Prospects for X-ray astronomy from the lunar surface

Steve Sembay ([email protected])To Moon and Beyond: DGLR International Symposium

14-16 March 2007, Bremen, Germany

Prospects for X-ray astronomy from the

lunar surfaceSteven Sembay

Co-I of the EPIC-MOS X-ray camera on XMM-Newton

Jenny Carter, Michael Collier, George Fraser and Steve Snowden

Department of Physics and Astronomy, University of Leicester, Leicester, UK.

Laboratory for Geospace Physics, NASA/GSFC, Greenbelt, USA.

X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, USA.



Why would you place an X-ray

telescope on the lunar surface?

What would be its scientific goals?

What design would you employ?

XEUS:

2020+?

~5 m2

XMM:

1999-?

~0.5 m2



Speculative 21st Century High Throughput

(>100 m2) Lunar X-ray Observatory

Science Goals include:

Large scale structure of the universe to z>=2 through survey of cluster Fe emission

Evolution of accretion disk in AGN to z>=2 through study of Fe fluoresence line

c.f. Gorenstein, P. 1990, High throughput X-ray telescope on a lunar base, in “Astrophysics from the Moon; Proceedings of the Workshop”, AIP, 207, 382



Lunar X-ray Observatory (LXO) on a more

practical scale….

X-ray telescopes which are small

instrument packages that can

be delivered via an astronaut

program or on a soft lander…

i.e. one part of a much larger scientific payload.



Science Goals of an LXO:

Primary: Study of solar wind interaction

with the lunar atmosphere and the terrestrial

magnetosheath via soft X-ray emission from

the solar wind charge exchange (SWCX)

process

Secondary: All-sky monitor for extra-solar

system transient objects



A soft X-ray spectrum of the SWCX spectrum from a comet taken with Suzaku demonstrates the need for spectral resolution to distinguish the different constituents of the (variable) solar wind.

Aq+ + B → A(q-1)+* + B+

A(q-1)+* → A(q-1) + hν

SWCX Mechanism:Heavy solar wind ion in collision

with neutral target atom or molecule

Process first detected in X-ray emission from comets:

Rosat/HRI Image

GSFC/MPE

Porter et al. in prep



Lunar-Based Soft X-ray Science Objectives:

Sites of SWCX emission:• Comets

• Planetary atmospheres…including the lunar atmosphere

• Geocoronal neutrals at the terrestrial magnetosheath

• Inter-stellar neutral atoms within the heliosphere and at the

heliospheric boundary



Soft X-ray background (0.1<E<1.5 keV) has substantial structure

from contributions from beyond Solar System sources, namely…

1) Unresolved background from AGN

2) Extended Galactic Halo at 106.5 K

3) Irregular distribution from 106 K plasma in lower Galactic Halo

4) The Local Hot Bubble, a 106 K plasma filling a cavity in the

Galactic disk surrounding the Sun.

Only in the last decade (from ~1997) has strong/variable emission

due to SWCX from terrestrial and inter-planetary sources been

recognised as a significant contribution in measurements of the

diffuse X-ray background.

The soft X-ray sky: diffuse emission



Correlation of the strength of the solar wind and the strength of the soft X-ray emission as seen by ROSAT (1990’s) in low Earth orbit. ROSAT Long Term Enhancements (LTE) in background attributed to SWCX with interplanetary and geocoronal neutrals.

This correlation allows remote sensing of the strength of the solar wind using soft X-ray fluxes as a proxy.

Correlation of Soft X-ray Flux (ROSAT) with Solar Wind



XMM-EPIC detection of SWCX during observation of Hubble Deep Field North

Snowden, Collier and Kuntz, 2004, ApJ, 610, 1182



A Lunar X-ray Observatory properly placed on the Moon will be able to observe

soft X-ray emission from the interaction of the solar wind with both the lunar

atmosphere and the magnetosheath.

The Moon is located in a prime spot to study SWCX



FOV of an observatory on the

lunar surface with a fixed look

angle will sweep past the densest

part of the magnetosheath each

month.

