FRACTIONAL AMPLITUDE OF KILOHERTZ QUASI-PERIODIC OSCILLATION FROM 4U 1728-34: EVIDENCE OF DECLINE AT HIGHER ENERGIES
- Tata Institute of Fundamental Research, Mumbai-400005 (India)
A kilohertz quasi-periodic oscillation (kHz QPO) is an observationally robust high-frequency timing feature detected from neutron star low-mass X-ray binaries (LMXBs). This feature can be very useful to probe the superdense core matter of neutron stars and the strong gravity regime. Although many models exist in the literature, the physical origin of kHz QPO is not known, and hence this feature cannot be used as a tool yet. The energy dependence of kHz QPO fractional rms amplitude is an important piece of the jigsaw puzzle to understand the physical origin of this timing feature. It is known that the fractional rms amplitude increases with energy at lower energies. At higher energies, the amplitude is usually believed to saturate, although this is not established. We combine tens of lower kHz QPOs from a neutron star LMXB 4U 1728-34 in order to improve the signal-to-noise ratio. Consequently, we, for the first time to the best of our knowledge, find a significant and systematic decrease of the fractional rms amplitude with energy at higher photon energies. Assuming an energy spectrum model, blackbody+powerlaw, we explore if the sinusoidal variation of a single spectral parameter can reproduce the above-mentioned fractional rms amplitude behavior. Our analysis suggests that the oscillation of any single blackbody parameter is favored over the oscillation of any single power-law parameter, in order to explain the measured amplitude behavior. We also find that the quality factor of a lower kHz QPO does not plausibly depend on photon energy.
- OSTI ID:
- 22092460
- Journal Information:
- Astrophysical Journal, Vol. 756, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
SPECTRAL-TIMING ANALYSIS OF THE LOWER kHz QPO IN THE LOW-MASS X-RAY BINARY AQUILA X-1
STUDYING FREQUENCY RELATIONSHIPS OF KILOHERTZ QUASI-PERIODIC OSCILLATIONS FOR 4U 1636-53 AND Sco X-1: OBSERVATIONS CONFRONT THEORIES
Related Subjects
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
AMPLITUDES
ASTROPHYSICS
BINARY STARS
COSMIC PHOTONS
DATA ANALYSIS
ENERGY DEPENDENCE
ENERGY SPECTRA
GAMMA ASTRONOMY
GRAVITATION
KHZ RANGE
MASS
NEUTRON STARS
OSCILLATIONS
PERIODICITY
QUALITY FACTOR
SIGNAL-TO-NOISE RATIO
X RADIATION
X-RAY DETECTION