89 research outputs found
Interplay between heartbeat oscillations and wind outflow in microquasar IGR J17091-3624
During the bright outburst in 2011, the black hole candidate IGR J17091-3624
exhibited strong quasi-periodic flare-like events (on timescales of tens of
seconds) in some characteristic states, the so-called heartbeat state. From the
theoretical point of view, these oscillations may be modeled by the process of
accretion disk instability, driven by the dominant radiation pressure and
enhanced heating of the plasma. Although the mean accretion rate in this source
is probably below the Eddington limit, the oscillations will still have large
amplitudes. As the observations show, the source can exhibit strong wind
outflow during the soft state. This wind may help to partially or even
completely stabilize the heartbeat. Using our hydrodynamical code GLADIS, we
modeled the evolution of an accretion disk responsible for X-ray emission of
the source. We accounted for a variable wind outflow from the disk surface. We
examined the data archive from the Chandra and XMM-Newton satellites to find
the observed limitations on the wind physical properties, such as its velocity
and ionization state. We also investigated the long-term evolution of this
source, which lasted over about 600 days of observations, using the data
collected by the Swift and RXTE satellites. During this long period, the
oscillations pattern and the observable wind properties changed systematically.
We found that this source probably exhibits observable outbursts of appropriate
timescales and amplitudes as a result of the disk instability. Our model
requires a substantial wind component to explain the proper variability
pattern, and even complete suppression of flares in some states. The wind
mass-loss rate extracted from the data agrees quantitatively well with our
scenario.Comment: 12 pages, 8 figures. Published in Astronomy and Astrophysic
Non-linear variability in microquasars in relation with the winds from their accretion disks
The microquasar IGR J17091-3624, which is the recently discovered analogue of
the well known source GRS 1915+105, exhibits quasi-periodic outbursts, with a
period of 5-70 seconds, and regular amplitudes, referred to as "heartbeat
state". We argue that these states are plausibly explained by accretion disk
instability, driven by the dominant radiation pressure. Using our GLobal
Accretion DIsk Simulation hydrodynamical code, we model these outbursts
quantitatively. We also find a correlation between the presence of massive
outflows launched from the accretion disk and the stabilization of its
oscillations. We verify the theoretical predictions with the available timing
and spectral observations.
Furthermore, we postulate that the underlying non-linear differential
equations that govern the evolution of an accretion disk are responsible for
the variability pattern of several other microquasars, including XTE J1550-564,
GX 339-4, and GRO J1655-40. This is based on the signatures of deterministic
chaos in the observed lightcurves of these sources, which we found using the
recurrence analysis method. We discuss these results in the frame of the
accretion disk instability model.Comment: 6 pages, 3 figures; to be published in the conference proceedings of
"High Energy Phenomena in Relativistic Outflows V" (La Plata, October 2015
Energy scaling of the "heartbeat" pulse width of GRS 1915+105, IGR J17091-3624, and MXB 1730-335 from Rossi-XTE observations
We investigate some key aspects of the "heartbeat" variability consisting of series of bursts with a slow rise and a fast decay, thus far detected only in GRS 1915+105, IGR J17091-3624, and MXB 1730-335. A previous analysis based on BeppoSAX data of GRS 1915+105 revealed a hard-X delay (HXD), that is a lag of the burst rise at higher energies with respect to lower ones; this leads to narrower pulse widths, w, at higher energies. We here use some light curves of Rossi-XTE observations of GRS 1915+105 for a deeper analysis of this effect and search for its presence in those extracted from some IGR J17091-3624 and MXB 1730-335 observations performed with the same satellite. Our results show that, at variance with GRS 1915+105, no HXD is evident in the light curves of MXB 1730-335 and only a marginal HXD may be argued for IGR J17091-3624. For GRS 1915+105 we find a decreasing trend of the pulse width with energy following a power law w = A ⋅ E ˆ (-s) with an index s ≈ 0.8. Furthermore, we confirm the increase of the HXD with the recurrence time T_rec of the bursts in each series that was already found in previous works using BeppoSAX data. Based on a spectral analysis of these three sources we conclude that the differences highlighted in the properties of the "heartbeat" variability are probably related to the different accreting compact object and the eventual presence of a corona in these binary interacting systems
