Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor

Hoi Fung Yu, Jochen Greiner, Hendrik van Eerten, J. Michael Burgess, P. Narayana Bhat, Michael S. Briggs, Valerie Connaughton, Roland Diehl, Adam Goldstein, David Gruber, Peter A. Jenke, Andreas von Kienlin, Chryssa Kouveliotou, William S. Paciesas, Veronique Pelassa, Robert D. Preece, Oliver J. Roberts, Bin-Bin Zhang

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Abstract

Context. We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. Aims. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Methods. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1 keV–1 MeV fluence f> 1.0 × 10-4 erg cm-2 and a signal-to-noise ratio level of S/N ≥ 10.0 above 900 keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index α, the high-energy power-law index β, the peak energy in the observed νFν spectrum Ep, and the difference between the low- and high-energy power-law indices Δs = α − β. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies Eb,1 and Eb,2, the middle segment power-law index β, and the Planck function temperature kT. Results. The Band function parameter distributions are α = -0.73+0.16-0.21, β =ي-2.13+0.28-0.56, Ep = 374.4+307.3-187.7 , , keV (log10Ep = 2.57+0.26-0.30), and Δs = 1.38+0.54-0.31 , with average errors σα ~ 0.1, σβ ~ 0.2, and σEp ~ 0.1Ep. Using the distributions of Δs and β, the electron population index p is found to be consistent with the “moderately fast” scenario, in which fast- and slow-cooling scenarios cannot be distinguished. The physically motivated synchrotron-fitting function parameter distributions are Eb,1 = 129.6+132.2-32.4 keV, Eb,2 = 631.4+582.6-309.6 keV, β = -1.72+0.48-0.25 , and kT = 10.4+4.9-3.7 keV, with average errors σβ ~ 0.2, σEb,1 ~ 0.1Eb,1, σEb,2 ~ 0.4Eb,2, and σkT ~ 0.1kT. This synchrotron function requires the synchrotron injection and cooling break (i.e., Emin and Ecool) to be close to each other within a factor of ten, often in addition to a Planck function. Conclusions. A synchrotron model is found that is consistent with most of the time-resolved spectra for eight energetic Fermi GBM bursts with good high-energy photon statistics as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by including a thermal component or when an evolving magnetic field is accounted for.
Original languageEnglish
Article numberA81
Pages (from-to)A81
JournalAstronomy & Astrophysics
Volume573
DOIs
Publication statusPublished - 1 Jan 2015

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gamma ray bursts
monitors
synchrotrons
energetics
cooling
power law
energy
statistics
injection
Fermi Gamma-ray Space Telescope
photons
erg
spectral analysis
signal-to-noise ratio
spectrum analysis
index
bursts
fluence
signal to noise ratios
distribution

Keywords

  • gamma rays: stars, gamma-ray burst: general, radiation mechanisms: non-thermal, methods: data analysis

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Yu, H. F., Greiner, J., van Eerten, H., Burgess, J. M., Narayana Bhat, P., Briggs, M. S., ... Zhang, B-B. (2015). Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor. Astronomy & Astrophysics, 573, A81. [A81]. https://doi.org/10.1051/0004-6361/201424858

Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor. / Yu, Hoi Fung; Greiner, Jochen; van Eerten, Hendrik; Burgess, J. Michael; Narayana Bhat, P.; Briggs, Michael S.; Connaughton, Valerie; Diehl, Roland; Goldstein, Adam; Gruber, David; Jenke, Peter A.; von Kienlin, Andreas; Kouveliotou, Chryssa; Paciesas, William S.; Pelassa, Veronique; Preece, Robert D.; Roberts, Oliver J.; Zhang, Bin-Bin.

In: Astronomy & Astrophysics, Vol. 573, A81, 01.01.2015, p. A81.

