Constraints on r-modes and Mountains on Millisecond Neutron Stars in Binary Systems

Abstract

Continuous gravitational waves are nearly monochromatic signals emitted by asymmetries in rotating neutron stars. These signals have not yet been detected. Deep all-sky searches for continuous gravitational waves from isolated neutron stars require significant computational expense. Deep searches for neutron stars in binary systems are even more expensive, but these targets are potentially more promising emitters, especially in the hundreds of Hertz region, where ground-based gravitational-wave detectors are most sensitive. We present here an all-sky search for continuous signals with frequency between 300 and 500 Hz, from neutron stars in binary systems with orbital periods between 15 and 60 days and projected semimajor axes between 10 and 40 lt-s. This is the only binary search on Advanced LIGO data that probes this frequency range. Compared to previous results, our search is over an order of magnitude more sensitive. We do not detect any signals, but our results exclude plausible and unexplored neutron star configurations, for example, neutron stars with relative deformations greater than 3 × 10−6 within 1 kpc from Earth and r-mode emission at the level of α ∼ a few 10−4 within the same distance.

Density-clustering of continuous gravitational wave candidates from large surveys

“…All-sky binary searches are computationally extremely expensive and so are the follow-ups. A first test of Density Clustering on the results-data from [27] showed promising results within a few hours of clustering in 6 dimensions (f, α, δ, τ asc , P b , a), showcasing the flexibility and ease of use of the method presented here.…”

Opportunistic Search for Continuous Gravitational Waves from Compact Objects in Long-period Binaries

“…While these upper limits may be impressive considering the sheer volume of the binary parameter space considered, they are nonetheless set in a region which is computationally cheaper to explore with implicit studies such as this one. In contrast, other recent searches (Covas & Sintes 2020;Abbott et al 2021b;Covas et al 2022) have explored binary parameter spaces (see Figure 4), where implicit searches are useless, leaving computationally expensive explicit searches as the only option. This impacts both the "breadth" and the sensitivity of those searches.…”

Improved all-sky search method for continuous gravitational waves from unknown neutron stars in binary systems

“…where for the present application (such as [1]) at most first-or second-order u k will be needed in practice, as discussed in Sec. III C 1.…”

“…The usage of a limited number of Taylor coordinates u k incurs an intrinsic mismatch due to the corresponding approximation of the signal waveform. In practice we currently envisage using only u 1 or at most up to order u 2 , which turns out to be sufficient for currently considered practical all-sky binary searches (similar to the recent search [1] using only u 1 ) due to computational constraints. Therefore we quantify the mismatch and corresponding constraints on the maximum coherent segment length T seg due to truncation to order u 1 or u 2 .…”

“…The development of more sensitive all-sky binary search methods is of utmost importance since more than half of all known millisecond pulsars are part of a binary system 1 [20]. Furthermore, accretion from a companion gives a plausible mechanism to generate an asymmetry or excite an r-mode with a detectable amplitude in the current generation of gravitational-wave detectors, as recently discussed in [1]. This paper is organized as follows: in Sec.…”