In 2007, a bright (>30 Jansky) millisecond burst of radio waves was reported. It was the first major unexpected astronomical discovery in decades. Subsequently, many such fast radio bursts (FRBs) have been discovered and it is estimated that there are about ten thousand per day coming from random directions across the entire sky. In 2016, one source discovered by the Arecibo Telescope, FRB 121102, was found to generate multiple bursts every few hours. This allowed follow-up observations to pin-point its host galaxy, which is at a cosmological distance of ~1 Gpc (or 3 billion light years).

 

In this talk, I first show that the progenitors of FRBs cannot be determined only by their event rate, duration and energetics. Understanding their radiation mechanism should provide the missing insights, which will be described.

 

The high brightness temperatures (> 1e35 K) of FRBs mean that the emission process must be coherent. Two general types of coherent radiation mechanisms are considered --- maser and the antenna mechanism. We use the observed properties of the repeater FRB 121102 to constrain the plasma conditions for these two mechanisms. We have looked into a wide variety of maser mechanisms operating in vacuum or plasma and find that none of them can explain the high luminosity of FRBs without invoking unrealistic or fine-tuned plasma conditions. The most favorable mechanism is the curvature emission by charge bunches, where the power comes from magnetic reconnection near the surface of a magnetar (B > 1e14 G).