MagEX: A Proposal for a Lunar-based X-ray Telescope

Steven SembayAndrew Read & Jenny Carter

Department of Physics and Astronomy

University of Leicester

• Lunar-based X-ray Astronomy – a short review

• The MagEX concept

Speculative 21st Century High Throughput

(>100 m2) Lunar X-ray Observatory

“High Throughput X-ray Telescope on a Lunar Base”

Paul Gorenstein, 1990, in “Astrophysics from the Moon”, AIP

Possible timeline for evolution of effective area of X-ray

Astronomy Satellites (Gorenstein 1990)

Phase 1: Late 1990’s 1 m2

Phase 2: 2010 10 m2

Phase 3: 2040 100 m2

XMM-Newton

0.45 m2 @ 1.5 keV

Launched: Dec 1999

Xeus

5 m2 @ 1.0 keV

Launch: 2020’s?

Existing technology (1990’s) implied ~400 ton facility

Economic Argument: Assuming an existing lunar industrial

infrastructure, cheaper to construct on the Moon than launch from Earth

0.075 m2 / 956 kg

Chandra

XMM-Newton

0.45 m2 / 1,050 kg

X-ray Mirror Technologies – Resolution v Area density relation

Si Square Pore Optic

XEUSGeneration-X ??

~100 m2 / ~ 2-3 tonnes

Adaptive Optics

~ 5 m2 / ~ 1,296 kg

X-ray Mirror Technologies – Resolution v Area density relation

In the foreseeable future the “industrial” argument for lunar-based

Large X-ray telescopes has been weakened by advances in mirror

technology, although large space observatories would benefit from

increased lift capacity generated by a space exploration programme.

Far-UV Camera/Spectrograph carried on Apollo 16

If not LARGE then how about SMALL?

Analogue: SuperWASP

wide-field optical monitor

Applications for small Lunar-based X-ray Telescopes

Chandra/CXC/M.Weiss

RX J1242-11Stellar Capture Event

1) Network of wide area monitors for studying extra-solar system

transients and variables

Applications for small Lunar-based X-ray Telescopes

LEO Ext. OrbitMoon

Contiguous light curves NoYes

Particle background Lowest Highest

Thermal stability (poles)

Yes

X-ray background Low Low

GoodGood

Low

Highest

PoorThermal stability (equator) Poor

Case must be made on economic grounds. Is a network of simple

X-ray Telescopes “piggybacking” on lunar (e.g.) missions cheaper

than a dedicated spacecraft?

1) Network of wide area monitors for studying extra-solar system

transients and variables

Applications for small Lunar-based X-ray Telescopes

2) Remote sensing of the Terrestrial environment

Aq+ + B → A(q-1)+* + B+

A(q-1)+* → A(q-1)+ + hν

Solar Wind Charge X-rays:

Heavy solar wind ions in collision

with neutral target atoms

e.g. X-ray Emission from the SWCX process in the Magnetosheath

Program: Concept Studies for Lunar Sortie Science Opportunities

solicitation within NASA Research Announcement:

Research Opportunities in Space and Earth Sciences (ROSES) – 2006

PI: Michael Collier (NASA/GSFC)

NASA/GSFC, Univ. of Kansas, Univ. of Leicester UK, Acad. Sci. Czech Rep.

MagEX: Magnetosheath Explorer in X-rays

MagEX X-ray Telescope is

compact (< 50 cm side)

low mass (< 20-30 kg)

wide field of view (~30°)

imaging capable (psf ~ 1.5 arcminutes FWHM)

detector energy resolution (~50 eV FWHM @ 600 eV)

MagEX: Magnetosheath Explorer in X-rays

Proposal was funded (US) by NASA for a technical

feasibility study, result due Autumn 2008

Awaiting result of an application to STFC for UK funding

to support this study

Program: Concept Studies for Lunar Sortie Science Opportunities

solicitation within NASA Research Announcement:

Research Opportunities in Space and Earth Sciences (ROSES) – 2006

PI: Michael Collier (NASA/GSFC)

Collaborators: Univ. of Kansas, Univ. of Leicester UK, Acad. Sci. Czech Rep.

Optic Technology

Optic PSF:

~ 1.5’ FWHM

(Lab Measurement)

Optic of desired sizeformed by holdingcurved plates(3cm x 3cm) in asegmented bracket.Total mass ~ 1 kg

Channel width = 20µm

Slumped Glass Micropore Optics: Wide field of view & low mass

~ 30 cm

Optic Technology

R = 50 cm

FOV = 30°Focal Plane geometric area depends onthe Radius of curvature of the optic and the Field of view.

