A reverse shock in GRB L60509A
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138 (United States)
- Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 (United States)
- Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astrophysics, Northwestern University, Evanston, IL 60208 (United States)
- Department of Astronomy, University of California, 501 Campbell Hall, Berkeley, CA 94720-3411 (United States)
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia)
- Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)
- Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY (United Kingdom)
- University of Nova Gorica, Vipavska 13, 5000 Nova Gorica (Slovenia)
- Max-Planck-Institut für Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
We present the second multi-frequency radio detection of a reverse shock in a γ-ray burst. By combining our extensive radio observations of the Fermi-Large Area Telescope γ-ray burst 160509A at z = 1.17 up to 20 days after the burst with Swift X-ray observations and ground-based optical and near-infrared data, we show that the afterglow emission comprises distinct reverse shock and forward shock contributions: the reverse shock emission dominates in the radio band at ≲10 days, while the forward shock emission dominates in the X-ray, optical, and near-infrared bands. Through multi-wavelength modeling, we determine a circumburst density of n{sub 0}≈10{sup −3} cm{sup −3}, supporting our previous suggestion that a low-density circumburst environment is conducive to the production of long-lasting reverse shock radiation in the radio band. We infer the presence of a large excess X-ray absorption column, N {sub H} ≈ 1.5 × 10{sup 22} cm{sup −2}, and a high rest-frame optical extinction, A {sub V} ≈ 3.4 mag. We identify a jet break in the X-ray light curve at t{sub jet}≈6 days, and thus derive a jet opening angle of θ{sub jet}≈4{sup ∘}, yielding a beaming-corrected kinetic energy and radiated γ-ray energy of E{sub K}≈4×10{sup 50} erg and E{sub γ}≈1.3×10{sup 51} erg (1–10{sup 4} keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of t{sub dec} ≈460 s ≈ T {sub 90}, a Lorentz factor of Γ(t{sub dec})≈330, and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of R{sub B}≡ϵ{sub B,RS}/ϵ{sub B,FS}≈8. Our study highlights the power of rapid-response radio observations in the study of the properties and dynamics of γ-ray burst ejecta.
- OSTI ID:
- 22868358
- Journal Information:
- Astrophysical Journal, Vol. 833, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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