Research output: Contribution to journalArticle

Yu, HF, Greiner, J, van Eerten, H, Burgess, JM, Narayana Bhat, P, Briggs, MS, Connaughton, V, Diehl, R, Goldstein, A, Gruber, D, Jenke, PA, von Kienlin, A, Kouveliotou, C, Paciesas, WS, Pelassa, V, Preece, RD, Roberts, OJ & Zhang, B-B 2015, 'Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor', Astronomy & Astrophysics, vol. 573, A81, pp. A81. https://doi.org/10.1051/0004-6361/201424858
Yu, Hoi Fung ; Greiner, Jochen ; van Eerten, Hendrik ; Burgess, J. Michael ; Narayana Bhat, P. ; Briggs, Michael S. ; Connaughton, Valerie ; Diehl, Roland ; Goldstein, Adam ; Gruber, David ; Jenke, Peter A. ; von Kienlin, Andreas ; Kouveliotou, Chryssa ; Paciesas, William S. ; Pelassa, Veronique ; Preece, Robert D. ; Roberts, Oliver J. ; Zhang, Bin-Bin. / Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor. In: Astronomy & Astrophysics. 2015 ; Vol. 573. pp. A81.
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title = "Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor",
abstract = "Context. We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. Aims. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Methods. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1 keV–1 MeV fluence f> 1.0 × 10-4 erg cm-2 and a signal-to-noise ratio level of S/N ≥ 10.0 above 900 keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index α, the high-energy power-law index β, the peak energy in the observed νFν spectrum Ep, and the difference between the low- and high-energy power-law indices Δs = α − β. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies Eb,1 and Eb,2, the middle segment power-law index β, and the Planck function temperature kT. Results. The Band function parameter distributions are α = -0.73+0.16-0.21, β =ي-2.13+0.28-0.56, Ep = 374.4+307.3-187.7 , , keV (log10Ep = 2.57+0.26-0.30), and Δs = 1.38+0.54-0.31 , with average errors σα ~ 0.1, σβ ~ 0.2, and σEp ~ 0.1Ep. Using the distributions of Δs and β, the electron population index p is found to be consistent with the “moderately fast” scenario, in which fast- and slow-cooling scenarios cannot be distinguished. The physically motivated synchrotron-fitting function parameter distributions are Eb,1 = 129.6+132.2-32.4 keV, Eb,2 = 631.4+582.6-309.6 keV, β = -1.72+0.48-0.25 , and kT = 10.4+4.9-3.7 keV, with average errors σβ ~ 0.2, σEb,1 ~ 0.1Eb,1, σEb,2 ~ 0.4Eb,2, and σkT ~ 0.1kT. This synchrotron function requires the synchrotron injection and cooling break (i.e., Emin and Ecool) to be close to each other within a factor of ten, often in addition to a Planck function. Conclusions. A synchrotron model is found that is consistent with most of the time-resolved spectra for eight energetic Fermi GBM bursts with good high-energy photon statistics as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by including a thermal component or when an evolving magnetic field is accounted for.",
keywords = "gamma rays: stars, gamma-ray burst: general, radiation mechanisms: non-thermal, methods: data analysis",
author = "Yu, {Hoi Fung} and Jochen Greiner and {van Eerten}, Hendrik and Burgess, {J. Michael} and {Narayana Bhat}, P. and Briggs, {Michael S.} and Valerie Connaughton and Roland Diehl and Adam Goldstein and David Gruber and Jenke, {Peter A.} and {von Kienlin}, Andreas and Chryssa Kouveliotou and Paciesas, {William S.} and Veronique Pelassa and Preece, {Robert D.} and Roberts, {Oliver J.} and Bin-Bin Zhang",
year = "2015",
month = "1",
day = "1",
doi = "10.1051/0004-6361/201424858",
language = "English",
volume = "573",
pages = "A81",
journal = "Astronomy & Astrophysics",
issn = "0004-6361",
publisher = "Springer Verlag",

}

TY - JOUR

T1 - Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor

AU - Yu, Hoi Fung

AU - Greiner, Jochen

AU - van Eerten, Hendrik

AU - Burgess, J. Michael

AU - Narayana Bhat, P.

AU - Briggs, Michael S.

AU - Connaughton, Valerie

AU - Diehl, Roland

AU - Goldstein, Adam

AU - Gruber, David

AU - Jenke, Peter A.

AU - von Kienlin, Andreas

AU - Kouveliotou, Chryssa

AU - Paciesas, William S.

