Astrophys. J., 833, 88-88 (2016/December-2)
A reverse shock in GRB 160509A.
LASKAR T., ALEXANDER K.D., BERGER E., FONG W.-F., MARGUTTI R., SHIVVERS I., WILLIAMS P.K.G., KOPAC D., KOBAYASHI S., MUNDELL C., GOMBOC A., ZHENG W., MENTEN K.M., GRAHAM M.L. and FILIPPENKO A.V.
Abstract (from CDS):
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 n0~10–3cm–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, NH ≃ 1.5 x 1022 cm–2, and a high rest-frame optical extinction, AV ≃ 3.4 mag. We identify a jet break in the X-ray light curve at tjet~6 days, and thus derive a jet opening angle of θjet~4^○, yielding a beaming-corrected kinetic energy and radiated γ-ray energy of EK~4×1050 erg and Eγ~1.3×1051 erg (1-104 keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of tdec ~460 s ≃ T90, a Lorentz factor of Γ(tdec)~330, and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of RB≡εB,RS/εB,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.
© 2016. The American Astronomical Society. All rights reserved.
gamma-ray burst: general - gamma-ray burst: individual: GRB 160509A - gamma-ray burst: individual: GRB 160509A
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<Available at CDS (J/ApJ/833/88): table1.dat>
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