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

R. Margutti, C. Guidorzi, D. Lazzati, D. Milisavljevic, A. Kamble, T. Laskar, J. Parrent, N. C. Gehrels, A. M. Soderberg

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

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.
Original languageEnglish
Pages (from-to)159
Number of pages6
JournalAstrophysical Journal
Volume805
Issue number2
DOIs
Publication statusPublished - 29 May 2015

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