104 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
Tracking the X-Ray Polarization of the Black Hole Transient Swift J1727.8–1613 during a State Transition
We report on an observational campaign on the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by the Imaging X-ray Polarimetry Explorer. These observations track for the first time the evolution of the X-ray polarization of a BH X-ray binary across a hard to soft state transition. The 2–8 keV polarization degree decreased from ∼4% to ∼3% across the five observations, but the polarization angle remained oriented in the north–south direction throughout. Based on observations with the Australia Telescope Compact Array, we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher-spatial-resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long (≳10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8–1613 is a member of a hitherto undersampled subpopulation
An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing
We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole
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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