IN CONFIDENCE
HESP(07)
SCIENCE AND TECHNOLOGY RESEARCH COUNCIL
HIGH ENERGY SUB-PANEL: FINAL REPORT
Background
1. The High Energy Sub-Panel (HESP) was set up in late 2006/early 2007 at the
instigation of PPARC and tasked with carrying out a review of the future prospects
for space-based high energy astrophysics in the UK, covering the period from the
present up to ~2020. The terms of reference of HESP (see Appendix I) noted the
need to identify, and make recommendations on, key science goals, potential future
mission opportunities and issues relating to underpinning technology.
The
membership of HESP is listed in Appendix II.
2. With the advent of STFC, the terms of reference were updated to reflect the new
advisory structure, with HESP reporting to the Particle Physics, Astronomy and
Nuclear Physics Science Committee (PPAN) and the STFC executive.
3. The Panel recognised from the outset that it would be carrying out its review
against a backdrop of relative uncertainty with respect to the future mission portfolio
in both ESA and NASA, with the results of the ESA Cosmic Vision process expected
in October 2007 and the conclusions of the NASA review of its Beyond Einstein
Program set for release a month earlier.
4. In the event, the HESP met on three occasions in the first half of 2007 (Feb 16,
April 10, June 8) and on the basis of these meetings produced an Interim Report.
Subsequently, in late-October 2007 with the outcome of the ESA and NASA reviews
known, the Panel finalised its report via a teleconference and email correspondence.
UK Heritage in High Energy Astrophysics
5. The UK community has made a major contribution to the field of high energy
astrophysics since the 1960s. Particularly in X-ray astronomy, the combination of
instrumentation expertise, hardware provision for international missions and broad
capabilities in data exploitation and interpretation have all contributed to a very strong
national programme. Highly successful missions with a significant UK hardware
involvement include Ariel V (UK), EXOSAT (ESA), Ginga (Japan/UK), ROSAT
(Germany/NASA/UK) and, more recently, XMM-Newton (ESA) and Swift
(NASA/Italy/UK). Simultaneously UK groups have played internationally leading
roles in developing astrophysical insights, for example in using X-rays to probe the
process of accretion onto compact objects and to trace baryonic and dark matter
distributions in clusters of galaxies.
The Importance of the Science
6. X-ray and Gamma-ray observations provide unique information relating to the
high temperature (T >105 K) thermal plasmas in which the bulk of the baryonic matter
of the Universe resides. Similarly this waveband provides a key probe of the nonthermal processes which are a signature of extreme conditions in a very wide range of
astrophysical settings. As a consequence the high energy regime is central to three of
the nine key Science questions in the STFC Road Map:
 What is the Universe made of and how does it evolve?
 How do galaxies, stars and planets form and evolve?
 What are the laws of physics in extreme conditions?
X-ray and Gamma-ray observations are also of direct relevance to a fourth Road Map
question:
 What are the origins and properties of the energetic particles reaching the Earth?
7. In discussing the role and importance of X-ray and gamma-ray observations to
astrophysics as a whole, the Panel elaborated on (a slightly modified version of) the
Road Map questions by identifying an associated set of key science themes that
depend crucially on input from the high energy regime. The themes are as follows:
1) What is the Universe made of and what is its structure?
 Clusters, groups and galaxies; gas fractions, dark matter content and
other properties
 Cluster surveys and the equation of state of dark energy
 The warm hot IGM as the reservoir of most of the baryons
 Enrichment and dispersal of chemical elements throughout the
Universe
 The influence of accretion power through cosmic time
2) What are the laws and phenomena of physics in extreme conditions?
 Physics in the extreme gravity near black holes
 States of dense nuclear matter (as in neutron stars)
 Physics in ultra-strong magnetic fields (as in magnetars)
 The formation of relativistic flows (as in jets and winds)
 Accretion onto compact objects; mechanisms and processes
 The acceleration of cosmic rays
 Supernovae and gamma-ray bursts
3) How do galaxies and their constituent parts form and evolve?
 Feedback processes in galaxy evolution
 Large-scale winds and outflows and their influence on the hot phase of
the ISM and IGM.
 Formation and evolution of super-massive black holes and their impact
on their host galaxies
 Star formation and stellar end points
Future observatory-class missions in high energy astrophysics, for example XEUS,
offer significant capability directly relevant to almost all of the key science themes
identified above, whereas more specialist missions necessarily focus on a subset of
these themes (see Appendix III for more details).
