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 fromP−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 faint (⩽10−12  ergs cm−2  s−1) sources was a clear candidate for either a GRB counterpart, or for an X-ray transient, although this possibility is still being explored.


Space Science Center, Physics

Publication Date


Journal Title

AIP Conference Proceedings


AIP Publishing

Digital Object Identifier (DOI)


Document Type

Conference Proceeding


© 1996 American Institute of Physics