Science case study and scientific simulations for the enhanced X-ray Timing Polarimetry mission, eXTP
The X-ray astronomy mission eXTP (enhanced X-ray Timing Polarimetry) is designed to study matter under extreme conditions of density, gravity and magnetism. Primary
goals are the determination of the equation of state (EoS) of matter at supranuclear density,
the physics in extremely strong magnetic fields, the study of accretion in strong-field gravity
(SFG) regime. Primary targets include isolated and binary neutron stars, strong magneticfield systems like magnetars, and stellar-mass and supermassive black holes. In this paper
we report about key observations and simulations with eXTP on the primary objectives
involving accretion under SFG regimes and determination of NS-Eo
The X-ray Polarization Probe mission concept
The X-ray Polarization Probe (XPP) is a second generation X-ray polarimeter
following up on the Imaging X-ray Polarimetry Explorer (IXPE). The XPP will
offer true broadband polarimetery over the wide 0.2-60 keV bandpass in addition
to imaging polarimetry from 2-8 keV. The extended energy bandpass and
improvements in sensitivity will enable the simultaneous measurement of the
polarization of several emission components. These measurements will give
qualitatively new information about how compact objects work, and will probe
fundamental physics, i.e. strong-field quantum electrodynamics and strong
gravity.Comment: submitted to Astrophysics Decadal Survey as a State of the Profession
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X-ray polarimetry reveals the magnetic field topology on sub-parsec scales in Tycho's supernova remnant
Supernova remnants are commonly considered to produce most of the Galactic
cosmic rays via diffusive shock acceleration. However, many questions about the
physical conditions at shock fronts, such as the magnetic-field morphology
close to the particle acceleration sites, remain open. Here we report the
detection of a localized polarization signal from some synchrotron X-ray
emitting regions of Tycho's supernova remnant made by the Imaging X-ray
Polarimetry Explorer. The derived polarization degree of the X-ray synchrotron
emission is 9+/-2% averaged over the whole remnant, and 12+/-2% at the rim,
higher than the 7-8% polarization value observed in the radio band. In the west
region the polarization degree is 23+/-4%. The X-ray polarization degree in
Tycho is higher than for Cassiopeia A, suggesting a more ordered magnetic-field
or a larger maximum turbulence scale. The measured tangential polarization
direction corresponds to a radial magnetic field, and is consistent with that
observed in the radio band. These results are compatible with the expectation
of turbulence produced by an anisotropic cascade of a radial magnetic-field
near the shock, where we derive a magnetic-field amplification factor of
3.4+/-0.3. The fact that this value is significantly smaller than those
expected from acceleration models is indicative of highly anisotropic
magnetic-field turbulence, or that the emitting electrons either favor regions
of lower turbulence, or accumulate close to where the magnetic-field
orientation is preferentially radially oriented due to hydrodynamical
instabilities.Comment: 31 pages, 7 figures, 3 tables. Accepted for publication in ApJ.
Revised versio
Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer
We present measurements of the polarization of X-rays in the 2-8 keV band
from the pulsar in the ultracompact low mass X-ray binary 4U1626-67 using data
from the Imaging X-ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were
clearly detected throughout the IXPE observations as well as in the NICER soft
X-ray observations, which we use as the basis for our timing analysis and to
constrain the spectral shape over 0.4-10 keV energy band. Chandra HETGS
high-resolution X-ray spectra were also obtained near the times of the IXPE
observations for firm spectral modeling. We find an upper limit on the
pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there
was no significant detection of polarized flux in pulse phase intervals when
subdividing the bandpass by energy. However, spectropolarimetric modeling over
the full bandpass in pulse phase intervals provide a marginal detection of
polarization of the power-law spectral component at the 4.8 +/- 2.3% level (90%
confidence). We discuss the implications concerning the accretion geometry onto
the pulsar, favoring two-component models of the pulsed emission.Comment: 19 pages, 7 figures, 7 tables; accepted for publication in the
Astrophysical Journa
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