AU - Pelassa, Veronique

AU - Preece, Robert D.

AU - Roberts, Oliver J.

AU - Zhang, Bin-Bin

PY - 2015/1/1

Y1 - 2015/1/1

N2 - Context. We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. Aims. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Methods. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1 keV–1 MeV fluence f> 1.0 × 10-4 erg cm-2 and a signal-to-noise ratio level of S/N ≥ 10.0 above 900 keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index α, the high-energy power-law index β, the peak energy in the observed νFν spectrum Ep, and the difference between the low- and high-energy power-law indices Δs = α − β. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies Eb,1 and Eb,2, the middle segment power-law index β, and the Planck function temperature kT. Results. The Band function parameter distributions are α = -0.73+0.16-0.21, β =ي-2.13+0.28-0.56, Ep = 374.4+307.3-187.7 , , keV (log10Ep = 2.57+0.26-0.30), and Δs = 1.38+0.54-0.31 , with average errors σα ~ 0.1, σβ ~ 0.2, and σEp ~ 0.1Ep. Using the distributions of Δs and β, the electron population index p is found to be consistent with the “moderately fast” scenario, in which fast- and slow-cooling scenarios cannot be distinguished. The physically motivated synchrotron-fitting function parameter distributions are Eb,1 = 129.6+132.2-32.4 keV, Eb,2 = 631.4+582.6-309.6 keV, β = -1.72+0.48-0.25 , and kT = 10.4+4.9-3.7 keV, with average errors σβ ~ 0.2, σEb,1 ~ 0.1Eb,1, σEb,2 ~ 0.4Eb,2, and σkT ~ 0.1kT. This synchrotron function requires the synchrotron injection and cooling break (i.e., Emin and Ecool) to be close to each other within a factor of ten, often in addition to a Planck function. Conclusions. A synchrotron model is found that is consistent with most of the time-resolved spectra for eight energetic Fermi GBM bursts with good high-energy photon statistics as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by including a thermal component or when an evolving magnetic field is accounted for.

AB - Context. We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. Aims. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Methods. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1 keV–1 MeV fluence f> 1.0 × 10-4 erg cm-2 and a signal-to-noise ratio level of S/N ≥ 10.0 above 900 keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index α, the high-energy power-law index β, the peak energy in the observed νFν spectrum Ep, and the difference between the low- and high-energy power-law indices Δs = α − β. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies Eb,1 and Eb,2, the middle segment power-law index β, and the Planck function temperature kT. Results. The Band function parameter distributions are α = -0.73+0.16-0.21, β =ي-2.13+0.28-0.56, Ep = 374.4+307.3-187.7 , , keV (log10Ep = 2.57+0.26-0.30), and Δs = 1.38+0.54-0.31 , with average errors σα ~ 0.1, σβ ~ 0.2, and σEp ~ 0.1Ep. Using the distributions of Δs and β, the electron population index p is found to be consistent with the “moderately fast” scenario, in which fast- and slow-cooling scenarios cannot be distinguished. The physically motivated synchrotron-fitting function parameter distributions are Eb,1 = 129.6+132.2-32.4 keV, Eb,2 = 631.4+582.6-309.6 keV, β = -1.72+0.48-0.25 , and kT = 10.4+4.9-3.7 keV, with average errors σβ ~ 0.2, σEb,1 ~ 0.1Eb,1, σEb,2 ~ 0.4Eb,2, and σkT ~ 0.1kT. This synchrotron function requires the synchrotron injection and cooling break (i.e., Emin and Ecool) to be close to each other within a factor of ten, often in addition to a Planck function. Conclusions. A synchrotron model is found that is consistent with most of the time-resolved spectra for eight energetic Fermi GBM bursts with good high-energy photon statistics as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by including a thermal component or when an evolving magnetic field is accounted for.

KW - gamma rays: stars, gamma-ray burst: general, radiation mechanisms: non-thermal, methods: data analysis

UR - http://dx.doi.org/10.1051/0004-6361/201424858

U2 - 10.1051/0004-6361/201424858

DO - 10.1051/0004-6361/201424858

M3 - Article

VL - 573

SP - A81

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

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