1,596 research outputs found
Modelling correlated variability in accreting black holes:the effect of high density and variable ionization on reverberation lags
We present a new release of the RELTRANS model to fit the complex
cross-spectrum of accreting black holes as a function of energy. The model
accounts for continuum lags and reverberation lags self-consistently in order
to consider the widest possible range of X-ray variability timescales. We
introduce a more self-consistent treatment of the reverberation lags,
accounting for how the time variations of the illuminating flux change the
ionisation level of the accretion disc. This process varies the shape of the
reflection spectrum in time causing an additional source of lags besides the
light crossing delay. We also consider electron densities in the accretion disc
up to cm, which are found in most of the stellar mass black
holes and in some AGN. These high densities increase the amplitude of the
reverberation lags below keV since the reflection flux enhances in the same
energy range. In addition, we investigate the properties of hard lags produced
by variations in the power-law index of the continuum spectrum, which can be
interpreted as due to roughly variability in the corona's optical depth
and temperature. As a test case, we simultaneously fit the lag energy spectra
in a wide range of Fourier frequency for the black hole candidate MAXI
J1820+070 observed with NICER. The best fit shows how the reverberation lags
contribute even at the longer timescales where the hard lags are important.
This proves the importance of modelling these two lags together and
self-consistently in order to constrain the parameters of the system.Comment: Accepted for publication in MNRA
Modelling correlated variability in accreting black holes:the effect of high density and variable ionization on reverberation lags
Contribution of the HMPID detector to the high-pT physics at LHC
The LHC will deliver unexplored energy regimes for proton-proton and
heavy-ion collisions. As shown by the RHIC experiments, particle identification
over a large momentum range is essential to disentangle physics processes,
especially in the intermediate p (1 GeV/c) region. The novel
design of the High-Momentum Particle Identification Detector (HMPID), based on
large surface CsI photocathodes, is able to identify , ,
and in the momentum region where bulk medium properties and hard
scatterings interplay. Furthermore, measurement of resonance particles such as
the could provide information on the system evolution. The
HMPID layout and segmentation are optimized to study particle correlations at
high momenta describing the early phase and the dynamical evolution of the
collision. At LHC, the increased hard cross section will significantly be
enhanced compared to RHIC. Jet reconstruction via Deterministic Annealing can
address jet quenching and detailed measurements of jet properties. In this
paper, we present these selected topics from the possible HMPID contributions
to the physics goals of LHC.Comment: 6 pages, 7 figures, Contribution to QCD @ Work 2007: International
Workshop on Quantum Chromodynamics Theory and Experiment, Martina Franca,
Italy, 16-20 June 200
INFN What Next: Ultra-relativistic Heavy-Ion Collisions
This document was prepared by the community that is active in Italy, within
INFN (Istituto Nazionale di Fisica Nucleare), in the field of
ultra-relativistic heavy-ion collisions. The experimental study of the phase
diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP)
deconfined state will proceed, in the next 10-15 years, along two directions:
the high-energy regime at RHIC and at the LHC, and the low-energy regime at
FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the
present and future programme of the ALICE experiment, the upgrade of which will
open, in the 2020s, a new phase of high-precision characterisation of the QGP
properties at the LHC. As a complement of this main activity, there is a
growing interest in a possible future experiment at the SPS, which would target
the search for the onset of deconfinement using dimuon measurements. On a
longer timescale, the community looks with interest at the ongoing studies and
discussions on a possible fixed-target programme using the LHC ion beams and on
the Future Circular Collider.Comment: 99 pages, 56 figure
The NICER "Reverberation Machine":A Systematic Study of Time Lags in Black Hole X-Ray Binaries
Highly Coherent Quasiperiodic Oscillations in the âHeartbeatâ Black Hole X-Ray Binary IGR J17091-3624
