astro-ph/0403554 2004, nucl. phys. b 134, p.78-80 martin elvis, spie, orlando fl, may 2006 extreme...
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Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics Explorer: A Mission to Test Basic Physics
Martin ElvisHarvard-Smithsonian Center for Astrophysics
An International, multi-agency mission of opportunity?
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
What is the Future of X-ray Binary Research?
Fields go through 3 phases: 1. Discovery: mapping basic properties
Widespread excitement rockets, UHURU to EXOSAT
2. Understanding: detailed study & physics Specialist interest only EXOSAT to Rossi XTE
3. Tool: use understanding to ask new questionsWidespread interest begun by Chandra, XMM-Newton
Is X-ray binary research ending phase 2? Is phase 3 the
testing of Extreme Physics?
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Black Holes, Magnetars & Neutron Stars are cosmic laboratories for Extreme Physics:
• Gravity at the event horizon -- Black HolesFrame dragging, metric in strong gravity -- AGNs, BH binaries
• Magnetic fields with energy densities greater than an electron -- Magnetars BQED=4.4x1013 g
• Densities of nuclear matter or beyond -- ‘neutron’ stars
Reynolds C.
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Neutron star surfaces… … explore extreme physics … have a hard surface enabling
precision measurements … have a thin atmosphere that
imprints sharp atomic features in their spectra
• Enables spectroscopic tests of extreme physics
… are intrinsically X-ray sources
deDeo & Psaltis, 2003 astro-ph/0302095Space-Time curvature
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Gravitational redshift at neutron star surfaceCottam J. Paerels F. & Mendez M., 2002, Nature, 420, 51
EX Hya: HETG R~500 vradial= 58.2 +/- 3.7 km/s
Relative velocity only requires stability
not absolute calibration
Hoogerwerf et al. 2004 ApJ 160 411
z=0.35 +/-0.04, 10% errors
Spectrum integrated over spin period, several bursts
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Spectroscopy: NS Equation of State
Example: So far M only from orbit solution
Spectroscopy adds: Gravitational redshift due to
neutron star: zg ~ M/R Bhattacharya et al. 2006 ApJ
+ Doppler shift vs. phase• ~12 km/s
• R x sin i Map R vs. M of EoS Van den Heuvel
zg~ 0.3 czg~100,000 km s-1
1% errors ~1000 km/s -> R ~ 300
• E ~ 20 eV @ 6 keV
• E = 2eV @ 1 keV
Lattimer & Prakash 2000 Phys. Rep. 333, 121.
Radius (km)M
ass
(Mso
l)
zg
spin Doppler shift
Orbit solution...
Extreme Magnetic Fields: X-ray Pulsars
Polarized by:• Emission process: cyclotron
• Scattering on highly magnetized
plasma: σ║ ≠ σ┴
•Swing of polarization angle vs. phase measures:
• orientation of rotation axis on the sky &
• inclination of the magnetic field
the case 45°, 45° (from Meszaros et al. 1988)
Thanks to Enrico Costa
Testing GR in strong field: bending of light in Galactic Black-Hole Binaries
The Polarization angle from an accretion disk in the ‘Newtonian’ case is either parallel to the major axis of the sky-projected disk (positive) or parallel to the sky-projected disk symmetry axis (negative)
If the field is strong enough polarization is altered by gravitational effects.
The polarization plane rotates continuously with energy because of General Relativistic effects. This is a signature of the presence of a black-hole Stark & Connors, Connors& Stark, 1977, Connors, Piran & Stark, 1980.
Polarimetry gives the orientation of Polarimetry gives the orientation of an accretion disk on th skyan accretion disk on th sky
Sunyaev & Titarchuk, 1985
Thanks to Enrico Costa
Simulated observation
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Requirements for using Compact Objects as Physics Labs
Compact object = ‘accelerator’X-ray telescope = ‘experiment’Observational Requirements: High spectral resolution R~500
• precise measurements of zg, B High time resolution t = 100sec
• Resolve 10 phase bins in msec period Large area 5-10 sq.m: to collect
enough photons:• few x 103 counts in few x 103 ~1 eV spectral bins x 10 phase bins• 106 photons to measure 10 1% polarization• Gratings need a good (<10” HPD) mirror
Polarization • Quantum critical B-field effects
Crab = 104 ct/s/sq.m
XRBs ~103 ct/s/sq.m
Dreaming?
