By Ron Cowen
ANNAPOLIS, Md. — It takes a powerful beast to unleash a gamma-ray burst, the most energetic type of explosion since the Big Bang. But the exact nature of the cosmic powerhouse that generates the various kinds of bursts has been a matter of debate for nearly 20 years.
A new finding reported November 3 at the Gamma Ray Burst 2010 meeting suggests that rapidly spinning magnetars, which have the strongest known magnetic fields in the universe, may be the driving force behind a larger population of gamma-ray bursts than scientists had 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 gamma-ray bursts, energetic flashes of radiation that endure for more than two seconds. Calculations by Paul O’Brien and Antonia Rowlinson of the University of Leicester in England and their colleagues now show that a magnetar could also account for a short gamma-ray burst, specifically a 36-millisecond flash observed on May 15, 2009, by NASA’s Swift satellite and dubbed GRB 090515. Estimates vary, but short gamma-ray bursts may account for about 10 percent of all bursts. If the magnetar model proves correct, it may indicate that a larger reservoir of stars than previously estimated could power gamma-ray bursts, 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.