Abstract
The LIGO's discovery of binary black hole mergers has opened up a new era of transient gravitational wave astronomy. The potential detection of gravitational radiation from another class of astronomical objects, rapidly spinning non-axisymmetric neutron stars, would constitute a new area of gravitational wave astronomy. Scorpius X-1 (Sco X-1) is one of the most promising sources of continuous gravitational radiation to be detected with present-generation ground-based gravitational wave detectors, such as Advanced LIGO and Advanced Virgo. As the sensitivity of these detectors improve in the coming years, so will power of the search algorithms being used to find gravitational wave signals. Those searches will still require integation over nearly year long observational spans to detect the incredibly weak signals from rotating neutron stars. For low mass X-ray binaries such as Sco X-1 this difficult task is compounded by neutron star "spin wandering" caused by stochastic accretion fluctuations. In this paper, we analyze X-ray data from the RXTE satellite to infer the fluctuating torque on the neutron star in Sco X-1. We then perform a large-scale simulation to quantify the statistical properties of spin-wandering effects on the gravitational wave signal frequency and phase evolution. We find that there are a broad range of expected maximum levels of frequency wandering corresponding to maximum drifts of between 0.3-50 {\mu}Hz/sec over a year at 99% confidence. These results can be cast in terms of the maximum allowed length of a coherent signal model neglecting spin-wandering effects as ranging between 5-80 days. This study is designed to guide the development and evaluation of Sco X-1 search algorithms.
Highlights
AND MOTIVATIONIt has long been proposed that rapidly spinning neutron stars could emit detectable gravitational waves (GWs) [1,2,3] and that neutron stars in low-mass X-ray binary (LMXB) systems form an especially interesting class of objects
In the contrasting continuous emission scenario, GWs generated from the neutron star within the Scorpius X-1 (Sco X-1) system are an exciting prospect for detection
We studied the spin-wandering effect of the neutron star in Sco X-1 using the x-ray observations of the source with all-sky monitor (ASM) and Proportional Counter Array (PCA) instruments onboard the RXTE satellite
Summary
It has long been proposed that rapidly spinning neutron stars could emit detectable gravitational waves (GWs) [1,2,3] and that neutron stars in low-mass X-ray binary (LMXB) systems form an especially interesting class of objects. The spin-down torque due to GW and EM emission is generally unlikely to change by a significant amount during the observation period (∼1 year), the mass accretion rate can change appreciably over this timescale, leading to an appreciable change in the instantaneous stellar spin-frequency and affect cumulative rotational phase. Such fluctuations make it challenging to integrate a GW signal coherently and achieve ideal detection efficiency. Numerical results are presented for expected fluctuation effects on the GW frequency (fGW) and GW phase (φGW) as a function of search integration time ranging over time scales of ∼ hour to greater than a year
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
