A. L. Stuver3, T. Z. Summerscales57, M. Sung9, S. Susmithan16, P. J. Sutton36, G. P. Szokoly45,D. Talukder22, D. B. Tanner8, S. P. Tarabrin4,11, J. R. Taylor4,11, R. Taylor1, P. Thomas7, K. A. Thorne3,K. S. Thorne23, E. Thrane41, A. Thuring4,11, K. V. Tokmakov52, C. Torres3, C. I. Torrie1,2, G. Traylor3,

M. Trias49, K. Tseng6, D. Ugolini61, K. Urbanek6, H. Vahlbruch4,11, B. Vaishnav18, M. Vallisneri23, C. Van DenBroeck36, M. V. van der Sluys43, A. A. van Veggel2, S. Vass1, R. Vaulin5, A. Vecchio10, J. Veitch36,

P. J. Veitch48, C. Veltkamp4,11, A. E. Villar1, C. Vorvick7, S. P. Vyachanin20, S. J. Waldman15, L. Wallace1,A. Wanner4,11, R. L. Ward1, P. Wei25, M. Weinert4,11, A. J. Weinstein1, R. Weiss15, L. Wen16,23, S. Wen3,P. Wessels4,11, M. West25, T. Westphal4,11, K. Wette4,11, J. T. Whelan62, S. E. Whitcomb1, D. White38,

B. F. Whiting8, C. Wilkinson7, P. A. Willems1, H. R. Williams21, L. Williams8, B. Willke4,11,L. Winkelmann4,11, W. Winkler4,11, C. C. Wipf15, A. G. Wiseman5, G. Woan2, R. Wooley3, J. Worden7,

J. Yablon43, I. Yakushin3, K. Yamamoto4,11, H. Yamamoto1, H. Yang23, D. Yeaton-Massey1, S. Yoshida63, P. Yu5,M. Zanolin46, L. Zhang1, Z. Zhang16, C. Zhao16, N. Zotov56, M. E. Zucker15, J. Zweizig1

1LIGO - California Institute of Technology, Pasadena, CA 91125, USA2University of Glasgow, Glasgow, G12 8QQ, United Kingdom3LIGO - Livingston Observatory, Livingston, LA 70754, USA

4Albert-Einstein-Institut, Max-Planck-Institut fur Gravitationsphysik, D-30167 Hannover, Germany5University of Wisconsin–Milwaukee, Milwaukee, WI 53201, USA

6Stanford University, Stanford, CA 94305, USA7LIGO - Hanford Observatory, Richland, WA 99352, USA

8University of Florida, Gainesville, FL 32611, USA9Louisiana State University, Baton Rouge, LA 70803, USA

10University of Birmingham, Birmingham, B15 2TT, United Kingdom11Leibniz Universitat Hannover, D-30167 Hannover, Germany

12Albert-Einstein-Institut, Max-Planck-Institut fur Gravitationsphysik, D-14476 Golm, Germany13Montana State University, Bozeman, MT 59717, USA

14Carleton College, Northfield, MN 55057, USA15LIGO - Massachusetts Institute of Technology, Cambridge, MA 02139, USA

16University of Western Australia, Crawley, WA 6009, Australia17Columbia University, New York, NY 10027, USA

18The University of Texas at Brownsville and Texas Southmost College, Brownsville, TX 78520, USA19San Jose State University, San Jose, CA 95192, USA20Moscow State University, Moscow, 119992, Russia

21The Pennsylvania State University, University Park, PA 16802, USA22Washington State University, Pullman, WA 99164, USA

23Caltech-CaRT, Pasadena, CA 91125, USA24University of Oregon, Eugene, OR 97403, USA25Syracuse University, Syracuse, NY 13244, USA

26Rutherford Appleton Laboratory, HSIC, Chilton, Didcot, Oxon OX11 0QX United Kingdom27University of Maryland, College Park, MD 20742, USA

28University of Massachusetts - Amherst, Amherst, MA 01003, USA29The University of Mississippi, University, MS 38677, USA

30NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA31Tsinghua University, Beijing 100084, China

32University of Michigan, Ann Arbor, MI 48109, USA33Charles Sturt University, Wagga Wagga, NSW 2678, Australia

