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Papers by the External Triggers Group

[1] LIGO Scientific Collaboration and K. Hurley. Implications for the Origin of GRB 070201 from LIGO Observations. The Astrophysical Journal, 681(2):1419-1430, 2008. [ bib | DOI | http ]
We analyzed the available LIGO data coincident with GRB 070201, a short duration hard spectrum gamma-ray burst whose electromagnetically determined sky position is coincident with the spiral arms of the Andromeda galaxy (M31). Possible progenitors of such short hard GRBs include mergers of neutron stars or a neutron star and black hole, or soft gamma-ray repeater (SGR) flares. These events can be accompanied by gravitational-wave emission. No plausible gravitational wave candidates were found within a 180 s long window around the time of GRB 070201. This result implies that a compact binary progenitor of GRB 070201, with masses in the range 1 Msun < m1 < 3 Msun and 1 Msun < m2 < 40 Msun, located in M31 is excluded at >99% confidence. Indeed, if GRB 070201 were caused by a binary neutron star merger, we find that D < 3.5 Mpc is excluded, assuming random inclination, at 90% confidence. The result also implies that an unmodeled gravitational wave burst from GRB 070201 most probably emitted less than 4.4 x 10(-4) Msun c2 (7.9 x 10(50) ergs) in any 100 ms long period within the signal region if the source was in M31 and radiated isotropically at the same frequency as LIGO's peak sensitivity (f   150 Hz). This upper limit does not exclude current models of SGRs at the M31 distance.

[2] LIGO Scientific Collaboration. Search for gravitational waves associated with 39 gamma-ray bursts using data from the second, third, and fourth LIGO runs. Physical Review D (Particles, Fields, Gravitation, and Cosmology), 77(6):062004, 2008. [ bib | DOI | http ]
We present the results of a search for short-duration gravitational-wave bursts associated with 39 gamma-ray bursts (GRBs) detected by gamma-ray satellite experiments during LIGO's S2, S3, and S4 science runs. The search involves calculating the crosscorrelation between two interferometer data streams surrounding the GRB trigger time. We search for associated gravitational radiation from single GRBs, and also apply statistical tests to search for a gravitational-wave signature associated with the whole sample. For the sample examined, we find no evidence for the association of gravitational radiation with GRBs, either on a single-GRB basis or on a statistical basis. Simulating gravitational-wave bursts with sine-Gaussian waveforms, we set upper limits on the root-sum-square of the gravitational-wave strain amplitude of such waveforms at the times of the GRB triggers. We also demonstrate how a sample of several GRBs can be used collectively to set constraints on population models. The small number of GRBs and the significant change in sensitivity of the detectors over the three runs, however, limits the usefulness of a population study for the S2, S3, and S4 runs. Finally, we discuss prospects for the search sensitivity for the ongoing S5 run, and beyond for the next generation of detectors.

[3] LIGO Scientific Collaboration. Search for gravitational wave radiation associated with the pulsating tail of the SGR 1806-20 hyperflare of 27 December 2004 using LIGO. Physical Review D (Particles, Fields, Gravitation, and Cosmology), 76(6):062003, 2007. [ bib | DOI | http ]
We have searched for gravitational waves (GWs) associated with the SGR 1806-20 hyperflare of 27 December 2004. This event, originating from a Galactic neutron star, displayed exceptional energetics. Recent investigations of the x-ray light curve's pulsating tail revealed the presence of quasiperiodic oscillations (QPOs) in the 30–2000 Hz frequency range, most of which coincides with the bandwidth of the LIGO detectors. These QPOs, with well-characterized frequencies, can plausibly be attributed to seismic modes of the neutron star which could emit GWs. Our search targeted potential quasimonochromatic GWs lasting for tens of seconds and emitted at the QPO frequencies. We have observed no candidate signals above a predetermined threshold, and our lowest upper limit was set by the 92.5 Hz QPO observed in the interval from 150 s to 260 s after the start of the flare. This bound corresponds to a (90% confidence) root-sum-squared amplitude hrss-det90%=4.5×10-22 strain Hz-1/2 on the GW waveform strength in the detectable polarization state reaching our Hanford (WA) 4 km detector. We illustrate the astrophysical significance of the result via an estimated characteristic energy in GW emission that we would expect to be able to detect. The above result corresponds to 7.7×1046 erg (=4.3×10-8 M[sun]c2), which is of the same order as the total (isotropic) energy emitted in the electromagnetic spectrum. This result provides a means to probe the energy reservoir of the source with the best upper limit on the GW waveform strength published and represents the first broadband asteroseismology measurement using a GW detector.

