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

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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

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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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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

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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

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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