261 research outputs found
On the outburst evolution of H1743-322: a 2008/2009 comparison
We present two observational campaigns performed with the RXTE satellite on
the black hole transient H 1743-322. The source was observed in outburst on two
separate occasions between October-November 2008 and May-July 2009. We have
carried out timing and spectral analysis of the data set, obtaining a complete
state classification of all the observations. We find that all the observations
are well described by using a spectral model consisting of a disk-blackbody, a
powerlaw + reflection + absorption and a gaussian emission component. During
the 2009 outburst the system followed the canonical evolution through all the
states seen in black hole transients. In the 2008 outburst only the hard states
were reached. The early evolution of the spectral parameters is consistent
between the two epochs, and it does not provide clues about the subsequent
behavior of the source. The variation of the flux associated to the two main
spectral components (i.e. disk and powerlaw) allows us to set a lower limit to
the orbital inclination of the system of >= 43{\deg}.Comment: 13 pages, 5 figures. Accepted for publication in MNRA
Fast variability as a tracer of accretion regimes in black hole transients
We present the rms-intensity diagram for black hole transients. Using
observations taken with the Rossi X-ray timing explorer we study the relation
between the root mean square (rms) amplitude of the variability and the net
count-rate during the 2002, 2004 and 2007 outbursts of the black hole X-ray
binary GX 339-4. We find that the rms-flux relation previously observed during
the hard state in X-ray binaries does not hold for the other states, when
different relations apply. These relations can be used as a good tracer of the
different accretion regimes. We identify the hard, soft and intermediate states
in the rms-intensity diagram. Transitions between the different states are seen
to produce marked changes in the rms-flux relation. We find that one single
component is required to explain the ~ 40 per cent variability observed at low
count rates, whereas no or very low variability is associated to the
accretion-disc thermal component.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
A connection between accretion state and in an accreting neutron star: black hole-like soft state winds?
High resolution X-ray spectra of accreting stellar mass Black Holes reveal
the presence of accretion disc winds, traced by high ionisation Fe K lines.
These winds appear to have an equatorial geometry and to be observed only
during disc dominated states in which the radio jet is absent. Accreting
neutron star systems also show equatorial high ionisation absorbers. However,
the presence of any correlation with the accretion state has not been
previously tested. We have studied EXO 0748-676, a transient neutron star
system, for which we can reliably determine the accretion state, in order to
investigate the Fe K absorption/accretion state/jet connection. Not one of
twenty X-ray spectra obtained in the hard state revealed any significant Fe K
absorption line. However, intense Fe and Fe
(as well as a rarely observed Fe line plus S ; a blend of S and Ar ; Ca and Ca
, possibly produced by the same high ionisation
material) absorption lines ( eV, eV) are clearly detected during the only soft state
observation. This suggests that the connection between Fe K absorption and
states (and anticorrelation between the presence of Fe K absorption and jets)
is also valid for EXO 0748-676 and therefore it is not a unique property of
black hole systems but a more general characteristic of accreting sources.Comment: Accepted for publication in MNRAS Letter
Time-Delayed transfer functions simulations for LMXBs
Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)
have demonstrated that Bowen flourescence is a very efficient tracer of the
companion star in LMXBs. We present a numerical code to simulate time-delayed
transfer functions in LMXBs, specific to the case of reprocessing in emission
lines. The code is also able to obtain geometrical and binary parameters by
fitting observed (X-ray + optical) light curves using simulated annealing
methods. In this work we present the geometrical model for the companion star
and the analytical model for the disc and show synthetic time-delay transfer
functions for different orbital phases and system parameters.Comment: Contribution presented at the conference "Interacting Binaries:
Accretion, Evolution and Outcomes", held in Cefalu, Sicily (Italy) in July
2004. To be published by AIP (American Institute of Physics), eds. L. A.
Antonelli, L. Burderi, F. D'Antona, T. Di Salvo, G.L. Israel, L. Piersanti,
O. Straniero, A. Tornambe. 4 pages, 4 figure
The evolution of the disc variability along the hard state of the black hole transient GX 339-4
We report on the analysis of hard-state power spectral density function (PSD)
of GX 339-4 down to the soft X-ray band, where the disc significantly
contributes to the total emission. At any luminosity probed, the disc in the
hard state is intrinsically more variable than in the soft state. However, the
fast decrease of disc variability as a function of luminosity, combined with
the increase of disc intensity, causes a net drop of fractional variability at
high luminosities and low energies, which reminds the well-known behaviour of
disc-dominated energy bands in the soft state. The peak-frequency of the
high-frequency Lorentzian (likely corresponding to the high-frequency break
seen in active galactic nuclei, AGN) scales with luminosity, but we do not find
evidence for a linear scaling. In addition, we observe that this characteristic
frequency is energy-dependent. We find that the normalization of the PSD at the
peak of the high-frequency Lorentzian decreases with luminosity at all
energies, though in the soft band this trend is steeper. Together with the
frequency shift, this yields quasi-constant high frequency (5-20 Hz) fractional
rms at high energies, with less than 10 percent scatter. This reinforces
previous claims suggesting that the high frequency PSD solely scales with BH
mass. On the other hand, this constancy breaks down in the soft band (where the
scatter increases to ~30 percent). This is a consequence of the additional
contribution from the disc component, and resembles the behaviour of optical
variability in AGN.Comment: 12 pages, 8 figures, accepted for publication in MNRA
Tracing the reverberation lag in the hard state of black hole X-ray binaries
We report results obtained from a systematic analysis of X-ray lags in a
sample of black hole X-ray binaries, with the aim of assessing the presence of
reverberation lags and studying their evolution during outburst. We used
XMM-Newton and simultaneous RXTE observations to obtain broad-band energy
coverage of both the disc and the hard X-ray Comptonization components. In most
cases the detection of reverberation lags is hampered by low levels of
variability signal-to-noise ratio (e.g. typically when the source is in a soft
state) and/or short exposure times. The most detailed study was possible for GX
339-4 in the hard state, which allowed us to characterize the evolution of
X-ray lags as a function of luminosity in a single source. Over all the sampled
frequencies (~0.05-9 Hz) we observe the hard lags intrinsic to the power law
component, already well-known from previous RXTE studies. The XMM-Newton soft
X-ray response allows us to detail the disc variability. At low-frequencies
(long time scales) the disc component always leads the power law component. On
the other hand, a soft reverberation lag (ascribable to thermal reprocessing)
is always detected at high-frequencies (short time scales). The intrinsic
amplitude of the reverberation lag decreases as the source luminosity and the
disc-fraction increase. This suggests that the distance between the X-ray
source and the region of the optically-thick disc where reprocessing occurs,
gradually decreases as GX 339-4 rises in luminosity through the hard state,
possibly as a consequence of reduced disc truncation.Comment: 15 pages, 9 figures, 2 tables, accepted for publication in Ap
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