| Soft gamma repeaters (SGR) are a rare class of objects characterized by repetitive emission of hard X-ray/low energy gamma-ray bursts. At least three of the four currently-known SGRs are associated with slowly spinning neutron stars which additionally exhibit a large spin-down behavior. Their cumulative properties strongly suggest that SGRs are extremely magnetized (1014–1015 G) isolated neutron stars making them unique laboratories in nature where we can study physical processes in the presence of strong magnetic fields.; In this dissertation, we present the statistical properties of the bursts from SGR 1806−20 and SGR 1900+14 obtained from a much larger database than the one used in previous statistical investigations. We find that the fluence (size) distribution of bursts is well described by power law of index ∼1.6. We also confirm that the distribution of time intervals between successive bursts is represented by a lognormal function and there is no correlation between the burst intensity and the waiting times till the next burst. In all these statistical properties, SGR bursts resemble a self-organized critical system. We construct the first comprehensive history of the (energy resolved) pulse profile evolution of the persistent emission of SGR 1806−20 and SGR 1900+14, spanning ∼five years. Our results support the hypothesis that the energy source for SGRs is their own evolving, strong magnetic fields, rather than any accretion or nuclear power. |
