Radiation Signatures of Sub-Larmor Scale Magnetic Fields

Abstract

Spontaneous rapid growth of strong magnetic fields is rather ubiquitous in high-energy density environments ranging from astrophysical sources (e.g., gamma-ray bursts and relativistic shocks), to reconnection, to laserplasma interaction laboratory experiments, where they are produced by kinetic streaming instabilities of the Weibel type. Relativistic electrons propagating through these sub-Larmor-scale magnetic fields radiate in the jitter regime, in which the anisotropy of the magnetic fields and the particle distribution have a strong effect on the produced radiation. Here we develop the general theory of jitter radiation, which includes (i) anisotropic magnetic fields and electron velocity distributions, (ii) the effects of trapped electrons and (iii) extends the description to large deflection angles of radiating particles thus establishing a cross-over between the classical jitter and synchrotron regimes. Our results are in remarkable agreement with the radiation spectra obtained from particle-in-cell simulations of the classical Weibel instability. Particularly interesting is the onset of the field growth, when the transient hard synchrotron-violating spectra are common as a result of the dominant role of the trapped population. This effect can serve as a distinct observational signature of the violent field growth in astrophysical sources and lab experiments. It is also interesting that a system with small-scale fields tends to evolve toward the small-angle jitter regime, which can, under certain conditions, dominate the overall emission of a source.

JITTER SELF-COMPTON PROCESS: GeV EMISSION OF GRB 100728A

“…This prevents us from further investigating the topologies of the turbulent and magnetic fields in detail. However, we can compare our result and the result of Reynolds et al (2010) and Medvedev et al (2011) in the one-dimensional case. For example, in the study of Medvedev et al (2011), the isotropic turbulence has the form of f (k) ∼ k −2β after the nonlinear evolution and the magnetic field is B 2 = f (k), while it is B 2 = k ζ p −1 in our work.…”

“…Therefore, in the one-dimensional case, we obtain β = (ζ p − 1)/2. Moreover, from the study of Medvedev et al (2011), we know that f (k) is strongly related to the topology of turbulence and the view angle θ . The jitter parameter is given as K = eBl cor /mc 2 , where l cor is the correlation scale, so we can clearly see that the jitter parameter is also strongly related to the topologies of the turbulent and magnetic fields.…”

“…Alternatively, we propose that the turbulent cascade process can also produce the random and small-scale magnetic field (Mao & Wang 2007. As the magnetic field may have a subLarmor length scale, the jitter radiation in this sub-Larmor scale magnetic field was fully studied by Medvedev et al (2011). The small-scale turbulent dynamo with large Reynolds numbers at a saturated state in a fluid flow was simulated by Schekochihin et al (2004).…”

Diffusion and radiation in magnetized collisionless plasmas with small-scale Whistler turbulence

“…It has been shown Medvedev (2006), Reville & Kirk (2010), Medvedev et al (2011) and Teraki & Takahara (2011) that mono-energetic ultrarelativistic electrons in this prescribed sub-Larmor-scale turbulence produce a flat angle-averaged spectrum below the spectral break and a power-law spectrum above the break, that is: 43) where the spectral break is ω j = γ 2 k min c, (2.44) which is called the jitter frequency. Similarly, the high-frequency break is…”

Radiation from particles moving in small-scale magnetic fields created in solid-density laser-plasma laboratory experiments

“…8,[31][32][33][34][35] We will show that the direct observation of mildly relativistic Weibler radiation may be feasible in the laboratory setting. We will focus our attention upon the experiment discussed in Ref.…”