8. The Panel also noted that a set of key future objectives for the high energy
community could also be defined in terms of the need for, and the application of,
specific observational capabilities. In this context some key future goals, many of
which are realistically attainable in the next decade, are:






The full exploitation of the diagnostic potential of high resolution, high
sensitivity X-ray spectroscopy
The availability of wide-field X-ray monitoring data for applications in multiwaveband and temporal domain astrophysics
The completion of one or more deep all-sky surveys leading to significant
advances in our knowledge of faint X-ray source populations
The flight of instrument combinations providing a high sensitivity pointed
capability over a very broad (0.1-300 keV) spectral range
The exploitation, essentially for the first time, of astrophysical X-ray
polarimetry
The eventual exploitation of very high spatial resolution X-ray imaging
In relation to the above observational goals, a future observatory-class mission, such
as XEUS, would provide primarily a “work-horse” facility for imaging X-ray
spectroscopy (plus a reasonably wide energy range coverage and possibly some
polarimetry). In contrast, the all-sky surveys and wide field monitoring are better
considered in the context of one or more specialist missions. The eventual
exploitation of advanced techniques, such as X-ray interferometry from space, will
necessarily build on a broad range of developments in space technology.
9. The Panel concluded that high energy astrophysics has grown over the last four
decades into one of the main pillars of modern multi-waveband astrophysics. The
high energy regime provides unique information essential to the task of addressing
several of the challenging questions identified in the STFC Road Map. It follows that
any strategy to address the Road Map questions will necessarily include the
maintenance and enhancement of the observational capabilities in high energy
astrophysics as a high priority element.
Current status of X-ray and Gamma-Ray Space Astronomy
10. The last ten years have seen a “golden period” for high energy astrophysics
carried out from space platforms. RXTE(NASA), Chandra(NASA), XMMNewton(ESA), Integral(ESA), Suzaku(Japan/NASA) and Swift(NASA,Italy,UK) are
all major international missions in current operation to which the UK community have
access (mostly through competitive AOs, although access is limited in the case of
Suzaku).
The projected operational lifetimes of these missions, governed by a
combination of both technical and funding constraints are as follows:
RXTE – NASA operations funding likely to continue until 2008/9.
Chandra – the projected lifetime extends beyond 2010. NASA does not appear to
have any plans for early termination of the mission.
XMM-Newton – the mission lifetime could extend to ~2018. Currently approved until
2010, ESA budgetary limitations put extension beyond 2012 in doubt.
Integral – the mission lifetime could extend to ~2015. Currently approved until 2010,
ESA budgetary limitations put extension beyond 2012 in doubt.
Suzaku – Japanese funding looks to be secure until the end of the mission lifetime in
~5 years time.
Swift – NASA funding is secure for the next two years with good prospects for
support thereafter given that Swift continues to be highly rated in reviews.
In addition to the above, the Italian Agile mission, launched in April 2007, combines a
Gamma-ray imager with a hard X-ray imager in a very compact configuration. An
Agile guest observer programme will open to the astrophysics community in Dec.
2007.
11. Looking ahead, over the period up to ~2010, several other high energy missions
should become operational. The largest of these is GLAST (NASA, France, Italy,
Japan & Sweden), a successor to the Compton Observatory, operating in the hard
Gamma-ray regime (10 MeV – 100 GeV). GLAST is scheduled for launch in January
2008; at present UK involvement in this mission is rather limited. Astrosat, an Indian
mission incorporating a Leicester-designed soft X-ray camera similar to that flown on
Swift is scheduled for launch in the 2008/9 timeframe. In addition, MAXI, a Japanese
all-sky monitor, is scheduled for deployment on the ISS.
12. The Panel concluded that the prospects for high astrophysics over the next few
years remain reasonably buoyant. However, beyond the ~2010/12 timeframe, the
future of high energy astrophysics, particularly from a UK perspective, is less certain.
Future Mission Opportunities in ESA
13. Three proposals in high energy astrophysics of significant interest to the UK
community were submitted in response to the recent ESA Cosmic Vision AO. These
were: XEUS, a large mission proposal for a next generation X-ray observatory, in
effect a successor mission to XMM-Newton; EDGE, a medium-class mission which
would trace the cosmic history of baryons through the study of cosmic filaments,
clusters of galaxies and gamma-ray bursts; and the Gamma-Ray Imager (GRI) a next
generation gamma-ray observatory, in effect a successor mission to Integral.
14. In its discussion of the above missions, the Panel agreed that XEUS would be the
high energy mission of choice for a large fraction of the UK community. Nevertheless
the Panel recognised that there was also significant interest in both EDGE and the
GRI within the UK. In the event, neither EDGE nor GRI was selected by ESA for
further study, leaving XEUS as the sole high energy astrophysics contender within the
framework of the Cosmic Vision Programme.