34Australian National University, Canberra, 0200, Australia35The University of Melbourne, Parkville VIC 3010, Australia

36Cardiff University, Cardiff, CF24 3AA, United Kingdom37University of Salerno, I-84084 Fisciano (Salerno), Italy and INFN (Sezione di Napoli), Italy

38The University of Sheffield, Sheffield S10 2TN, United Kingdom39Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India

40Southern University and A&M College, Baton Rouge, LA 70813, USA41University of Minnesota, Minneapolis, MN 55455, USA

42California Institute of Technology, Pasadena, CA 91125, USA43Northwestern University, Evanston, IL 60208, USA

44The University of Texas at Austin, Austin, TX 78712, USA45Eotvos Lorand University, Budapest, 1117 Hungary

46Embry-Riddle Aeronautical University, Prescott, AZ 86301, USA47National Astronomical Observatory of Japan, Tokyo 181-8588, Japan

48University of Adelaide, Adelaide, SA 5005, Australia49Universitat de les Illes Balears, E-07122 Palma de Mallorca, Spain

50University of Southampton, Southampton, SO17 1BJ, United Kingdom51Institute of Applied Physics, Nizhny Novgorod, 603950, Russia52University of Strathclyde, Glasgow, G1 1XQ, United Kingdom

53University of Rochester, Rochester, NY 14627, USA54Hobart and William Smith Colleges, Geneva, NY 14456, USA

55University of Sannio at Benevento, I-82100 Benevento, Italy and INFN (Sezione di Napoli), Italy56Louisiana Tech University, Ruston, LA 71272, USA57Andrews University, Berrien Springs, MI 49104, USA

58McNeese State University, Lake Charles, LA 70609, USA59Sonoma State University, Rohnert Park, CA 94928, USA

60California State University Fullerton, Fullerton CA 92831, USA61Trinity University, San Antonio, TX 78212, USA

62Rochester Institute of Technology, Rochester, NY 14623, USA63Southeastern Louisiana University, Hammond, LA 70402, USA

Implications for the Origin of GRB 051103 from LIGO Observations 3

a now at the Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario, M5S 3H8, Canadab now at Department of Physics, University of Trento, 38050, Povo, Trento, Italy and

c now at the Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India

M. A. Bizouard1, A. Dietz2, G. M. Guidi3ab, and M. Was1

1LAL, Universite Paris-Sud, IN2P3/CNRS, F-91898 Orsay, France2Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Universite de Savoie,CNRS/IN2P3, F-74941 Annecy-Le-Vieux,

France and3INFN, Sezione di Firenze, I-50019 Sesto Fiorentinoa; Universita degli Studi di Urbino ’Carlo Bo’, I-61029 Urbinob, Italy

(Dated: November 19, 2018)LIGO-P1000097-v12

ABSTRACT

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103,a short-duration hard-spectrum gamma-ray burst whose electromagnetically determined sky positionis coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A mergerprogenitor would produce a characteristic GW signal that should be detectable at the distance ofM81, while GW emission from an SGR is not expected to be detectable at that distance. We foundno evidence of a GW signal associated with GRB 051103. Assuming weakly beamed γ-ray emissionwith a jet semi-angle of 30◦ we exclude a binary neutron star merger in M81 as the progenitor with aconfidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the eventoccurred in M81 our findings support the hypothesis that GRB 051103 was due to an SGR giant flare,making it the most distant extragalactic magnetar observed to date.Subject headings: gamma-ray bursts – gravitational waves – compact object mergers – soft gamma-ray

repeaters

1. INTRODUCTION

GRB 051103 was a short-duration, hard-spectrumgamma-ray burst (GRB) which occurred at 09:25:42UTC on 3 November 2005 (Hurley et al. 2010) and waspossibly located in the nearby galaxy M81, at a distance3.63±0.14 Mpc from Earth (Golenetskii et al. 2005; Dur-rell et al. 2010). A preliminary quadrilateral error boxobtained by the third interplanetary network of satellites(IPN3) was consistent with a source in the M81 group(Golenetskii et al. 2005). The refined 3-σ error ellipse,shown with a solid black line in Figure 1, has an area of104 square arcminutes, and excludes the possibility thatthe GRB’s source was the inner disk of M81 (Hurley et al.2010). The location of the progenitor of GRB 051103 is,however, consistent with the outer disk of M81.

