805 research outputs found
On the Optical -- X-ray correlation from outburst to quiescence in Low Mass X-ray Binaries: the representative cases of V404 Cyg and Cen X-4
Low mass X-ray binaries (LMXBs) show evidence of a global correlation of
debated origin between X-ray and optical luminosity. We study for the first
time this correlation in two transient LMXBs, the black hole V404 Cyg and the
neutron star Cen X-4, over 6 orders of magnitude in X-ray luminosity, from
outburst to quiescence. After subtracting the contribution from the companion
star, the Cen X-4 data can be described by a single power law correlation of
the form , consistent with disk reprocessing. We
find a similar correlation slope for V404 Cyg in quiescence (0.46) and a
steeper one (0.56) in the outburst hard state of 1989. However, V404 Cyg is
about times optically brighter, at a given keV X-ray
luminosity, compared to Cen X-4. This ratio is a factor of 10 smaller in
quiescence, where the normalization of the V404 Cyg correlation also changes.
We show that once the bolometric X-ray emission is considered and the known
main differences between V404 Cyg and Cen X-4 are taken into account (a larger
compact object mass, accretion disk size, and the presence of a strong jet
contribution in the hard state for the black hole system) the two systems lie
on the same correlation. In V404 Cyg, the jet dominates spectrally at
optical-infrared frequencies during the hard state, but makes a negligible
contribution in quiescence, which may account for the change in its correlation
slope and normalization. These results provide a benchmark to compare with data
from the 2015 outburst of V404 Cyg and, potentially, other transient LMXBs as
well.Comment: Accepted on ApJ, 12 pages, 4 figures, 4 table
Determining the optimal locations for shock acceleration in magnetohydrodynamical jets
Observations of relativistic jets from black holes systems suggest that
particle acceleration often occurs at fixed locations within the flow. These
sites could be associated with critical points that allow the formation of
standing shock regions, such as the magnetosonic modified fast point. Using the
self-similar formulation of special relativistic magnetohydrodynamics by
Vlahakis & K\"onigl, we derive a new class of flow solutions that are both
relativistic and cross the modified fast point at a finite height. Our
solutions span a range of Lorentz factors up to at least 10, appropriate for
most jets in X-ray binaries and active galactic nuclei, and a range in injected
particle internal energy. A broad range of solutions exists, which will allow
the eventual matching of these scale-free models to physical boundary
conditions in the analysis of observed sources.Comment: 9 pages, 4 figures, accepted for publication in Ap
X-ray states and radio emission in the black hole candidate XTE J1550-564
We report on radio and X-ray observations of the black hole candidate (BHC)
XTE J1550-564 performed during its 2000 X-ray outburst. Observations have been
conducted with the Australia Telescope Compact Array (ATCA) and have allowed us
to sample the radio behavior of XTE J1550-564 in the X-ray Low Hard and
Intermediate/Very High states. We observed optically thin radio emission from
XTE J1550-564 five days after a transition to an Intermediate/Very High state,
but we observed no radio emission six days later, while XTE J1550-564 was still
in the Intermediate/Very High state. In the Low Hard state, XTE J1550-564 is
detected with an inverted radio spectrum. The radio emission in the Low Hard
state most likely originates from a compact jet; optical observations suggest
that the synchrotron emission from this jet may extend up to the optical range.