15. A proposal to support core technological development directly relevant to XEUS
was put to PPARC and eventually approved in 2005. The aims of “The Roadmap to
XEUS” (RMTX) programme are to place the UK in a strong position as the XEUS
mission concept develops, particularly in the areas of telescope optics, cooler
technology, cryogenic detectors and CCDs. In the event, funding cuts of ~50%
relatively to the original bid were imposed at the outset. Subsequently, in 2006, the
actual funding was reduced to ~30% of the original request and then, due to recent
circumstances in the STFC, this funding line has been subject to further pressure (the
funding is now down to <20% of the original bid). Appendix IV provides a brief
summary of the areas supported under the restricted current RMTX funding. In its
discussion the Panel agreed that the funding of the RMTX programme should be
restored as soon as possible to a level commensurate with or greater than that
originally recommended by PPRP. The Panel also recommended a review so as to
ensure a focussed programme fully aligned with the goal of delivering a significant
eventual UK involvement in the XEUS mission.
16. It is clear that the constraints on the ESA budget set the earliest conceivable
timeframe for the launch of a new mission at ~2017. For a large mission, such as
XEUS, the relevant timeframe is ~2018 if selected for the first large mission slot, with
the next opportunity being ~2022. The obvious conclusion is that if high energy
astrophysics is to remain a strength within UK astronomy during the period 20102020, opportunities outside of ESA will need to be pursued. In fact this simply
represents a continuation of the strong UK heritage of exploiting bilateral (or
multilateral) opportunities in high energy astrophysics as and when they arise, the
most notable examples being Ginga, ROSAT and, more recently, Swift.
Future Mission Opportunities outside of ESA
17. In the USA, the Beyond Einstein Programme encompasses up to 5 missions
including the next-generation X-ray observatory Constellation-X (Con-X) and the
Black-Hole Finder Probe (an imaging hard X-ray mission previously known as
EXIST). The priority order in which the Beyond Einstein missions should be pursued
was announced in September 2007. The Joint Dark Energy Mission (JDEM) was
recommended as the first mission to be undertaken with the Laser Interferometer
Space Antenna (LISA) earmarked as the eventual flagship of the Beyond Einstein
Program. The recommendation on Con-X was that it should receive “continued
support” in preparation for the next decadal survey of astronomy and astrophysics.
Clearly the future direction of the NASA programme remains of huge importance to
the field of high energy astrophysics, with the long-term implications of recent
decisions yet to be fully evaluated.
18. Outside of ESA and NASA there are several other major international missions
currently under study with prospective launch dates in the 2011-2015 timeframe.
Brief details are as follows:
Spectrum-RG. A new Russian mission planned for launch in 2011/12. The baseline
payload includes the German eRosita instrument, a UK-led wide-field X-ray telescope
(WFT) and a Russian hard X-ray concentrator. Discussions are also underway on the
possibility of flying a cryogenic spectrometer (to be provided by a Dutch/Japanese/US
consortium). An SOI relating to the funding of the WFT instrument was submitted to
STFC and considered at the September 2007 PPAN meeting; the outcome was
inconclusive with the decision on whether to invite a full Spectrum-RG/WFT
proposal delayed until the STFC completes its internal programmatic review early in
the new year.
HXMT. A Chinese-led mission due for launch in ~2011. It is understood that CCDs
for the soft X-ray instrument are being procured from the UK (Brunel/e2v). In
discussing HXMT the Panel expressed the view that this is not a very well coordinated
mission and comparatively less exciting scientifically than some of the missions under
consideration.
SVOM. A French/Chinese bi-lateral mission to study Gamma-Ray Bursts involving a
multi-instrument payload (X-ray and Gamma-ray cameras, gamma-ray monitor,
visible telescope). The project is currently in Phase A. The proposed launch date is
~2012.
Simbol-X. A hard X-ray imaging mission lead by France and Italy. It will serve as a
technology demonstrator for formation flying and as such has strong support from
CNES and ASI. The proposed launch date is late 2013. Although currently UK
groups are not involved in this mission there will undoubtedly be strong interest in the
science.
NEXT. The next high energy astrophysics within the Japanese programme planned
for launch in 2013/14. In terms of funding it is probably the most secure of all the
future X-ray missions. This is an observatory-class X-ray mission with hard X-ray
imaging capabilities exploiting multi-layer mirror technology under development in
Japan. Although currently there is no UK hardware involvement in this mission, there
will certainly be strong interest in the science.
19. In its discussion of the non-ESA future mission opportunities, the Panel noted
that if the UK, hypothetically, aspired to be involved in a mission such as Con-X, an
investment of the order of £10M might not be sufficient to secure involvement at a PI
level. Amongst the other missions, NeXT mission and Simbol-X appear to have
excellent scientific potential. There is no current UK hardware involvement in these
missions; however, the possibility of “buying-in” to these missions, perhaps through
the provision of a sub-system, is a potential future option.