[4] LIGO Scientific Collaboration. Search for gravitational waves associated with the gamma ray burst GRB030329 using the LIGO detectors. Physical Review D (Particles, Fields, Gravitation, and Cosmology), 72(4):042002, 2005. [ bib | DOI | http ]
We have performed a search for bursts of gravitational waves associated with the very bright gamma ray burst GRB030329, using the two detectors at the LIGO Hanford Observatory. Our search covered the most sensitive frequency range of the LIGO detectors (approximately 80–-2048 Hz), and we specifically targeted signals shorter than  =150 ms. Our search algorithm looks for excess correlated power between the two interferometers and thus makes minimal assumptions about the gravitational waveform. We observed no candidates with gravitational-wave signal strength larger than a predetermined threshold. We report frequency-dependent upper limits on the strength of the gravitational waves associated with GRB030329. Near the most sensitive frequency region, around  =250 Hz, our root-sum-square (RSS) gravitational-wave strain sensitivity for optimally polarized bursts was better than hRSS =6×10-21 Hz-1/2. Our result is comparable to the best published results searching for association between gravitational waves and gamma ray bursts.

Keywords: gravitational waves; gravitational wave detectors; light interferometry; supernovae; gamma-ray bursts

Other Interesting Papers

[1] R. M. O'Leary, B. Kocsis, and A. Loeb. Gravitational waves from scattering of stellar-mass black holes in galactic nuclei. ArXiv e-prints, 807, July 2008. [ bib | http ]
Stellar mass black holes (BHs) are expected to segregate and form a steep density cusp around supermassive black holes in galactic nuclei. We follow the evolution of a multi-mass system of BHs and stars by numerically integrating the Fokker-Planck energy diffusion equations for a variety of BH mass distributions. We find that the BHs “self-segregate”, and that the rarest, most massive BHs dominate the scattering rate closest to the SMBH (< .1 pc). BH-BH binaries form out of gravitational wave emission during BH encounters. We find that the expected rate of BH coalescence events detectable by Advanced LIGO is  1-1000/yr, depending on the initial mass function of stars in galactic nuclei and the mass of the most massive BHs. The BH binaries that form this way in galactic nuclei have significant eccentricities as they enter the LIGO band (90% with e > 0.9), and are therefore distinguishable from other binaries, which circularize before becoming detectable. We also show that eccentric mergers can be detected to larger distances and greater BH masses than circular mergers, up to  700 M_sun. Future ground-based gravitational wave observatories will be able to constrain both the mass function of BHs and stars in galactic nuclei.

Keywords: Astrophysics
[2] A. M. Soderberg, E. Berger, K. L. Page, P. Schady, J. Parrent, D. Pooley, X. Y. Wang, E. O. Ofek, A. Cucchiara, A. Rau, E. Waxman, J. D. Simon, D. C. J. Bock, P. A. Milne, M. J. Page, J. C. Barentine, S. D. Barthelmy, A. P. Beardmore, M. F. Bietenholz, P. Brown, A. Burrows, D. N. Burrows, G. Byrngelson, S. B. Cenko, P. Chandra, J. R. Cummings, D. B. Fox, A. Gal-Yam, N. Gehrels, S. Immler, M. Kasliwal, A. K. H. Kong, H. A. Krimm, S. R. Kulkarni, T. J. Maccarone, P. Meszaros, E. Nakar, P. T. O'Brien, R. A. Overzier, M. de Pasquale, J. Racusin, N. Rea, and D. G. York. An extremely luminous X-ray outburst at the birth of a supernova. 2008. [ bib | http ]
Massive stars end their short lives in spectacular explosions, supernovae, that synthesize new elements and drive galaxy evolution. Throughout history supernovae were discovered chiefly through their delayed optical light, preventing observations in the first moments (hours to days) following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the break-out of the supernova shock-wave from the progenitor, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We forecast that future wide-field X-ray surveys will catch hundreds of supernovae each year in the act of explosion, and thereby enable crucial neutrino and gravitational wave detections that may ultimately unravel the explosion mechanism.