D ~ 13 cm for R = 50 cm & fov = 30°

Optic of desired sizeformed by holdingcurved plates(3cm x 3cm) in asegmented bracket.Total mass ~ 1 kg

D ~ 13cm

Channel width = 20µm

Slumped Glass Micropore Optics: Wide field of view & low mass

~ 30 cm

Detector Technology

Wide area CCDs provide:

Hamamatsu, BI CCD, 6.7 cm x 3.2 cm

e2V, BI/FI CCD, 6.1 cm x 6.1 cm

Soft X-ray sensitivityGood energy resolutionGood spatial resolution

Near-contiguous detection plane

Observational Goals

Primary and Unique…

Study of the dynamical interaction of the solar wind with the Earth’s magnetosheath on global scales via observations of X-ray emission from the Solar Wind Charge Exchange Process

Additional Goals….

Study of the interaction of the solar wind with the Lunar Exospherevia X-ray emission from SWCX

Monitoring of Terrestrial Auroral soft X-ray emission

Lunar distance to Earth

is well matched to size of

SWCX emitting region and

FOV (30°) of MagEX

Lunar location provides a natural

Platform for Earth observations

Telescope in Lunar night for

half the orbit

Optimum view of region

AND optimum

operating conditions

(CCDs @ -100°C)

What do we expect to see?

PX-ray = α nsw usw nn

Efficiency factor α depends on solarwind ion and target neutral composition

α ~ 9.4 x 10-16 eV cm2 (slow wind)α ~ 3.3 x 10-16 eV cm2 (fast wind)

uswnsw nn

Robertson & Cravens (2003, 2006)

Exosphere model (Hodges 1994)MHD model

X-ray power depends on SW densityand velocity and exosphere density

Predicted SWCX Maps – View from 50 RE

Proton flux as measured byWind and Ace spacecraft

Robertson & Cravens (2003) Robertson & Cravens (2006)

Model including the cusps

Average SW10 ksSrc 5.7 cts/sSky 126 cts/sInst. 3.1 cts/s

Average SW100 ksSrc 5.7 cts/sSky 126 cts/sInst. 3.1 cts/s

Storm SW1 ksSrc 75 cts/sSky 126 cts/sInst. 3.1 cts/s

Storm SW10 ksSrc 75 cts/sSky 126 cts/sInst. 3.1 cts/s

Telescope Simulation

Detection of SWCX by XMM (30’ diam. fov)

Enhancement in X-rays seen before spike in SW density measured by ACE at L1!

Ongoing global studies of XMM-Newton detections of SWCX show no simplecorrelation with SW flux as measured by ACE (Snowden, Kuntz, Carter, Sembay)

Aq+ + B → A(q-1)+* + B+

A(q-1)+* → A(q-1)+ + hν

SWCX: Heavy solar wind ion in collision

with neutral target atom or molecule

• SWCX X-rays map the global interaction of the SW with the bow-shock and magnetosphere

• X-ray emitting region is temporally andspatially highly variable as the SWflux varies and compresses the region

• SW heavy ion species can produceidentifiable lines in the X-ray spectrumso the composition of this component of the SW can be mapped on large scales.

• X-ray observations can simultaneously help test models of the exospheric density distribution

Primary Science Goals

The tenuous lunar atmosphere (surface density ~ 105 cm-3, exponential scale height ~ 40 km) is a significant source of SWCX X-rays.

X-ray emission as function of view angle

Solar wind density in vicinity of Moon

Lunar atmosphere component strongly dependant on view angle:

varies from ~ 0 – 35 keV cm-2 s-1 sr-1

c.f. Magnetosheath ~ 5-10 keV cm-2 s-1 sr-1

- Average Solar ConditionsTrávniček et al. (2005)

Lunar Contribution

Polar Viewpoint

Intensity ~ 104 cts cm-2 s-1 sr-1

Region ~ 0.3° x 0.3° (6x6 pixels for 3’ psf)

In range 2-12 keV.

Chandra observations suggest ~ 30% of cts in hard band (2-10 keV)~ 70% of cts in soft band (0.1-2 keV)

Estimated count rate in MagEX:

Solid angle at Moon ~ 2.7 x 10-5 srEff. Area of Telescope ~ 5 cm2

Auroral (bright) rate ~ 3.1 cts s-1

c.f. rates in same size sold angle

Sky bgd ~ 0.03 cts s-1

Sheath (storm) ~ 0.015 cts s-1

Sensitivity to Auroral X-raysBright Event: 4th May 1998

~ 80 MagEX resolution elements

Concluding Remarks

o MagEX will provide the first global view of the dynamical interaction of the Solar wind with the Earth’s magnetosheath and the lunar atmosphere

o The Moon is an ideal location for looking back at the Earth because the geometry of the Earth-Moon system, the size and brightness of the X-ray emitting region under study and the technology of the MagEX telescope are all well-matched.

MagEX: Magnetosheath Explorer in X-rays