The total power of the compact jet might therefore be a significant fraction of
the total luminosity of the system. We suggest that the optically thin
synchrotron radio emission detected five days after the transition to the
Intermediate/Very High state is due to a discrete ejection of relativistic
plasma during the state transition. Subsequent to the decay of the optically
thin radio emission associated with the state transition, it seems that in the
Intermediate/Very High state the radio emission is quenched by a factor greater
than 50, implying a suppression of the outflow. We discuss the properties of
radio emission in the X-ray states of BHCs.Comment: 15 pages, including 3 figures. Accepted for publication in ApJ,
scheduled for the vol. 553 Jun 1, 2001 issu
Neutrino flares from black hole coronae
We present a model for neutrino flares in accreting black holes based on the
injection of a non-thermal population of relativistic particles in a magnetized
corona. The most important products of hadronic and photohadronic interactions
at high energies are pions. Charged pions decay into muons and neutrinos; muons
also decay yielding neutrinos. Taking into account these effects, coupled
transport equations are solved for all species of particles and the neutrino
production is estimated for the case of accreting galactic black holes.Comment: 13 pages, 8 figures, accepted for publication in Advances in Space
Researc
Detailed Radio to Soft Gamma-ray Studies of the 2005 Outburst of the New X-ray Transient XTE J1818-245
XTE J1818-245 is an X-ray nova that experienced an outburst in 2005, first
seen by the RXTE satellite. The source was observed simultaneously at various
wavelengths up to soft gamma-rays with the INTEGRAL satellite, from 2005
February to September. X-ray novae are extreme systems that often harbor a
black hole, and are known to emit throughout the electromagnetic spectrum when
in outburst. We analyzed radio, (N)IR, optical, X-ray and soft gamma-ray
observations and constructed simultaneous broad-band X-ray spectra. Analyzing
both the light curves in various energy ranges and the hardness-intensity
diagram enabled us to study the long-term behavior of the source. Spectral
parameters were typical of the Soft Intermediate States and the High Soft
States of a black hole candidate. The source showed relatively small spectral
variations in X-rays with considerable flux variation in radio. Spectral
studies showed that the accretion disc cooled down from 0.64 to 0.27 keV in 100
days and that the total flux decreased while the relative flux of the hot
medium increased. Radio emission was detected several times, and,
interestingly, five days after entering the HSS. Modeling the spectral energy
distribution from the radio to the soft gamma-rays reveals that the radio
flares arise from several ejection events. XTE J1818-245 is likely a black hole
candidate transient source that might be closer than the Galactic Bulge. The
results from the data analysis trace the physical changes that took place in
the system at a maximum bolometric luminosity of (0.4-0.9)e38 erg/s (assuming a
distance between 2.8-4.3 kpc) and they are discussed within the context of disc
and jet models.Comment: Accepted for publication in Astronomy and Astrophysics. 11 Figures, 3
Table
The Galactic black hole transient H1743-322 during outburst decay: connections between timing noise, state transitions and radio emission
Multi-wavelength observations of Galactic black hole transients during
outburst decay are instrumental for our understanding of the accretion geometry
and the formation of outflows around black hole systems. H1743-322, a black
hole transient observed intensely in X-rays and also covered in the radio band
during its 2003 decay, provides clues about the changes in accretion geometry
during state transitions and also the general properties of X-ray emission
during the intermediate and the low-hard states. In this work, we report on the
evolution of spectral and temporal properties in X-rays and the flux in the
radio band with the goal of understanding the nature of state transitions
observed in this source. We concentrate on the transition from the thermal
dominant state to the intermediate state that occurs on a timescale of one day.
