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First ALMA Light Curve Constrains Refreshed Reverse Shocks and Jet Magnetization in GRB 161219B

Laskar, Tanmoy and Alexander, Kate D. and Berger, Edo and Guidorzi, Cristiano and Margutti, Raffaella and Fong, Wen-Fai and Kilpatrick, Charles D. and Milne, Peter and Drout, Maria R. and Mundell, C. G. and Kobayashi, Shiho and Lunnan, Ragnhild and Barniol Duran, Rodolfo and Menten, Karl M. and Ioka, Kunihito and Williams, Peter K. G. (2018) First ALMA Light Curve Constrains Refreshed Reverse Shocks and Jet Magnetization in GRB 161219B. Astrophysical Journal, 862 (2). Art. No. 94. ISSN 1538-4357.

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We present detailed multiwavelength observations of GRB 161219B at z = 0.1475, spanning the radio to X-ray regimes, and the first Atacama Large Millimeter/submillimeter Array (ALMA) light curve of a γ-ray burst (GRB) afterglow. The centimeter- and millimeter-band observations before 8.5 days require emission in excess of that produced by the afterglow forward shock (FS). These data are consistent with radiation from a refreshed reverse shock (RS) produced by the injection of energy into the FS, signatures of which are also present in the X-ray and optical light curves. We infer a constant-density circumburst environment with an extremely low density, n_0 ≈ 3 x 10^(-4) cm^(-3), and show that this is a characteristic of all strong RS detections to date. The Karl G. Lansky Very Large Array (VLA) observations exhibit unexpected rapid variability on roughly minute timescales, indicative of strong interstellar scintillation. The X-ray, ALMA, and VLA observations together constrain the jet break time, t_(jet) ≈ 32 days, yielding a wide jet opening angle of θ_(jet) ≈ 13°, implying beaming-corrected γ-ray and kinetic energies of E_γ ≈ 4.9 x 10^(48) erg and E_K ≈ 1.3 x 10^(50) erg, respectively. Comparing the RS and FS emission, we show that the ejecta are only weakly magnetized, with relative magnetization, R_B ≈ 1, compared to the FS. These direct, multifrequency measurements of a refreshed RS spanning the optical to radio bands highlight the impact of radio and millimeter data in probing the production and nature of GRB jets.

Item Type:Article
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URLURL TypeDescription
Laskar, Tanmoy0000-0003-1792-2338
Alexander, Kate D.0000-0002-8297-2473
Berger, Edo0000-0002-9392-9681
Guidorzi, Cristiano0000-0001-6869-0835
Margutti, Raffaella0000-0003-4768-7586
Fong, Wen-Fai0000-0002-7374-935X
Kilpatrick, Charles D.0000-0002-5740-7747
Milne, Peter0000-0002-0370-157X
Drout, Maria R.0000-0001-7081-0082
Kobayashi, Shiho0000-0001-7946-4200
Lunnan, Ragnhild0000-0001-9454-4639
Menten, Karl M.0000-0001-6459-0669
Ioka, Kunihito0000-0002-3517-1956
Williams, Peter K. G.0000-0003-3734-3587
Additional Information:© 2018 The American Astronomical Society. Received 2017 October 17; revised 2018 May 8; accepted 2018 June 4; published 2018 July 26. We thank the anonymous referee for their helpful comments on improvements of the manuscript. T.L. is a Jansky Fellow of the National Radio Astronomy Observatory. The Berger Time-Domain Group at Harvard is supported in part by the NSF under grant AST-1411763 and by NASA under grant NNX15AE50G. C.G.M. acknowledges support from the Science and Technology Facilities Council. We thank Peter Nugent for generating the SN model. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.00819.T and ADS/JAO.ALMA#2016.A.00015.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. VLA observations for this study were obtained via project 15A-235. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work makes use of data supplied by the UK Swift Science Data Centre at the University of Leicester and of data obtained through the High Energy Astrophysics Science Archive Research Center On-line Service, provided by the NASA/Goddard Space Flight Center. This work includes data obtained with the Swope Telescope at Las Campanas Observatory, Chile, as part of the Swope Time Domain Key Project (PI Piro; co-PIs Shappee, Drout, Madore, Phillips, Foley, and Hsiao). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research has made use of the SVO Filter Profile Service, supported by the Spanish MINECO through grant AyA2014-55216.
Funding AgencyGrant Number
National Radio Astronomy ObservatoryUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)AyA2014-55216
Subject Keywords:gamma-ray burst: general – gamma-ray burst: individual (GRB 161219B)
Issue or Number:2
Record Number:CaltechAUTHORS:20180808-161430679
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Official Citation:Tanmoy Laskar et al 2018 ApJ 862 94
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88678
Deposited By: Tony Diaz
Deposited On:09 Aug 2018 14:36
Last Modified:09 Mar 2020 13:18

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