Parametric excitation of an extremely low-frequency radio pulse by an extragalactic gamma-ray burst on December 27, 2004

Abstract

We simulate an electromagnetic pulse excited by a sharp descent of the charged upper wall of the Earth–ionosphere cavity. The ionosphere descent by 20 km was detected over the dayside Earth’s hemisphere during a giant extragalactic gamma-ray burst in the constellation of Sagittarius (SGR 1806–20). We show that a sharp change in the ionosphere altitude can cause a discrete pulse of extremely low-frequency radiation with the spectrum having some specific features and the amplitude significantly exceeding the natural regular noise background. The time of arrival of the radio pulse to an observer coincides with the gamma-burst time.