Peter G. Jonker
University of Amsterdam
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Peter G. Jonker.
The Astrophysical Journal | 2002
Jeroen Homan; Michiel van der Klis; Peter G. Jonker; Rudy Wijnands; Erik Kuulkers; Mariano Mendez; W. H. G. Lewin
We have analyzed ~600 ks of Rossi X-Ray Timing Explorer data of the neutron star low-mass X-ray binary and Z source GX 17+2. A study was performed of the properties of the noise components and quasi-periodic oscillations (QPOs) as a function of the broadband spectral properties, with the main goal to study the relation between the frequencies of the horizontal branch (HBO) and upper kHz QPOs. It was found that when the upper kHz QPO frequency is below 1030 Hz these frequencies correlate, whereas above 1030 Hz they anticorrelate. GX 17+2 is the first source in which this is observed. We also found that the frequency difference of the high-frequency QPOs was not constant and that the quality factors (Q-values) of the HBO, its second harmonic, and the kHz QPOs are similar and vary almost hand in hand by a factor of more than 3. Observations of the normal branch oscillations during two type I X-ray bursts showed that their absolute amplitude decreased as the flux from the neutron star became stronger. We discuss these and other findings in terms of models that have been proposed for these phenomena. We also compare the behavior of GX 17+2 and other Z sources with that of black hole sources and consider the possibility that the mass accretion rate might not be the driving force behind all spectral and variability changes.
The Astrophysical Journal | 2000
Eric C. Ford; Michiel van der Klis; Mariano Mendez; Rudy Wijnands; Jeroen Homan; Peter G. Jonker; Jan van Paradijs
We measure simultaneously the properties of the energy spectra and the frequencies of the kilohertz quasi-periodic oscillations (QPOs) in 15 low-mass X-ray binaries covering a wide range of X-ray luminosities. In each source, the QPO frequencies cover the same range of approximately 300-1300 Hz, although the sources differ by 2 orders of magnitude in their X-ray luminosities (as measured from the unabsorbed 2-50 keV flux). So the X-ray luminosity does not uniquely determine the QPO frequency. This is difficult to understand since the evidence from individual sources indicates that the frequency and luminosity are very well correlated at least over short timescales. Perhaps beaming effects or bolometric corrections change the observed luminosities, or perhaps part of the energy in mass accretion is used to power outflows, thus reducing the energy emitted in X-rays. It is also possible that the parameters of a QPO model are tuned in such a way that the same range of frequencies appears in all sources. Different modes of accretion may be involved (for example, disk and radial), or multiple parameters may conspire to yield the same frequencies.
The Astrophysical Journal | 2000
Peter G. Jonker; Michiel van der Klis; Rudy Wijnands; Jeroen Homan; Jan van Paradijs; Mariano Mendez; Eric C. Ford; Erik Kuulkers; Frederick K. Lamb
We present an analysis of ~390 ks of data of the Z source GX 340+0 taken during 24 observations with the Rossi X-Ray Timing Explorer satellite. We report the discovery of a new broad component in the power spectra. The frequency of this component varied between 9 and 14 Hz and remained close to half that of the horizontal-branch quasi-periodic oscillations (HBOs). Its rms amplitude was consistent with being constant around ~5%, while its FWHM increased with frequency from 7 to 18 Hz. If this sub-HBO component is the fundamental frequency, then the HBO and its second harmonic are the second and fourth harmonic component, while the third harmonic was not detected. This is similar to what was recently found for the black hole candidate XTE J1550-564. The profiles of both the horizontal- and the normal-branch quasi-periodic oscillation peaks were asymmetric when they were strongest. We describe this in terms of a shoulder component at the high-frequency side of the quasi-periodic oscillation peak, of which the rms amplitudes were approximately constant at ~4% and ~3%, respectively. The peak separation between the twin kilohertz quasi-periodic oscillations was consistent with being constant at 339±8 Hz, but a trend similar to that seen in, e.g., Sco X-1 could not be excluded. We discuss our results within the framework of the various models that have been proposed for the kilohertz QPOs and low-frequency peaks.