Two other galaxies are noted to lie within the originalerror box: PGC028505 (distance estimated at 80 Mpc,Lipunov et al. (2005)) and PGC2719634 (distance un-known). PGC2719634 lies on the 18% confidence con-tour of the refined ellipse and constitutes a plausiblehost galaxy. PCG028505, however, lies on the 0.03%contour and is unlikely to be the host. Furthermore,PGC028505 was observed in the R and V bands butno evidence for brightening due to an underlying tran-sient source was found (Klose et al. 2005) and it is notthought to be a plausible host of GRB 051103 (Hurleyet al. 2010; Lipunov et al. 2005). Observations of theoriginal quadrilateral error box in optical and radio con-cluded that GRB 051103 was not associated with anytypical supernova at z . 0.15 (Ofek et al. 2006). Noneof the known supernova remnants in M81 fall within therefined elliptical error region.

The progenitors of most short duration GRBs arewidely thought to be the coalescence of a neutron star-neutron star (NS-NS) or neutron star-black hole (NS-BH) binary system (see, for example, Nakar 2007 and

Fig. 1.— The central region of the M81 group, showing the origi-nal error trapezium (red dashed line) from the IPN and the refined3-σ error ellipse (solid black). The blue boxes are the regions stud-ied in the optical. Figure from Hurley et al. (2010) Copyright (c)2010 RAS.

references therein). With the right combination of bi-nary masses and spins, the neutron star matter is be-lieved to be tidally disrupted leading to the formationof a massive torus. Accretion of matter from this torusonto the final post-merger object leads to the formationof highly relativistic outflows along the axis of total angu-lar momentum of the system (e.g., Setiawan et al. 2004;Shibata & Taniguchi 2006; Rezzolla et al. 2011). Internalshocks in the relativistic jet give rise to the prompt γ-ray

4 Abbott et al.

emission observed in short, hard GRBs.These binary systems also produce a characteristic

gravitational-wave (GW) signal in the last few secondsbefore coalescence that is detectable by the current gen-eration of interferometric GW detectors, such as those ofthe Laser Interferometer Gravitational-wave Observatory(LIGO, Abbott et al. 2004, 2009a), to O(10) Mpc. Thus,if M81 was indeed the host of a binary merger progenitorof GRB 051103, LIGO should have detected a GW sig-nal associated with the event. A similar hypothesis wastested for GRB 070201, whose error box overlapped thespiral arms of M31 (which is 770 kpc from Earth). LIGOwas able to exclude a compact binary progenitor in M31at > 99% confidence (Abbott et al. 2008a) and placed alower limit of 3.5 Mpc on its distance at 90% confidence.

Up to 15% of short GRBs might be giant flares fromsoft gamma repeaters (SGRs) in the local universe (Tan-vir et al. 2005; Chapman et al. 2009). SGRs are believedto be magnetars; neutron stars with extremely large mag-netic fields (B ∼ 1015 G). However, only a few percent ofshort GRBs are thought to share the SGR-like proper-ties exhibited by GRB 051103 (Frederiks et al. 2007). Forexample, the light curve exhibits the steep rise (∼ 4 ms)and decaying tail observed in the initial pulses of SGR gi-ant flares (Frederiks et al. 2007; Ofek et al. 2006; Hurleyet al. 2010). At the distance of M81 the characteristiclate-time weaker, oscillatory phase expected of a SGRgiant flare, which follows the rotation of the underly-ing neutron star, would not be detectable (Hurley et al.2010). Second, the spectrum of GRB 051103 shows thehard-to-soft evolution characteristic of SGR giant flares(Frederiks et al. 2007). Also, if we assume the sourcewas in M81, the isotropic electromagnetic energy releaseis approximately 3.6 × 1046 erg (Golenetskii et al. 2005),consistent with the energy release (∼ 4× 1046 erg) of theSGR 1806−20 giant flare (Hurley et al. 2005). We notethat a number of UV-bright regions contained within theelliptical error box indicate star-forming regions in theouter disk of M81 which may host magnetars (Ofek et al.2006; Hurley et al. 2010). If confirmed, the identificationof an SGR in M81 would be the second and most distantextra-galactic SGR flare observed to date.

