Optical Modulation in the X-Ray Binary 4U 1543-624 Revisited*
Abstract
The X-ray binary 4U 1543-624 has been provisionally identified as an ultra-compact system with an orbital period of ≃ 18 min. We have carried out time-resolved optical imaging of the binary to verify the ultra-short orbital period. Using 140 min of high-cadence r'-band photometry, we recover the previously-seen sinusoidal modulation and determine a period P = 18.20 ± 0.09 min. In addition, we also see a 7.0 × 10-4 mag min-1 linear decay, likely related to variations in the source's accretion activity. Assuming that the sinusoidal modulation arises from X-ray heating of the inner face of the companion star, we estimate a distance of 6.0-6.7 kpc and an inclination angle of 34°-61° (90% confidence) for the binary. Given the stability of the modulation, we can confirm that the modulation is orbital in origin and 4U 1543-624 is an ultra-compact X-ray binary.
- Publication:
-
Publications of the Astronomical Society of Australia
- Pub Date:
- October 2015
- DOI:
- 10.1017/pasa.2015.36
- arXiv:
- arXiv:1407.1937
- Bibcode:
- 2015PASA...32...35W
- Keywords:
-
- binaries: close;
- stars: individual (4U 1543-624);
- stars: low-mass- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 6 pages, 3 figures, accepted for publication in Publications of the Astronomical Society of Australia (PASA)