Prospects for X-ray astronomy from the

1
Prospects for X-ray astronomy from the lunar
surface
Steven 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.
2
Why would you place an X-ray telescope on the
lunar surface?
What would be its scientific goals?
What design would you employ?
3
Speculative 21st Century High Throughput (gt100
m2) Lunar X-ray Observatory
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
Science Goals include Large scale structure of
the universe to zgt2 through survey of cluster Fe
emission Evolution of accretion disk in AGN to
zgt2 through study of Fe fluoresence line
4
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.
5
Science Goals of an LXO
Primary Study of solar wind interaction with
the lunar atmosphere and the terrestrial magnetosh
eath via soft X-ray emission from the solar wind
charge exchange (SWCX) process
Secondary All-sky monitor for extra-solar system
transient objects
6
Aq B ? A(q-1) B A(q-1) ? A(q-1) h?
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
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.
7
Lunar-Based Soft X-ray Science Objectives

• Sites of SWCX emission
• Comets
• Planetary atmospheresincluding the lunar
  atmosphere
• Geocoronal neutrals at the terrestrial
  magnetosheath
• Inter-stellar neutral atoms within the
  heliosphere and at the
• heliospheric boundary

8
The soft X-ray sky diffuse emission

• Soft X-ray background (0.1ltElt1.5 keV) has
  substantial structure
• from contributions from beyond Solar System
  sources, namely
• Unresolved background from AGN
• Extended Galactic Halo at 106.5 K
• Irregular distribution from 106 K plasma in lower
  Galactic Halo
• 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.
9
Correlation of Soft X-ray Flux (ROSAT) with Solar
Wind
Correlation of the strength of the solar wind and
the strength of the soft X-ray emission as seen
by ROSAT (1990s) 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.
10
XMM-EPIC detection of SWCX during observation of
Hubble Deep Field North
Snowden, Collier and Kuntz, 2004, ApJ, 610, 1182
11
The Moon is located in a prime spot to study SWCX
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.
12
Scanning of magnetosheath over the lunar orbit
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.
13
Magnetosheath contribution.
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.
14
Lunar atmosphere contribution.
Simulation of the soft X-ray emission as a
function of Position in the lunar
sky. (Trávnicek et al. 2005)
Suggests optimum location to provide greatest
contrast is polar position with view zenith angle
900
15
Secondary (Added Value) Science Goals
An LXO as an all-sky-monitor to study time-domain
astrophysics in the soft X-ray regime
16
Secondary (Added Value) Science Goals
An LXO as an all-sky-monitor to study time-domain
astrophysics in the soft X-ray regimeOne example
Stellar Capture events by super-massive black
holes in the centre of galaxies Soft X-ray
flares lasting weeks-months L gt 1043 erg s-1 Rate
every 104 105 years / galaxy Only handful
detected so far by chance
17
Secondary (Added Value) Science Goals
An LXO as an all-sky-monitor to study time-domain
astrophysics in the soft X-ray regimeOne example
Statistics on the frequency and luminosity
function of these events will give strong
constraints on the mass distribution of
SMBHs (with M lt 108-9 Msolar) and the
co-evolution of SMBHs with their host galaxies.
18
Telescope proposal and design
Lunar X-ray Observatory (LXO)
19
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.
20
LSSO concept similar to. ALSEP Apollo Lunar
Surface Experiment Package
Apollo 16 experiments
Jim Lovell (CMDR Apollo 13) practising
Central Station
RTG
Passive Seismic Experiment
Image www.myspacemuseum.com
Image en.wikipedia.com
21
Lunar X-ray Observatory (LXO) example
configuration
Basic Constraints based on ALSEP
experience Mass lt 40 kg Power lt 75W

• Mass lt 40 kg (self-contained power system, i.e.
  solar cells battery)
• Mass lt 20 kg (external PSU common to multiple
  experiments)
• Power lt 70W if actively cooled with Thermal
  Electric Cooler (TEC)
• Power lt 20-30W if passively cooled and operated
  during lunar night.

22
Competing Technologies for LXO Detector
23
Competing Technologies for LXO Detector
24
Slumped Microchannel Plate Compact/Lightweight
X-ray Optics
MCP optic for LOBSTER ASM R 70 cm (f 37.5
cm) Single module fov 300 x 300
Univ. of Leicester
Eye structure of a Lobster
25
LOBSTER optic designed for primary science goal
as an ASM so optimises telescope grasp (fov x
effective area)
Eff. Area of nickel-coated glass MCP optic of
varying focal lengths
For LXO we would enhance soft X-ray
sensitivity f 50 cm gives useful 90 x 90 fov
in a compact form.
26
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 (NASAs
  Vision for
• Space Exploration).