A low-magnetic-field soft gamma repeater.
Soft gamma repeaters (SGRs) 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, that is, neutron stars powered by extreme magnetic fields, B ~ 10(14) to 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 7.5 × 10(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.
Institut de Ciéncies de l'Espai, Consejo Superior de Investigaciones Científicas, Institut d'Estudis Espacials de Catalunya, Facultat de Ciéncies, Campus UAB, Torre C5-parell, 2a planta, 08193 Bellaterra (Barcelona), Spain. rea@ieec.uab.es
N
N
Rea
P
P
Esposito
R
R
Turolla
G L
GL
Israel
S
S
Zane
L
L
Stella
S
S
Mereghetti
A
A
Tiengo
D
D
Götz
E
E
Göğüş
C
C
Kouveliotou