  Soft gamma repeaters and anomalous x-ray pulsars form a rapidly increasing
group of x-ray sources exhibiting sporadic emission of short bursts. They are
believed to be magnetars, i.e. neutron stars powered by extreme magnetic
fields, B~10^{14}-10^{15} Gauss. We report on a soft gamma repeater with low
magnetic field, SGR 0418+5729, recently detected after it emitted bursts
similar to those of magnetars. X-ray observations show that its dipolar
magnetic field cannot be greater than 7.5x10^{12} Gauss, well in the range of
ordinary radio pulsars, implying that a high surface dipolar magnetic field is
not necessarily required for magnetar-like activity. The magnetar population
may thus include objects with a wider range of B-field strengths, ages and
evolutionary stages than observed so far.

High Energy Astrophysical Phenomena;Astrophysics of Galaxies