On Some Prospects of the LOFT Mission: QPO Models
Gabriel Török
Institute of Physics, Silesian University in Opava
CZ.1.07/2.3.00/20.0071 Synergy , GAČR 209/12/P740, 202/09/0772, SGS-01-2010, www.physics.cz
1. Introduction
MOTIVATION
LMXBs
Compact object:
- black hole or neutron star (>10^10gcm^3)
LMXB Accretion disc
T ~ 10^6K
>90% of radiation
in X-ray
Companion:
• density comparable to the Sun
• mass in units of solar masses
• temperature ~ roughly as the T Sun
• more or less optical wavelengths
Observations: The X-ray radiation is absorbed by the Earth atmosphere and must
be studied using detectors on orbiting satellites representing a rather expensive
research tool. On the other hand, it provides a unique chance to probe effects in
the strong-gravity-field region (GM/r~c^2) and test extremal implications of
General Relativity (or other theories).
Figs: space-art, nasa.gov
1. Introduction
MOTIVATION
Sco X-1
power
LMXBs short-term X-ray variability:
peaked noise (Quasi-Periodic Oscillations)
Individual peaks can be related to a
set of oscillators, as well as to time
evolution of a single oscillator.
• Low frequency QPOs (up to 100Hz)
frequency
• hecto-hertz QPOs (100-200Hz),...
• HF QPOs (~200-1500Hz):
Lower and upper QPO feature
forming twin peak QPOs
Fig: nasa.gov
The
HF QPO origin remains
questionable,
it is most often
expected that it is associated to
orbital motion in the inner part of the
accretion disc.
2. LOFT
LOFT is specifically designed to exploit the diagnostics of very rapid X-ray
flux and spectral variability (already known to exist) that directly probe
the motion of matter down to distances very close to black holes and
neutron stars. Its factor of ~20 larger effective area than RXTE’s PCA (the
largest area X-ray instrument ever flown) is crucial in this respect.
(from LOFT webpage)
2. LOFT
LOFT/LAD’s much improved energy resolution (better than 260 eV)
compared to that of RXTE/PCA will also allow the simultaneous
exploitation of spectral diagnostics, in particular the relativistically
broadened 6-7 keV Fe-K lines. The timescales that LOFT will investigate
range from submillisecond quasi-periodic oscillations (QPOs) to years long
transient outbursts. LOFT is required to answer two fundamental
questions of ESA's Cosmic Vision Theme Matter under extreme conditions:
• Does matter orbiting close to the event horizon follow the predictions
of general relativity?
• What is the equation of state of matter in neutron stars?
(from LOFT webpage)
3. LOFT & QPO Models (SFG1 Group Goals)
(Several of) Competing models variously identify observed QPOs with the
relativistic radial and vertical epicyclic frequencies or relativistic nodal and
periastron precession. Very high-signal-to-noise LOFT/LAD measurements of the
QPOs will unambiguously discriminate between such interpretations and in the
process tease out yet untested general relativistic effects such as frame
dragging, strong-field periastron precession, and the presence of an innermost
stable orbit. Crucially, LOFT will provide access for the first time to types of
information in these signals that are qualitatively new due to the capability to
measure dynamical timescale phenomena within their coherence time, where so
far only statistical averages of signals were accessible. This will allow studies that
directly witness QPO formation and propagation and tie in with what state-ofthe-art numerical work is just beginning to address.
(from LOFT webpage)
3. LOFT & QPO Models (SFG1 Group Goals)
Very high-signal-to-noise LOFT measurements of the QPOs will unambiguously
discriminate between QPO interpretations.
“Models predict frequencies but give very little insights on amplitude - It is
however likely that we see the tip of the iceberg (the fundamental, which is
actually close to the PCA sensitivity) and that the clue is in the harmonic
content of the signal, and this is a problem, because we don't know at which
amplitude levels they will show up.”
(from SFG1 materials)
3. LOFT & QPO Models (SFG1 Group Goals)
Very high-signal-to-noise LOFT measurements of the QPOs will unambiguously
discriminate between QPO interpretations.
Lightcurves corresponding to different disc oscillation modes and
lightcurves corresponding to hot-spot models should be modelled
including both the current models and the process of observation
in order to obtain relevant PDS.
