Relativistic Shocks: Particle Acceleration and Magnetization

Sironi, Lorenzo; Keshet, Uri; Lemoine, Martin

doi:10.1007/s11214-015-0181-8

Cited by 219 publications

(166 citation statements)

References 129 publications

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“…It indicates that only ∼ 1% electrons are accelerated and they carry ∼ 10% of the energy when they cross the shock. This should correspond to the cases in which the relativistic electron-ion shock is of low magnetizations (σ ≤ 10 −3 ) according to the simulations of Sironi & Spitkovsky (2011) and Sironi et al (2015).…”

Section: Discussionmentioning

confidence: 77%

“…Previous studies indicate that η p ≥ 10 should be satisfied for the internal shock model to explain the GRB spectra (see Kumar & Zhang 2015 for a review). Whether this requirement can be fulfilled within the simulation of collisionless ionelectron shocks is still under debate (Sironi et al 2015). This issue goes beyond the scope of our current study.…”

Section: Constraints From Observationsmentioning

confidence: 87%

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Low-energy Spectra of Gamma-Ray Bursts from Cooling Electrons

Geng

Huang

et al. 2018

ApJS

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The low-energy spectra of gamma-ray bursts' (GRBs) prompt emission are closely related to the energy distribution of electrons, which is further regulated by their cooling processes. We develop a numerical code to calculate the evolution of the electron distribution with given initial parameters, in which three cooling processes (i.e., adiabatic, synchrotron and inverse Compton cooling) and the effect of decaying magnetic field are coherently considered. A sequence of results are presented by exploring the plausible parameter space for both the fireball and the Poynting-flux-dominated regime. Different cooling patterns for the electrons can be identified and they are featured by a specific dominant cooling mechanism. Our results show that the hardening of the low-energy spectra can be attributed to the dominance of synchrotron self-Compton cooling within the internal shock model, or to decaying synchrotron cooling within the Poynting-flux-dominated jet scenario. These two mechanisms can be distinguished by observing the hard low-energy spectra of isolated short pulses in some GRBs. The dominance of adiabatic cooling can also lead to hard low-energy spectra when the ejecta is moving at an extreme relativistic speed. The information from the time-resolved low-energy spectra can help to probe the physical characteristics of the GRB ejecta via our numerical results.

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Section: Discussionmentioning

confidence: 77%

Section: Constraints From Observationsmentioning

confidence: 87%

Low-energy Spectra of Gamma-Ray Bursts from Cooling Electrons

Geng

Huang

et al. 2018

ApJS

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“…We estimate that the strongest shock in our slow disturbance cases can only reach a nonthermal particle spectrum of power-law index of ∼4, which is too soft to fit the general blazar SEDs. In addition, relativistic collisionless shocks in the highly magnetized regime may be unable to generate fluctuating magnetic fields and hence inhibit Fermi acceleration (e.g., Sironi et al 2015). Therefore, a slow shock/disturbance may not efficiently accelerate nonthermal particles that are necessary to generate a flare.…”

Section: Discussion and Summarymentioning

confidence: 99%

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Zhang

Deng

et al. 2016

ApJ

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The optical radiation and polarization signatures in blazars are known to be highly variable during flaring activities. It is frequently argued that shocks are the main driver of the flaring events. However, the spectral variability modelings generally lack detailed considerations of the self-consistent magnetic field evolution modeling; thus, so far the associated optical polarization signatures are poorly understood. We present the first simultaneous modeling of the optical radiation and polarization signatures based on 3D magnetohydrodynamic simulations of relativistic shocks in the blazar emission environment, with the simplest physical assumptions. By comparing the results with observations, we find that shocks in a weakly magnetized environment will largely lead to significant changes in the optical polarization signatures, which are seldom seen in observations. Hence an emission region with relatively strong magnetization is preferred. In such an environment, slow shocks may produce minor flares with either erratic polarization fluctuations or considerable polarization variations, depending on the parameters; fast shocks can produce major flares with smooth polarization angle rotations. In addition, the magnetic fields in both cases are observed to actively revert to the original topology after the shocks. All these features are consistent with observations. Future observations of the radiation and polarization signatures will further constrain the flaring mechanism and the blazar emission environment.

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“…We explore the predicted X-ray signatures of collimated θ j =5°outflows with ò e =0.1 and ò B =0.01 (as derived from first-principle simulations of relativistic shocks, e.g., Sironi et al 2015), isotropic kinetic energy in the range E 10 10 erg k,iso 52 55 = -, environment density in the range n 10 10 cm Marshall et al 2004;van Loon et al 2005;Crowther 2007;Massey et al 2015). Type IIb SNe (blue diamonds) explode in the densest environments, while SNe with broad spectroscopic features (orange squares and triangles) are associated with the lowest-density media.…”

Section: Constraints On On-axis and Off-axis Collimated And Noncollimmentioning

confidence: 99%

Results from a Systematic Survey of X-Ray Emission from Hydrogen-poor Superluminous SNe

Margutti

Chornock

Metzger

et al. 2018

ApJ

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We present the results from a sensitive X-ray survey of 26 nearby hydrogen-poor superluminous supernovae (SLSNe-I) with Swift, Chandra, and XMM. This data set constrains the SLSN evolution from a few days until ∼2000 days after explosion, reaching a luminosity limit L x ∼10 40 erg s −1 and revealing the presence of significant X-ray emission possibly associated with PTF 12dam. No SLSN-I is detected above L 10 erg s-, suggesting that the luminous X-ray emission L x ∼10 45 erg s −1 associated with SCP 60F6 is not common among SLSNe-I. We constrain the presence of off-axis gamma-ray burst (GRB) jets, ionization breakouts from magnetar engines and the density in the sub-parsec environments of SLSNe-I through inverse Compton emission. The deepest limits rule out the weakest uncollimated GRB outflows, suggesting that if the similarity of SLSNe-I with GRB/SNe extends to their fastest ejecta, then SLSNe-I are either powered by energetic jets pointed far away from our line of sight (θ>30°), or harbor failed jets that do not successfully break through the stellar envelope. Furthermore, if a magnetar central engine is responsible for the exceptional luminosity of SLSNe-I, our X-ray analysis favors large magnetic fields B 2 10 14 >´G and ejecta masses M M 3 ej > ☉ , in agreement with optical/UV studies. Finally, we constrain the pre-explosion mass-loss rate of stellar progenitors of SLSNe-I. For PTF 12dam we infer M M 2 10 yr 5 1 <´--☉, suggesting that the SN shock interaction with an extended circumstellar medium is unlikely to supply the main source of energy powering the optical transient and that some SLSN-I progenitors end their lives as compact stars surrounded by a low-density medium similar to long GRBs and type Ib/c SNe.

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Relativistic Shocks: Particle Acceleration and Magnetization

Cited by 219 publications

References 129 publications

Low-energy Spectra of Gamma-Ray Bursts from Cooling Electrons

Low-energy Spectra of Gamma-Ray Bursts from Cooling Electrons

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Results from a Systematic Survey of X-Ray Emission from Hydrogen-poor Superluminous SNe

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