none

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

Connect with NRAO

The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.