On some prospects of the LOFT mission
Gabriel Török, Pavel Bakala, Vladimír Karas, Michal
Dovčiak, Martin Wildner, Dalibor Wzientek
Institute of Physics, Silesian University in Opava
Astronomical Institute, Prague
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 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
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-of-the-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 (the official claim).
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.
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
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
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
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
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…