Configuration for observations during lunar night.

Scanning of magnetosheath over the lunar orbit…



A model of the strength of the magnetospheric SWCX emission as a function

of position around the Earth (at origin) (Robertson & Cravens 2003). This is NOT a

static picture: soft X-ray imaging can be used to study the dynamical interaction

between the magnetosheath and the solar wind.

Magnetosheath contribution….



Simulation of the soft X-ray

emission as a function of

Position in the lunar sky.

(Trávniček et al. 2005)

Lunar atmosphere contribution….

Suggests optimum location to provide

greatest contrast is polar position with

view zenith angle ~ 900



Secondary (“Added Value”) Science Goals:An LXO as an all-sky-monitor to study time-domain astrophysics

in the soft X-ray regime…




in the soft X-ray regime…One example…

Stellar Capture events by super-massive

black holes in the centre of galaxies

Soft X-ray flares lasting weeks-months

L > 1043 erg s-1

Rate every ~ 104 – 105 years / galaxy

Only handful detected so far by chance Chandra/CXC/M.Weiss

RX J1242-11




in the soft X-ray regime…One example…

Statistics on the frequency and luminosity function of these events

will give strong constraints on the

mass distribution of SMBHs

(with M < 108-9 Msolar) and the co-evolution of SMBHs with their host galaxies.

Chandra/CXC/M.Weiss

RX J1242-11



Telescope proposal and design:

Lunar X-ray Observatory (LXO)



Program: Concept Studies for Lunar Sortie Science Opportunities solicitation within NASA Research Announcement:

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

Title of Investigation: Lunar-Based Soft X-ray Science

PI: Michael Collier

PI Institution: NASA/Goddard Space Flight Center

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

Current Status: NASA has budgeted ~$750K for 5-10 concept

studies which are expected to take 6-9 months duration.

Proposal has been submitted. Expect result spring 2007.



LSSO concept similar to….

ALSEP: Apollo Lunar Surface Experiment Package

Apollo 16 experiments

Image: www.myspacemuseum.com

Jim Lovell (CMDR Apollo 13) practising

Image: en.wikipedia.com

RTG

Central Station

Passive Seismic Experiment



• Mass < 40 kg (self-contained power system, i.e. solar cells + battery)

• Mass < 20 kg (external PSU common to multiple experiments)

• Power < 70W if actively cooled with Thermal Electric Cooler (TEC)

• Power < 20-30W if passively cooled and operated during lunar night.

Lunar X-ray Observatory (LXO): example configuration

Basic Constraints based

on ALSEP experience:

Mass < 40 kg

Power < 75W



Competing Technologies for LXO Detector



Competing Technologies for LXO Detector

Solid state detectors have sufficient energy resolution to

spectrally resolve individual solar wind ions



Slumped Microchannel Plate: Compact/Lightweight X-ray Optics

Eye structure of a Lobster

MCP optic for LOBSTER ASM

R = 70 cm (f = 37.5 cm)

Single module fov = 300 x 300

Univ. of Leicester



0

2

4

6

8

10

12

14

0 2 4 6 8 10E (keV)

Eff

ecti

ve a

rea (

cm2 )

f=100cm; L:D = 75:1

f=50cm; L:D = 50:1

f=37.5cm; L:D = 20:1

LOBSTER optic designed for primary science goal as an ASM so

optimises telescope grasp (fov x effective area)

For LXO we would enhance soft X-ray sensitivity:

f = 50 cm gives useful 90 x 90 fov in a compact form.

Eff. Area of nickel-coated glass MCP optic of varying focal lengths



Summary:

• The moon is an ideal location for soft X-ray astrophysics,

both for studying Solar System SWCX processes directly

and for helping to decouple this emission from Cosmic

astrophysical sources.

• The LXO is practical (the technology is mature and well

understood) and is relatively low cost because it is

piggy-backing onto a larger program (NASA’s Vision for

Space Exploration).

Documents

Prospects for X-ray astronomy from the lunar surface