Several searches for GWs associated with magnetarevents have already been performed (Abbott et al. 2007,2008b, 2009c; Abadie et al. 2011). No evidence ofa GW signal was found in these searches, includingthe 2004 giant flare from the Galactic magnetar SGR1806−20, which is a factor of ∼300 closer to Earth thanM81 (Abbott et al. 2008b). A detectable GW signal froma magnetar giant flare in M81 would therefore probablyrequire > 105 more energy in the GW emission over SGR1806−20.

At the time of the GRB, the LIGO detectors were infinal preparations for their fifth science run, S5, whichbegan the following day. For this reason, the data fromaround the time of GRB 051103 has not been included inprevious searches associated with GRBs or SGRs in S5data. Nonetheless, data taken by the LIGO 2 km detec-tor in Hanford, WA (H2) and the LIGO 4 km detector inLivingston, LA (L1) is available. Motivated by interestfrom the astronomical community and the potential fora GW detection, we have performed a search using theestablished data analysis pipelines from the S5 searches.

The data was calibrated as described in Abadie et al.(2010a). The validity of the calibration was establishedby comparing records of the detector configuration at theGRB epoch to those near the start of the science run, andestimates of the calibration uncertainty are accounted forin the GW searches. Data quality studies and techniquesfor vetoing problematic segments were similar to thoseused during S5 (Abbott et al. 2009b). These detectorcharacterization studies have established that the datais of science quality and equivalent to that shortly afterthe official start of S5.

In this paper we report on the LIGO search for GWsassociated with GRB 051103, and the resulting impli-cations for the origin of this GRB. Three independentanalysis packages, designed for different purposes, wereused. In § 2 we describe the method and results of search-ing for theoretically predicted gravitational waveformsemitted during compact binary mergers. In § 3, we de-scribe the results of two searches using analyses whichare designed to be sensitive to unmodelled short-duration(. 1 s) bursts of GWs. The first is an analysis designedto search for GW bursts from magnetar flares. The sec-ond performs a search for generic GW bursts from GRBsin the sensitive band of the LIGO instruments. Finally,we summarise our findings in § 4.

2. SEARCH FOR GWS FROM A COMPACT BINARYPROGENITOR

2.1. Search Method

The method used to search for the GW signal from bi-nary coalescence is identical to that reported in Abadieet al. (2010b): matched filtering is used to correlate the-oretically motivated template waveforms with the datastreams from the detectors.

The GW signal from binary coalescence is expected toprecede the prompt γ-ray emission by no more than a fewseconds. We therefore search for GW signals whose endtime lies in an on-source window of [−5,+1) s around thereported GRB time. The significance of candidate GWsignals is estimated from the background distribution of324 off-source trials, each 6 s long (the number of whichis dictated by the quality of the data around the time ofthe GRB).

The form of the GW signal from compact binary coa-lescence depends on the masses (mNS,mcomp) and spinsof the neutron star and its companion (either a neutronstar or a black hole), as well as the spatial location rel-ative to the detectors, the inclination angle ι betweenthe orbital axis and the line of sight, and the polariza-tion angle specifying the orientation of the orbital axis.The data from each detector is filtered through a dis-crete bank of template waveforms designed such that themaximum loss of signal-to-noise ratio (SNR) due to dis-cretization effects for a binary with negligible spins is 3%.Although the template bank used ignores spin, we laterevaluate our sensitivity to spinning systems and verifythat such systems are still detectable. It is assumed thatat least one member of the binary is a neutron star withmass 1M� ≤ mNS ≤ 3M�. For the companion object,we test masses in the range 1M� ≤ mcomp ≤ 25M� toallow the possiblity of a either a neutron star-neutronstar or neutron star-black hole merger. We note thatblack hole masses greater than 25M� seem likely to“swallow” the neutron star whole, without tidally dis-

Implications for the Origin of GRB 051103 from LIGO Observations 5

rupting the neutron star and forming a sufficiently mas-sive accretion disk to power a GRB jet (Belczynski et al.2008).