4. Lightcurve Modelling: Implementation Basis & “Reverse Engineering”
COLLABORATION:
Pavel Bakala, Vladimír Karas, Michal Dovčiak, Martin Wildner, Dalibor
Wzientek, Marek Abramowicz, Eva Šrámková, Kateřina Goluchová, Frederic
Vincent, Grzegorz Mazur
 Institute of Physics, Silesian University in Opava, CZ
 Astronomical Institute, Prague, CZ
 Copernicus Astronomical Center, Warszawa, PL
 Institute for Theoretical Physics, University of Warsaw,PL
 Laboratoire AstroParticule et Cosmologie, CNRS, Universite Paris Diderot, FR
TOTAL SOURCE FLUX MODEL
4. Lightcurve Modelling: Implementation Basis & “Reverse Engineering”
Global Empirical
Model of Variability
and Spectra (GRS
1915+105, SPL State)
+
QPO MODEL
TOTAL SOURCE FLUX MODEL
4. Lightcurve Modelling: Implementation Basis & “Reverse Engineering”
Global Empirical
Model of Variability
and Spectra (GRS
1915+105, SPL State)
+
QPO MODEL
TOTAL SOURCE FLUX MODEL
4. Lightcurve Modelling: Implementation Basis & “Reverse Engineering”
Global Empirical
Model of Variability
and Spectra (GRS
1915+105, SPL State)
+
Response Matrices
(Detector)
“DATA” Time and
Spectral Distribution
of Detected Counts
QPO MODEL
TIMING
ANALYSIS
RESULTS
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code).
Expectation:
Keplerian frequency + harmonics
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code). [~1Crab source countrate]
Expectation:
Keplerian frequency + harmonics
Signal Strength (relative hot-spot brigthness)
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code). [~1Crab source countrate]
Expectation:
Keplerian frequency + harmonics
Signal Strength
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code). [~1Crab source countrate]
Expectation:
Keplerian frequency + harmonics
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code). [~1Crab source countrate]
Expectation:
Keplerian frequency + harmonics
5. Some Results: Signal Strength
Model: Single spot orbiting close to inner edge of the accretion disc
(simulation using KY Spot code). [~1Crab source countrate]
Expectation:
Keplerian frequency + harmonics
5. Some Results: Signal Strength
Current BH status: weak signal with sporadic RXTE QPO detections
- The applied simple model clearly illustrates the LOFT capability in
such situation.
5. Some Results: Comparison Between QPO Models
RXTE simulations
Multiple spost created around two
SPOTS (ISCO, nurmax)
preferred radii (using KY Spot code).
Power
Power
SPOTS (ISCO, nurmax)
LOFT simulations
M = 11M⊙, D = 65°, a = 0, R1= 6M,
R2=8M, n=0.1.
Frequency
The m=0 epicyclic oscillations of the
Torus (Epicyclic Modes)
optically thin torus drifting through
the resonant radius.
Power
Power
Torus (Epicyclic Modes)
Frequency
M = 5.6M⊙, D = 65°, a = 0, R0= 10.8M,
n=0.1.
Frequency
Frequency
5. Some Results: Comparison Between QPO Models
RXTE simulations
Power
SPOTS (ISCO, nurmax)
LOFT simulations
Multiple spost created around two
SPOTS (ISCO, nurmax)
preferred radii (using KY Spot code).
M = 11M⊙, D = 65°, a = 0, R1= 6M,
R2=8M, n=0.1.
Frequency
The m=0 epicyclic oscillations of the
Torus (Epicyclic Modes)
optically thin torus drifting through
the resonant radius.
Power
Power
Torus (Epicyclic Modes)
Frequency
M = 5.6M⊙, D = 65°, a = 0, R0= 10.8M,
n=0.1.
Frequency
Frequency
5. Some Results: Comparison Between QPO Models
RXTE simulations
LOFT simulations
SPOTS (ISCO, nurmax)
Power
Power
SPOTS (ISCO, nurmax)
Frequency
Torus (Epicyclic Modes)
Torus (Epicyclic Modes)
Power
Power
Frequency
Frequency
Frequency
5. Some Results: Comparison Between QPO Models
RXTE simulations
LOFT simulations
SPOTS (ISCO, nurmax)
Power
Power
SPOTS (ISCO, nurmax)
Frequency
Frequency
GR
Torus (Epicyclic Modes)
Power
Power
Torus (Epicyclic Modes)
Frequency
Frequency
END
Thank you for your attention…