Magnetars may fuel Gamma-ray bursts

Its an interesting news which came in spacenews on Nov 2010 (had been thinking of posting it for a long time, but procrastination won!). According to this new finding, magnetars may be the driving force behind a larger population of gamma-ray bursts (GRBs) than scientists had earlier thought. 

Magnetars that last several minutes before they collapse under their own weight to form black holes had previously been invoked to explain the formation of some long GRBs (bursts that last for more than 2 seconds). Calculations by Paul O’Brien and Antonia Rowlinson of the University of Leicester in England and their colleagues show that a magnetar could also account for a short GRB, specifically a 36-millisecond flash (GRB 090515) observed on May 15, 2009, by NASA’s Swift satellite. About 10% of all bursts are believed to be short GRBs. If the magnetar model proves correct, it may indicate that a larger reservoir of stars than previously estimated could power GRBs, O’Brien said.

Gamma-ray burst aficionados cite two reasons for their interest in magnetars. First, the enormous rotational energy of these stars, which can spin hundreds of times a second, is sufficient to power some gamma-ray bursts. In addition, a short-lived magnetar could account for the brief but steady X-ray afterglow that immediately follows some long bursts. Unlike a smoldering ember, these unusual X-ray afterglows radiate at a constant brightness until they abruptly die away. The duration of the steady emission matches the lifetime of the magnetar, theorists propose.

In analyzing the afterglow of the short burst GRB 090515, the team led by O’Brien and Rowlinson found that the X-ray emission was unusually steady until it dropped off sharply a few hundred seconds later, just like the afterglows of 10 long gamma-ray bursts they had also recently examined. Aside from the magnetar, “there are no other sensible models” to explain a steady X-ray afterglow that suddenly drops to zero, said theorist Péter Mészáros of Pennsylvania State University in University Park. 

Researchers agree that because magnetars have a maximum rate of rotation, these spinning stars are limited to powering bursts less energetic than 3 times 10^52 ergs — about the energy that would be unleashed if 3 percent of the sun’s mass were converted into energy. Bursts with higher energies would require a black hole to power them, said Brian Metzger of Princeton University.

Here's the paper featuring these findings.