If the matched filter SNR exceeds a threshold, thetemplate masses and the time of the maximum SNRare recorded. These triggers between detectors are thentested for coincidence in their time and mass parameters(Robinson et al. 2008). This significantly reduces thenumber of background triggers that arise from matchedfiltering in each detector independently. Further back-ground suppression is achieved by applying signal con-sistency tests, specifically a χ2 test (Allen 2005) and ther2 veto (Rodriguez 2007). The SNR and χ2 from a sin-gle detector are combined into an effective SNR (Abbottet al. 2008c), which is then summed in quadrature acrossdetectors to form the combined effective SNR which isused as the ranking statistic.

The distribution of effective SNRs can vary signifi-cantly across the range of masses being searched, withshorter, higher mass templates more susceptible to non-stationary background noise. Consequently, we split upthe search space by mass and re-rank triggers in eachmass bin by their likelihood of having arisen due to agravitational wave signal. This is defined as the effi-ciency with which we detect plausible gravitational wavesignals divided by the false-alarm probability, for a givencombined effective SNR. The false-alarm probability isthe probability of obtaining a candidate louder than thatobserved in the on-source trial in the same region ofmass space from noise alone; it is measured using theoff-source trials. The detection efficiency is computed byadding simulated gravitational wave signals to the datafrom off-source trials and counting the fraction which arerecovered by the detection pipeline.

2.2. Search Results

The matched-filter search found no evidence for a GWsignal produced by compact binary coalescence at thetime of GRB 051103. The most significant candidateevent in the on-source region around the time of the GRBhad a false alarm probability of 76%. That is, therewas a 76% chance of observing a candidate this loud orlouder in any given off-source trial due to an accidentalcoincident noise fluctuation in each detector.

The null-detection result allows us to compute the fre-quentist confidence with which we may exclude binarycoalescence in M81 as the progenitor for this GRB. Weused the approach of Feldman & Cousins (1998) to com-pute regions in distance where GW events would, witha given confidence, have produced results inconsistentwith our observations. The Feldman-Cousins confidenceregions are computed by analyzing a family of simulatedgravitational wave signals, with a choice of priors for theintrinsic parameters motivated by astrophysical observa-tions. Results are quoted explicitly in terms of either afiducial NS-NS or NS-BH merger.

In the case of NS-NS mergers, masses are drawn from aGaussian distribution with mean 1.4M�, standard devi-ation 0.2M� and truncated at [1.0, 3.0]M�. The dimen-sionless spins, a = Jc/GM2, where J is the spin angularmomentum and M is the mass, are uniformly distributedwithin [0.0, 0.4]. The upper bound is chosen to be com-patible with the spin of the fastest observed millisecond

pulsar (Hessels et al. 2006). Our fiducial NS-BH systemshave black hole masses drawn from Gaussian with mean10.0M�, standard deviation 6.0M� and truncated at[2.0, 25.0]M�. To reflect the greater uncertainty arisingfrom a lack of observed NS-BH systems, the neutron starmass is drawn from a Gaussian distribution with mean1.4M� and standard deviation 0.4M�. Black hole spinsare distributed uniformly within [0.0, 0.98). Additionally,population synthesis studies of NS-BH mergers appearto indicate that the tilt angle (the angle between the BHspin direction and the NS orbital axis) must be < 45◦ inmost systems to allow for tidal disruption of the NS andformation of a sufficiently massive torus able to powerthe gamma-ray burst (Belczynski et al. 2008). Recentnumerical simulations of NS-BH mergers lend support tothis restriction and find that the tilt angle is likely < 60◦

(Rantsiou et al. 2008; Foucart et al. 2011). We restrictthe tilt angle to be < 60◦.

The outflows from the accretion jets in a GRB are di-rected along the rotational axis of the final object. Rel-ativistic beaming and collimation due to the ambientmedium confines the jet to a semi-angle θjet. The obser-vation of prompt γ-ray emission is, therefore, indicativethat the inclination of the total angular momentum withrespect to the line of sight lies within the jet cone. Es-timates of θjet are based on jet breaks observed in X-rayafterglows and vary across GRBs. Indeed, many GRBsdo not even exhibit a jet break. However, studies of ob-served jet breaks in Swift GRB X-ray afterglows find amean (median) value of θjet = 5.4◦(6.4◦), with a tail ex-tending almost to 25◦ (Racusin et al. 2009). In at leastone case where no jet break is observed, the inferredlower limit is 25◦ and could be as high as 79◦ (Grupeet al. 2006). In order to probe the range of predicted jetopening angles, we perform separate sets of simulationswhere the inclination of the total angular momentum isrestricted to jet semi-angles of 10◦, 20◦, . . . , 60◦ and 90◦,allowing an estimate of exclusion confidence as a functionof jet semi-angle.

