Joseph Gelfand: Radio Emission from the Magnetar SGR 1806-20 Giant Flare

The 2004 Decemeber 27 giant flare from SGR 1900+14 was the most energetic giant flare ever observed. The radio light curve had a t^-1.5 to ^ 2.2 dependence 9 to 25 days after the event. After that it had a t^-3 dependence. The source rebrightened 25 to 35 days later. After 35 days the flux decreased as t^-1. The radio spectrum had an average spectral index of -0.7+/-0.3. This is what is expected from shock heated electrons. In the first few days after the event, not much motion was observed in the position of the radio nebula; however, 9 to 31 days later, constant proper motion was observed at 1/2 of the expansion rate. This motion was observed along the major axis. No coherent motion 31 days later. All these results were found via modeling the UV data. The emission seems to be a one-sided outflow. He interprets this behaviour as being due to the giant flare ejecting material into the surroundings. The collision compressed ejecta into a thin shell. What is the ejecta? Either the ejection of a magnetic flux loop or baryons ablated off the surface of the neutron star. Both give ejecta mass of 10^24.5 g.