Solar Activity Associated with Electron Plasma Oscillations in the Interstellar Medium Observed By Voyager 1

The Plasma Wave Science (PWS) instrument on Voyager 1 has now observed three episodes of plasma oscillations in the interstellar medium, during the time frames October-November 2012, April-May 2013, and most recently May-July 2014. The frequency of the plasma oscillations, in the range of 2 to 3 kHz provides evidence for dense plasma directly in the range of the ~0.08 cm-3 expected for the very local interstellar medium. Each of these events has plausible triggers in coronal mass ejection (CME) activity in September-October 2011, March 2012, and May 2012, respectively. The CME activity is thought to coalesce into global merged interaction regions (GMIRs) and associated shocks which can propagate through the solar wind and into the interstellar medium. The GMIR-associated shocks are thought to be sources of electron beams that can excite electron plasma oscillations such as those observed by Voyager. The plasma oscillations were predicted as the source of 2-3 kHz heliospheric radio emissions observed by Voyager beginning in the early 1980s, hence, their discovery in the interstellar medium was long-expected. We discuss the methods by which the propagation of the shocks through the interplanetary and interstellar media can be estimated.