The situation on the Russian Spectrum-RG mission is different since there is an
existing invitation to fly a Wide Field X-ray Telescope (WFT) as a core payload
component. The WFT has attracted significant support within the UK community
(following on from the recent Leicester meeting). The SOI recently submitted to
STFC costs the UK participation in the mission at a level of £8-10M (with roughly an
equal share of the costs of the WFT coming from international partners). One issue
relating to this mission relates to what is a realistic launch date (the Russians are
currently proposing 2011 whereas a launch in late-2012 is probably the earliest
feasible for UK involvement). The Panel agreed that it would strongly support
involvement in the Spectrum-RG mission if a viable launch date and equitable data
division and access could be negotiated.
20.
The Panel also noted that other mission opportunities were bound to arise over
the next five years. For example within NASA, a Small Explorer Mission (SMEX)
AO has recently been announced. Similarly there may well be opportunities for
future collaborations with countries such as India, China and Brazil.
21. The Panel agreed that opportunities will undoubtedly arise in high energy
astrophysics over the coming decade despite recent programmatic difficulties in ESA
and NASA. However, if the UK is to maintain its position as a major player across
the areas of instrument development, mission hardware (and associated software)
provision and cutting-edge astrophysics research, then resources will need to allocated
consistent with this strategic goal.
The benefits of a balanced programme
22. The Panel recognised that the current strong UK position in high energy
astrophysics could be linked to a “virtuous circle” of activity. This refers to the
process whereby internationally competitive laboratory-based instrument
development programmes lead to mission opportunities, which in turn provide a
stimulus to a broad user community to the exploit the mission data and hence
contribute to the general development of astrophysics expertise. The circle is closed
by the identification, on the basis of established astrophysics insight and instrument
expertise, of what is required of, and achievable by, the next generation of
instruments. The state-of-the-art instrumentation and technology base inherent in this
model then provides significant potential for knowledge exchange of direct benefit to
UK industry.
23. In the past the UK programme in high energy astrophysics has greatly benefited
from the activity cycle identified above, leading for example to a very strong UK
participation in XMM-Newton (encompassing the hardware provision, the science data
segment and exploitation of the mission data by a wide UK community). However,
there are signs that a failure, in recent years, to invest adequately in laboratory-based
development programmes is beginning to impact on the country’s international
competitiveness (for example, the RMTX situation noted above).
24. The long-term nature of instrument development programmes and the need for a
significant technical infrastructure are ingredients that are not always properly
recognised by ad-hoc peer review processes. One of the papers on technological
development received by the panel (see below) summed up the situation “This
funding (for technological development) needs to be underpinning, long-term and not
linked to whether instrument X, or mission Y, is likely to fly in year Z. A failure to
provide this underlying funding will lead to the UK losing its ability to provide
hardware into these missions…’ Unfortunately, with funding lines under pressure,
the need for X, Y and Z to be fully specified has tended to become a requisite.
Defining a Strategic Goal
25. As noted earlier there are a set of very fundamental astrophysical questions that
are best addressed, and in some cases can only be addressed, through X-ray/Gammaray observations. Given the UK’s heritage and current high standing in the field, it is
entirely appropriate that UK should seek to take a leading role in the future of this
field of astrophysics through its ability to deliver world-class instrumentation, data
analysis systems and astrophysical knowledge and insight.
26.
In terms of technological development, the UK should pursue a targeted
investment strategy aimed at delivering PI status on instruments to be flown on major
future missions such as XEUS plus the capacity for UK groups to be involved as co-Is
on other smaller missions, as and when such opportunities arise. As a guide, one
might hope that PI involvements might be affordable at least once every 10 years,
with perhaps two or three co-I level contributions supported in the period between the
major provisions. Given the limited size of the UK community with expertise in
hardware development, strong collaborations between groups will be vital if these
goals are to be achieved on a sustainable basis.
The Status of Instrument Development Programmes in the UK
27.
In order to form a clearer view as to the current status of technological
development programmes in the UK relevant to X-ray and gamma-ray astronomy, the
Panel sought advice from several leading experts in UK community. In particular for
a number of specified technologies, identified experts were asked to provide their
vision on how the UK should frame a programme of technological development over
a period of up 5 yrs (in the first instance) aimed at developing and maintaining worldclass expertise. The consultation involved both the submission of briefing papers and
short presentations to the Panel as follows:
1) Smart Optics (Prof Alan Smith, MSSL)
2) X-ray Interferometry (Prof George Fraser, Leicester)
3) Advanced Cooling Systems (Dr Ian Hepburn, MSSL)
4) Integrated Cooler Systems (Dr Jamie Reed, Astrium)
5) Advanced Calorimetry and Polarimetery (Prof George Fraser, Leicester)
6) Semiconductor Detectors (Prof Andrew Holland, Brunel)1
Full details of the technology submissions and the Panel comments are available in
the minutes of the 2nd and 3rd HESP meetings. A synopsis of the detailed Panel
conclusions are provided in Appendix V of this document.
