Discovery of kHz Fluctuations in Centaurus X-3: Evidence for Photon Bubble Oscillations (PBO) and Turbulence in a High Mass X-ray Binary Pulsar (original) (raw)
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Millisecond Pulsations from a Low‐Mass X‐Ray Binary in the Galactic Center Region
The Astrophysical Journal, 1997
We report the detection with the proportional counter array (PCA) onboard the Rossi X-Ray T iming Explorer (RXT E) of 589 Hz oscillations during three type I X-ray bursts from a low-mass X-ray binary located in the Galactic center region. The bursts, which occurred on 1996 May 15.814, June 4.612, and June 19.414 UT, were observed serendipitously during routine monitoring observations of GRO J1744[28 by RXT E. The strongest pulsations were observed from the May 15 burst, reaching an amplitude of 18% of the [8 keV Ñux in this burst. The pulsation amplitudes in each burst are a strong function of photon energy since no signals were detected in the 1È8 keV band, but there were strong detections above 8 keV. The evolution of the X-ray spectrum through each burst is consistent with modest radius expansion. The pulsations are conÐned to the postcontraction portion of each burst proÐle, consistent with the oscillations recently reported in a burst from KS 1731[26 and also some bursts from 4U 1728[34. The location of the burster in the 1¡ (FWHM) PCA Ðeld of view is constrained by comparing the count rates in the Ðve independent detectors of the PCA. This analysis strongly excludes GRO J1744[28 as the source of these bursts but does not yet allow a deÐnitive identi-Ðcation of the source with any known burster in the Ðeld of view. However, the derived position strongly overlaps that of MXB 1743[29, identifying this source as a strong candidate for the 589 Hz burster. We argue that the observed oscillations are consistent with rotational modulation of the X-ray brightness.
2013
We have investigated properties of the Quasi Periodic Oscillation (QPO) features in the accretion powered X-ray pulsar Cen X-3 over a period of about four years using observations carried out with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer. The observations cover a wide range of X-ray intensity of the source in excess of the binary intensity modulation. We have detected QPOs in 11 out of a total 81 pointings with the PCA with rms intensity fluctuation upto 10%. The QPO peak frequency shows clustering around 40 and 90 mHz with the QPO frequency having no dependence on X-ray intensity. This indicates that either (a) the observed X-ray luminosity of the source is not related to the mass accretion rate or inner radius of the accretion disk or (b) that the QPO generation mechanism in Cen X-3 is different from the beat frequency model or Keplerian frequency model that is believed to be operational in most other transient and persistent X-ray pulsars. We have a...
Low frequency quasi-periodic oscillations in the hard X-ray emission from Cygnus X-1
Advances in Space Research, 2000
The observations of the black hole binary Cygnus X-l were made in the energy band of 20-100keV with a balloon-borne Xenonfilled multiwire proportional counter telescope on 5th April 1992. Timing analysis of the data revealed the presence of Quasi-Periodic Oscillations (QPO) in the hard X-ray emission from the source. The QPO feature in the power density spectrum is broad with a peak at a frequency of 0.06 Hz. This result is compared with similar reports of QPOs in Cyg X-l in soft and hard X-rays. Short time scale random intensity variations in the X-ray light curve are described with a shot noise model.
The Astrophysical Journal, 1997
We have detected quasi-periodic oscillations (QPOs) near 1 kHz from the low mass X-ray binary 4U 0614+091 in observations with XTE. The observations span several months and sample the source over a large range of X-ray luminosity. In every interval QPOs are present above 400 Hz with fractional RMS amplitudes from 3 to 12%. At high count rates, two high frequency QPOs are detected simultaneously. The difference of their frequency centroids is consistent with 323 Hz in all observations. During one interval a third signal is detected at 328 ± 2 Hz. This suggests the system has a stable 'clock' which is most likely the neutron star with spin period 3.1 msec. Thus, our observations and those of another neutron star system by provide the first evidence for millisecond pulsars within low-mass X-ray binary systems and reveal the 'missing-link' between millisecond radiopulsars and the late stages of binary evolution in low mass X-ray binaries . We suggest that the kinematics of the magnetospheric beat-frequency model applies to these QPOs. In this interpretation the high frequency signal is associated with the Keplerian frequency of the inner accretion disk and the lower frequency 'beat' signal arises from the differential rotation frequency of the inner disk and the spinning neutron star. Assuming the high frequency QPO is a Keplerian orbital frequency for the accretion disk, we find a maximum mass of 1.9M ⊙ and a maximum radius of 17 km for the neutron star.
