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LOFT Large Observatory For x-ray Timing
A mission proposal selected by ESA as a candidate CV M3 mission
devoted to X-ray timing and designed to investigate
the space-time around collapsed objects
Marco Feroci (INAF), Jan-Willem den Herder (SRON) on behalf of the LOFT Consortium
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LOFT in one plot
2 1.0 10.0 100.0
Energy [keV]0
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10Ef
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ASTROSAT-LAXPCRXTE-PCAXMM-EPIC-pn
The high frequency QPOs in the BHC XTE J1550-564
ν1=188 Hz, ν2=268 Hz, frac rms ν1= 2.8%, frac rms ν2=6.2% (Miller et al. 2001), flux = 1 Crab, RXTE Exposure 54 ks,
significance ∼3-4σ LOFT simulation: Texp=1 ks
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Jan-Willem den Herder SRON, the Netherlands Marco Feroci INAF/IASF-Rome, Italy Luigi Stella INAF/OAR-Rome, Italy Michiel van der Klis Univ. Amsterdam, the Netherlands Thierry Courvousier ISDC, Switzerland Silvia Zane MSSL, United Kingdom Margarita Hernanz IEEC-CSIC, Spain Søren Brandt DTU, Copenhagen, Denmark Andrea Santangelo Univ. Tuebingen, Germany Didier Barret IRAP, Toulouse, France Renè Hudec CTU, Czech Republic Andrzej Zdziarski N. Copernicus Astronomical Center, Poland Juhani Huovelin Univ. of Helsinki, Finland Paul Ray Naval Research Lab, USA Joao Braga INPE, Brazil
on behalf of more than 250 scientists from: Brazil, Canada, Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Israel, Italy, Japan, the Netherlands, Poland, Spain,
Switzerland, Turkey, United Kingdom, USA
Mission has been studied for M3 by Thales-Alenia Space
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LOFT will fully address Fundamental Question 3.3
“Matter under extreme conditions” put forward by the ESA’s Cosmic Vision
The LOFT Mission
• LOFT will exploit the diagnostics of very rapid X-ray flux and spectral variability that probes the motion of matter very close to black holes and neutron stars, as well as the physical state of ultradense matter.
• LOFT will investigate variability from submillisecond QPO’s to years long transient outbursts.
• The LOFT LAD has an effective area ~20 times larger than the Proportional Counter Array onboard RossiXTE and a much improved energy resolution.
• The LOFT WFM will discover and localise X-ray transients and impulsive events and monitor spectral state changes, triggering follow-up observations and providing important science in its own.
The LOFT Science Drivers Neutron Star Structure and Equation of State of ultradense matter:
- neutron star mass and radius measurements - neutron star crust properties
Strong gravity and the mass and spin of black holes
- QPOs in the time domain - Relativistic precession - Fe line reverberation studies in bright AGNs
Pulse Shape Modelling and Fitting in Neutron Stars
Simulation of the 401 Hz pulse profile measurement (SAX J1808.4-3658) On coherent pulsations and/or burst oscillations: 5% uncertainty (90% confidence level) on mass and radius
R=11,12,13 km
M=1.3,1.4,1.5 Msun
X-ray oscillations are produced by hot spots rotating at the neutron star surface. Modeling of the pulses (shape, energy dependence) taking into account Doppler boosting, time dilation, gravitational light bending and frame dragging will constrain the M/R of the NS.
Poutanen and Gierlinski 2003
LOFT Constraints to NS EOS from M-R measurements
4U 1636-53 (582 Hz)
from Demorest et al. 2010
LOFT study of the QPO evolution with flux and fractional rms
Different models still fit the available data. Once the ambiguity of the interpretation of the QPO phenomena is resolved, the frequency of the QPOs will provide access to general relativistic effects (e.g, Lense-Thirring or strong-field periastron precession) and to the mass and spin of the black hole.
Fe line reverberation studies in bright AGNs
LOFT simulation of a steady and variable Fe line. F=3mCrab, a=0.99, rin=1rg, rout=100rg, q=45°, e~r-3, rsp=10rg, Torb=4 ks Texp=16 ks à mapping 4 phases (1 ks each) in four cycles M=3-4 x 106 Msun a=0.93-0.99 R=0.98(0.02)
rout
rin
rsp
The LOFT Observatory
As for RXTE/PCA (but at much higher sensitivity), with a high flexibility in its observing program, LOFT will also be an Observatory for virtually all classes of relatively bright sources.