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics ExplorerA mission designed to study physics in the extreme environments provided by neutron
stars and black holesNot an X-ray astronomy mission
• A physics mission • though utilizing X-ray astronomy techniques
Achieves:• Large collecting area• High time resolution• High spectral resolution• Sensitive polarimetry
Targets:• Galactic neutron star and black hole binaries,
including magnetars, transients• Long observations
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Microcalorimeters as timing devices Pulse rise time ~50 sec Event timing to ~5 s Energy resolution <5 eV
• R>200 @ 1keV Con-X, NEW, DIOS goal 2 eV
• R=500 @1 keV = RGS, HETGS QE ~ 1 (down to ~0.5 keV) Ideal for neutron starsBUTBUT: Count rate limit ~103 Hz
• Event duration ~100 sec• Constellation-X cannot observe X-ray
binaries with XRS SMALL ~1 cm2 area
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Overcoming microcalorimeter limitations: 1. Area
Galactic X-ray neutron star binaries emit ~103 ct/s/sq.m
Need ~107 counts/observation Observation should be small fraction of hours-days binary
orbit: ~104s -> Area ~1 - 5 sq. m. = mirrors. Con-X mirrors weigh 280 kg m-2
• too much for a MIDEX
But: Good imaging is bad for microcalorimeter timing: Need to spread out the signal.
~1 arcminute HPD optics are about right.
• SOLUTION: microchannel plate mirrors: 3.7 kg m-2
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Microchannel Plate Mirrors = LOBSTER optics
• Well developed (U. Leicester)
• Not XEUS Micropore optics
Lightweight: 3.7 kg m-2
• 1/10 area/mass ratio of next lightest X-ray mirrors (ASCA/Suzaku foils)
• Plate-like, robust: fold/deploy easily Units ~1.7m dia. Deploy to 5m dia.
1 arcmin HPD: • Demonstrated Bavdaz et al 2002 SPIE
• Not so bad: low background, confusion: can reach 10’s of AGNs
High aperture utilization Thermal control?
George Fraser & Gareth Price 2003, priv.comm.
3 m2 @ 10 keV
7 m2 @ 1 keV
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Long Focal LengthNeeds ~40m focal length to get area
• f-number is fixed for grazing incidence mirrors 1arcmin ~ 1.5cm @ focal plane: good size for microcalorimeters
Flight-tested light-weight deployable optical benches exist• Able Engineering: UARS, GGC WDIND, GGS POLAR, Cassini, Lunar
Prospector, IMAGE
Slow slewing: long observations
5m
40
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Overcoming microcalorimeter limitations: 2. Count rate
Count rate limit is per pixel:• 32x32 array can count at 1 MHz - for uniform illumination
• C.f. 105 ct/s 10sq.m X-ray binary
C.f. Con-X: 32x32, 2eV; NEW 32x32 2eV; DIOS 16x16 6eV
Slightly larger arrays allow for aspect jitter:• 5 arcsec rms -> ~10 arcsec 90% -> 5 pixels -> 42x42 array
Pixel size ~ 500 m (~ 2 arcsec) • 50 meter focal length (to get needed area)
1 arcsec ~0.25 mm 1 arcmin beam size ~9 mm dia.
• ~ 2 x Con-X = DIOSE = 2.36x 2m1/4 (kT2C/)1/2 , C=heat capacity = a(pixel size)2
Trade-off: technical difficulty of larger arrays vs. E
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Optimizing Microcalorimeter Energy resolution
Challenging spectral resolutionE = 2eV, R = 500 @ 1 keV
Easier to achieve over limited bandwidth: thinner converter, lower heat capacity
Divide high and low energy signal between two detector arrays, few arcmin apart
Tilt outer shells by ~5 arcmin~10% of 1 keV graze angle Degradation of beam shape small
compared with 1 arcmin HPD Also enables ~doubling of maximum
count rate Keep polarimeter on axis - avoid
instrumental polarization
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5 arcmin
Cryostat/ Microcalorimeter
Hi E fociLo E foci
Polarimeter
50 cm
21 arcmin
Optical axis
?
