80 research outputs found
Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564
We present the results of radio observations of the black hole binaries GRO
J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope
Compact Array. Neither system was detected. Radio flux density upper limits (3
sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40,
and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for
XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra
X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical
observations (XTE J1550-564) we find that these systems provide the first
evidence of relatively `radio quiet' black hole binaries at low luminosities;
indicating that the scatter observed in the hard state X-ray:radio correlation
at higher luminosities may also extend towards quiescent levels.Comment: Accepted for publication in MNRA
Millimetre observations of a sub-arcsecond jet from Circinus X-1
We present results from the first successful millimetre (combined 33 GHz and
35 GHz) observations of the neutron star X-ray binary Circinus X-1, using the
Australia Telescope Compact Array. The source was clearly detected in all three
observing epochs. We see strong evidence for a periastron flare beginning at
MJD 55519.9 \pm 0.04 with estimated peak flux densities of up to 50 mJy and
which proceeds to decline over the following four days. We directly resolve jet
structures on sub-arcsecond scales. Flux density variability and distance from
the core of nearby components suggests recent shock re-energisation, though we
are unable to directly connect this with the observed flare. We suggest that,
if the emission is powered by an unseen outflow, then a phase delay exists
between flare onset and subsequent brightening of nearby components, with flows
reaching mildly relativistic velocities. Given resolved structure positions, in
comparison to past observations of Cir X-1, we find evidence that jet direction
may vary with distance from the core, or the source's precession parameters
have changed.Comment: Accepted for publication in MNRA
Parsec-Scale Bipolar X-ray Shocks Produced by Powerful Jets from the Neutron Star Circinus X-1
We report the discovery of multi-scale X-ray jets from the accreting neutron
star X-ray binary, Circinus X-1. The bipolar outflows show wide opening angles
and are spatially coincident with the radio jets seen in new high-resolution
radio images of the region. The morphology of the emission regions suggests
that the jets from Circinus X-1 are running into a terminal shock with the
interstellar medium, as is seen in powerful radio galaxies. This and other
observations indicate that the jets have a wide opening angle, suggesting that
the jets are either not very well collimated or precessing. We interpret the
spectra from the shocks as cooled synchrotron emission and derive a cooling age
of approximately 1600 yr. This allows us to constrain the jet power to be
between 3e35 erg/s and 2e37 erg/s, making this one of a few microquasars with a
direct measurement of its jet power and the only known microquasar that
exhibits stationary large-scale X-ray emission.Comment: 5 pages, 4 figures, to be published in the Astrophysical Journal
Letter
A complete X-ray spectral coverage of the 2010 May-June outbursts of Circinus X-1
Circinus X-1 is a neutron-star-accreting X-ray binary in a wide (P = 16.6 d), eccentric orbit. After two years of relatively low X-ray
luminosity, in May 2010 Circinus X-1 went into outburst, reaching 0.4 Crab
flux. This outburst lasted for about two orbital cycles and was followed by
another shorter and fainter outburst in June. We focus here on the broadband
X-ray spectral evolution of the source as it spans about three order of
magnitudes in flux. We attempt to relate luminosity, spectral shape, local
absorption, and orbital phase. We use multiple Rossi-XTE/PCA (3.0--25 keV) and
Swift/XRT (1.0--9.0 keV) observations and a 20 ks long Chandra/HETGS
observation (1.0--9.0 keV), to comprehensively track the spectral evolution of
the source during all the outbursting phases. These observations were taken
every two/three days and cover about four orbital cycles. The PCA data mostly
cover the major outburst, the XRT data monitor the declining phase of the major
outburst and all the phases of the minor outburst, and Chandra data provide an
essential snapshot of the end of this overall outbursting phase. The X-ray
spectrum can be satisfactorily described by a thermal Comptonization model with
variable neutral local absorption in all phases of the outburst. No other
additive component is statistically required. The first outburst decays
linearly, with an ankle in the light curve as the flux decreases below
\,5 10 erg cm s. At the same time, the
source shows a clear spectral state transition from an optically thick to an
optically thin state. While the characteristics of the first, bright, outburst
can be interpreted within the disk-instability scenario, the following, minor,
outburst shows peculiarities that cannot be easily reconciled in this
framework.Comment: Accepted for publication in Astronomy and Astrophysic
An overview of jets and outflows in stellar mass black holes
In this book chapter, we will briefly review the current empirical
understanding of the relation between accretion state and and outflows in
accreting stellar mass black holes. The focus will be on the empirical
connections between X-ray states and relativistic (`radio') jets, although we
are now also able to draw accretion disc winds into the picture in a systematic
way. We will furthermore consider the latest attempts to measure/order jet
power, and to compare it to other (potentially) measurable quantities, most
importantly black hole spin.Comment: Accepted for publication in Space Science Reviews. Also to appear in
the Space Sciences Series of ISSI - The Physics of Accretion on to Black
Holes (Springer Publisher
Radio observations of Circinus X-1 over a complete orbit at an historically faint epoch
We present results from the first radio observations of a complete orbit (~
17 days) of the neutron star X-ray binary Circinus X-1 using the Australia
Telescope Compact Array Broadband Backend, taken while the system was in an
historically faint state. We have captured the rapid rise and decline of a
periastron passage flare, with flux densities for 9 days prior to the event
stable at ~ 1 mJy at 5.5 GHz and ~ 0.5 mJy at 9 GHz. The highest flux densities
of 43.0 +/- 0.5 mJy at 5.5 GHz and 29.9 +/- 0.6 mJy at 9 GHz were measured
during the flare's decline (MJD 55206.69) which continues towards pre-flare
flux densities over the following 6 days. Imaging of pre-flare data reveals
steady structure including two stable components within 15 arc-seconds of the
core which we believe may be persistent emission regions within the system's
outflows, one of which is likely associated with the system's counter-jet.
