152 research outputs found
The Physics of Disk Winds, Jets,and X-ray Variability in GRS 1915+105
We present new insights about accretion and ejection physics based on joint
RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the
first time, with fast phase-resolved spectroscopy of the rho state, we are able
to show that changes in the broadband X-ray spectrum (RXTE) on timescales of
seconds are associated with measurable changes in absorption lines (Chandra
HETGS) from the accretion disk wind. Additionally, we make a direct detection
of material evaporating from the radiation-pressure-dominated inner disk. Our
X-ray data thus reveal the black hole as it ejects a portion of the inner
accretion flow and then drives a wind from the outer disk, all in a bizarre
cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that
the accretion disk wind may be sufficiently massive to play an active role in
GRS 1915+105, not only in quenching the jet on long timescales, but also in
possibly producing or facilitating transitions between classes of X-ray
variability.Comment: 3 pages, 1 Figure. Proceedings of IAU Symposium 275 (Jets at all
Scales), Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon
Comparison of time/phase lags in the hard state and plateau state of GRS 1915+105
We investigate the complex behavior of energy- and frequency-dependent
time/phase lags in the plateau state and the radio-quiet hard state of GRS
1915+105. In our timing analysis, we find that when the source is faint in the
radio, QPOs are observed above 2 Hz and typically exhibit soft lags (soft
photons lag hard photons), whereas QPOs in the radio-bright plateau state are
found below 2.2 Hz and consistently show hard lags. The phase lag at the QPO
frequency is strongly anti-correlated with the QPO frequency, changing sign at
2.2 Hz. However, the phase lag at the frequency of the first harmonic is
positive and nearly independent of frequency at at ~0.172 rad, regardless of
the radio emission. The lag-energy dependence at the first harmonic is also
independent of radio flux. However, the lags at the QPO frequency are negative
at all energies during the radio-quiet state, but lags at the QPO frequency
during the plateau state are positive at all energies and show a
'reflection-type' evolution of the lag-energy spectra with respect to the
radio-quiet state. The lag-energy dependence is roughly logarithmic, but there
is some evidence for a break around 4-6 keV. Finally, the Fourier
frequency-dependent phase lag spectra are fairly flat during the plateau state,
but increase from negative to positive during the radio-quiet state. We discuss
the implications of our results in the light of some generic models.Comment: 9 pages, 7 figures, accepted for publication in Ap
The Physics of the 'Heartbeat' State of GRS 1915+105
We present the first detailed phase-resolved spectral analysis of a joint
Chandra High Energy Transmission Grating Spectrometer and Rossi X-ray Timing
Explorer observation of the rho variability class in the microquasar GRS
1915+105. The rho cycle displays a high-amplitude, double-peaked flare that
recurs roughly every 50 s, and is sometimes referred to as the "heartbeat"
oscillation. The spectral and timing properties of the oscillation are
consistent with the radiation pressure instability and the evolution of a local
Eddington limit in the inner disk. We exploit strong variations in the X-ray
continuum, iron emission lines, and the accretion disk wind to probe the
accretion geometry over nearly six orders of magnitude in distance from the
black hole. At small scales (1-10 R_g), we detect a burst of bremsstrahlung
emission that appears to occur when a portion of the inner accretion disk
evaporates due to radiation pressure. Jet activity, as inferred from the
appearance of a short X-ray hard state, seems to be limited to times near
minimum luminosity, with a duty cycle of ~10%. On larger scales (1e5-1e6 R_g)
we use detailed photoionization arguments to track the relationship between the
fast X-ray variability and the accretion disk wind. For the first time, we are
able to show that changes in the broadband X-ray spectrum produce changes in
the structure and density of the accretion disk wind on timescales as short as
5 seconds. These results clearly establish a causal link between the X-ray
oscillations and the disk wind and therefore support the existence of a
disk-jet-wind connection. Furthermore, our analysis shows that the mass loss
rate in the wind may be sufficient to cause long-term oscillations in the
accretion rate, leading to state transitions in GRS 1915+105.Comment: Accepted to ApJ. 22 pages, 14 figures, uses emulateap
eXTP: Enhanced X-ray Timing and Polarization mission
EXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m 2 and 0.6 m 2 at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering < 180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m 2 , between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) - a set of 2 X-ray telescope, for a total effective area of 250 cm 2 at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees × 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025
A SUPER-EDDINGTON, COMPTON-THICK WIND IN GRO J1655–40?
