Astronomy Tea Talks at Caltech

"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.

More astronomy-related talks
CalTech Today calendar. CalTech astronomy colloquia (3:45pm Wednesdays, Robinson library). IPAC lunch talks (12:15pm Wednesdays, IPAC Conference Room 102). Theoretical Astrophysics and Relativity Seminars (2pm Fridays, 114 E. Bridge). Carnegie Observatories colloquia and lunches (4pm Tuesdays & 12:15pm Fridays, OCIW). Solange Ramírez's weekly compilation of astro talks in Pasadena.
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Last modified on 20th Jul 2011 by Scott Schnee.