Precision Ephemerides for Gravitational-wave Searches. I. Sco X-1
Abstract
Rapidly rotating neutron stars are the only candidates for persistent high-frequency gravitational wave emission, for which a targeted search can be performed based on the spin period measured from electromagnetic (e.g., radio and X-ray) observations. The principal factor determining the sensitivity of such searches is the measurement precision of the physical parameters of the system. Neutron stars in X-ray binaries present additional computational demands for searches due to the uncertainty in the binary parameters. We present the results of a pilot study with the goal of improving the measurement precision of binary orbital parameters for candidate gravitational wave sources. We observed the optical counterpart of Sco X-1 in 2011 June with the William Herschel Telescope and also made use of Very Large Telescope observations in 2011 to provide an additional epoch of radial-velocity measurements to earlier measurements in 1999. From a circular orbit fit to the combined data set, we obtained an improvement of a factor of 2 in the orbital period precision and a factor of 2.5 in the epoch of inferior conjunction T 0. While the new orbital period is consistent with the previous value of Gottlieb et al., the new T 0 (and the amplitude of variation of the Bowen line velocities) exhibited a significant shift, which we attribute to variations in the emission geometry with epoch. We propagate the uncertainties on these parameters through to the expected Advanced LIGO-Virgo detector network observation epochs and quantify the improvement obtained with additional optical observations.
Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 087.D-0278.- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2014
- DOI:
- 10.1088/0004-637X/781/1/14
- arXiv:
- arXiv:1311.6246
- Bibcode:
- 2014ApJ...781...14G
- Keywords:
-
- ephemerides;
- gravitational waves;
- stars: neutron;
- techniques: radial velocities;
- X-rays: binaries;
- X-rays: individual: Sco X-1;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 9 pages, 6 figures, accepted by ApJ