Systematic errors are treated identically to those inAbadie et al. (2010b): amplitude calibration uncertaintyand Monte-Carlo counting statistics from injections arethe dominant errors. Amplitude calibration uncertaintyis accounted for by multiplying exclusion distances by1.28×(1+δcal), where δcal is the overall fractional uncer-tainty in amplitude calibration, estimated at 25%. Thisis significantly larger than typical science run calibrationuncertainties (see e.g., Abadie et al. (2010a)) as fewercalibration measurements were available from this pre-science run time. The factor of 1.28 corresponds to a90% pessimistic fluctuation, assuming Gaussianity. Weincorporate Monte-Carlo uncertainties from the compu-tationally limited number of simulations by stretchingthe Feldman-Cousins confidence regions to cover a prob-ability interval CL + 1.28

√CL(1 − CL)/n, where CL is

the desired confidence limit and n is the number of sim-ulations used in constructing the interval.

Figure 2 shows exclusion confidence for NS-NS and NS-BH mergers as a function of jet semi-angle θjet, assuminga distance to M81 of 3.63 Mpc. If we assume isotropicγ-ray (i.e., unbeamed) emission from GRB 051103 thepossibility of NS-NS coalescence in M81 as its progeni-tor is excluded with 71% confidence. Taking a fiducial

6 Abbott et al.

10 20 30 40 50 60 70 80 90Jet semi-opening angle (deg)

0.5

0.6

0.7

0.8

0.9

1.0E

xclu

sion

confi

denc

e

NS-NSNS-BH

Fig. 2.— Exclusion confidences for the two classes of compactbinary coalescences considered in the matched-filter analysis asa function of jet semi-opening angle and assuming a distance of3.63 Mpc to GRB 051103. The estimate is based on simulationswhere neutron star masses are Gaussian distributed with mean1.4M� and standard deviation 0.2M�. Black hole masses arealso Gaussian distributed with mean 10.0M� and standard devi-ation 6.0M�. The reduced confidence below 30◦ is purely due tonumerical corrections for limited simulation size.

10 20 30 40 50 60 70 80 90Jet semi-opening angle (deg)

0

2

4

6

8

10

12

90%

Exc

lusi

on(M

pc)

NS-NSNS-BHDM81

Fig. 3.— 90%-confidence exclusion distance as a function of jetsemi-angle for binary coalescences, given LIGO observations at thetime of GRB 051103.

jet semi-angle of θjet = 30◦, exclusion confidence risesto 98%. NS-BH mergers with isotropic emission are ex-cluded at 93% confidence, rising to > 99% for θjet = 30◦.

To address how far we can exclude binary coalescencesif GRB 051103 was not in M81, figure 3 shows thedistance at which we reach 90% exclusion confidenceas a function of jet semi-angle. Assuming unbeamedemission, NS-NS mergers are excluded with 90% con-fidence out to a distance of 2.1 Mpc, rising to 5.2 Mpcfor θjet = 30◦. The corresponding distances for NS-BHcoalescences are 5.3 Mpc and 10.7 Mpc, respectively.

The increase in exclusion confidence for smaller jet an-gles is due to the fact that the average amplitude of theGW signal from compact binary coalescence is smaller forsystems whose orbital plane is viewed ‘edge-on’ (wherethe detector receives the flux from just one GW polariza-tion) than for systems viewed ‘face-on’ (where the detec-tor receives the flux from both GW polarizations); smalljet angles imply a system closer to face-on.

3. SEARCH FOR A GW BURST

3.1. Search Methods

We perform two searches for a GW burst associatedwith GRB 051103. As discussed previously, there is evi-dence that a fraction of short GRBs are caused by nearbymagnetar flares, so we perform a search tailored to theexpected GW signal arising from such a flare. Addition-ally, we perform a search for a generic GW burst in thetime around the GRB.

