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Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Extreme Physics Explorer: A Mission to Test Basic Physics An International, multi-agency mission of opportunity? Martin Elvis Harvard-Smithsonian Center for Astrophysics Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, 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 3. EXOSAT to Rossi XTE Tool: use understanding to ask new questions Widespread interest begun by Chandra, XMM-Newton Is X-ray binary research ending phase 2? Is phase 3 the testing of Extreme Physics? Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Black Holes, Magnetars & Neutron Stars are cosmic laboratories for Extreme Physics: • Gravity at the event horizon -- Black Holes Frame 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 2006 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 Space-Time curvature Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 deDeo & Psaltis, 2003 astro-ph/0302095 Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Gravitational redshift at neutron star surface Hoogerwerf et al. 2004 ApJ 160 411 EX Hya: HETG R~500 Dvradial= 58.2 +/- 3.7 km/s Relative velocity only requires stability z=0.35 +/-0.04, 10% errors Spectrum integrated over spin period, several bursts not absolute calibration Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Spectroscopy: NS Equation of State So far M only from orbit solution Spectroscopy adds: Gravitational redshift due to neutron star: zg ~ M/R Bhattacharya et al. 2006 ApJ Mass (Msol) Example: zg .. . Orbit solution + 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 • DE ~ 20 eV @ 6 keV • DE = 2eV @ 1 keV spin Doppler shift Radius (km) Extreme Magnetic Fields: X-ray Pulsars Polarized by: Thanks to Enrico Costa • Emission process: cyclotron • Scattering on highly magnetized plasma: σ║ ≠ σ┴ 9 keV 3.8 keV 1.6 keV •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) 9 keV 3.8 keV 1.6 keV 9 keV 3.8 keV 1.6 keV Testing GR in strong field: bending of light in Galactic Black-Hole Binaries Thanks to Enrico Costa Polarimetry gives the orientation of an accretion disk on th sky 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 skyprojected disk symmetry axis (negative) Sunyaev & Titarchuk, 1985 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. Simulated observation Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, 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 Dreaming? • precise measurements of zg, B High time resolution Dt = 100msec • 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 10s 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 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Extreme Physics Explorer A mission designed to study physics in the extreme environments provided by neutron stars and black holes Not 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 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Microcalorimeters as timing devices Pulse rise time ~50 msec Event timing to ~5 ms 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 stars BUT: Count rate limit ~103 Hz • Event duration ~100 msec • Constellation-X cannot observe X-ray binaries with XRS SMALL ~1 cm2 area Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 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 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Microchannel Plate Mirrors = LOBSTER optics George Fraser & Gareth Price 2003, priv.comm. • 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? 7 m2 @ 1 keV 3 m2 @ 10 keV Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Long Focal Length Needs ~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 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 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 mm (~ 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 = DIOS DE = 2.36x 2m1/4 (kT2C/a)1/2 , C=heat capacity = a(pixel size)2 Trade-off: technical difficulty of larger arrays vs. DE Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Optimizing Microcalorimeter Energy resolution Challenging spectral resolution: DE = 2eV, R = 500 @ 1 keV 5 arcmin 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 50 cm QuickTime™ TIFF (Uncompressed) Focal Plane are needed to see layout 21 arcmin Cryostat/ Polarimeter Microcalorimeter Hi E foci ? Lo E foci Optical axis Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 One Polarimeter Option: Micro Pattern Gas Detector 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 msec • High count rate: few 104 ct/s Put in ‘warm’ focal plane 1020arcmin from mcalorimeter. Thanks to Enrico Costa Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 A fast evolving technique Chip I (2003) 2101 pixel; pitch Thanks to Enrico Costa 80mm; 4 mm Ø Chip II (2004) 20000 pixel; pitch 80mm; 11 × 11 mm2 Chp III (2006) 105600 pixel: pitch 50 mm 15 × 15 mm2 Morover in Chip III each pixel has independent trigger and capability to convert only triggered channels → very fast read-out, few msec Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, 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? Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 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 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Extreme Physics Explorer A Next Generation RXTE 10 times area 100 times spectral resolution 1/1000 beam size 5ms time resolution polarimetry Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 Extreme Physics Explorer A Mission of Opportunity? NASA Appeals to: Fundamental Physics; RXTE community SAO [mirror partner, ops/data center] GSFC [mcalorimeter] 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 mcalorimeter as XEUS prep. • Funding less clear: UK (Leicester) microchannel plate mirror Italy (ASI) U. Rome [polarimeter] Martin Elvis, SPIE, Orlando FL, May 2006 Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Extreme Physics Explorer Time 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 features email [email protected] if you want to join in Black Hole or `neutron’ star QuickTime™ and a MassTIFF (Uncompressed) decompressor are needed to see this picture. donor star X-ray binary The next accelerator Astro-ph/0403554 2004, Nucl. Phys. B 134, p.78-80 Martin Elvis, SPIE, Orlando FL, May 2006 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, 500mm pixels • Low E: DE=2eV R=500 @ 1 keV, v +/-30 km/s • High E: DE=6eV R=1000 @ 6 keV Polarimeter: • TBD: several candidate technologies