The Astrophysical Journal | 1999
Dimitrios Psaltis; Rudy Wijnands; Jeroen Homan; Peter G. Jonker; Michiel van der Klis; M. Coleman Miller; Frederick K. Lamb; Erik Kuulkers; Jan van Paradijs; W. H. G. Lewin
Three types of quasi-periodic oscillations (QPOs) have been discovered so far in the persistent emission of the most luminous neutron star low-mass X-ray binaries, the Z sources: ~10-60 Hz horizontal-branch and ~6-20 Hz normal/flaring-branch oscillations and ~200-1200 Hz kilohertz QPOs, which usually occur in pairs. Here we study the horizontal-branch oscillations and the two simultaneous kilohertz QPOs, which were discovered using the Rossi X-Ray Timing Explorer, comparing their properties in five Z sources with the predictions of the magnetospheric beat-frequency and Lense-Thirring precession models. We find that the variation of the horizontal-branch oscillation frequency with accretion rate predicted by the magnetospheric beat-frequency model for a purely dipolar stellar magnetic field and a radiation-pressure-dominated inner accretion disk is consistent with the observed variation. The model predicts a universal relation between the horizontal-branch oscillation, stellar spin, and upper kilohertz QPO frequencies that agrees with the data on five Z sources. The model implies that the neutron stars in the Z sources are near magnetic spin equilibrium, that their magnetic field strengths are ~109-1010 G, and that the critical fastness parameter for these sources is 0.8. If the frequency of the upper kilohertz QPO is an orbital frequency in the accretion disk, the magnetospheric beat-frequency model requires that a small fraction of the gas in the disk does not couple strongly to the stellar magnetic field at 3-4 stellar radii but instead drifts slowly inward in nearly circular orbits until it is within a few kilometers of the neutron star surface. The Lense-Thirring precession model is consistent with the observed magnitudes of the horizontal-branch oscillation frequencies only if the moments of inertia of the neutron stars in the Z sources are ~4-5 times larger than the largest values predicted by realistic neutron star equations of state. If instead the moments of inertia of neutron stars have the size expected and their spin frequencies in the Z sources are approximately equal to the frequency separation of the kilohertz QPOs, Lense-Thirring precession can account for the magnitudes of the horizontal-branch oscillation frequencies only if the fundamental frequency of the horizontal-branch oscillation is at least 4 times the precession frequency. We argue that the change in the slope of the correlation between the frequency of the horizontal-branch oscillation and the frequency of the upper kilohertz QPO, when the latter is greater than 850 Hz, is directly related to the varying frequency separation of the kilohertz QPOs.
The Astrophysical Journal | 1998
Dimitrios Psaltis; Mariano Mendez; Rudy Wijnands; Jeroen Homan; Peter G. Jonker; Michiel van der Klis; Frederick K. Lamb; Erik Kuulkers; Jan van Paradijs; W. H. G. Lewin
Pairs of quasi-periodic oscillations (QPOs) at kilohertz frequencies are a common phenomenon in several neutron-star low-mass X-ray binaries. The frequency separation of the QPO peaks in the pair appears to be constant in many sources and directly related to the neutron star spin frequency. However, in Sco X-1 and possibly in 4U 1608-52, the frequency separation between the QPO peaks decreases with increasing inferred mass accretion rate. We show that the currently available Rossi X-Ray Timing Explorer data are consistent with the hypothesis that the peak separations in all sources vary by amounts similar to the variation in Sco X-1. We discuss the implications for models of the kilohertz QPOs.
The Astrophysical Journal | 1998
Peter G. Jonker; Rudy Wijnands; Michiel van der Klis; Dimitrios Psaltis; Erik Kuulkers; Frederick K. Lamb
We discovered two simultaneous kHz quasi-periodic oscillations (QPOs) in the bright low-mass X-ray binary and Z source GX 5-1 with the Rossi X-ray Timing Explorer. In the X-ray color-color and hardness-intensity diagram a clear Z track is traced out, which shifted between observations. The frequencies of the two kHz QPOs increased from ~215 and ~500 Hz on the left part of the horizontal branch to ~700 and ~ 890 Hz, respectively, on the upper part of the normal branch. With increasing frequency the FWHM and rms amplitude (8.6-60 keV) of the higher frequency kHz QPO decreased from 300 to 30 Hz, and from 6.6% to 2.4%, respectively. The FWHM and amplitude of the lower frequency kHz QPO (50-100 Hz and 3%-4% rms) did not correlate with the position of the source on the Z track. The kHz QPO separation was consistent with being constant at 298±11 Hz. Simultaneously with the kHz QPOs horizontal branch oscillations were detected with frequencies between 18 and 56 Hz.
