407 research outputs found
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
Swift J1357.2-0933: the faintest black hole?
Swift J1357.2-0933 is the first confirmed very faint black hole X-ray
transient and has a short estimated orbital period of 2.8 hr. We observed Swift
J1357.2-0933 for ~50 ks with XMM-Newton in 2013 July during its quiescent
state. The source is clearly detected at a 0.5-10 keV unabsorbed flux of
~3x10^-15 erg cm-2 s-1. If the source is located at a distance of 1.5 kpc (as
suggested in the literature), this would imply a luminosity of ~8x10^29 erg
s-1, making it the faintest detected quiescent black hole LMXB. This would also
imply that there is no indication of a reversal in the quiescence X-ray
luminosity versus orbital period diagram down to 2.8 hr, as has been predicted
theoretically and recently supported by the detection of the 2.4 hr orbital
period black hole MAXI J1659-152 at a 0.5-10 keV X-ray luminosity of ~ 1.2 x
10^31 erg s-1. However, there is considerable uncertainty in the distance of
Swift J1357.2-0933 and it may be as distant as 6 kpc. In this case, its
quiescent luminosity would be Lx ~ 1.3 x 10^31 erg s-1, i.e., similar to MAXI
J1659-152 and hence it would support the existence of such a bifurcation
period. We also detected the source in optical at r' ~22.3 mag with the
Liverpool telescope, simultaneously to our X-ray observation. The X-ray/optical
luminosity ratio of Swift J1357.2-0933 agrees with the expected value for a
black hole at this range of quiescent X-ray luminosities.Comment: 5 pages, 3 figures, Accepted for publication in MNRA
The truncated and evolving inner accretion disc of the black hole GX 339-4
The nature of accretion onto stellar mass black holes in the low/hard state
remains unresolved, with some evidence suggesting that the inner accretion disc
is truncated and replaced by a hot flow. However, the detection of relativistic
broadened Fe emission lines, even at relatively low luminosities, seems to
require an accretion disc extending fully to its innermost stable circular
orbit. Modelling such features is however highly susceptible to degeneracies,
which could easily bias any interpretation. We present the first systematic
study of the Fe line region to track how the inner accretion disc evolves in
the low/hard state of the black hole GX 3394. Our four observations display
increased broadening of the Fe line over two magnitudes in luminosity, which we
use to track any variation of the disc inner radius. We find that the disc
extends closer to the black hole at higher luminosities, but is consistent with
being truncated throughout the entire low/hard state, a result which renders
black hole spin estimates inaccurate at these stages of the outburst.
Furthermore, we show that the evolution of our spectral inner disc radius
estimates corresponds very closely to the trend of the break frequency in
Fourier power spectra, supporting the interpretation of a truncated and
evolving disc in the hard state.Comment: Accepted for publication in A&A. Some typos corrected from version
Revealing accretion onto black holes: X-ray reflection throughout three outbursts of GX 339-4
Understanding the dynamics behind black hole state transitions and the
changes they reflect in outbursts has become long-standing problem. The X-ray
reflection spectrum describes the interaction between the hard X-ray source
(the power-law continuum) and the cool accretion disc it illuminates, and thus
permits an indirect view of how the two evolve. We present a systematic
analysis of the reflection spectrum throughout three outbursts (500+
observations) of the black hole binary GX 339-4, representing the largest study
applying a self-consistent treatment of reflection to date. Particular
attention is payed to the coincident evolution of the power-law and reflection,
which can be used to determine the accretion geometry. The hard state is found
to be distinctly reflection weak, however the ratio of reflection to power-law
gradually increases as the source luminosity rises. In contrast the reflection
is found dominate the power-law throughout most of the soft state, with
increasing supremacy as the source decays. We discuss potential dynamics
driving this, favouring inner disc truncation and decreasing coronal height for
the hard and soft states respectively. Evolution of the ionisation parameter,
power-law slope and high-energy cut-off also agree with this interpretation.Comment: Accepted for publication in MNRA
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