Figure 1---The 2.7
and 8.1 GHz light curves of QSO 0954+658, the
prototypical and exemplary extreme scattering event. The horizontal
bar at the top of the top panel shows the approximate duration of the
ESE. (From Fiedler et al. 1994)[US Navy] [Navy Recruiting] [Navy FOIA] [Office of Naval Research] [Naval Research Laboratory]
Extreme scattering events (ESE) are a class of dramatic changes in the
flux density of radio sources (Fiedler et
al. 1987; Fiedler et
al. 1994). They are marked typically by a decrease (~ 50%)
in the flux density near 1 GHz for a period of several weeks to
months, bracketed by substantial increases, viz. Fig. 1. Because of the simultaneity of the
events at different wavelengths, the time scales of the events, and
light travel time arguments, ESEs are likely due to strong scattering
by the Galactic interstellar medium (ISM; Fiedler et al. 1987; Romani, Blandford, & Cordes 1987;
but see Walker & Wardle 1998).
First identified in the light curves of extragalactic sources, ESEs
have since been observed during a timing program of the pulsars
PSR B1937+21 (Cognard et
al. 1993; Lestrade, Rickett, &
Cognard 1998) and PSR J1643-1224 (Maitia, Lestrade, &
Cognard 1998).
Figure 1---The 2.7
and 8.1 GHz light curves of QSO 0954+658, the
prototypical and exemplary extreme scattering event. The horizontal
bar at the top of the top panel shows the approximate duration of the
ESE. (From Fiedler et al. 1994)
ESEs were first discovered at the Naval Research Laboratory, and this Web site aims to provide a database of known ESEs as well as links to on-going research.
Data from the Navy-NRAO Green Bank Interferometer monitoring program, from which the original ESEs were found.
Simulations and models
Follow-up or ancillary observations
Bibliography and other ESE references
This is an official U.S. Navy Web site.
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Approving Official: Dr. L. J Rickard, Superintendent, Remote Sensing Division, NRL
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