Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model

Abstract

We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h 95% 0 ¼ 3.47 × 10 −25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.

All-sky search in early O3 LIGO data for continuous gravitational-wave signals from unknown neutron stars in binary systems

“…A [15,45] [10, 40] B [7,15] [5, 15] C [5,7] [2, 10] D [3, 5] [2, 5] The number count statistic can be efficiently computed by means of the look up table (LUT) approach described in [15]. Incidentally, this strategy simplifies the cost by analyzing multiple sky positions (called sky patches) together.…”

“…All-sky searches, such as the one reported in this paper, impose the least amount of constraints on the CW emission. The latest results obtained by the LIGO-Virgo collaboration using Advanced LIGO [3] and Advanced Virgo [4] data, covering targeted (known pulsars), directed (known sky locations), and all-sky searches, can be found in [5][6][7][8][9][10].…”

Science case for the Einstein telescope

“…No continuous gravitational wave signal has so far been observed by Advanced LIGO and Advanced Virgo, see e.g. [46][47][48][49][50][51] for recently obtained upper limits. The detection of continuous GWs from NS by ET would be a fundamental breakthrough, that would provide clues about the condition of formation of isolated NS, their spin, thermal evolution and magnetic field.…”

Search for continuous gravitational waves from Fomalhaut b in the second Advanced LIGO observing run with a hidden Markov model

“…A great deal of work has been carried out to develop methods and conduct searches for CWs. There are three main types of CW searches: (1) targeted searches for pulsars whose sky positions and ephemerides are well measured electromagnetically (e.g., [9,10]), (2) directed searches for neutron stars with known sky positions but unknown rotation frequencies (e.g., [11][12][13][14]), and (3) all-sky searches, surveys done over the whole sky to search for emitting sources (e.g., [15]).…”

“…Thus, although fully coherent searches are still of interest in certain systems with negligible timing noise, we conduct a computationally efficient semicoherent search based on a hidden Markov model (HMM) scheme, equipped to track the evolving signal frequency due to secular spin down and stochastic timing noise [22]. The tracking scheme has its origins in engineering, and has recently been used in many CW searches (e.g., [11,14,[23][24][25]).…”