Astrophysical Journal, 1997
We have detected high-frequency (HF) quasi-periodic oscillations (QPOs) from the low-mass X-ray binary 4U 1820Ϫ303 during observations performed in 1996 October using the Rossi X-ray Timing Explorer. The QPOs are visible when the source occupies the low-state luminosity range L X ϭ 2.4 -3.1 ϫ 10 37 ergs s Ϫ1 (2-20 keV, at 6.4 kpc); the centroid frequency of the main QPO peak varies between 546 H 2 Hz and 796 H 6 Hz and is tightly correlated with the source count rate. The measured QPO widths are typically 120 Hz, with mean rms amplitude 4.1% H 0.3%. At the upper end of this luminosity range a second significant QPO peak appears with frequency 1065 H 7 Hz, width 40 H 20 Hz, and rms amplitude 3.2% H 0.8%. When both QPOs are visible simultaneously, the difference between their frequencies is 275 H 8 Hz. When the source brightens beyond L X ϭ 3.1 ϫ 10 37 ergs s Ϫ1 (110% of the Eddington limit for a helium-rich envelope), neither QPO is detected. Neither the magnetospheric beat frequency model nor the sonic point model of HF QPOs provides a perfect explanation of the phenomenology we observe.
Quasi-periodic Oscillations in XTE J0111.2-7317: Highest Frequency among the HMXB Pulsars
Astrophysical Journal, 2007
We report here discovery of Quasi Periodic Oscillations (QPOs) in the High Mass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburst in this source in December 1998. Using observations made with the proportional counter array of the Rossi X-ray Timing Explorer during the second peak and the declining phase of this outburst we have discovered a QPO feature at a frequency of 1.27 Hz. We have ruled out the possibility that the observed QPOs can instead be from the neighbouring bright X-ray pulsar SMC X-1. This is the highest frequency QPO feature ever detected in any HMXB pulsar. In the absence of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along with the pulse period and X-ray flux measurement measurement helps us to constrain the magnetic field strength of the neutron star.
Astrophysical Journal, 2007
IGR J00291+5934 is one of the seven accreting millisecond pulsars (AMPs) discovered so far. We report on the aperiodic timing and color analysis of its X-ray flux, using all the RXTE observations of the 2004 outburst. Flat-top noise and two harmonically related quasi-periodic oscillations, all of them at very low frequencies (0.01-0.1 Hz), were present in the power spectra during most of the outburst as well as a very high fractional variability (∼50 %). These properties are atypical not only for AMPs but also for neutron star low-mass X-ray binaries (LMXBs) in general. There are instead some remarkable similarities with the variability observed in black hole systems, reinforcing the connections between these two types of LMXB, as well as some interesting differences. We note finally that the results of this paper are difficult to reconcile with interpretations where any break frequency of power density spectra scales inversely with the mass of the central object at an accuracy sufficient to distinguish between the masses of neutron stars and black holes in LMXBs.
The Astrophysical Journal, 1999
We study systematically the ≃ 0.1 − 1200 Hz quasi-periodic oscillations (QPOs) and broad noise components observed in the power spectra of non-pulsing neutron-star and black-hole low-mass X-ray binaries. We show that among these components we can identify two, occurring over a wide range of source types and luminosities, whose frequencies follow a tight correlation. The variability components involved in this correlation include neutron-star kilohertz QPOs and horizontal-branch oscillations, as well as black-hole QPOs and noise components. Our results suggest that the same types of variability may occur in both neutron-star and black-hole systems over three orders of magnitude in frequency and with coherences that vary widely but systematically. Confirmation of this hypothesis will strongly constrain theoretical models of these phenomena and provide additional clues to understanding their nature.