28. On the basis of its albeit incomplete review, the Panel concluded that there was
evidence for chronic under-funding of instrumentation and technology programmes in
the UK in support of high energy astrophysics, certainly compared to the levels of
support available to many of our international competitors. Nevertheless, there
remained opportunities in the areas of X-ray optics, advanced cooling systems and in
X-ray detector development, where the existing expertise and demonstrated trackrecord might be taken forward so as to maintain and enhance the UK position within
the international arena. In particular, the Panel felt that there was a strong case for
technological excellence to be identified at an early stage and then resourced at a level
commensurate with converting that excellence through long-term development
programmes to PI level involvements in major missions.
29. The Panel agreed that it should make a strong recommendation to STFC that, in
order to achieve the strategic objective identified in paragraph 26 above, the level of
support devoted to instrumentation and technological development in high energy
astrophysics will need a significant uplift. Ideally there would be earmark funding for
this purpose, paralleling the approach for some ground-based programmes such as
ELT and SKA. Such funding would enable a strategic long-term programme to be set
in place consistent with the long-term potential of the field, and the aspirations of the
1
By written submission only
UK community. The proposed programme would also offer huge benefits for
knowledge exchange and the general competitiveness of UK plc. The Panel
concluded that a resource (over and above any current support) of ~£2M per year on a
rolling basis, but initially guaranteed over a 5-yr period, would transform the UK
position. The number of projects so supported might be quite small, perhaps 2 or 3, so
as to ensure the available effort is sufficiently focussed to achieve world-leading
status in the earmarked areas. The Panel envisaged the issuing of a themed call and
that the resulting programme would be managed by an appropriate Oversight
Committee. Furthermore, the programme should be co-ordinated in the context of
existing activities, noting that support was currently available via rolling grants and
other mechanisms (e.g., through PPRP). However, the crucial point is the need for a
substantial uplift in the available funding.
Conclusions
30. The main conclusions of the HESP review are:
(a) Many of the key challenges in contemporary astrophysics, as exemplified by the
STFC Road Map Questions, are uniquely addressed through X-ray and gamma-ray
observations. It follows that any strategy to address the Road Map questions must
include the development of new observational capabilities and the enhancement of
core expertise in high energy astrophysics, as high priority elements. Unquestionably,
this a field in which UK has a very strong heritage and an extraordinarily high
reputation. Over the last four decades a whole series of highly successful space
missions have benefited from state of the art UK-supplied instrumentation and, over
the same period, UK groups have played leading roles in developing new insights into
high energy phenomena. In the view of the Panel, the STFC and the astronomical
community, working in concert, should seek a leading role for the UK in the future of
high energy astrophysics.
(b) The recent selection of XEUS as one of the large missions to be studied within
the ESA Cosmic Vision programme (together with LISA and an outer planets mission)
represents a very important first step towards securing a long-term future for high
energy astrophysics in Europe. Building on its strong involvement to date in the
mission definition activities and on the existing STFC-supported ‘Roadmap to XEUS’
(RMTX) programme, the UK should aim for a major future role in this project. In
this context the Panel recommends that the resources within the RMTX programme
should be restored as soon as possible to a level commensurate with or greater than
that originally recommended by the PPRP. It would also be timely for STFC to
undertake a review of the RMTX programme so as to ensure a focus fully aligned
with the goal of delivering a significant eventual UK involvement in the XEUS
mission.
(c) Even in the most optimistic scenario in which XEUS is selected for the first
available large mission slot within the Cosmic Vision programme, the prospective
launch date is ~2018, with the next opportunity being ~2022. On the other hand, many
of the currently operational missions in high energy astrophysics will have come to
the end of their design lifetime by the start of the next decade (although in the case of
XMM-Newton the prospects for mission operations extending well beyond 2010, i.e.,
ten years post-launch, currently look rather favourable). Nevertheless, many of the
key scientific themes identified in section 7 of this report will be addressed in the
intervening period (e.g., 2011-2016) by focussed nationally-led missions. For the UK
community to continue to be at the forefront of this unique area of research it must be
able to participate in selected future bilateral programmes, following the well
established and highly successful pattern of activity in this field. In this context, the
UK-led Wide Field Telescope on Spectrum-RG appears to be the most promising
bilateral opportunity currently identifiable. However, missions such as Simbol-X and
NeXT missions also have excellent scientific potential and merit consideration as
potential future bilateral opportunities. In the view of the Panel, a significant UK
involvement in one or more bilateral missions during the period 2011-2016 should be
considered as an absolute prerequisite for the long-term health of high energy
astrophysics research in the UK. For budgetary purposes, the level of resource
required can be estimated to be in the range £5-10M.
