An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536

Details An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536 An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536

2005-05-19

arxiv.org/abs/astro-ph/0505402v1

Mon.Not.Roy.Astron.Soc. 361 (2005) 855-860

Astronomy and Astrophysics

Astrophysics

Accepted for publication in MNRAS, 7 pages, 5 figures (1 in color)

Scientific paper

10.1111/j.1365-2966.2005.09214.x

Using archival data from the Rossi X-ray Timing Explorer (RXTE), we study in a systematic way the variation of the quality factor and amplitude of the lower and upper kHz quasi-periodic oscillations (QPO) in the low-mass X-ray binary 4U1636-536, over a frequency range from ~550 Hz to ~1200 Hz. When represented in a quality factor versus frequency diagram, the upper and lower QPOs follow two different tracks, suggesting that they are distinct phenomena, although not completely independent because the frequency difference of the two QPOs, when detected simultaneously, remains within ~60 Hz of half the neutron star spin frequency (at 581 Hz). The quality factor of the lower kHz QPO increases with frequency up to a maximum of ~200 at ~850 Hz, then drops precipitously to Q~50 at the highest detected frequencies ~920 Hz. A ceiling of the lower QPO frequencies at 920 Hz is also clearly seen in a frequency versus count rate diagram. The quality factor provides a measure of the coherence of the underlying oscillator. For exponentially damped sinusoidal shots, the highest Q observed corresponds to an oscillator coherence time of ~ 0.1 seconds. All existing QPO models face challenges in explaining such a long coherence time and the significantly different behaviours of the quality factors of the upper and lower QPOs reported here. It is therefore difficult to be certain of the implications of the abrupt change in the lower QPO at ~850 Hz. We discuss various possible causes, including that the drop in coherence is ultimately caused by effects related to the innermost stable circular orbit (abridged).

Affiliated with

Also associated with

No associations

Rating

An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536 will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-582498