web science | 1998
Paul J. De Groot; Titus J. Galama; Paul M. Vreeswijk; R.A.M.J. Wijers; E. Pian; E. Palazzi; J. van Paradijs; C. Kouveliotou; J. J. M. in 't Zand; J. Heise; C. R. Robinson; Nial R. Tanvir; C. Lidman; C. G. Tinney; M. Keane; Michael Stephen Briggs; K. Hurley; J.-F. Gonzalez; Patrick B. Hall; M. Smith; R. Covarrubias; Peter G. Jonker; J. Casares; N. Masetti; F. Frontera; M. Feroci; Luigi Piro; Enrico Costa; Roger Smith; B. Jones
We report the discovery of the optical counterpart to GRB 980326. Its rapid optical decay can be characterized by a power law with exponent - 2.10+/-0.13 and a constant underlying source at R_{{c}}=25.5+/-0.5 . Its optical colors 2.1 days after the burst imply a spectral slope of - 0.66+/-0.70 . The gamma -ray spectrum as observed with BATSE shows that it is among the 4% softest bursts ever recorded. We argue that the rapid optical decay may be a reason for the nondetection of some low-energy afterglows of GRBs
Monthly Notices of the Royal Astronomical Society | 2001
C. Brocksopp; Peter G. Jonker; R. P. Fender; Paul J. De Groot; M. van der Klis; S.J. Tingay
We present observations of the 1997 outburst of the X-ray transient GS 1354−64 (BW Cir) at X-ray, optical and, for the first time, radio wavelengths; our results include upper limits to the linear and circular polarization for the radio data. The X-ray outburst was unusual in thatxa0the source remained in the low/hard X-ray state throughout; the X-ray peak was also preceded by at least one optical outburst, suggesting that it was an ‘outside-in’ outburst – similar to those observed in dwarf novae systems, although possibly taking place on a viscous time-scale in this case. It therefore indicates that the optical emission was not dominated by the reprocessing of X-rays, but that instead we see the instability directly. While the radio source was too faint to detect any extended structure, spectral analysis of the radio data and a comparison with other similar systems suggest that mass ejections, probablyxa0in the form of a jet, took place and that the emitted synchrotron spectrum may have extended as far as infrared wavelengths. Finally, we compare this 1997 outburst of GS 1354−64 with possible previous outbursts and also with other hard-state objects, both transient and persistent. It appears that a set of characteristics – such as a weak, flat-spectrum radio jet, a mHz QPO increasing in frequency, a surprisingly high optical/X-ray luminosity ratio, and the observed optical peak preceding the X-ray peak – may be common to all hard-state X-ray transients.
Monthly Notices of the Royal Astronomical Society | 2002
Peter G. Jonker; M. van der Klis; Jeroen Homan; Mariano Mendez; W. H. G. Lewin; Rudy Wijnands; William W. Zhang
ABSTRA C T We report on a detailed analysis of data obtained over nearly four years with the Rossi X-ray Timing Explorer of the Z source GX 5 ‐ 1. From a spectral analysis using a hardness ‐intensity diagram it was found that the source traced out the typical Z-shaped pattern. The study of the power spectral properties showed that when the source moved on the horizontal branch towards the normal branch the fractional rms amplitudes and time-scales of all variability decreased, while their FWHMs increased. The frequency separation of the two kHz QPO peaks decreased from 344 ^ 12 to 232 ^ 13 Hz, while the frequency of the lower and upper kHz QPO increased from 172 ^ 10 to 608 ^ 6 Hz and from 516 ^ 10 to 840 ^ 12 Hz, respectively. At low frequencies, besides the horizontal branch oscillation (HBO) and its second harmonic, two additional broad Lorentzian components were needed to obtain acceptable fits. These broad Lorentzians have Q-values of , 1 ‐2 and frequencies 0.5 and 1.5 times the HBO frequency. When interpreted as being related to the HBO, they seem to favour disc models for the HBO over the magnetic beat-frequency model. The frequency of the normal branch oscillations changed slightly and non-monotonically, while on the normal branch between , 6 Hz at both ends and 5:25 ^ 0:05 Hz near the middle of the branch. It evolved into a flat-topped noise component on the flaring branch. We compared the timing properties of the some of the Z sources. We also compare the timing properties and colour ‐ colour diagrams (CDs) of GX 5 ‐1 with those of the back hole candidate XTE J1550 ‐ 564 and the atoll source 4U 1608 ‐ 52. The CDs are strikingly similar when a colour scheme commonly employed in back hole studies is used. However, this may be a degeneracy as the CDs turn out to be more complicated when colours common in neutron star studies are employed. Apart from some remarkable similarities between the CD of XTE J1550 ‐ 564 and that of 4U 1608 ‐ 52, several differences can be seen between these CDs and that of GX 5 ‐1. Conclusions on spectral states or properties based solely on the use of CDs using the ‘black hole scheme’ should be regarded with caution.
The Astrophysical Journal | 2001
Peter G. Jonker; Michiel van der Klis
We report the discovery of 0.59 s X-ray pulsations from the low-mass X-ray binary, 5.57 hr dipping and eclipsing accretion disk corona source 2A 1822-371. Pulse arrival time analysis indicates a circular orbit with e < 0.03 (95% confidence) and an a sin i for the neutron star of 1.006(5) lt-s, implying a mass function of (2.03 ± 0.03) × 10-2 M☉. The barycentric pulse period was 0.59325(2) s in 1996.270 and 0.59308615(5) s in 1998.205, indicating an average spin-up with /P = (-1.52 ± 0.02) × 10-4 yr-1. For a magnetic field strength of ~(1-5) × 1012 G as derived from the X-ray spectrum, the implied intrinsic X-ray luminosity is ~(2-4) × 1037 ergs s-1. The pulse amplitude is low but increases steeply as a function of energy from a sinusoidal amplitude of 0.25% in 2-5.4 keV to ~3% above 20 keV. We discuss the constraints on the masses of the companion star and the fact that several aspects of the energy spectrum are in qualitative accordance with that of a strongly magnetized neutron star.