(d) There is a strong argument for a significant uplift in the level of support devoted
to basic research in instrumentation and technology in the field of high energy
astrophysics. Such funding, which would not be linked to specific mission
opportunities, would enable a strategic long-term programme to be set in place
consistent with the long-term potential of the field, and the aspirations of the UK
community. The proposed programme would help “level the playing field” in terms of
the investments being made by other major players in the field and, at the same time,
offer huge benefits for knowledge exchange and the general competitiveness of UK
plc. The panel recommends that STFC consider a substantial targeted programme of
investment in this area at a suggested level of ~£2M per year over an initial 5-yr
period. The programme should, of course, be co-ordinated in the context of any
existing STFC-funded activities, but the crucial point is the need for a substantial
uplift in the available resources.
(e)
The UK community has been very successful in exploiting high energy
astrophysics missions, particularly those in X-ray astronomy, for which there has been
good data access through either direct project involvement and/or competitive AOs.
As a result the UK has developed a broad expertise base and gained a strong
international reputation in this field. This has benefited UK astronomy as a whole,
bearing in mind that the X-ray and gamma-ray regime represents one of the main
pillars of modern multi-wavelength astrophysics, often providing the crucial
information for studies of particular classes of object and phenomena. The Panel
considers continuing broad support for high energy astrophysics over the next
decade, encompassing all aspects of observation, interpretation and theory, is vital
both for the full exploitation of major new facilities in other wavebands such as
ALMA, SKA, ELT and JWST, but also as a precursor to a strong UK involvement in
the astrophysics made accessible by XEUS.
APPENDIX I
HIGH ENERGY SUB-PANEL: TERMS OF REFERENCE
The timescale for the launch of the next major observatory-class mission in X-ray
astronomy now extends possibly beyond 2020. In the intervening period a number of
smaller mission concepts and proposals are very likely to arise within the international
context, some of which will be of significant interest to the UK community. A review
of the potential future mission opportunities in X-ray astronomy would therefore be
very timely, particularly given the fact that important decisions on some missions will
probably be required next year. Here X-ray is taken to mean the broad bandpass
between soft X-rays and low-energy Gamma-rays (i.e., 0.1 keV to 300 keV).
The goals of the review will be:

To identify the key science goals in the field of X-ray Astronomy that might
realistically be attainable in the next 10 years and beyond, taking account of
the relevance of these goals in a multi-wavelength context.

To identify the potential future mission opportunities in X-ray Astronomy over
the next decade, which address one or more of the key science goals, and
engage in international discussions.

To develop a roadmap for X-ray Astronomy in the UK covering the next
decade with defined scientific priorities which might be translated into a
realistic 10-yr forward look programme within the STFC portfolio.

To provide advice on these issues to STFC executives and advisory bodies
(PPAN and SSAC) and BNSC, with a target of reporting by late spring 2007.

To provide recommendations on corresponding technology priorities.
APPENDIX II
Membership of the HESP
Prof R Warwick (Chair), Leicester
Prof A Fabian, Cambridge
Prof R Fender, Southampton
Dr J-W den Herder, SRON
Prof A Smith, MSSL
Prof M Ward, Durham
Dr D Telfer (Secretary), Science and Technology Facilities Council
APPENDIX III
The Panel constructed the matrix shown below, indicating how the possible future
missions XEUS, Edge, GRI, NeXT, Simbol-X and Spectrum-XG compared in terms of
their ability to address the top-level science questions and themes identified in
paragraph 7 of the main report. This exercise confirmed that Simbol-X and GRI were
both specialised missions addressing a smaller number of questions fully and also
reaffirmed the huge scientific potential of XEUS.
Edge
What is the Universe made
of and how does it evolve?
Cluster properties and
investigating dark matter
Cluster surveys/the equation
of state of dark energy
The warm hot IGM as the
reservoir of baryons
Enrichment and dispersion of
chemical elements
Charting the influence of
accretion power
What are the laws and
phenomena of physics in
extreme conditions?
Extreme gravity near black
holes
States of dense nuclear matter
(as in neutron stars)
Physics in ultra-strong
magnetic fields
The formation of relativistic
flows (jets)
Accretion onto comp. objects
Acceleration of cosmic rays
Formation of black holes and
compact objects in SN/GRB
How do galaxies evolve?