[3] Robert Chapman, Robert S. Priddey, and Nial R. Tanvir. Short gamma-ray bursts from SGR giant flares and neutron star mergers: two populations are better than one, 2008. [ bib | http ]
There is increasing evidence of a local population of short duration Gamma-ray Bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible Luminosity Functions (LF) for both neutron star binary mergers and giant flares from Soft Gamma Repeaters (magnetars, SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single population alone of progenitors can reproduce both the overall BATSE sGRB number counts and a local population, or whether a dual progenitor population is required. In addition we compare the predicted redshift distribution from our best fit models with the sGRB redshift distribution from the Swift era. We find that only a bimodal population consisting of lower and higher luminosity populations can reproduce both the overall BATSE sGRB number counts and a local population, as well as being consistent with Swift redshifts. Furthermore, the best fit luminosity parameters agree well with the known properties of SGR giant flares and classic short GRBs.

[4] G. Rowell. Gamma-Ray, Neutrino & Gravitational Wave Detection: OG 2.5,2.6,2.7 Rapporteur. 2008. [ bib | http ]
This report is based on a rapporteur talk presented at the 30th International Cosmic Ray Conference held in Merida, Mexico (July 2007), and covers three of the OG sessions devoted to neutrino, gravitational wave, and gamma-ray detection.

[5] Thierry Pradier. Antares/Virgo Coincidences : a feasibility study. 2008. [ bib | http ]
Sources of gravitational waves (GW) and emitters of high energy (HE) neutrinos both involve compact objects and matter moving at relativistic speeds. Coincidences between Virgo and Antares would give a unique insight on the physics of the most powerful objects in the Universe. The feasibility of such GW/HE neutrino coincidences is analysed.

[6] B. E. Zhilyaev and D. L. Dubinovska. The last stages of evolution of close binaries composed of compact companions. 2008. [ bib ]
Gamma-ray bursts (GRB) are the most powerful transient phenomena in the Universe. Nowadays dozens of speculations on the origin of GRB were undertaken, but so far a single model for the origin of, in particular, short GRBs does not exist. The black hole (BH) - neutron star (NS) coalescence is a promising candidate source for short GRBs. Most of binary mergers numerical simulations were carried out with the purpose of investigating the emission of gravitational waves. Such a scenario consists of an inspiral, merging and ringdown phase. In this paper we present the comparison of the observational results and analytical predictions for a test particle in a quasicircular orbit around the BH. The emission of gravitational waves causes a rapid decrease of the orbital radius and a rise of a it chirp of radiation. Matter orbiting the black hole would be expected to produce high-frequency oscillations (HFO). Timescales of the coalescence process are of the order of milliseconds and oscillation frequencies of hundreds Hz for a system with a solar mass BH companion. We report on the detection of HFO in two short gamma-ray bursts in this paper. The frequencies and durations of the oscillations are in agreement with the predicted values. A it chirp phenomenon is identified also. We therefore argue in favor of BH-NS mergers as a scenario for the production of short gamma-ray bursts.

[7] A. Passamonti, B. Haskell, N. Andersson, D. I. Jones, and I. Hawke. Oscillations of rapidly rotating stratified neutron stars. 2008. [ bib ]
We use time-evolutions of the linear perturbation equations to study the oscillations of rapidly rotating neutrons stars. Our models account for the buoyancy due to composition gradients and we study, for the first time, the nature of the resultant g-modes in a fast spinning star. We provide detailed comparisons of non-stratified and stratified models. This leads to an improved understanding of the relationship between the inertial modes of a non-stratified star and the g-modes of a stratified system. In particular, we demonstrate that each g-mode becomes rotation-dominated, i.e. approaches a particular inertial mode, as the rotation rate of the star is increased. We also discuss issues relating to the gravitational-wave driven instability of the various classes of oscillation modes.

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To have a paper added to this page please email Gareth Jones on the Ext Trig mailing list.

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