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Today's Colloquium: Relativistic jets: Some unconventional notions; An annoying X-ray problem; and how LOFAR might help

Submitter: Dan Harris (CfA)
Description: We argue that most observations of extragalactic jets do not directly inform us of basic jet physics. Rather, the radiation we see comes from plasmas which are produced by the conversion of jet power to relativistic electrons and B fields. What we want is a determination of the underlying electron spectrum, N(E), over as wide a range as possible for the emitting regions and thereby, gain insights into the conversion process (shocks and magnetic reconnection). For powerful quasar jets, the primary X-ray problem is our uncertainty as to the emission process: if the X-rays are from synchrotron emission we learn about extremely high energy electrons (gamma ~ 10^7), whereas IC/CMB models require large numbers of low energy electrons (gamma ~ 100). LOFAR, with arcsec resolution at low frequencies, should permit us to track N(E) to energies low enough so as to decide if the extrapolation from higher energies (a necessary ingredient of IC/CMB calculations) is correct or not.

The River Analogy for Relativistic Jets: Imagine a jet is like a river; smoothly transporting energy. When there is a rock near the surface or a waterfall, white water occurs: a fraction of the river's energy is converted to random motion. When we 'see' a jet, we are viewing only the white water, not 'the jet' itself.

Editor's note: Dan was one of our first six post-docs, back in the late 70s. In those days, SRZM (ASTRON) was not supposed to do any science. We finally persuaded the universities that a few astronomers would help us build better instruments. The first batch all went on to greatness.
Copyright: Dan Harris
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