Scientific Seminars

How to switch on and off a Gamma-ray burst through a magnetar

M. G. Bernardini
INAF-OABrera

2014-01-10    11.30    Merate - POE

One of the most elusive features of Gamma Ray Bursts (GRBs) is the sporadic emission prior to the main prompt event. These precursors have properties similar to the main prompt emission, are separated from the main event by a quiescent time that may be extremely long, and, in some cases, more than one precursor has been observed in the same burst. Precursors are still a puzzle: despite many attempts none of the proposed models can account for all the observed features. We propose a new scenario for which precursors are explained by assuming that the central GRB engine is a newly born magnetar. In this model the precursor and the prompt emission arise from accretion of matter onto the surface of the magnetar. The accretion process can be halted by the centrifugal drag exerted by the rotating magnetosphere onto the in--falling matter, allowing for multiple precursors and very long quiescent times. On a broader perspective, the rate of Supernovae Ibc hosting a magnetar is comparable to the rate of long GRBs, suggesting that a large fraction of GRBs is ultimately powered by magnetars. We show the ultra-bright GRB 130427A without precursors as an example.