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"WHIM-ex: a X-Ray NASA Explorer to Solve the MIssing Baryons Problem"
Dr. Fabrizio Nicastro
(1) Istituto Nazionale di Astrofisica - Osservatorio Astronomico di  Roma,  Italy
(2) Harvard-Smithsonian Center for Astrophysics, USA


When:  Tuesday 19 April 2011 at 15:00
Where: 2nd Floor Seminar Room

Abstract:

In times of decadence empires shrink, at all levels. The first
unavoidable consequence is intellectual decline. Science communities can
do nothing but adapt. Space-Astrophysics is no exception: e.g., in the
X-rays, the simultaneous operative presence (now for longer than a
decade) of two large space observatories is only a fortunate
circumstance (due to the natural lag between the conception of ambitious
ideas and their expensive realization), and also an unrepeatable event
for years to come. Big space observatories are too costly and, in
intellectual-declining phases, poorly justifiable because of the lack of
either low-cost innovative technologies or strong science drivers, or
both. 
In such conditions the highest risk, but also most likely, scenario is
the progressive 'extinction' of those scientific communities (e.g. the
high-energy community in astronomy) that have not been able to move
forward from a soporific and comfortable heritage anchored to the
"splendor of the past", to a redesigned short-term future, based on
revolutionary ideas and concepts re-sized to the challenging
budget-shrink.

An exciting opportunity for space-astronomy, is offered by the revived
and energetic NASA-Explorer program (on the US side) foreseen for the
next decade.  NASA Explorers are small, light, relatively cheap (250
MUSD), fast-to-be-launched and one-main-science-driver focused missions,
which can in principle compensate for the lack of big multi-purpose
observatories (e.g. the original IXO design could easily be replaced by
3 or 4 well-designed explorers focused on well-distinct science
drivers).
Here we present one of these concepts, WHIM-Ex, which is mainly designed
to solve one of the most controversial problem of modern astrophysics,
that of the 'Missing Baryons', but that is also perfectly suited to
deeply investigate into a much wider scientific context: from AGN/IGM
and IGM/galaxy feedback, to Doppler-maps of active X-ray star coronae,
to the outskirts of galaxy clusters, etc.
WHIM-Ex is one of the candidates for selection at the current NASA
Explorer call (selection foreseen in fall 2011), and is a very high
spectral resolution (R=4000), large throughput (A>250 cm2), soft X-ray
(0.1-1 keV) spectrometer, based on a smart, innovative optical design
that optimizes efficiency, feasibility and costs, by integrating the
grating spectrometers into the optical modules, sub-aperturing, and
exploiting four-photon reflections by pairs of 296 identical
parabola-hyperbola-flattening-grating modules.

WHIM-Ex will detect >100 Warm-Hot Intergalactic Medium filaments within
the first year of operation (~ 15 Ms, i.e. 70% of the total time
available during the first year, factored at a visibility efficiency of
66%, due to the low-Earth orbit of WHIM-ex), and so will measure the
Cosmological Mass Density of baryons in the Universe with a precision
better than 10%.
A progressively increasing fraction of GO time will be reserved to the
community, after the first year of operation. The minimum mission
life-time is of 3 years (with launch in 2017, if selected), but
extensions are likely, based on single-electronic performance reviews.


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