These include: X-ray bursters, High mass X-ray binaries X-ray transients (all classes) Cataclismic Variables Magnetars Gamma ray bursts (serendipitous) Nearby galaxies (SMC, LMC, M31, …) Bright AGNs …
Observing program
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Source Type TOO Sources Pointings Total Time (ks)
BH transient outbursts Yes 4 800 2400
Persistent BH No 2 400 1600 AGN No 30 50 8000 Msec pulsar outburst Yes 3 250 1000
NS transient bright outburst Yes 3 250 1800
Persistent bright NS No 12 350 4800
NS transient weak outburst Yes 6 6 120
Persistent weak NS No 14 14 280
Bursters Yes 10 40 1000
Total: 4 years with a goal of 5 years. Significant part (50%) available for observatory science
The LOFT Mission
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LAD: 10m2 collimated area ΔE ~ 260 eV
WFM: coded mask detector to identify strong transients > 100 mCrab, 1 s
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1.0 10.0 100.0Energy [keV]
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LAD: Large Area Detector
• A large area detector with a collimated field of view (1 degree)
• Good spectral resolution using Silicon Drift Detectors (~ 260 eV) based on detectors developed for the LHC/ALICE (INFN)
• Mounted on deployable panels • A high level of modularity (different detector segments operate
independently) increasing the level of redundancy • The capability to monitor data rates in the LAD instrument and
onboard storage to enable switching modes in case the data rates get too high (e.g. to re-binned mode)
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Large Area Detector
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instrument size
Collimator, alignment
SDD and orbit
TM rates
Silicon Drift Detector heritage of the Inner Tracking System of the ALICE experiment,
Large Hadron Collider (CERN)
INFN Trieste, in collaboration with Canberra Inc., designed, built, tested and calibrated 1.5 m2 of SDD detectors (approximately 300 units), now operating since ∼2 years. High TRL & proven mass production.
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Thickness 450 µm Monolithic Active Area 76 cm2
Drift time <5 µs Single-channel area 0.3 cm2
The LAD – concept 1 of 6 Detector:
• SDD on 450µm thick Si, Top= -30°C
• ASIC FEE mounted on PCB backside
• HV required for drift anodes (max 1300V)
• Each detector is 72 x 121 mm2
• Separated in 2 halves, each 112 anodes or pixels
• Each event is recorded in 1 or 2 pixels
• Energy resolution limited by electronic noise, itself limited by EOL detector leakage current
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8 discrete read-out channel prototype - Room Temperature
Current Operating SDD Prototype (53 cm2) Measured Spectroscopy Performance
• Capillary plate
• High Pb content glass
• FoV ~40’
• Heritage BC MIXS-C
• Pitch ~25um, holes ~20um, height ~2mm
• MCP covered with Al filter
• Slumped MCP for flat-top response over ~12’
• Individual alignments and pointing accuracy need to be in this limit
LAD collimators
Collimation vs Energy: GEANT Montecarlo simulations
Achieving 10 m2 (~15 m2 geometerical)
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modular and redundant approach: 16 independent detectors per Module 21 independent Modules per Detector Panel 6 independent Detector Panels per LAD Total panel surface 21 m2
The Wide Field Monitor
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Wide Field Monitor (FoV few sr)
• trigger levels – bright transients is 100 mCrab for part of sky accessible to LAD – weaker transients (about 2 mCrab, duration few days), ~ 50%
detected
• FoV is a compromise between the accessible sky (only ½ of sky accessible to the LAD) and the size of the galactic bulge (~60 degree).
• Sensitivity (5 σ for countrate) over 50 ks < 5 mCrab (TBC) for 2 -
50 keV (no source confusion thus outside the galactic bulge). • Location accuracy < 1 arcmin for a 10 σ source.
