DUST IN THE WIND: THE ROLE OF RECENT MASS LOSS IN LONG GAMMA-RAY BURSTS

We study the late-time (t 0.5> days) X-ray afterglows of nearby (z 0.5<) long gamma-ray bursts (GRBs) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index 3xΓ>) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (NH 6 10 cmx i, 21 2> × − ) and prompt γ-ray emission with extremely long duration (T 100090> s). The chance association of these three rare properties (i.e., large NHx i, , super-soft xΓ, and extreme duration) in the same class of explosions is statistically unlikely. We associate these properties with the turbulent mass-loss history of the progenitor star that enriched and shaped the circumburst medium. We identify a natural connection between NHx i, , xΓ, and T90 in these sources by suggesting that the late-time super-soft X-rays originate from radiation reprocessed by material lost to the environment by the stellar progenitor before exploding (either in the form of a dust echo or as reprocessed radiation from a long-lived GRB remnant), and that the interaction of the explosionʼs shock/jet with the complex medium is the source of the extremely long prompt emission. However, current observations do not allow us to exclude the possibility tha