We study the late-time (t > 0.5 days) X-ray afterglows of nearby (z < 0.5) long Gamma-Ray Bursts (GRB) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index Gamma_x > 3) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (NHx,i > 6×1021 cm-2) and prompt -ray emission with extremely long duration (T90 > 1000 s). Chance association of these three rare properties (i.e. large NHx,i, super-soft Gamma_x 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 circum-burst medium. We identify a natural connection between NHx,i, Gamma_x 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 froma long-livedGRB remnant), and that the interaction of the explosion’s shock/jetwith the complex medium is the source of the extremely long prompt emission. However, current observations do not allow us to exclude the possibility that super-soft X-ray emitters originate from peculiar stellar progenitors with large radii that only form in very dusty environments.
Dust in the wind: the role of recent mass loss in long gamma-ray bursts
GUIDORZI, Cristiano;
2015
Abstract
We study the late-time (t > 0.5 days) X-ray afterglows of nearby (z < 0.5) long Gamma-Ray Bursts (GRB) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index Gamma_x > 3) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (NHx,i > 6×1021 cm-2) and prompt -ray emission with extremely long duration (T90 > 1000 s). Chance association of these three rare properties (i.e. large NHx,i, super-soft Gamma_x 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 circum-burst medium. We identify a natural connection between NHx,i, Gamma_x 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 froma long-livedGRB remnant), and that the interaction of the explosion’s shock/jetwith the complex medium is the source of the extremely long prompt emission. However, current observations do not allow us to exclude the possibility that super-soft X-ray emitters originate from peculiar stellar progenitors with large radii that only form in very dusty environments.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