Focal Plane layout
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Costa et al. Polarization from tracks of
photoelectron: 50% modulation, 5.4 keV
imaged by a finely subdivided gas detector, PIXI
High time resolution: few sec
• High count rate: few 104 ct/s Put in ‘warm’ focal plane 10-
20arcmin from calorimeter.
Thanks to Enrico CostaOne Polarimeter Option:
Micro Pattern Gas Detector
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
A fast evolving technique
ChipChip I I (2003)(2003) 2101 pixel2101 pixel;; pitchpitch 8080mm; 4 mm Ø; 4 mm Ø
ChipChip II II (2004) (2004) 20000 pixel20000 pixel;; pitch pitch 8080mm;; 11 × 11 mm 11 × 11 mm22
ChpChp III III (2006)(2006) 10560105600 pixel0 pixel:: pitch pitch 50 50 m 1m 155 × × 1155 mm mm22
Morover in Chip III Morover in Chip III each pixel has each pixel has independent trigger independent trigger and capability to and capability to convert only convert only triggered channels triggered channels →→ very fast read-out, very fast read-out, few few secsec
Thanks to Enrico Costa
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
MIDEX Scale Mission Mass Feasible mass budget:
• 10 m2 microchannel plate mirror: 37 kg• Mirror support assembly: 37 kg• Optical bench (extending to 40m): 40 kg• Optical bench canister: 50kg• Calorimeter & cryostat: 123 kg• Spacecraft: 200 kg• 20% reserve: 83 kg
• TOTAL: 585 kg Easily within MIDEX range
• Add small polarimeter, ASM mass• Use excess to achieve a high orbit
gives long continuous coverage
• Geostationary? Continuous data contact:
– 104 ct s-1 x 64 bits/event = 0.1 Mbaud continuous But high background?
Not important for bright X-ray binaries May overload telemetry?
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Challenges 2 eV 42x42 microcalorimeter array Mass production of microchannel plate optics Deployment of MCP optics Data rate: 0.1 MB continuous 40 meter optical bench Polarimeter Small cryostat; no cryogen? All Sky Monitor for transients? Science case development
• Spectro-timing, Polarimetric tests not fully developed
• Need simulations for specific sources
• Form Science Working Group
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics Explorer -A Next Generation RXTE
10 times area 100 times spectral resolution 1/1000 beam size 5s time resolution polarimetry
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics Explorer -A Mission of Opportunity?
NASA Appeals to: Fundamental Physics; RXTE communitySAO [mirror partner, ops/data center] GSFC [calorimeter]
DoE? Fundamental Physics connection (&much cheaper than JDEM!)
Potential International partners:• With likely funding:
Canada want a mission; Kaspi (McGill) pushing X-ray binaries
Netherlands (SRON) want to fly a calorimeter as XEUS prep.
• Funding less clear:UK (Leicester) microchannel plate mirrorItaly (ASI) U. Rome [polarimeter]
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics ExplorerTime is ripe for X-ray emitting Compact Objects research
to move to 3rd phase: Extreme Physics Physics-Astrophysics collaboration on Extreme Physics?Need theoretical predictions of spectral featuresemail [email protected] if you want to join in
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X-ray binary
Black Hole or`neutron’ star
Mass donor star
The next accelerator
Martin Elvis, SPIE, Orlando FL, May 2006Astro-ph/04035542004, Nucl. Phys. B 134, p.78-80
Extreme Physics Explorer MIDEX scale: 500kg, deployed optics, 40m focal length,
GEO orbit? Microchannel plate Mirror:
• Area ~5-10 m2 at ~0.5 - ~10 keV [goal 20keV?] ~10 x RXTE (PCA), ~500 x Chandra (HETG, LETG) Arcminute imaging
• Long focal length ~40m
Microcalorimeter: 2 42x42 arrays, 500m pixels• Low E: E=2eV R=500 @ 1 keV, v +/-30 km/s • High E: E=6eV R=1000 @ 6 keV
Polarimeter:• TBD: several candidate technologies