9 research outputs found
RXTE Observations of the Be star X-ray Transient X0726-260 (4U0728-25) - Orbital and Pulse Periods
Rossi X-ray Timing Explorer (RXTE) All Sky Monitor observations of the
transient Be star X-ray source X0726-260 suggest a 34.5 day period. This is
apparently confirmed by a serendipitous RXTE Proportional Counter Array (PCA)
slew detection of the source on 1997 May 5, near the time of a predicted flux
maximum. A subsequent 5000 second pointed observation of X0726-260 with the
RXTE PCA detector was carried out on 1997 June 7, when X0726-260 was predicted
to be bright again, and this revealed pulsations at a period of 103.2 seconds.
If the 34.5 day period is orbital, then the pulse period is surprisingly long
compared to that predicted by the correlation between orbital period and spin
period observed for other Be/neutron star systems. A possible similarity with
GROJ2058+42 is briefly discussed.Comment: 7 pages LateX, 7 figures. To be published in Astrophysical Journal
Letter
A Second Intense Burst with Photospheric Radius Expansion from X2127+119 in M15
In 2000 September we observed a bright X-ray burst from X2127+119 with the
Rossi X-ray Timing Explorer. This burst has a multi-peaked profile, a peak
luminosity of ~6.5x10^{38} erg s^{-1}, a total integrated energy of ~2x10^{40}
ergs, and significant photospheric radius expansion to a maximum extent of
R=118+-5 km. From the luminosity-temperature relation during the expansion
phase we derive estimates for the gravitational redshift at the neutron star
surface, the corrected Eddington luminosity, and the neutron star mass. We
detect no slow (~30s) radial oscillations or fast (100-1200 Hz) coherent
oscillations or QPO during the burst.
The 2000 September event is only the second burst ever observed from this
globular cluster binary (in M15 = NGC 7078), and it shares many characteristics
with the event detected by Ginga in 1988 October (Dotani et al. 1990; van
Paradijs et al. 1990), the key difference probably being the total amount of
material consumed in the thermonuclear flash.Comment: 8 pages, 5 figures; accepted for publication in Ap
The rms-flux relations in different branches in Cyg X-2
In this paper, the rms-flux (root mean square-flux) relation along the
Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data
of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e.
positive, negative, and 'arch'-like correlations are found in different
branches. The rms is positively correlated with flux in normal branch (NB), but
anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation
shows an 'arch'-like shape in the horizontal branch (HB). We also try to
explain this phenomenon using existing models.Comment: Accepted for publication in Astrophysics & Space Scienc
The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays
For the first time a quasi-simultaneous multi-wavelength campaign has been
performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band.
4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these
observations it was also observed in the X-ray band with Swift and RXTE, in the
optical and NIR with Gemini North and in the radio with the WSRT. In this paper
we present the source-energy distribution. The spectral results obtained in the
individual wave bands do not connect smoothly; apparently components of
different origin contribute to the total spectrum. Remarkable is that the
INTEGRAL hard X-ray spectrum (power-law index 0.79 +/- 0.10) is now measured up
to an energy of ~230 keV with no indication of a spectral break. Extrapolation
of the INTEGRAL power-law spectrum to lower energies passes orders of magnitude
underneath the NIR and optical fluxes, as well as the low ~30 microJy (2 sigma)
upper limit in the radio band.Comment: 6 pages, 1 figure. To be published in the proceedings of the
conference "Isolated Neutron Stars: from the Interior to the Surface" (April
24-28, 2006, London, UK), eds. S. Zane, R. Turolla and D. Pag
States and transitions in black-hole binaries
With the availability of the large database of black-hole transients from the
Rossi X-Ray Timing Explorer, the observed phenomenology has become very
complex. The original classification of the properties of these systems in a
series of static states sorted by mass accretion rate proved not to be able to
encompass the new picture. I outline here a summary of the current situation
and show that a coherent picture emerges when simple properties such as X-ray
spectral hardness and fractional variability are considered. In particular,
fast transition in the properties of the fast time variability appear to be
crucial to describe the evolution of black-hole transients. Based on this
picture, I present a state-classification which takes into account the observed
transitions. I show that, in addition to transients systems, other black-hole
binaries and Active Galactic Nuclei can be interpreted within this framework.
The association between these states and the physics of the accretion flow
around black holes will be possible only through modeling of the full time
evolution of galactic transient systems.Comment: 30 pages, 11 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009