• Low energy threshold matches the threshold of the LAD
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Wide Field Monitor
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Camera dimensions
Detector, coded mask
FoV, camera location
Ground contacts
Two options under study: SDD (LAD/Alice) • Commonality LAD • 1/1.5 D imaging • Low energy threshold • High TRL level
Micro-strip (AMS, FOXSI, ASTRO-H) • Independent development • Flight heritage • 2-D imaging
FoV matches sky visibility of LAD
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Silicon Drift Detectors 1D
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Imaging:
• coded mask
• Elements are 250µmx16mm
• 2 orthogonal projections
• FoV 90° x 90° (zero response)
• Resolution of 1 camera: 5’ x 5°
• Combination of 2 orthogonally oriented cameras gives 5’x 5’
• 2 cameras form 1 Unit
• Mask also integrates thermal shield/light filter (Kapton/Al/Si2O)
µstrip (silicon Drift Detectors, APC/CEA)
• Full 2 D imaging • 4 double sided microstrip
detctors (9 x 9 cm2, strip pitch 150 µm)
• 32 channels/ASIC: 152 ASICs • 150 mm tantalum coded mask
(300 x 300 mm elements) • Set of cameras (4) to cover full
field of view (180 x 30o) • Sensitivity ~ 1 mCrab in 50 ks
(TBC) • Angular resolution 3.6’
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Mission Implementation
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Marco Feroci (IASF Rome) 30
Item Requirement goal
Net observing time core science 21 Msec 33 Msec Additional open observing time observatory science
20 Msec 30 Msec
Calibration time 5% 2% minimum science observing times (during night time)
1 minute (1 source during 2 weeks per year) 10 minutes (10 sources during 2 weeks per year)
Accessible sky fraction (daytime)
>50 % 75%
Mission duration 4 year 5 year
Pointing accuracy (satellite + instruments combined)
1 arcmin 0.5 arcmin
Relative pointing error (RPE over observation)
1 arcmin 0.5 arcmin
Pointing knowledge for each axis over the full orbit (AMA, 3σ, 10 Hz)
<20 arcsec <5 arcsec
ToO (following alert of SOC) 24 hours for 70% of the time
< 8 hours for 33% of the time + 24 hours for 66% of the time
Orbit LEO, <600 km, < 5 deg LEO, 550 km, <2 deg Slews per orbit (average) 0.5 2
Instrument data rate (typical)1) LAD: 200 kbps (~ 150 mCrab) + WFM: 100 kbps
WFM in event mode
Instrument data rate (sustained)
LAD: 600 kbps (~ 500 mCrab) + WFM 100 kbps1)
LAD: ~1 Crab
data transfer per orbit 6.5 Gbit/orbit 14 Gbit/orbit
Sun constraints
consumables
ToO will not drive GS
The LOFT satellite
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LAD
WFM
Solar Array
Bus
folded
Industrial study by Thales Alenia Space - Italia
Satellite: • 1800 W • 1800 kg
The LOFT satellite
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deployed
stowed in the fairing
Vega not impossible
!
The LOFT Mission: summary
Detector 450 µm thick SDD Energy Range 2-30 keV (2-50 keV extended range) Field of View 43 arcmin Geometric Area 15m2 Effective area(@8 keV) 10 m2 (17x RXTE/PCA) Energy Resolution <260 eV (<200 eV for 40%) Time Resolution 5 µs Crab Count Rate 3x105 cts/s Deadtime <1% for 1 Crab Sensitivity LAD 1 mCrab/1s Supporting Experiment: Wide Field Monitor (4 sr) Satellite Mass ∼1800 kg Telemetry <1 Mbps Orbit Low-Earth, equatorial
1.0 10.0Energy [keV]
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LOFT in context
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10m2 @ 8 keV
1.0 m2 @30 keV
activities
• ESA is studying mission in house (sept/oct) • 2 parallel industrial studies in 2012
• Instrument consortium is working on payload: – WFM: Hernanz (IEEC/CSIC) and Brandt (DTU) – LAD: Zane (MSSL)
• Science case – Coordinated by Stella (INAF), vd Klis (UvA) and Jonker
(SRON) – Science meeting in Amsterdam (26-28 October) – Yellow book for ESA down selection end 2012
• Selection of M3 missions first half 2013
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The First LOFT International Science Workshop
Amsterdam, Science Park 26-28 October 2011
Public Announcements and LOFT Web Page http://www.isdc.unige.ch/loft
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LOFT is one of the 4 missions selected by the ESA WGs and
SSAC as a candidate CV-M3
LOFT is a simple mission, relying on solid hardware heritage,
offering both breakthrough and observatory science.
http://www.isdc.unige.ch/loft