A 164-day period in γ-ray bursts from GBS0526–66?

Abstract

The γ-ray burst history of GBS0526–66 is unique among observed burst sources¹ being that of the brightest burst on record (5 March 1979) and one of only two from which recurrent bursts (at least 15 of similar temporal and spectral pattern) have been observed (though much less intense² than the first), and the only one whose source direction coincides with that of a previously known object—its 0.1 arc min² error box lies within the supernova remnant N49 in the Large Magellanic Cloud³. We have found evidence for a pattern in the recurrence times of these bursts, showing an apparent period of 164 day, which we suggest reflects periodic accretion to a neutron star from an eccentric (e ∼ 0.9) binary companion. We propose that this system drives two types of bursts: (1) the relatively frequent but weak recurrent bursts produced by either magnetospheric gating, or thermonuclear runaway, of periodically accreting matter around the neutron star, and (2) the much rarer intense bursts, like that of 5 March 1979, produced by tidally-triggered star quakes.