Feedback processes in galaxy
evolution
Large-scale winds and
outflows in the ISM/IGM.
Formation and evolution of
supermassive black holes
Star formation and stellar
endpoints
GRI
XX
NEXT SXG
X
X
SimX
XX
XEUS
XX
XX
XX
X
X
X
X
XX
X
X
XX
X
XX
XX
X
X
X
X
X
XX
X
X
X
X
X
XX
X
X
X
X
X
X
X
X
X
XX
X
XX
XX
X
XX
X
X
XX
X
X
XX
X
X
XX
X
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17
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26
APPENDIX IV
An outline of the programme supported by the interim “Roadmap to XEUS” (RMTX)
grant as of autumn 2007 (information provided by Professor Martin Turner).
Telescope Optics. Dr R Willingale (Leicester) is well placed to compete for the
position of XEUS Telescope Scientist (effectively Optics PI). The main work
packages currently supported relate to modelling and optics design, and the analysis
of test results obtained by ESA. Of immediate interest is a full computer ray-trace
model that will allow the design of efficient baffling to prevent single reflection
image disturbance. Other work packages include contribution to mission definition,
support for consortium development, and participation in key project working groups.
(1 PDRA at Leicester, supported for 3.5 years).
XEUS Wide-Field Imager (WFI). UK participation in a credible European consortium
for this instrument is predicated upon the development of low background CCDs and
accurate modelling of CCD background in orbit. The performance of the WFI is
critically dependent on background levels, which are not well understood. Major work
packages include building a Geantt 4 radiation model and its calibration using in-orbit
data from XMM-Newton, ASCA, SWIFT and Suzaku. Other work involves CCD
design and trade-off studies. (1 PDRA at Brunel, supported for 2 years.)
XEUS Narrow Field Imager (NFI). Support is essential to maintain a relatively small
but critical UK role in the likely SRON-led XEUS NFI detector consortium. The work
complements a range of externally-funded resources directed towards the agreed UK
work components, which relate to testing TES devices produced by SRON and
theoretical modelling of TES performance. The first tests of alternative magnetic
calorimeter devices manufactured at Leicester will determine if these can improve on
the resolution and readout capability of TES devices. (1 PDRA at Leicester, supported
for 2 years.)
ADR Cryo-Cooler for XEUS. Magnetoresistive heat switch technology has been
identified as the key immediate R&D activity leading-in to a much larger future
programme aimed at the development of the tandem ADR cooler concept (which
promises continuous operation of the NFI). ESA have recently indicated a desire to
continue development of a continuous ADR system and it is anticipated that MSSL
will be the recipients of a major contract from ESA in this area. At this stage a
relatively modest investment has the potential to leverage a substantial additional
return to the UK from ESA. (1 PDRA at MSSL supported for 2 years.)
APPENDIX V
A brief summary of the HESP review of technological development programmes in
the UK relevant to X-ray and gamma-ray astronomy. Full details of the technology
submissions and the Panel comments appear in the minutes of the 2nd and 3rd HESP
meetings.
Advanced Cooling Systems. The proposal centred upon the further development of an
Adiabatic Demagnetisation Refrigerator (ADR) for application in major missions
such as XEUS. The immediate specific programme objectives are to secure an ESA
contract for a continuous milli-kelvin cooler (on the basis of a properly resourced ongoing UK programme) and also to develop both miniaturization technology and an
ADR capable of running from a temperature > 4K.
Although this programme is
currently funded via the RMTX programme, rolling grant support and a PIPPS grant
this, in effect, amounts only to a “stay alive” level of support. It was noted that much
of the early “cutting-edge” work in this area had been undertaken in the UK but that
other groups in Europe, the USA and Japan were now attempting to catch-up. The
Panel heard that ESA’s decision to move to a continuous ADR was based on the UK
study. However, the UK would be forced to relinquish its lead if it proved impossible
to secure sufficient appropriate future funding.
Cryogenic instruments were agreed to be key to future X-ray missions and the Panel
acknowledged that coolers were a crucial supporting technology. The Panel
commented that the running of a programme on the basis of insufficient funding made
little sense in strategic terms. In total the proposed “properly funded” programme
amounted to an uplift of £1.5 M over the period 2008-2012. The Panel noted that the
Advanced Cooler Systems proposal was closely linked to the Integrated Cooler
Systems proposal and that it made sense for the two programmes to be considered in
tandem (see below).
