Searches for periodic gravitational waves from unknown isolated sources and Scorpius X-1: Results from the second LIGO science run

Abstract

We carry out two searches for periodic gravitational waves using the most sensitive few hours of data from the second LIGO science run. Both searches exploit fully coherent matched filtering and cover wide areas of parameter space, an innovation over previous analyses which requires considerable algorithm development and computational power. The first search is targeted at isolated, previously unknown neutron stars, covers the entire sky in the frequency band 160 -728.8 Hz, and assumes a frequency derivative of less than 4 10 ÿ10 Hz=s. The second search targets the accreting neutron star in the lowmass x-ray binary Scorpius X-1 and covers the frequency bands 464-484 Hz and 604-624 Hz as well as the two relevant binary orbit parameters. Because of the high computational cost of these searches we limit the analyses to the most sensitive 10 hours and 6 hours of data, respectively. Given the limited sensitivity and duration of the analyzed data set, we do not attempt deep follow-up studies. Rather we concentrate on demonstrating the data analysis method on a real data set and present our results as upper limits over large volumes of the parameter space. In order to achieve this, we look for coincidences in parameter space between the Livingston and Hanford 4-km interferometers. For isolated neutron stars our 95% confidence level upper limits on the gravitational wave strain amplitude range from 6:6 10 ÿ23 to 1 10 ÿ21 across the frequency band; for Scorpius X-1 they range from 1:7 10 ÿ22 to 1:3 10 ÿ21 across the two 20-Hz frequency bands. The upper limits presented in this paper are the first broadband wide parameter space upper limits on periodic gravitational waves from coherent search techniques. The methods developed here lay the foundations for upcoming hierarchical searches of more sensitive data which may detect astrophysical signals.

First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data

“…Various emission mechanisms could generate such a signal, as reviewed in Sec. IIA of [15]. In interpreting our results we will consider a spinning compact object with a fixed, nonaxisymmetric l ¼ m ¼ 2 mass quadrupole, described by an equatorial ellipticity ε.…”

“…A number of all-sky searches have been carried out on initial LIGO data, [2][3][4][5][6][7][8][9][10][11][12][13][14][15], of which [2,3,7,9,14] also ran on Einstein@Home. Einstein@Home is a distributed computing project which uses the idle time of computers volunteered by the general public to search for GWs.…”

Report on an all-sky LIGO search for periodic gravitational waves in the S4 data

“…The reader should notice that the Hough search sensitivity improves with the summing of powers from two or more interferometers. Over the LIGO frequency band of sensitivity, these S4 all-sky upper limits are approximately an order of magnitude better than those published previously from the second science run (S2) [20,12]. The best population-based upper limit with 95% confidence on the gravitationalwave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin-axes, is 4.28×10 −24 (near 140 Hz) for the multi-interferometer Hough search.…”

Searches for Gravitational Waves from Binary Neutron Stars: A Review

“…This is also true of colliding black holes or neutron stars, which should emit large amounts of energy in gravitational waves. In fact, there are only two sources for ground-based interferometers, inspiralling binary neutron stars and perturbed intermediate mass (∼100 M ⊙ ) black holes, for which the physics is well enough understood that it is believed that the waveforms calculated provide a high degree of confidence for detection 4 .…”

“…There are four categories of gravitational wave signals which ground-based interferometers are currently trying to detect: quasi-periodic signals, such as those expected from pulsars [3,4,5,6,7], stochastic background signals, such as remnant gravitational waves from the Big Bang [8,9,10,11,12], unmodeled burst signals, such as those that might be emitted by supernovae [13,14,15,16,17,18,19], and inspiral signals, such as those from neutron star or black hole binaries [20,21,22,23,24,25,26]. In this article, we will only be concerned with the last of these searches, and in particular the search for neutron star binaries [20,23,25,26].…”