During its 2005 outburst, GRO J1655–40 was observed at high spectral resolution with the Chandra High-Energy Transmission Grating Spectrometer, revealing a spectrum rich with blueshifted absorption lines indicative of an accretion disk wind—apparently too hot, too dense, and too close to the black hole to be driven by radiation pressure or thermal pressure (Miller et al.). However, this exotic wind represents just one piece of the puzzle in this outburst, as its presence coincides with an extremely soft and curved X-ray continuum spectrum, remarkable X-ray variability (Uttley & Klein-Wolt), and a bright, unexpected optical/infrared blackbody component that varies on the orbital period. Focusing on the X-ray continuum and the optical/infrared/UV spectral energy distribution, we argue that the unusual features of this "hypersoft state" are natural consequences of a super-Eddington Compton-thick wind from the disk: the optical/infrared blackbody represents the cool photosphere of a dense, extended outflow, while the X-ray emission is explained as Compton scattering by the relatively cool, optically thick wind. This wind obscures the intrinsic luminosity of the inner disk, which we suggest may have been at or above the Eddington limit.United States. National Aeronautics and Space Administration (Grant HST-HF2-51343.001- A)United States. National Aeronautics and Space Administration. Einstein Postdoctoral Fellowship Award (Grant PF2-130097
Evidence for simultaneous jets and disk winds in luminous low-mass X-ray binaries
Recent work on jets and disk winds in low-mass X-ray binaries (LMXBs)
suggests that they are to a large extent mutually exclusive, with jets observed
in spectrally hard states and disk winds observed in spectrally soft states. In
this paper we use existing literature on jets and disk winds in the luminous
neutron star (NS) LMXB GX 13+1, in combination with archival Rossi X-ray Timing
Explorer data, to show that this source is likely able to produce jets and disk
winds simultaneously. We find that jets and disk winds occur in the same
location on the source's track in its X-ray color-color diagram. A further
study of literature on other luminous LMXBs reveals that this behavior is more
common, with indications for simultaneous jets and disk winds in the black hole
LMXBs V404 Cyg and GRS 1915+105 and the NS LMXBs Sco X-1 and Cir X-1. For the
three sources for which we have the necessary spectral information, we find
that the simultaneous jets/winds all occur in their spectrally hardest states.
Our findings indicate that in LMXBs with luminosities above a few tens of
percent of the Eddington luminosity, jets and disk winds are not mutually
exclusive, and that the presence of disk winds does not necessarily result in
jet suppression.Comment: Updated to match published version (2016, ApJ, 830, L5
Study of localization in the quantum sawtooth map emulated on a quantum information processor
Quantum computers will be unique tools for understanding complex quantum
systems. We report an experimental implementation of a sensitive, quantum
coherence-dependent localization phenomenon on a quantum information processor
(QIP). The localization effect was studied by emulating the dynamics of the
quantum sawtooth map in the perturbative regime on a three-qubit QIP. Our
results show that the width of the probability distribution in momentum space
remained essentially unchanged with successive iterations of the sawtooth map,
a result that is consistent with localization. The height of the peak relative
to the baseline of the probability distribution did change, a result that is
consistent with our QIP being an ensemble of quantum systems with a
distribution of errors over the ensemble. We further show that the previously
measured distributions of control errors correctly account for the observed
changes in the probability distribution.Comment: 20 pages, 9 figure
Statistics of X-ray flares of Sagittarius A*: evidence for solar-like self-organized criticality phenomenon
X-ray flares have routinely been observed from the supermassive black hole,
Sagittarius A (Sgr A), at our Galactic center. The nature of
these flares remains largely unclear, despite of many theoretical models. In
this paper, we study the statistical properties of the Sgr A X-ray
flares, by fitting the count rate (CR) distribution and the structure function
(SF) of the light curve with a Markov Chain Monte Carlo (MCMC) method. With the
3 million second \textit{Chandra} observations accumulated in the Sgr A
X-ray Visionary Project, we construct the theoretical light curves through
Monte Carlo simulations. We find that the keV X-ray light curve can be
decomposed into a quiescent component with a constant count rate of
count s and a flare component with a power-law
fluence distribution with . The duration-fluence correlation can also be modelled as a
power-law with (
confidence). These statistical properties are consistent with the theoretical
prediction of the self-organized criticality (SOC) system with the spatial
dimension . We suggest that the X-ray flares represent plasmoid
ejections driven by magnetic reconnection (similar to solar flares) in the
accretion flow onto the black hole.Comment: to appear in Ap
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