Limits on Gravitational-Wave Emission from Selected Pulsars Using LIGO Data

Abstract

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multi-detector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational wave signals. The unprecedented sensitivity of the detectors allow us to set strain upper limits as low as a few times 10 −24 . These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10 −5 for the four closest pulsars.

Searching for gravitational waves from Cassiopeia A with LIGO

“…The LSC uses both fully coherent [1][2][3][4][5] and semi-coherent [6][7][8][9] methods to search for periodic gravitational waves. Semi-coherent methods are computationally cheaper than coherent methods, but coherent methods can achieve greater sensitivity if the cost is feasible.…”

“…Since computational costs are higher for younger objects, we play it safe by taking 300 years (the approximate lower bound) as our fiducial age estimate. In what follows we use the canonical neutron star moment of inertia of 10 45 g cm 2 , although modern equations of state predict values higher for most neutron stars by a factor of 2 or 3 [15].…”

“…The LIGO Scientific Collaboration (LSC) has so far published three types of searches for periodic gravitational waves (GWs): searches for known non-accreting pulsars [1][2][3][4], for the non-pulsing low-mass x-ray binary Sco X-1 [5,6] and all-sky searches for as yet unknown neutron stars [5,[7][8][9]. The first and last types of searches are approaching the indirect upper limits on gravitational wave emission inferred from the observed spindowns (spin frequency derivatives) of pulsars and supernova-based estimates of the neutron star population of the galaxy [5].…”

AXPs/SGRs: Magnetars or quark-stars?

“…The maximum elastic quadrupole deformations sustainable by normal neutron stars and solid strange quark stars might result in distinguishable maximum ellipticities (Owen, 2005), and the gravitational radiation may show the nature of pulsar-like stars. Though we shouldn't detect gravitational wave because of the low spindown powers in the second LIGO science run (Abbott et al, 2005;Owen, 2006), a result of search for known pulsars in future LIGO run might only show upper limits of masses (or radii) for the targets since the gravitational wave radiation could be mass-dependent . It is also worth noting that gravitational wave emission associated with the energetic superflares of SGRs may be gathered from the LIGO data (Horvath, 2005), and that, in fact, LIGO Scientific Collaboration (2007) had put an upper limit on the gravitational wave emission, 7.7 × 10 46 erg, for the 92.5 Hz QPO of SGR 1806-20.…”

Gravitational wave: gamma-ray burst connections

“…All have involved the LIGO detectors, and the GEO detector was involved in three of the first four data runs and has been operating fully in the fifth data run for the past five months. From the earlier science runs, upper limit results on the signals from a number of potential sources such as pulsars and coalescing compact binary stars, as well as on burst events and the level of a stochastic background, have been set (Abbott et al 2005a(Abbott et al ,b, 2006a and a limit on the GW flux associated with GRB030329 has been set (Abbott et al 2005c). It should be noted that there had been early searches for correlations between GRBs and GW bursts using low-temperature bar detectors, see Tricarico et al (2003) and Abbott et al (2005c) for example.…”