Current Workshop | Overview | Back | Home | Search | | |||||||
![]() |
Cosmic Ray Interactions: Bridging High and Low Energy Astrophysics |
![]() | ||
Cosmic rays are an
energetically important ingredient of the interstellar medium (ISM), but until
recently it was difficult to map the cosmic ray content of the Galaxy. With the
coming of age of GeV/TeV
gamma-ray astronomy this situation has dramatically changed, because the radiative effects of cosmic rays can be imaged directly with
arcminute resolution.
At the same time there is a wealth of information from radio, submm, and infrared wavebands on the magnetic field
configuration, and the distribution and abundance of dense matter in the Galaxy
with which cosmic rays interact. This provides vital information for the
researchers working on GeV/TeV
observations, in understanding the targets for accelerated particles. In
parallel, researchers working in low energy astrophysics need information about
the low-energy end of the cosmic ray distribution because it provides an
important, perhaps sometimes even the only, source of ionization in dense,
cold, molecular clouds. Thus even though
the low and high energy cosmic rays are separated by decades in energy, by
using both gamma-ray and molecular cloud chemistry as tracers, a new lever arm
for understanding source physics and cosmic ray acceleration can be
exploited. At the same time,
understanding the complications of UV vs. X-ray vs
cosmic ray ionization is a burgeoning new field. During this workshop all the
above mentioned aspects were discussed. Both the organizers and the
participants were very satisfied with the workshop, as there are otherwise few
occasions where such different scientific communities interact. The format of the workshop
consisted of many long talks intended to bring both communities up to date, and
some contributed talks on recent, interesting results. At the last day four
groups, two from each community, presented their ideas of what they think
researchers from the other community could investigate. During the week time
was reserved for the groups to work on these final talks. There was some
confusion concerning this idea, as participants were not quite sure how
detailed their proposals for research should be, but in the end participants
were pleased by what this format had accomplished, namely lively discussions
during the group sessions, on what they had just learned from fields that were
new to them. During the workshop the high
energy astrophysicists became much more aware of the molecular tracers of
cosmic rays interactions, with H3+ being one of the most important
molecules. They also became aware of the importance of low energy cosmic rays
(up to 10 MeV). These cosmic rays are usually ignored
by cosmic ray scientists because they are difficult to detect, due to
interference caused, e.g. by solar modulations, although future MeV gamma-ray satellite missions could fill that gap. The low energy
astrophysicists were brought up to date on the recent developments in GeV and TeV astronomy, and
learned how these fields have revealed the presence of cool regions in the ISM
that escaped the attention of radio, submm and
infrared astronomy. Participants also became more aware of the potential
diagnostic power of Fe-K fluorescent lines around 6.4 keV,
which could be induced by interactions between cold gas and MeV
protons. These lines were also discussed during the meeting in the context of
cosmic ray interactions in the Galactic Center region. The 6.4 keV feature is detected from many clouds there, but there
is a debate on whether it is induced by a past bright X-ray flare from the
central black hole, or whether it is caused by low energy electron or ion
cosmic rays. In fact, different cloud
complexes within the Galactic Center prefer different ionization mechanisms,
respectively. The impression of the
organizers, which is supported by comments and e-mails from the participants,
is that this was an extremely useful and timely workshop. Both communities
learned a lot from each other. The talks were in general very good, and
speakers tried to bring across their arguments keeping in mind that they were
addressing a diverse community. It was also interesting to see how the
different communities have sometimes overlapping jargon with different
meanings. An example was the confusion about the term “secondary electrons”,
which for low energy astrophysicists means the electrons liberated after
ionizations, whereas for a cosmic ray physicists means the electron created
after the decay of pions, which themselves are
created after high energy proton-proton collisions. Some ideas that came out of
this workshop are: the use of H3+ molecules to trace the
distribution and origin of low energy cosmic rays; the importance of future MeV satellite telescopes to do the same; the potential use
of 6.4 keV line emission to
trace low energy cosmic ray interactions. The general feeling at the
end of the workshop was that we should stay in touch as an interdisciplinary
community, and exchange more information about ideas and potential observing
campaigns. To that end we are in the
process of setting up a Wiki. All Lorentz Center participants will have access
to the Wiki, and already several non participants have asked to be
involved. We will post there the
presentations and papers from our Lorentz Center workshop website, as well as
start new pages for questions and observation organization. There was also a call for trying to do a
similar meeting in two years time, so our sense is that we have put something
in motion with this workshop that will have lasting effects, perhaps even
leading to larger conferences, since the interest level was so high. [Back] |
![]() ![]() ![]() |