Image of Alice in Wonderland at the Mad Hatter's tea party You are cordially invited to afternoon tea and biscuits wine and chocolate

Astronomy Tea Talks at Caltech

Mondays, Hameetman auditorium (Cahill)
Tea:  4.00pm
Talk: 4.15pm

Organized by:

2008 - 2009 season:
5 May 2009
David Jauncey (CSIRO/ATNF)

"ISS and IDV; telling the difference"

Interstellar scintillation (ISS) in AGN was suggested as the
explanation for the low-frequency variability seen 36 years ago by
Hunstead at 408 MHz 36. Twenty years later Dave Heeschen discovered
"flickering" of flat-spectrum AGN at 2.7 GHz, but reported no Galactic
latitude dependence as would be expected if the phenomenon were due to
ISS. Soon afterwards Heeschen went the MPI, and while working with the
Bonn group, thay reported significant intra-day variability (IDV) in
many flat-spectrum AGN at cm wavelengths. Their preferred explanation
was that the changes were intrinsic in nature. For the next decade and
a half the debate continued between an intrinsic and extrinsic
explanation. The discovery of the three very fast variables,
PKS0405-385, J1819+3845 and PKS1257-326, has allowed measurements of
the pattern time-delay between widely spaced telescopes for each of
these sources, as well as the discovery of an "annual cycle" in the
variability characteristics of a number of AGN. Such measurements
establish unequivocally that ISS is the principal mechanism.
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Last modified on 20th Jul 2011 by Scott Schnee.  

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