Gravitational waves from rotating neutron stars: Current limits and prospects
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ravitational Waves from Rotating Neutron Stars: Current Limits and Prospects1 M. Bejger Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00716 Warsaw, Poland email: [email protected] Abstract—Rotating neutron stars that emit continuous gravitational waves are among promising targets of the LIGO and Virgo detectors: sufficiently large nonaxisymmetrie deformation w.r.t. the axis of rotation of a star generates a timevarying massquadrupole moment and henceforth gravitational wave emission. The departure from an axisymmetrie shape may be caused by the internal magnetic field and/or elastic stresses in the crust/core. If detected, it will provide novel insight into the presently obscured details of the interior neu tronstar structure. This talk presents basic types of searches for such signals: from targeted searches from known pulsars to allsky wide parameter searches for unknown objects. Selected methods used in the data analysis and to calculate the upper limits on the gravitational waves in the initial phase of LIGO and Virgo projects are briefly described. Observational results of LIGO and Virgo collaborations include “beating” the spindown limit for the Crab and Vela pulsars [7, 11], search for a coherent signal from the direction of the Cas A supernova remnant [5], as well as the Galactic center [1], SN1987A and the ScoX1 binary with the crosscorrelation method [6], and the allsky searches for signals of unknown position and frequency [2, 4, 8]. DOI: 10.1134/S1063779615050081 1
1. INTRODUCTION
Gravitational waves (GWs) predicted by A. Einstein [16]—variations of the curvature of spacetime that propagate through spacetime in a wavelike fashion— are a direct consequence of the general theory of relativ ity. Some properties of GWs are similar to those of elec tromagnetic waves: speedoflight propagation and the presence of polarization (two distinct ones in general relativity). The indirect evidence for the existence of GWs comes form the observations of tight relativistic binary pulsar systems [18]. Direct detection of GWs will constitute a very precise test of the theory of relativity and open a new observational field: GW astronomy. The most promising GW detector concept is currently of the MichelsonMorley interferometer type. While a GW passes through such a detector, it changes the length of its arms and affects the interference pattern of the laser light circulating in the interferometer [24]. Stateoftheart interferometric GW detectors, LIGO2 in the USA, and the European (Italian French, with the contribution of Hungary, the Neth erlands and Poland) Virgo3 have collected a large amount of data in the socalled Initial Era. Mean while, the advanced LIGO and Virgo detectors are under construction and they are forecasted to start collecting new, more sensitive data in 2015. It is expected that these advanced detectors will be suffi 1 The article is published in the original. 2 http://www.ligo.org 3 https://wwwcascina.virgo.infn.it
ciently sensitive to
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