TY - JOUR
T1 - DUST IN THE WIND: THE ROLE OF RECENT MASS LOSS IN LONG GAMMA-RAY BURSTS
AU - Margutti, R.
AU - Guidorzi, C.
AU - Lazzati, D.
AU - Milisavljevic, D.
AU - Kamble, A.
AU - Laskar, T.
AU - Parrent, J.
AU - Gehrels, N. C.
AU - Soderberg, A. M.
PY - 2015/5/29
Y1 - 2015/5/29
N2 - We study the late-time ($t\gt 0.5$ days) X-ray afterglows of nearby ($z\lt 0.5$) long gamma-ray bursts (GRBs) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index ${{{\Gamma }}_{x}}\gt 3$) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (${\rm N}{{{\rm H}}_{x,i}}\gt 6\times {{10}^{21}}\;{\rm c}{{{\rm m}}^{-2}}$) and prompt γ-ray emission with extremely long duration (${{T}_{90}}\gt 1000$ s). The chance association of these three rare properties (i.e., large ${\rm N}{{{\rm H}}_{x,i}}$, 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 circumburst medium. We identify a natural connection between ${\rm N}{{{\rm H}}_{x,i}}$, ${{{\Gamma }}_{x}}$, and ${{T}_{90}}$ 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 explosion's 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 that super-soft X-ray emitters originate from peculiar stellar progenitors with large radii that only form in very dusty environments.
AB - We study the late-time ($t\gt 0.5$ days) X-ray afterglows of nearby ($z\lt 0.5$) long gamma-ray bursts (GRBs) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index ${{{\Gamma }}_{x}}\gt 3$) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (${\rm N}{{{\rm H}}_{x,i}}\gt 6\times {{10}^{21}}\;{\rm c}{{{\rm m}}^{-2}}$) and prompt γ-ray emission with extremely long duration (${{T}_{90}}\gt 1000$ s). The chance association of these three rare properties (i.e., large ${\rm N}{{{\rm H}}_{x,i}}$, 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 circumburst medium. We identify a natural connection between ${\rm N}{{{\rm H}}_{x,i}}$, ${{{\Gamma }}_{x}}$, and ${{T}_{90}}$ 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 explosion's 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 that super-soft X-ray emitters originate from peculiar stellar progenitors with large radii that only form in very dusty environments.
U2 - 10.1088/0004-637X/805/2/159
DO - 10.1088/0004-637X/805/2/159
M3 - Article
SN - 0004-637X
VL - 805
SP - 159
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -