A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A: Shell Collisions and Two Reverse Shocks

Tanmoy Laskar, Edo Berger, Raffaella Margutti, B. Ashley Zauderer, Peter K. G. Williams, Wen-fai Fong, Re’em Sari, Kate D. Alexander, Atish Kamble

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Abstract

We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to E k,iso ≈ 4.9 × 1054 erg, ${A}_{* }$ ≈ 2.6 × 10−2, ${\epsilon }_{{\rm{e}}}$ ≈ 2.5 × 10−2, ${\epsilon }_{{\rm{B}}}$ ≈ 5.9 × 10−2, p ≈ 2.6, and ${\theta }_{\mathrm{jet}}$ ≈ 1fdg1, yielding a beaming-corrected γ-ray and kinetic energy, ${E}_{\gamma }$ ≈ 2.3 × 1049 erg and ${E}_{{\rm{K}}}$ ≈ 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at ≈0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, t dec ≈ 100 s, the ejecta Lorentz factor, Γ(t dec) ≈ 300, and a low RS magnetization, R B ≈ 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.
Language English 134 Astrophysical Journal 859 2 10.3847/1538-4357/aabfd8 Accepted/In press - 15 Apr 2018

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A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A : Shell Collisions and Two Reverse Shocks. / Laskar, Tanmoy; Berger, Edo; Margutti, Raffaella; Zauderer, B. Ashley; Williams, Peter K. G.; Fong, Wen-fai; Sari, Re’em; Alexander, Kate D.; Kamble, Atish.

In: Astrophysical Journal, Vol. 859, No. 2, 15.04.2018, p. 134.

Research output: Contribution to journalArticle

Laskar, T, Berger, E, Margutti, R, Zauderer, BA, Williams, PKG, Fong, W, Sari, R, Alexander, KD & Kamble, A 2018, 'A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A: Shell Collisions and Two Reverse Shocks', Astrophysical Journal, vol. 859, no. 2, pp. 134. https://doi.org/10.3847/1538-4357/aabfd8
Laskar, Tanmoy ; Berger, Edo ; Margutti, Raffaella ; Zauderer, B. Ashley ; Williams, Peter K. G. ; Fong, Wen-fai ; Sari, Re’em ; Alexander, Kate D. ; Kamble, Atish. / A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A : Shell Collisions and Two Reverse Shocks. In: Astrophysical Journal. 2018 ; Vol. 859, No. 2. pp. 134.
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T1 - A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A

T2 - Astrophysical Journal

AU - Berger, Edo

AU - Margutti, Raffaella

AU - Zauderer, B. Ashley

AU - Williams, Peter K. G.

AU - Fong, Wen-fai

AU - Sari, Re’em

AU - Alexander, Kate D.

AU - Kamble, Atish

PY - 2018/4/15

Y1 - 2018/4/15

N2 - We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to E k,iso ≈ 4.9 × 1054 erg, ${A}_{* }$ ≈ 2.6 × 10−2, ${\epsilon }_{{\rm{e}}}$ ≈ 2.5 × 10−2, ${\epsilon }_{{\rm{B}}}$ ≈ 5.9 × 10−2, p ≈ 2.6, and ${\theta }_{\mathrm{jet}}$ ≈ 1fdg1, yielding a beaming-corrected γ-ray and kinetic energy, ${E}_{\gamma }$ ≈ 2.3 × 1049 erg and ${E}_{{\rm{K}}}$ ≈ 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at ≈0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, t dec ≈ 100 s, the ejecta Lorentz factor, Γ(t dec) ≈ 300, and a low RS magnetization, R B ≈ 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.

AB - We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to E k,iso ≈ 4.9 × 1054 erg, ${A}_{* }$ ≈ 2.6 × 10−2, ${\epsilon }_{{\rm{e}}}$ ≈ 2.5 × 10−2, ${\epsilon }_{{\rm{B}}}$ ≈ 5.9 × 10−2, p ≈ 2.6, and ${\theta }_{\mathrm{jet}}$ ≈ 1fdg1, yielding a beaming-corrected γ-ray and kinetic energy, ${E}_{\gamma }$ ≈ 2.3 × 1049 erg and ${E}_{{\rm{K}}}$ ≈ 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at ≈0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, t dec ≈ 100 s, the ejecta Lorentz factor, Γ(t dec) ≈ 300, and a low RS magnetization, R B ≈ 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.

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DO - 10.3847/1538-4357/aabfd8

M3 - Article

VL - 859

SP - 134

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

ER -