A New Type of Repetitive Behavior in a High-Energy Transient

The high-energy burster SGR 1806-20 (GB 790107) has been observed to repeat, on the order of 100 times, between 1978 August 13 and 1986 June 27. Most of the repetitions are in the latter part of 1983. All are clustered on time scales of hours to months. Simple analyses have shown the repetitive behavior to have very little correlation between burst intensity and interval between bursts. The tremendous range in intervals, with seconds to years (but usually <10⁵s) separating the bursts of comparable intensity, is amazing. The range in the intensities of the repetitions spans at least a factor of 30. The luminosity function can be approximated by a power law that flattens at low luminosities.