Extreme Physics Explorer: A Mission to Test Basic Physics

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?


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?


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.


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


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


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


Simulated observation


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?


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


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


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


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


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


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


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


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


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



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?


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


Extreme Physics Explorer -A Next Generation RXTE

10 times area 100 times spectral resolution 1/1000 beam size 5s time resolution polarimetry


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]


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


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

Extreme Physics Explorer: A Mission to Test Basic Physics

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