NRAO/Socorro Colloquium Series
Christopher Hirata
Caltech
Dispersion measures from continuous sources?
Electron column densities measured
from the dispersion of pulsar pulses are a well-established tool for
probing the distribution of ionized gas in the interstellar medium. The
quest for the missing cosmological baryons has motivated the study of
ways to measure electron columns over intergalactic sightlines, but
this requires a "backlight" visible at cosmological distances. In this
talk, I will discuss the theory behind attempts to obtain a dispersion
measure from continuous rather than pulsed sources. Several ideas along
these lines have emerged using correlation functions of the electric
field received from the source, or using the quantum nature of
electromagnetic radiation. In each case, the role of individual pulses
emitted by a pulsar is played by a statistical process, or by the
discreteness of photons. I will describe why, at least in their
simplest version, these methods will not work when applied to a
time-steady synchrotron or free-free source, and consider what
characteristics are needed for a source to be a candidate for providing
cosmological dispersion measures.
February 21, 2015
11:00 am
Array Operations Center Auditorium
All NRAO employees are invited to attend via video, available in Charlottesville 245, Green Bank Auditorium, Tucson N525, and NTC 400.
Local Host: Walter Max-Moerbeck/Chris Hales
