Evidence for supernova-synthesized dust from the rising afterglow of GRB 071025 at z∼ 5
Abstract
We present observations and analysis of the broad-band afterglow of Swift GRB 071025. 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2010
- DOI:
- 10.1111/j.1365-2966.2010.16772.x
- arXiv:
- arXiv:0912.2999
- Bibcode:
- 2010MNRAS.406.2473P
- Keywords:
-
- dust;
- extinction;
- gamma-ray burst: general;
- gamma-ray burst: individual: 071025;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Resubmitted to MNRAS following referee report. Contains additional figure and some extra analysis/discussion