Evidence for supernova-synthesized dust from the rising afterglow of GRB071025 at z ~ 5

Perley, Daniel A.; Bloom, J. S.; Klein, C. R.; Covino, S.; Minezaki, T.; Woźniak, P.; Vestrand, W. T.; Williams, G. G.; Milne, P.; Butler, N. R.; Updike, A. C.; Krühler, T.; Afonso, P.; Antonelli, A.; Cowie, L.; Ferrero, P.; Greiner, J.; Hartmann, D. H.; Kakazu, Y.; Küpcü Yoldaş, A.; Morgan, A. N.; Price, P. A.; Prochaska, J. X.; Yoshii, Y.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 406, Issue 4, pp. 2473-2487.

Advertised on:
8
2010
Number of authors
24
IAC number of authors
1
Citations
82
Refereed citations
74
Description
We present observations and analysis of the broad-band afterglow of Swift GRB071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ~30 s after the gamma-ray burst trigger in the host frame, during the initial rising phase of the afterglow. We associate the light-curve peak at ~580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Γ0 ~ 200. The red spectral energy distribution (even in regions not affected by the Lyman α break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000 and 3000 Å in the rest frame, inconsistent with any locally observed template but well fitted by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to ΔA3000 < 0.54 mag after t = 50 s in the rest frame. Together with studies of high-z quasars, our observations suggest a transition in dust properties in the early Universe, possibly associated with a transition between supernova-dominated and asymptotic giant branch-dominated modes of dust production.
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