Unlike past observations carried out in the system's brighter epochs, we
observe no significant structural variations within \approx 3 arc-seconds of
the core's position. Model subtraction and difference mapping provide evidence
for variations slightly further from the core: up to 5" away. If related to the
observed core flare, then these variations suggest very high outflow velocities
with {\Gamma} > 35, though this can be reduced significantly if we invoke phase
delays of at least one orbital period. Interestingly, the strongest structural
variations appear to the north west of the core, opposite to the strongest
arcsec-scale emission historically. We discuss the implications of this
behaviour, including the possibility of precession or a kinked approaching jet.Comment: Accepted for publication in MNRA
BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
During the last ~50 years, the population of black hole candidates in X-ray
binaries has increased considerably with 59 Galactic objects detected in
transient low-mass X-ray binaries, plus a few in persistent systems (including
~5 extragalactic binaries). We collect near-infrared, optical and X-ray
information spread over hundreds of references in order to study the population
of black holes in X-ray transients as a whole. We present the most updated
catalogue of black hole transients, which contains X-ray, optical and
near-infrared observations together with their astrometric and dynamical
properties. It provides new useful information in both statistical and
observational parameters providing a thorough and complete overview of the
black hole population in the Milky Way. Analysing the distances and spatial
distribution of the observed systems, we estimate a total population of ~1300
Galactic black hole transients. This means that we have already discovered less
than ~5% of the total Galactic distribution. The complete version of this
catalogue will be continuously updated online and in the Virtual Observatory,
including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in
Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table
Molecular characterization of the thermally labile fraction of biochar by hydropyrolysis and pyrolysis-GC/MS
Agroenvironmental benefits and limitations of biochar in soil applications require a full understanding of the stability and fate of the various carbon fractions. Analytical hydropyrolysis (HyPy) enables the determination of the stable black carbon (BCHyPy) and thermally labile (semi-labile; non-BCHyPy) fractions in biochar and soil samples. The non-BCHyPy fraction can be analysed at a molecular level by gas chromatography-mass spectrometry (GC-MS). In the present study, HyPy was applied to the characterisation of biochars produced from pine wood, beech wood and corn digestate with the same pyrolysis unit at low (340â400 °C) and high (600 °C) temperatures. Results were compared with those from Py-GC-MS. HyPy provided consistent information concerning the thermal stability of biochar samples, with BCHyPy levels related with the relative abundance of the charred fraction estimated by Py-GC-MS and the hydrogen/carbon (H/C) ratios. The non-BCHyPy fractions were featured by the presence of polycyclic aromatic hydrocarbons (PAHs) from two to seven rings, including alkylated derivatives up to C4. Partially hydrogenated PAHs were also detected. The yields of non-BCHyPy were higher for those biochars produced at lower temperatures and always more abundant than the levels of solvent-extractable PAHs. The methylated/parent PAH ratios from HyPy and Py-GC-MS exhibited lower values for the most charred biochar. The observed differences in the abundance of the stable fraction and the molecular chemistry of the semi-labile fraction can be usefully utilised to drive the process conditions to the desired properties of the resulting biochars and to predict the impact of biochar amendment to soil organic pools. The concentrations of priority PAHs in the semi-labile fraction was evaluated in the mg gâ1 level suggesting that it could be an important fraction of the polyaromatic carbon pool in soil
The black hole candidate MAXIJ1659-152 in and towards quiescence in X-ray and radio
In this paper we report on Expanded Very Large Array radio and Chandra and
Swift X-ray observations of the outburst decay of the transient black hole
candidate MAXI J1659-152 in 2011. We discuss the distance to the source taking
the high inclination into account and we conclude that the source distance is
probably 6+-2 kpc. The lowest observed flux corresponds to a luminosity of
2x10^31 (d/6 kpc)^2 erg/s This, together with the orbital period of 2.4 hr
reported in the literature, suggests that the quiescent X-ray luminosity is
higher than predicted on the basis of the orbital period -- quiescent X-ray
luminosity relationship. The relation between the accretion and ejection
mechanisms can be studied using the observed correlation between the radio and
X-ray luminosities as these evolve over an outburst. We determine the behaviour
of MAXI J1659-152 in the radio -- X-ray diagram at low X-ray luminosities using
the observations reported in this paper and at high X-ray luminosities using
values reported in the literature. At high X-ray luminosities the source lies
closer to the sources that follow a correlation index steeper than 0.6-0.7.
However, when compared to other sources that follow a steeper correlation
index, the X-ray luminosity in MAXI J1659-152 is also lower. The latter can
potentially be explained by the high inclination of MAXI J1659-152 if the X-ray
emission comes from close to the source and the radio emission is originating
in a more extended region. However, it is probable that the source was not in
the canonical low-hard state during these radio observations and this may
affect the behaviour of the source as well. At intermediate X-ray luminosities
the source makes the transition from the radio underluminous sources in the
direction of the relation traced by the 'standard' correlation similar to what
has been reported for H1743-322. (abridged)Comment: Accepted for publication by MNRAS, 9 pages, 4 figure
Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars
Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, ÎŽ13C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biocharâs environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa
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