\ua9 2024. The Author(s). Published by the American Astronomical Society.IGR J17091-3624 is a black hole X-ray binary (BHXB), often referred to as the âtwinâ of GRS 1915+105 because it is the only other known BHXB that can show exotic âheartbeatâ-like variability that is highly structured and repeated. Here, we report on observations of IGR J17091-3624 from its 2022 outburst, where we detect an unusually coherent quasiperiodic oscillation (QPO) when the broadband variability is low (total fractional rms âČ6%) and the spectrum is dominated by the accretion disk. Such spectral and variability behavior is characteristic of the soft state of typical BHXBs (i.e., those that do not show heartbeats), but we also find that this QPO is strongest when there is some exotic heartbeat-like variability (so-called Class V variability). This QPO is detected at frequencies between 5 and 8 Hz and has Q factors (defined as the QPO frequency divided by the width) âł50, making it one of the most highly coherent low-frequency QPOs ever seen in a BHXB. The extremely high Q factor makes this QPO distinct from typical low-frequency QPOs that are conventionally classified into type-A/B/C QPOs. Instead, we find evidence that archival observations of GRS 1915+105 also showed a similarly high-coherence QPO in the same frequency range, suggesting that this unusually coherent and strong QPO may be unique to BHXBs that can exhibit âheartbeatâ-like variability
The 2022 Outburst of IGR J17091-3624: Connecting the Exotic GRS 1915+105 to Standard Black Hole X-Ray Binaries
\ua9 2024. The Author(s). Published by the American Astronomical Society.While the standard X-ray variability of black hole X-ray binaries (BHXBs) is stochastic and noisy, there are two known BHXBs that exhibit exotic âheartbeatâ-like variability in their lightcurves: GRS 1915+105 and IGR J17091-3624. In 2022, IGR J17091-3624 went into outburst for the first time in the NICER/NuSTAR era. These exquisite data allow us to simultaneously track the exotic variability and the corresponding spectral features with unprecedented detail. We find that as in typical BHXBs, the outburst began in the hard state, then continued in the intermediate state, but then transitioned to an exotic soft state, where we identify two types of heartbeat-like variability (Class V and a new Class X). The flux energy spectra show a broad iron emission line due to relativistic reflection when there is no exotic variability, and absorption features from highly ionized iron when the source exhibits exotic variability. Whether absorption lines from highly ionized iron are detected in IGR J17091-3624 is not determined by the spectral state alone, but rather is determined by the presence of exotic variability; in a soft spectral state, absorption lines are only detected along with exotic variability. Our finding indicates that IGR J17091-3624 can be seen as a bridge between the most peculiar BHXB GRS 1915+105 and ânormalâ BHXBs, because it alternates between the conventional and exotic behaviors of BHXBs. We discuss the physical nature of the absorbing material and exotic variability in light of this new legacy data set
Variability as a Predictor for the Hard-to-soft State Transition in GX 339â4
During the outbursts of black hole X-ray binaries (BHXRBs), their accretion flows transition through several states. The source luminosity rises in the hard state, dominated by nonthermal emission, before transitioning to the blackbody-dominated soft state. As the luminosity decreases, the source transitions back into the hard state and fades to quiescence. This picture does not always hold, as â40% of the outbursts never leave the hard state. Identifying the physics that govern state transitions remains one of the outstanding open questions in black hole astrophysics. In this paper we present an analysis of archival RXTE data of multiple outbursts of GX 339â4. We compare the properties of the X-ray variability and time-averaged energy spectrum and demonstrate that the variability (quantified by the power spectral hue) systematically evolves â10â40 days ahead of the canonical state transition (quantified by a change in spectral hardness); no such evolution is found in hard-state-only outbursts. This indicates that the X-ray variability can be used to predict if and when the hard-to-soft state transition will occur. Finally, we find a similar behavior in 10 outbursts of four additional BHXRBs with more sparse observational coverage. Based on these findings, we suggest that state transitions in BHXRBs might be driven by a change in the turbulence in the outer regions of the disk, leading to a dramatic change in variability. This change is only seen in the spectrum days to weeks later, as the fluctuations propagate inwards toward the corona
Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis
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