189 research outputs found
Using XMM-Newton to study the energy dependent variability of H 1743-322 during its 2014 outburst
Black hole transients during bright outbursts show distinct changes of their
spectral and variability properties as they evolve during an outburst, that are
interpreted as evidence for changes in the accretion flow and X-ray emitting
regions. We obtained an anticipated XMM-Newton ToO observation of H 1743-322
during its outburst in September 2014. Based on data of eight outbursts
observed in the last 10 years we expected to catch the start of the
hard-to-soft state transition. The fact that neither the general shape of the
observed power density spectrum nor the characteristic frequency show an energy
dependence implies that the source still stays in the low-hard state at the
time of our observation near outburst peak. The spectral properties agree with
the source being in the low-hard state and a Swift/XRT monitoring of the
outburst reveals that H 1743-322 stays in the low-hard state during the entire
outburst (a. k. a. 'failed outburst'). We derive the averaged QPO waveform and
obtain phase-resolved spectra. Comparing the phase-resolved spectra to the
phase averaged energy spectrum reveals spectral pivoting. We compare
variability on long and short time scales using covariance spectra and find
that the covariance ratio does not show an increase towards lower energies as
has been found in other black hole X-ray binaries. There are two possible
explanations: either the absence of additional disc variability on longer time
scales is related to the rather high inclination of H 1743-322 compared to
other black hole X-ray binaries or it is the reason why we observe H 1743-322
during a failed outburst. More data on failed outbursts and on high-inclination
sources will be needed to investigate these two possibilities further.Comment: 9 pages, 7 figures, accepted by MNRA
Detection of distinct power spectra in soft and hard X-ray bands in the hard state of GRS 1915+105
The well-known black hole X-ray binary GRS 1915+105 is a unique source in the
sense that it cannot be classified within the standard picture of black hole
binary states. In this work we study archival XMM-Newton observations taken
between 2003 and 2004 of the \c{hi} variability class of GRS 1915+105, which
corresponds to the hard state in the standard black hole X-ray binary state
classification. The crucial point of our study is that by using XMM-Newton data
we can access the variability below 3 keV, an energy range that is not covered
with RXTE. We focus on the study of the power spectral shape in the soft and
hard X-ray band, in light of our work done with Swift on MAXI J1659-152. In the
hard band (above 2.5 keV) power density spectra consist of band-limited noise
and quasi-periodic oscillations, corresponding to the power spectral shape seen
in the hard or intermediate state, while in the soft band the averaged power
density spectrum is consistent with a power-law noise, corresponding to the
power spectral shape usually seen in the soft state. The coexisting of two
different power spectral shapes in the soft and hard band, where the soft band
power spectrum is dominated by a power-law noise, is consistent with MAXI
J1659-152, and confirms the energy dependence of power spectral states. Our
additional spectral analysis shows that the disc component does contribute to
the soft band flux. These findings support that the observed black hole power
spectral state depends on which spectral component we are looking at, which
implies that power spectral analysis is probably a more sensitive method than
spectral modeling to trace the emergence of the disc component in the hard or
intermediate state.Comment: 9 pages, 5 figures, submitted to MNRA
Phase diagram and nucleation in the Polyakov-loop-extended Quark-Meson truncation of QCD with the unquenched Polyakov-loop potential
Unquenching of the Polyakov-loop potential showed to be an important
improvement for the description of the phase structure and thermodynamics of
strongly-interacting matter at zero quark chemical potentials with
Polyakov-loop extended chiral models. This work constitutes the first
application of the quark backreaction on the Polyakov-loop potential at nonzero
density. The observation is that it links the chiral and deconfinement phase
transition also at small temperatures and large quark chemical potentials. The
build up of the surface tension in the Polyakov-loop extended Quark-Meson model
is explored by investigating the two and 2+1-flavour Quark-Meson model and
analysing the impact of the Polyakov-loop extension. In general, the order of
magnitude of the surface tension is given by the chiral phase transition. The
coupling of the chiral and deconfinement transition with the unquenched
Polyakov-loop potential leads to the fact that the Polyakov-loop contributes at
all temperatures.Comment: 28 pages, 13 figures; version published in Phys. Rev.
NuSTAR and Swift observations of Swift J1357.2-0933 during an early phase of its 2017 outburst
We present a detailed spectral analysis of Swift and NuSTAR observations of
the very faint X-ray transient and black hole system Swift J1357.2-0933 during
an early low hard state of its 2017 outburst. Swift J1357.2-0933 was observed
at 0.02% of the Eddington luminosity (for a distance of 2.3 kpc and a
mass of 4 M). Despite the low luminosity, the broadband X-ray
spectrum between 0.3 and 78 keV requires the presence of a disk blackbody
component with an inner disk temperature of T 0.06 keV
in addition to a thermal Comptonization component with a photon index of
{\Gamma} 1.70. Using a more physical model, which takes strong
relativistic effects into account, and assuming a high inclination of
70, which is motivated by the presence of dips in optical light curves,
we find that the accretion disk is truncated within a few RISCO from the black
hole, independent of the spin.Comment: 11 pages, 5 figures, accepted for publication in Ap
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