Evaluating the Bulk Lorentz Factors of Outflow Material: Lessons Learned from the Extremely Energetic Outburst GRB 160625B

Wang, Yuan-Zhu; Wang, Hao; Zhang, Shuai; Liang, Yun-Feng; Jin, Zhi-Ping; He, Hao-Ning; Liao, Neng-Hui; Fan, Yi‐Zhong; Wei, Da-Ming

doi:10.3847/1538-4357/aa56c6

Cited by 18 publications

(20 citation statements)

References 46 publications

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“…We note, however, that a spectral analysis of the precursor is reported by Preece et al (2014), who find consistency with synchrotron emission. One of the GRBs included in our sample, GRB 160625B, was already analysed in Ravasio et al (2018), who identified a clear spectral break and a good consistency of the overall spectrum with synchrotron radiation in a marginally fast cooling regime (see also Zhang et al 2018;Wang et al 2017;Lü et al 2017). For homogeneity, here we reanalyse its spectra with the same procedure adopted in this work for the other bursts.…”

Section: The Samplementioning

confidence: 95%

Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

Ravasio

Ghirlanda

Nava

et al. 2019

A&A

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The long-lasting tension between the observed spectra of gamma-ray bursts (GRBs) and the predicted synchrotron emission spectrum might be solved if electrons do not completely cool. Evidence of incomplete cooling was recently found in Swift GRBs with prompt observations down to 0.1 keV, and in one bright Fermi burst, GRB 160625B. Here we systematically search for evidence of incomplete cooling in the spectra of the ten brightest short and long GRBs observed by Fermi. We find that in eight out of ten long GRBs there is compelling evidence of a low-energy break (below the peak energy) and good agreement with the photon indices of the synchrotron spectrum (respectively -2/3 and -3/2 below the break and between the break and the peak energy). Interestingly, none of the ten short GRBs analysed shows a break, but the low-energy spectral slope is consistent with -2/3. In a standard scenario, these results imply a very low magnetic field in the emission region (B ∼ 10 G in the comoving frame), at odd with expectations.

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Section: The Samplementioning

confidence: 95%

Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

Ravasio

Ghirlanda

Nava

et al. 2019

A&A

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“…Covino & Gotz 2016). A study of the time variability characteristics is very important because bright GRBs whose spectra have been studied in great detail often found to have spectra deviating significantly from the standard Band function conventionally used to model the GRB spectra (Abdo et al 2009;Izzo et al 2012;Ackermann et al 2010;Vianello et al 2017;Wang et al 2017).…”

Section: Introductionmentioning

confidence: 99%

AstroSat-CZTI Detection of Variable Prompt Emission Polarization in GRB 171010A

Chand

Chattopadhyay

Oganesyan

et al. 2019

ApJ

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We present spectro-polarimetric analysis of GRB 171010A using data from AstroSat, Fermi, and Swift, to provide insights into the physical mechanisms of the prompt radiation and the jet geometry.Prompt emission from GRB 171010A was very bright (fluence > 10 −4 ergs cm −2 ) and had a complex structure composed of the superimposition of several pulses. The energy spectra deviate from the typical Band function to show a low energy peak ∼ 15 keV -which we interpret as a power-law with two breaks, with a synchrotron origin. Alternately, the prompt spectra can also be interpreted as Comptonized emission, or a blackbody combined with a Band function. Time-resolved analysis confirms the presence of the low energy component, while the peak energy is found to be confined in the range of 100-200 keV.Afterglow emission detected by Fermi-LAT is typical of an external shock model, and we constrain the initial Lorentz factor using the peak time of the emission. Swift-XRT measurements of the afterglow show an indication for a jet break, allowing us to constrain the jet opening angle to > 6 • .Detection of a large number of Compton scattered events by AstroSat-CZTI provides an opportunity to study hard X-ray polarization of the prompt emission. We find that the burst has high, time-variable polarization, with the emission have higher polarization at energies above the peak energy.We discuss all observations in the context of GRB models and polarization arising due to due to physical or geometric effects: synchrotron emission from multiple shocks with ordered or random magnetic fields, Poynting flux dominated jet undergoing abrupt magnetic dissipation, sub-photospheric dissipation, a jet consisting of fragmented fireballs, and the Comptonization model.

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“…The prompt emission is discussed in detail in Zhang et al (2016), Wang et al (2017), and Lü et al (2017).…”

Section: G-raysmentioning

confidence: 99%

A Reverse Shock and Unusual Radio Properties in GRB 160625B

Alexander

Laskar

Berger

et al. 2017

ApJ

133

164

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We present multi-wavelength observations and modeling of the exceptionally bright long γ-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of 3 . 6 j q »  and kinetic energy of E 2 10»´erg, propagating into a low-density (n 5 10 5 »´-cm −3 ) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of 100 0  G and an ejecta magnetization of R 1 100 B » -. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

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Evaluating the Bulk Lorentz Factors of Outflow Material: Lessons Learned from the Extremely Energetic Outburst GRB 160625B

Cited by 18 publications

References 46 publications

Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

AstroSat-CZTI Detection of Variable Prompt Emission Polarization in GRB 171010A

A Reverse Shock and Unusual Radio Properties in GRB 160625B

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