Multi-Wavelength Observations of GRB 111228a and Implications for the Fireball and Its Environment

et al. 2016

ApJ

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We report our observations of very bright prompt optical and reverse shock (RS) optical emission of GRB 140512A and analyze its multi-wavelength data observed with the Swift and Fermi missions. It is found that the joint optical-X-ray-gamma-ray spectrum with our first optical detection (R=13.09 mag) at T 0 + 136 seconds during the second episode of the prompt gamma-rays can be fit by a single power-law with index −1.32 ± 0.01. Our empirical fit to the afterglow lightcurves indicates that the observed bright optical afterglow with R=13.00 mag at the peak time is consistent with predictions of the RS and forward shock (FS) emission of external shock models. Joint optical-X-ray afterglow spectrum is well fit with an absorbed single power-law, with an index evolving with time from −1.86 ± 0.01 at the peak time to −1.57 ± 0.01 at late epoch, which could be due to the evolution of the ratio of the RS to FS emission fluxes. We fit the lightcurves with standard external models, and derive the physical properties of the outflow. It is found that the ratio R B ≡ ǫ B,r /ǫ B,f is 8187, indicating a high magnetization degree in the RS region. Measuring the relative radiation efficiency with R e ≡ ǫ e,r /ǫ e,f , we have R e = 0.02, implying the radiation efficiency of the RS is much lower than that in FS. We also show that the R B of GRBs 990123, 090102, and 130427A are similar to that of GRB 140512A and their apparent difference may be mainly attributed to the difference of the jet kinetic energy, initial Lorentz factor, and medium density among them.

Section: Theoretically Modeling the Afterglow Lightcurvesmentioning

confidence: 66%

Very Bright Prompt and Reverse Shock Emission of GRB 140512a

Huang

et al. 2016

ApJ

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“…To constrain these parameters, a Monte Carlo method is utillized to search for the best fit parameter set. Following the technique and the procedure (Xin et al, 2016b), the fitting results for GRB 140629A are illustrated in Figure 4, and the derived parameters and their probability distribution are shown in Figure 5. The 1σ confidence level estimated for the micro physical parameters are Γ 0 = 315 +44 −34 , ǫ e = (1.2 ± 0.1) × 10 −2 , ǫ B = (1.0 ± 0.1) × 10 −6 , n = 60 ± 9 cm −3 , E K,iso = (1.8 ± 0.1) × 10 55 erg, θ j = 0.04 +0.02 −0.01 rad and p = 2.72 ± 0.07.…”

Section: Afterglow Light Curve Fits With the External Shock Modelmentioning

confidence: 99%

Section: Afterglow Light Curve Fits With the External Shock Modelmentioning

confidence: 99%

Photometric and Spectroscopic Observations of GRB 140629A

Zhong

Liang

et al. 2018

ApJ

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We present our optical photometric and spectroscopical observations of GRB 140629A. A redshift of z = 2.275 ± 0.043 is measured through the metal absorption lines in our spectroscopic data. Using our photometric data and multiple observational data observed with other telescopes, we show that its optical light curve is well interpreted with the standard forward shock models in the thin shell case. Its optical-X-ray afterglow spectrum is jointly fitted with a single powerlaw function, yielding a photon index of −1.90 ± 0.05. The optical extinction and neutral hydrogen absorption of the GRB host galaxy are negligible. The fit to the light curve with the standard models shows that the ambient density is 60 ± 9 cm −3 and the GRB radiating efficiency is as low as ∼ 0.24%, likely indicating a baryonic-dominated ejecta of this GRB. This burst agrees well with the L p,iso − E ′ p − Γ 0 relation, but confidently violates those empirical relations involving geometric corrections (or jet break time). This gives rise to an issue of possible selection effect on these relations since the jet opening angle of this GRB is extremely narrow (0.04 rad).

“…Well-sampled multi-wavelength lightcurves in broad temporal coverage from very early to late epochs are valuable for modeling the lightcurves and revealing the properties of the GRB jets and even the GRB central engines as well as the progenitors (e.g., Xin et al 2016). This paper reports our very early optical observations for GRB 110530A and detailed modeling for the optical and X-ray afterglow lightcurves.…”

Section: Introductionmentioning

confidence: 99%

GRB 110530a: Peculiar Broad Bump and Delayed Plateau in Early Optical Afterglows

Zhong

Liang

et al. 2016

ApJ

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We report our very early optical observations of GRB 110530A and investigate its jet properties together with its X-ray afterglow data. A peculiar broad onset bump followed by a plateau is observed in its early R band afterglow lightcurve. The optical data in the other bands and the X-ray data are well consistent with the temporal feature of the R band lightcurve. Our joint spectral fits of the optical and X-ray data show that they are in the same regime, with a photon index of ∼ 1.70. The optical and X-ray afterglow lightcurves are well fitted with the standard external shock model by considering a delayed energy injection component. Based on our modeling results, we find that the radiative efficiency of the GRB jet is ∼ 1% and the magnetization parameter of the afterglow jet is < 0.04 with the derived extremely low ǫ B (the fraction of shock energy to magnetic field) of (1.64 ± 0.25) × 10 −6 . These results indicate that the jet may be matter dominated. Discussion on delayed energy injection from accretion of late fall-back material of its pre-supernova star is also presented.