503 research outputs found
Complete Multiwavelength Evolution of Galactic Black Hole Transients During Outburst Decay II: Compact Jets and X-ray Variability Properties
We investigated the relation between compact jet emission and X-ray
variability properties of all black hole transients with multiwavelength
coverage during their outburst decays. We studied the evolution of all power
spectral components (including low frequency quasi-periodic oscillations), and
related this evolution to changes in jet properties tracked by radio and
infrared observations. We grouped sources according to their tracks in
radio/X-ray luminosity relation, and show that the standards show stronger
broadband X-ray variability than outliers at a given X-ray luminosity when the
compact jet turned on. This trend is consistent with the internal shock model
and can be important for the understanding of the presence of tracks in the
radio/X-ray luminosity relation. We also observed that the total and the QPO
rms amplitudes increase together during the earlier part of the outburst decay,
but after the compact jet turns either the QPO disappears or its rms amplitude
decreases significantly while the total rms amplitudes remain high. We discuss
these results with a scenario including a variable corona and a non-variable
disk with a mechanism for the QPO separate from the mechanism that create broad
components. Finally, we evaluated the timing predictions of the magnetically
dominated accretion flow model which can explain the presence of tracks in the
radio/X-ray luminosity relation.Comment: Accepted for publication by Ap
Modeling the Optical-X-ray Accretion Lag in LMC X-3: Insights Into Black-Hole Accretion Physics
The X-ray persistence and characteristically soft spectrum of the black hole
X-ray binary LMC X-3 make this source a touchstone for penetrating studies of
accretion physics. We analyze a rich, 10-year collection of optical/infrared
(OIR) time-series data in conjunction with all available contemporaneous X-ray
data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing
Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks.
Motivated by this result, we develop a model that reproduces the complex OIR
light curves of LMC X-3. The model is comprised of three components of
emission: stellar light; accretion luminosity from the outer disk inferred from
the time-lagged X-ray emission; and light from the X-ray-heated star and outer
disk. Using the model, we filter a strong noise component out of the
ellipsoidal light curves and derive an improved orbital period for the system.
Concerning accretion physics, we find that the local viscous timescale in the
disk increases with the local mass accretion rate; this in turn implies that
the viscosity parameter alpha decreases with increasing luminosity. Finally, we
find that X-ray heating is a strong function of X-ray luminosity below ~50% of
the Eddington limit, while above this limit X-ray heating is heavily
suppressed. We ascribe this behavior to the strong dependence of the flaring in
the disk upon X-ray luminosity, concluding that for luminosities above ~50% of
Eddington, the star lies fully in the shadow of the disk.Comment: Accepted in ApJ (12 pages long in emulateapj format
The Mass of the Black Hole in LMC X-3
We analyze a large set of new and archival photometric and spectroscopic
observations of LMC X-3 to arrive at a self-consistent dynamical model for the
system. Using echelle spectra obtained with the MIKE instrument on the 6.5m
Magellan Clay telescope and the UVES instrument on the second 8.2m Very Large
Telescope we find a velocity semiamplitude for the secondary star of
km s, where the uncertainty includes an estimate of
the systematic error caused by X-ray heating. Using the spectra, we also find a
projected rotational velocity of km s.
From an analysis of archival and light curves as well as new and
light curves from the SMARTS 1.3m telescope, we find an inclination of
for models that do not include X-ray heating and an
inclination of for models that incorporate X-ray
heating. Adopting the latter inclination measurement, we find masses of
and for the companion star
and the black hole, respectively. We briefly compare our results with earlier
work and discuss some of their implications.Comment: 31 pages, 15 figures, substantial revisions, ApJ, accepte
Magnetic Field Amplification and Flat Spectrum Radio Quasars
We perform time-dependent, spatially-resolved simulations of blazar emission
to evaluate several flaring scenarios related to magnetic-field amplification
and enhanced particle acceleration. The code explicitly accounts for
light-travel-time effects and is applied to flares observed in the flat
spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/{\gamma}-ray
correlation at some times, but orphan optical flares at other times. Changes in
both the magnetic field and the particle acceleration efficiency are explored
as causes of flares. Generally, external Compton emission appears to describe
the available data better than a synchrotron self-Compton scenario, and in
particular orphan optical flares are difficult to produce in the SSC framework.
X-ray soft-excesses, {\gamma}-ray spectral hardening, and the detections at
very high energies of certain FSRQs during flares find natural explanations in
the EC scenario with particle acceleration change. Likewise, optical flares
with/without {\gamma}-ray counterparts can be explained by different
allocations of energy between the magnetization and particle acceleration,
which may be related to the orientation of the magnetic field relative to the
jet flow. We also calculate the degree of linear polarization and polarization
angle as a function of time for a jet with helical magnetic field. Tightening
of the magnetic helix immediately downstream of the jet perturbations, where
flares occur, can be sufficient to explain the increases in the degree of
polarization and a rotation by >= 180 degree of the observed polarization
angle, if light-travel-time effects are properly considered.Comment: 12 pages, 9 figures. Accepted for publication in MNRA
Complete multiwavelength evolution of galactic black hole transients during outburst decay I: conditions for "compact" jet formation
Compact, steady jets are observed in the near infrared and radio bands in the hard state of Galactic black hole transients as their luminosity decreases and the source moves towards a quiescent state. Recent radio observations indicate that the jets turn o completely in the soft state, therefore multiwavelength
monitoring of black hole transients are essential to probe the formation of jets. In this work we conducted a systematic study of all black hole transients with near infrared and radio coverage during their outburst decays. We characterized the timescales of changes in X-ray spectral and temporal properties and also in near infrared and/or in radio emission. We confirmed that state transitions occur in black hole transients at a very similar fraction of their respective Eddington luminosities. We also found that the near infrared flux increase that could be due to the formation of a compact jet is delayed by a time period of days with respect to the formation of a corona. Finally, we found a threshold disk Eddington luminosity fraction for the compact jets to form. We explain these results with a model such that the increase in the near infrared flux corresponds to a transition from a patchy, small scale height corona along with an optically thin out flow to a large scale height corona that allows for collimation of a steady compact jet. We discuss the timescale of jet formation in terms of transport of magnetic fields from the outer parts of the disk, and also consider two alternative explanations for the multiwavelength emission: hot inner accretion flows and irradiation
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
X-ray, Optical and Infrared Observations of GX 339-4 During Its 2011 Decay
We report multiwavelength observations of the black hole transient GX 339-4
during its outburst decay in 2011 using the data from RXTE, Swift and SMARTS.
Based on the X-ray spectral, temporal, and the optical/infrared (OIR)
properties, the source evolved from the soft-intermediate to the hard state.
Twelve days after the start of the transition towards the hard state, a
rebrightening was observed simultaneously in the optical and the infrared
bands. Spectral energy distributions (SED) were created from observations at
the start, and close to the peak of the rebrightening. The excess OIR emission
above the smooth exponential decay yields flat spectral slopes for these SEDs.
Assuming that the excess is from a compact jet, we discuss the possible
locations of the spectral break that mark the transition from optically thick
to optically thin synchrotron components. Only during the rising part of the
rebrightening, we detected fluctuations with the binary period of the system.
We discuss a scenario that includes irradiation of the disk in the intermediate
state, irradiation of the secondary star during OIR rise and jet emission
dominating during the peak to explain the entire evolution of the OIR light
curve.Comment: 10 pages with 11 figures, accepted for publication in Ap
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