kHz QUASI-PERIODIC OSCILLATIONS FROM THE 2000 AND 2010 X-RAY TRANSIENTS LOCATED IN THE GLOBULAR CLUSTER TERZAN 5: EXO1745-248 AND IGR J17480-2446
- Institut de Recherche en Astrophysique et Planetologie and Universite de Toulouse (UPS), 9 Avenue du Colonel Roche, BP 44346, 31028, Toulouse Cedex 4 (France)
EXO1745-248 is a transient neutron star low-mass X-ray binary located in the globular cluster Terzan 5. It was in outburst in 2000 and displayed during one Rossi X-ray Timing Explorer observation a highly coherent quasi-periodic oscillation (QPO) at frequencies between 670 and 715 Hz. Applying a maximum likelihood method to fit the X-ray power density spectrum, we show that the QPO can be detected on segments as short as T = 48 s. We find that its width is consistent with being constant, while previous analysis based on longer segment duration (200 s) found it variable. If the QPO frequency variations in EXO1745-248 follow a random walk (i.e., the contribution of the drift to the measured width increases like {radical}T), we derive an intrinsic width of {approx}2.3 Hz. This corresponds to an intrinsic quality factor of Q {approx} 297 {+-} 50 at 691 Hz. We also show that Q is consistent with being constant between 2.5 and 25 keV. IGR J17480-2446 is another X-ray transient located in Terzan 5. It is a very interesting object showing accretion-powered pulsations and burst oscillations at 11 Hz. We report on the properties of its kHz QPOs detected between October 18 and October 23, soon after the source had moved from the so-called Atoll state to the Z state. Its QPOs are typical of persistent Z sources; in the sense that they have low Q factors ({approx}30) and low rms amplitudes ({approx}5%). The highest frequency (at 870 Hz), if orbital, sets a lower limit on the inner disk radius of {approx}18.5 km and an upper limit to the dipole moment of the magnetic field {mu} {<=} 5 Multiplication-Sign 10{sup 26} G cm{sup 3}.
- OSTI ID:
- 22036910
- Journal Information:
- Astrophysical Journal, Vol. 753, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
ON THE FORMATION OF THE PECULIAR LOW-MASS X-RAY BINARY IGR J17480-2446 IN TERZAN 5
X-RAY BURSTS FROM THE TERZAN 5 TRANSIENT IGR J17480-2446: NUCLEAR RATHER THAN GRAVITATIONAL
Related Subjects
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
ASTROPHYSICS
BINARY STARS
DIPOLE MOMENTS
EMISSION SPECTRA
GAMMA ASTRONOMY
GRAPH THEORY
KEV RANGE
KHZ RANGE
MAGNETIC FIELDS
MAXIMUM-LIKELIHOOD FIT
NEUTRON STARS
OSCILLATIONS
PERIODICITY
POWER DENSITY
QUALITY FACTOR
STAR CLUSTERS
TRANSIENTS
X RADIATION
X-RAY SPECTRA