The Flare pipeline (Kalmus et al. 2007; Kalmus 2008)targets neutron star fundamental mode (f -mode) ring-downs as well as unmodeled short-duration GW signals.It has been used previously to search for GWs associatedwith Galactic magnetar bursts including the December2004 giant flare from SGR 1806−20 (Abbott et al. 2008b,2009c; Abadie et al. 2011). As in the previous mag-netar searches, we use an on-source region of [−2,+2] sabout the GRB 051103 trigger, and an off-source regionof 1000 s on either side of the on-source region to estimatethe significance of on-source events.

Flare produces a time-frequency pixel map from theconditioned and calibrated detector data streams in theFourier basis, groups pixels using density-based cluster-ing, and sums over the group to produce events. Thedata from each of the two detectors is combined by in-cluding detector noise floor measurements and antennaresponses to the source sky location as weighting factorsin the detection statistic. We divide the search into threefrequency bands: 1–3 kHz where f -modes are predictedto ring; and 100–200 Hz and 100–1000 Hz where the de-tectors are most sensitive. In the f -mode band we use aFourier transform length of 250 ms, which we find to beoptimal for f -mode signals expected to decay exponen-tially with a timescale τ in the 100–300 ms range (Benharet al. 2004).

The X-Pipeline analysis package (Sutton et al. 2009)searches for generic GW bursts in data from arbitrarynetworks of detectors. X-Pipeline was previously usedin the search for GW bursts associated with GRBs inLIGO science run 5 and Virgo science run 1, in 2005–2007 (Abbott et al. 2010). Since the analysis is not basedon a specific GW emission model, we keep the searchparameters broad to allow for a generic GW burst. Inparticular, we define our on-source region as the interval[−120,+60] s around the GRB trigger; this conservativewindow is large enough to accommodate the time delaybetween a GW signal and the onset of the gamma-ray sig-nal in most GRB progenitor models. We use 1.5 hoursof data on either side of the on-source region as the off-source region for background characterization. The fre-quency band of the X-Pipeline search is 64–1792 Hz.

X-Pipeline combines the data streams from each de-tector with weighting determined by the sensitivity ofeach detector as a function of frequency and sky posi-tion. This yields time-frequency maps of the signal en-ergy in each pixel. Candidate GW events are identifiedas the loudest 1% of pixels in the map. Each is assigned asignificance based on its energy and time-frequency vol-ume, using a χ2 distribution with two degrees of free-dom. These candidates are then refined by comparingthe degree of correlation between the H2 and L1 datastreams, rejecting low-correlation events as background.Surviving events are ranked by their significance, theneach is assigned a false-alarm probability by comparisonto events from the off-source region.

Implications for the Origin of GRB 051103 from LIGO Observations 7

3.2. Search Results

Neither the Flare magnetar search nor the X-Pipeline analysis yield evidence for a plausiblegravitational-wave burst signal associated with GRB051103. Consequently, we place model-dependent 90%confidence level upper limits on the isotropic energy emis-sion in gravitational waves EGW associated with thisGRB.

The limits from the Flare analysis were obtained fortwelve types of simulated GW signals: eight f -moderingdowns with circular and linear polarizations and de-cay times 200 ms; and four band- and time-limited whitenoise bursts with durations of 11 ms or 100 ms and span-ning the 100–200 Hz and 100–1000 Hz bands. Uncertain-ties from detector calibrations and Monte Carlo statis-tics were folded into upper limit estimates as describedin Abadie et al. (2011). The best (lowest) upper limiton EGW was 2.0 × 1051 erg, for 100–200 Hz white noisebursts lasting 100 ms. The lowest f -mode upper limitwas 1.6 × 1054 erg, for circularly polarized ringdowns at1090 Hz. These are the lowest frequency signals of eachmorphology; limits obtained for the other ten simulatedsignals scale with the noise floor of the LIGO detectorsas expected and the simulations provide a check of therobustness of the analysis to the large uncertainty in thefrequency of a putative GW signal (for more details onthe simulations used see Abadie et al. 2011).