Integrated Cooling Systems. The proposed programme includes the following themes:
development of the individual cooler systems required for XEUS; (ii) study and
development of critical components for a sub-Kelvin system (other than coolers); (iii)
provision of a sub-Kelvin test-bed for detector research in the UK. The UK has been
world-leading in this area since the 1980s. It is not anticipated that any of the
proposed activities would be funded solely by STFC given the strategic importance of
the area within the ESA programme. It was estimated that, perhaps, ~2 MEuro out of
a 2.6–2.8 MEuro full programme might be available from ESA. Undoubtedly
participation in this programme would take the UK to a position of significant
influence in this technology.
In summary the Panel strongly endorsed the two proposed programmes relating to the
provision of space-qualified cooling systems spanning a range of temperatures down
to 50 mK (as required by current state-of-the art X-ray instruments, specifically TES
cryogenic imaging spectrometers).
Semiconductor Detectors. This written input, which was not available at the time of
the Panel meeting, identifies important further development opportunities in the area
of MOS CCDs and in Hybrid Pixel Arrays. Recent work in this area has particularly
focussed on the detection of X-rays in the range 0.1-10 keV using silicon CCD
technology and in the 20-200 keV band using CdZnTe hybrid devices. Current
studies encompass: the development of ultra-deep depletion CCDs up to 200-300
microns thick for enhanced high energy quantum efficiency; detailed modelling of the
measured instrument background in current CCD-based instruments aimed at the
accurate prediction of the likely background in future missions; development of ASIC
technology for the read-out of future focal plane arrays; development of SCD (swept
charge device) technology for future space applications. The chronic under-funding
of the UK technology base was again emphasised.
Advanced Calorimetry. Cryogenic imaging detectors offering ~few eV spectral
resolution will be key payload elements for all future major X-ray observatories.
Currently the SRON-led EURECA consortium is well positioned to provide the
Narrow Field Instrument (NFI) for XEUS (and possibly other missions) on the basis
of its expertise in Transition Edge Sensor (TES) technology. Within the UK,
programmes aimed at developing cryogenic detectors for applications in X-ray
astronomy are supported currently only at marginal levels. The UK therefore faces an
important strategic decision, namely whether to renew its efforts in this area or to
withdraw completely from this field, perhaps with a view to focusing on cooler
subsystems. The latter course might well be interpreted as a de facto retreat from a
position of international leadership long held by the UK community in high energy
astrophysics. On the other hand opportunities can still be identified for innovative
programmes in cryogenic detector development drawing on the substantial expertise
which still resides within the UK community.
The Panel noted that the UK would need to “leap-frog” the current generation
technologies so as to overcome the short-comings within this crucial field. However,
it was agreed that a properly funded, focussed programme could lead to technologies
that out-strip the performance of TES-based instruments on a timescale of
approximately five years. The Panel concluded that there was a potential future for
the UK in the application of cryogenic detector technology to high energy
astrophysics provided a substantial investment (up to £4M over 5 years) is made. The
prime target for such a programme would be for missions proposed for launch post2020.
X-ray Polarimetry. The measurement of X-ray polarisation is potentially a vital tool
for high energy astrophysics providing unique information on emission mechanisms,
source geometries and magnetic fields. A new form of narrow-band X-ray polarimeter
is currently under development, which in effect acts as an X-ray Polaroid filter. Such
a filter might, for example, be inserted in the converging beam of an X-ray telescope
with signal readout via the main cryogenic imaging spectrometer, thus avoiding the
need for a separate focal plane instrument (which is the current XEUS baseline). The
X-ray polarimetry programme is currently funded via a rolling grant.
If this
preliminary programme is successful then a range of applications in both high energy
astrophysics and for other non-astrophysics programmes should follow. In the
subsequent discussion, the Panel endorsed the goals of the X-ray polarimetry
programme.
Smart Optics. Here the goal is to develop a mirror technology delivering Chandralike sub-arcsecond resolution but with a throughput more akin to that of the XMMNewton telescopes. The proposed programme represents, in essence, a three-year
extension of the existing Basic Technology Smart X-ray Optics Programme based on
a set of five identified work packages. The estimated cost was £940k over three
years. The Panel concluded that this was a unique area of work and one where the
UK definitely had a lead. The Panel gave a strong endorsement to this exciting
prospect in X-ray optics.
X-ray Interferometry. A new slatted-optic design provides the possibility that
astrophysical X-ray interferometry might one day be realisable in space. Currently
this novel concept is in a proof-of-principle phase in a 3-yr programme supported via
a rolling grant. If these preliminary experiments meet with success, then the next
step might be a pre-Phase A feasibility study to be carried out between academia and
industry leading to a flight-like prototype optical chain. The cost of such a study
might amount to ~£1 M over 2-3 years. The Panel agreed that this was an interesting
proposal but the potential might only be fully realised on a timescale of 15 years or
more. The Panel strongly endorsed this proposal as an important area of “blue skies”
research.