Phenomenology of Reverse-Shock Emission in the Optical Afterglows of Gamma-Ray Bursts

Japelj, J.; Kopač, D.; Kobayashi, S.; Harrison, R. M.; Guidorzi, C.; Virgili, F. J.; Mundell, C. G.; Melandri, A.; Gomboc, A.

doi:10.1088/0004-637x/785/2/84

Cited by 63 publications

(81 citation statements)

References 326 publications

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“…17 This is, of course, within the same time period that emission from a reverse shock might be expected (e.g., Sari & Piran 1999a;Japelj et al 2014), and extending our simulations to earlier times should allow us to characterize the rise time of the emission-assuming, of course, that these energies are not absorbed through the SSA process.…”

Section: Photon Spectramentioning

confidence: 77%

Nonlinear Particle Acceleration and Thermal Particles in GRB Afterglows

Warren

Ellison

Barkov

et al. 2017

ApJ

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The standard model for GRB afterglow emission treats the accelerated electron population as a simple power law, ( ) µ -N E E p for  p 2. However, in standard Fermi shock acceleration, a substantial fraction of the swept-up particles do not enter the acceleration process at all. Additionally, if acceleration is efficient, then the nonlinear back-reaction of accelerated particles on the shock structure modifies the shape of the nonthermal tail of the particle spectra. Both of these modifications to the standard synchrotron afterglow impact the luminosity, spectra, and temporal variation of the afterglow. To examine the effects of including thermal particles and nonlinear particle acceleration on afterglow emission, we follow a hydrodynamical model for an afterglow jet and simulate acceleration at numerous points during the evolution. When thermal particles are included, we find that the electron population is at no time well fitted by a single power law, though the highest-energy electrons are; if the acceleration is efficient, then the power-law region is even smaller. Our model predicts hard-soft-hard spectral evolution at X-ray energies, as well as an uncoupled X-ray and optical light curve. Additionally, we show that including emission from thermal particles has drastic effects (increases by factors of 100 and 30, respectively) on the observed flux at optical and GeV energies. This enhancement of GeV emission makes afterglow detections by future γ-ray observatories, such as CTA, very likely.

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Section: Photon Spectramentioning

confidence: 77%

Nonlinear Particle Acceleration and Thermal Particles in GRB Afterglows

Warren

Ellison

Barkov

et al. 2017

ApJ

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“…This favors the reverse shock detection in a good fraction of GRBs (e.g. Gomboc et al 2008;Harrison & Kobayashi 2013;Japelj et al 2014;Gao et al 2015). Since the upstream of RS is the ejecta from the central engine, a high R B value of GRB 140512A may hint a strongly magnetized central engine of this GRB (e.g., Fan et al 2002;Zhang et al 2003a;Zhang & Yan 2011;Lü et al 2014;.…”

Section: Conclusion and Discussionmentioning

confidence: 90%

Very Bright Prompt and Reverse Shock Emission of GRB 140512a

Huang

Xin

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.

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“…Bright optical flashes are now ruled out by observations in many events, while other events show complicated optical light curves that, like the prompt γ-ray emission, may originate instead from internal shocks (Kopač et al 2013;Japelj et al 2014). Some authors have proposed that RS emission may be easier to observe at longer wavelengths, where the emission peaks on timescales of days (Mundell et al 2007;Melandri et al 2010;Kopač et al 2015).…”

Section: Introductionmentioning

confidence: 99%

A Reverse Shock and Unusual Radio Properties in GRB 160625B

Alexander

Laskar

Berger

et al. 2017

ApJ

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132

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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Phenomenology of Reverse-Shock Emission in the Optical Afterglows of Gamma-Ray Bursts

Cited by 63 publications

References 326 publications

Nonlinear Particle Acceleration and Thermal Particles in GRB Afterglows

Nonlinear Particle Acceleration and Thermal Particles in GRB Afterglows

Very Bright Prompt and Reverse Shock Emission of GRB 140512a

A Reverse Shock and Unusual Radio Properties in GRB 160625B

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