The upper limits produced by the broad X-Pipelinesearch are computed in a similar way, although theymake use of circularly polarized sine-Gaussian waveformsat 150 Hz and 1000 Hz (for details, including handling ofuncertainties, see Abbott et al. 2010). We find upper lim-its on EGW of 1.2×1052 erg at 150 Hz and 6.0×1054 erg at1000 Hz. We can convert these results to lower limits onthe distance to GRB 051103 as a function of EGW, giv-ing 4.4 Mpc (EGW/0.01M�c

2)1/2 at 150 Hz and 0.20 Mpc(EGW/0.01M�c

2)1/2 at 1000 Hz.Even near the frequency of LIGO’s best sensitivity

our energy upper limits are several orders of magni-tude larger than the maximum energy available for emis-sion by SGRs in gravitational waves ∼ 1046–1049 erg(de Freitas Pacheco 1998; Ioka 2001; Owen 2005; Horvath2005; Corsi & Owen 2011). Indeed, the energy actuallyemitted as gravitational waves may be much less thanthis (Kashiyama & Ioka 2011; Levin & van Hoven 2011).We are therefore unable to inform the hypothesis of anSGR progenitor for GRB 051103.

4. CONCLUSION

We analyzed data from the LIGO L1 and H2 GW de-tectors in a frequency band spanning 40 Hz to 3 kHz,looking for a GW signal associated with the short-hardGRB 051103. Three data analysis pipelines were de-ployed, two of which are designed to search for unmod-elled, short-duration (. 1 s) burst-like GW signals andone which performs a matched-filter analysis using tem-plates based on the GW signal expected from compactbinary mergers. No evidence was found for a GW signalassociated with this GRB.

The sensitivity of the matched-filter search allows usto confidently exclude the hypothesis that the progeni-tor system was a compact binary merger progenitor inM81. Specifically, assuming an outflow jet semi-angleθjet = 30◦, we exclude a NS-NS merger in M81 at 98%confidence. NS-BH mergers with similarly beamed emis-sion are excluded at > 99% confidence. Relaxing the as-sumption of beaming such that we include systems whoseorbital plane is oriented edge-on to our line-of-sight, theconfidences for NS-NS and NS-BH mergers fall to 71%and 93%, respectively. As a measure of the distance towhich we are sensitive to such events, the 90%-confidenceexclusion distances for NS-NS and NS-BH systems withbeaming are 5.2 Mpc and 10.7 Mpc, respectively. As-suming no beaming, these distances drop to 2.1 Mpc and5.3 Mpc.

The null result of the searches for an unmodelled burstof GWs allows us to set upper limits on the GW en-ergy emission of GRB 051103. These limits are in therange 1051–1055 erg, depending primarily on the assumedGW frequency. These limits are several orders of magni-tude greater than the maximum observed electromag-netic emission from SGRs, ∼ 1046 erg, and the high-est predictions of the available resevoir of energy avail-able for gravitational wave emission, so we are not ableto constrain the hypothesis of an SGR progenitor forGRB 051103.

We conclude then, that it is highly unlikely that theprogenitor for GRB 051103 was a compact binary mergerin M81. If the event indeed occurred in M81, it seemslikely on the basis of LIGO observations that this wasindeed the most distant SGR giant flare observed to date.

The authors thank A. Rowlinson and N. Tanvir forbringing GRB 051103 to our attention. The authorsgratefully acknowledge the support of the United StatesNational Science Foundation for the construction and op-eration of the LIGO Laboratory and the Science andTechnology Facilities Council of the United Kingdom,the Max-Planck-Society, and the State of Niedersach-sen/Germany for support of the construction and opera-tion of the GEO600 detector. The authors also gratefullyacknowledge the support of the research by these agen-cies and by the Australian Research Council, the Interna-tional Science Linkages program of the Commonwealthof Australia, the Council of Scientific and Industrial Re-search of India, the Istituto Nazionale di Fisica Nucleareof Italy, the French Centre National de la Recherche Sci-entifique, the Spanish Ministerio de Educacion y Ciencia,the Conselleria d’Economia, Hisenda i Innovacio of theGovern de les Illes Balears, the Royal Society, the Scot-tish Funding Council, the Scottish Universities PhysicsAlliance, The National Aeronautics and Space Adminis-tration, the Carnegie Trust, the Leverhulme Trust, theDavid and Lucile Packard Foundation, the Research Cor-poration, and the Alfred P. Sloan Foundation. This doc-ument has been assigned LIGO Laboratory documentnumber LIGO-P10000097-v12.

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