We show that the state transition is associated with a sudden increase in
power-law flux. We determine that the ratio of the power-law flux to the
overall flux in the 3--25 keV band must exceed 0.6 to observe strong timing
noise. Even after the state transition, once this ratio was below 0.6, the
system transited back to the thermal dominant state for a day. We show that the
emission from the compact radio core does not turn on during the transition
from the thermal dominant state to the intermediate state but does turn on when
the source reaches the low-hard state, as seen in 4U 1543-47 and GX 339-4. We
find that the photon index correlates strongly with the QPO frequency and
anti-correlates with the rms amplitude of variability. We also show that the
variability is more likely to be associated with the power-law emission than
the disk emission.Comment: 23 pages, 5 Figures, 1 Table, accepted for publication in Ap
X-Ray Emission from the Jets of XTE J1550-564
We report on X-ray observations of the the large-scale jets recently
discovered in the radio and detected in X-rays from the black hole candidate
X-ray transient and microquasar XTE J1550-564. On 11 March 2002, X-ray emission
was detected 23 arcsec to the West of the black hole candidate and was extended
along the jet axis with a full width at half maximum of 1.2 arcsec and a full
width at 10% of maximum intensity of 5 arcsec. The morphology of the X-ray
emission matched well to that of the radio emission at the same epoch. The jet
moved by 0.52 +/- 0.13 arcsec between 11 March and 19 June 2002. The apparent
speed during that interval was 5.2 +/- 1.3 mas/day. This is significantly less
than the average apparent speed of 18.1 +/- 0.4 mas/day from 1998 to 2002,
assuming that the jet was ejected in September 1998, and indicates that the jet
has decelerated. The X-ray spectrum is adequately described by a powerlaw with
a photon index near 1.8 subject to interstellar absorption. The unabsorbed
X-ray flux was 3.4 x 10^-13 erg cm^-2 s^-1 in the 0.3-8 keV band in March 2002,
and decreased to 2.9 x 10^-13 erg cm^-2 s^-1 in June. We also detect X-rays
from the eastern jet in March 2002 and show that it has decelerated and dimmed
since the previous detections in 2000.Comment: accepted for publication in ApJ, 11 pages, several figures in colo
Optical and Near Infrared Monitoring of the Black-Hole X-ray Binary GX 339-4 During 2002-2010
We present the optical/infra-red lightcurve (O/IR) of the black hole X-ray
binary GX 339-4 collected at the SMARTS 1.3m telescope from 2002 to 2010.
During this time the source has undergone numerous state transitions including
hard-to-soft state transitions when we see large changes in the near-IR flux
accompanied by modest changes in optical flux, and three rebrightening events
in 2003, 2005 and 2007 after GX 339-4 transitioned from the soft state to the
hard. All but one outburst show similar behavior in the X-ray
hardness-intensity diagram. We show that the O/IR colors follow two distinct
tracks that reflect either the hard or soft X-ray state of the source. Thus,
either of these two X-ray states can be inferred from O/IR observations alone.
From these correlations we have constructed spectral energy distributions of
the soft and hard states. During the hard state, the near-IR data have the same
spectral slope as simultaneous radio data when GX 339-4 was in a bright optical
state, implying that the near-IR is dominated by a non-thermal source, most
likely originating from jets. Non-thermal emission dominates the near-IR bands
during the hard state at all but the faintest optical states, and the fraction
of non-thermal emission increases with increasing optical brightness. The
spectral slope of the optical bands indicate that a heated thermal source is
present during both the soft and hard X-ray states, even when GX 339-4 is at
its faintest optical state. We have conducted a timing analysis of the light
curve for the hard and soft states and find no evidence of a characteristic
timescale within the range of 4-230 days.Comment: Accepted for publication in AJ, Table 3 can be viewed at
http://www.astro.yale.edu/buxton/GX339
A classification of the X-ray and radio states of Cyg X-3 and their long-term correlations
We present a detailed classification of the X-ray states of Cyg X-3 based on
the spectral shape and a new classification of the radio states based on the
long-term correlated behaviour of the radio and soft X-ray light curves. We
find a sequence of correlations, starting with a positive correlation between
the radio and soft X-ray fluxes in the hard spectral state, changing to a
negative one at the transition to soft spectral states. The temporal evolution
can be in either direction on that sequence, unless the source goes into a very
weak radio state, from which it can return only following a major radio flare.
The flare decline is via relatively bright radio states, which results in a
hysteresis loop on the flux-flux diagram. We also study the hard X-ray light
curve, and find its overall anticorrelation with the soft X-rays. During major
radio flares, the radio flux responds exponentially to the level of a hard
X-ray high-energy tail. We also specify the detailed correspondence between the
radio states and the X-ray spectral states. We compare our results to those of
black-hole and neutron-star binaries. Except for the effect of strong
absorption and the energy of the high-energy break in the hard state, the X-ray
spectral states of Cyg X-3 closely correspond to the canonical X-ray states of
black-hole binaries. Also, the radio/X-ray correlation closely corresponds to
that found in black-hole binaries, but it significantly differs from that in
neutron-star binaries. Overall, our results strongly support the presence of a
black hole in Cyg X-3.Comment: MNRAS, in pres
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