Looking for the source of ∼Hour-long soft X-ray emission following GRB 780506

GRB 780506, a gamma-ray burst discovered in HEAO 1 A-4 data, was unusual in three respects. First, it was well-measured (by HEAO 1 A-2) in 2–60 keV X-rays. Second, two minutes after it ended, HEAO 1 A-2 detected a faint resurgence of 2–10 keV flux, lasting roughly an hour. From recently calculated position constraints, it appears the source of the extended flux is consistent with the source of the burst, and probably not from a serendipitous transient along the Galactic plane. Third, it now appears GRB 780506 belongs to a newly discovered softer subclass of gamma-rays bursts. This subclass is remarkable, as, in contrast to harder gamma-ray bursts, it is apparently homogeneous, with log(N > P) showing no turnover from P−3/2(1,2). Was GRB 780506 also unusual in having a detectable quiescent counterpart? A ROSAT Class C observation was scheduled which covered one side of the error box. The new HEAO 1 A-2 position constraints excluded all but four of the sixteen detected ROSAT sources. None of these four fain...