Precision Ephemerides for Gravitational-wave Searches – III. Revised system parameters of Sco X-1

Abstract

Neutron stars in low-mass X-ray binaries are considered promising candidate sources of continuous gravitational-waves. These neutron stars are typically rotating many hundreds of times a second. The process of accretion can potentially generate and support non-axisymmetric distortions to the compact object, resulting in persistent emission of gravitational-waves. We present a study of existing optical spectroscopic data for Sco X-1, a prime target for continuous gravitational-wave searches, with the aim of providing revised constraints on key orbital parameters required for a directed search with advanced-LIGO data. From a circular orbit fit to an improved radial velocity curve of the Bowen emission components, we derived an updated orbital period and ephemeris. Centre of symmetry measurements from the Bowen Doppler tomogram yield a centre of the disc component of 90 km s −1 , which we interpret as a revised upper limit to the projected orbital velocity of the NS K 1 . By implementing Monte Carlo binary parameter calculations, and imposing new limits on K 1 and the rotational broadening, we obtained a complete set of dynamical system parameter constraints including a new range for K 1 of 40-90 km s −1 . Finally, we discussed the implications of the updated orbital parameters for future continuous-waves searches.

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

“…The search range for a 0 is 1.45 ≤ a 0 =ð1 sÞ ≤ 3.25, which matches the most recent electromagnetic measurement [57] and widens the error bars on the widely cited and previous best published measurement, a 0 ¼ 1.44 AE 0.18 s [62].…”

“…The one-sigma uncertainty in the published value for T asc is AE50 s [57,59] for a time of ascension at GPS time 974416624 s (in November 2010). As O2 took place significantly after this time, to make a conservative estimate on appropriate error bars for T asc , we advance T asc by adding 3135 orbital periods to the time of ascension taken from Ref.…”

“…As O2 took place significantly after this time, to make a conservative estimate on appropriate error bars for T asc , we advance T asc by adding 3135 orbital periods to the time of ascension taken from Ref. [57]. As there is uncertainty associated with the measured orbital period, this widens the one-sigma uncertainty of T asc to AE144 s, which we round up to AE150 s. To cover a significant portion of the measured T asc range while keeping the search computationally feasible, we search a two-sigma range around the central T asc , namely, 1164 543 014 ≤ T asc =ð1 sÞ ≤ 1 164 543 614 (expressed for presentation purposes as the time of the last ascension before the start of O2).…”

Directional limits on persistent gravitational waves using data from Advanced LIGO’s first two observing runs

“…The uncertainty on the frequency for the SNR reported in Table II is a reflection of the original (uncombined) frequency bin width. The ephemeris for Scorpius X-1 has been updated since the publication of [11], and so the search presented below assumes a projected semimajor axis, a 0 , in the center of the range presented by [49].…”

Phase-resolved spectroscopy of Gaia14aae: line emission from near the white dwarf surface

“…For the Doppler map fitting method, we measured the positions of the two bright spots in velocity space by producing Doppler maps of the spectral lines and fitting the features with a two-dimensional Gaussian. Uncertainties on these values were derived using the bootstrapping method described by Wang et al (2017Wang et al ( , 2018. 2000 sets of bootstrapped spectra were produced as described above.…”