A low-magnetic-field soft gamma repeater |
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Authors: | Rea N Esposito P Turolla R Israel G L Zane S Stella L Mereghetti S Tiengo A Götz D Gö?ü? E Kouveliotou C |
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Institution: | 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 |
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Abstract: | 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. |
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