DISCOVERY OF A 552 Hz BURST OSCILLATION IN THE LOW-MASS X-RAY BINARY EXO 0748-676
- Center for Stellar and Planetary Astrophysics, Monash University, VIC 3800 (Australia)
- Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional amplitude was 15% (rms). The dynamic power density spectrum for each burst revealed an increase in frequency of {approx}1-2 Hz while the oscillation was present. The frequency drift, the high significance of the detections and the almost identical signal frequencies measured in two bursts separated by 11 months, confirms this signal as a burst oscillation similar to those found in 13 other sources to date. We thus conclude that the spin frequency in EXO 0748 - 676 is within a few Hz of 552 Hz, rather than 45 Hz as was suggested from an earlier signal detection by Villarreal and Strohmayer. Consequently, Doppler broadening must significantly affect spectral features arising from the neutron star surface, so that the narrow absorption features previously reported from an XMM-Newton spectrum could not have arisen there. The origin of both the previously reported 45 Hz oscillation and the X-ray absorption lines is now uncertain.
- OSTI ID:
- 21305104
- Journal Information:
- Astrophysical Journal Letters, Vol. 711, Issue 2; Other Information: DOI: 10.1088/2041-8205/711/2/L148; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
Similar Records
Optical studies of the x-ray transient EXO 0748-676
ECLIPSE TIMINGS OF THE TRANSIENT LOW-MASS X-RAY BINARY EXO 0748-676. IV. THE ROSSI X-RAY TIMING EXPLORER ECLIPSES