ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C

Tanmoy Laskar, Kate D. Alexander, Ramandeep Gill, Jonathan Granot, Edo Berger, C. G. Mundell, Rodolfo Barniol Duran, J. Bolmer, Paul Duffell, Hendrik Van Eerten, Wen Fai Fong, Shiho Kobayashi, Raffaella Margutti, Patricia Schady

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2-5.2 hr after the burst. We detect linear polarization at the ≈5σ level, decreasing from Π = (0.87 ±0.13)% to (0.60 ±0.19)%, and evolving in polarization position angle from (10 ±5)° to (-44 ±12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at ≲0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θ B ≈ 10-3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.

Original languageEnglish (US)
Article numberL26
JournalAstrophysical Journal Letters
Volume878
Issue number1
DOIs
StatePublished - Jun 10 2019

Fingerprint

polarization
shock
linear polarization
ejecta
bursts
radio
magnetic field
toroidal field
radio observation
temporal evolution
afterglows
magnetic fields
rays
detection
cooling
x rays

Keywords

  • gamma-ray burst: general
  • gamma-ray burst: individual (GRB 190114C)
  • polarization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Laskar, T., Alexander, K. D., Gill, R., Granot, J., Berger, E., Mundell, C. G., ... Schady, P. (2019). ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C. Astrophysical Journal Letters, 878(1), [L26]. https://doi.org/10.3847/2041-8213/ab2247
Laskar, Tanmoy ; Alexander, Kate D. ; Gill, Ramandeep ; Granot, Jonathan ; Berger, Edo ; Mundell, C. G. ; Duran, Rodolfo Barniol ; Bolmer, J. ; Duffell, Paul ; Eerten, Hendrik Van ; Fong, Wen Fai ; Kobayashi, Shiho ; Margutti, Raffaella ; Schady, Patricia. / ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C. In: Astrophysical Journal Letters. 2019 ; Vol. 878, No. 1.
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abstract = "We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2-5.2 hr after the burst. We detect linear polarization at the ≈5σ level, decreasing from Π = (0.87 ±0.13){\%} to (0.60 ±0.19){\%}, and evolving in polarization position angle from (10 ±5)° to (-44 ±12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at ≲0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θ B ≈ 10-3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.",
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Laskar, T, Alexander, KD, Gill, R, Granot, J, Berger, E, Mundell, CG, Duran, RB, Bolmer, J, Duffell, P, Eerten, HV, Fong, WF, Kobayashi, S, Margutti, R & Schady, P 2019, 'ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C', Astrophysical Journal Letters, vol. 878, no. 1, L26. https://doi.org/10.3847/2041-8213/ab2247

ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C. / Laskar, Tanmoy; Alexander, Kate D.; Gill, Ramandeep; Granot, Jonathan; Berger, Edo; Mundell, C. G.; Duran, Rodolfo Barniol; Bolmer, J.; Duffell, Paul; Eerten, Hendrik Van; Fong, Wen Fai; Kobayashi, Shiho; Margutti, Raffaella; Schady, Patricia.

In: Astrophysical Journal Letters, Vol. 878, No. 1, L26, 10.06.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C

AU - Laskar, Tanmoy

AU - Alexander, Kate D.

AU - Gill, Ramandeep

AU - Granot, Jonathan

AU - Berger, Edo

AU - Mundell, C. G.

AU - Duran, Rodolfo Barniol

AU - Bolmer, J.

AU - Duffell, Paul

AU - Eerten, Hendrik Van

AU - Fong, Wen Fai

AU - Kobayashi, Shiho

AU - Margutti, Raffaella

AU - Schady, Patricia

PY - 2019/6/10

Y1 - 2019/6/10

N2 - We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2-5.2 hr after the burst. We detect linear polarization at the ≈5σ level, decreasing from Π = (0.87 ±0.13)% to (0.60 ±0.19)%, and evolving in polarization position angle from (10 ±5)° to (-44 ±12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at ≲0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θ B ≈ 10-3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.

AB - We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2-5.2 hr after the burst. We detect linear polarization at the ≈5σ level, decreasing from Π = (0.87 ±0.13)% to (0.60 ±0.19)%, and evolving in polarization position angle from (10 ±5)° to (-44 ±12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at ≲0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θ B ≈ 10-3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.

KW - gamma-ray burst: general

KW - gamma-ray burst: individual (GRB 190114C)

KW - polarization

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Laskar T, Alexander KD, Gill R, Granot J, Berger E, Mundell CG et al. ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C. Astrophysical Journal Letters. 2019 Jun 10;878(1). L26. https://doi.org/10.3847/2041-8213/ab2247