Relativistic turbulence with strong synchrotron and synchrotron self-Compton cooling

Journal Article · 19 March 2018 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/sty721 · OSTI ID:1540627

Uzdensky, D. A. ^[1]

---

1. Univ. of Colorado, Boulder, CO (United States); Inst. for Advanced Study, Princeton, NJ (United States)

Many relativistic plasma environments in high-energy astrophysics, including pulsar wind nebulae (PWN), hot accretion flows on to black holes, relativistic jets in active galactic nuclei and gamma-ray bursts, and giant radio lobes, are naturally turbulent. The plasma in these environments is often so hot that synchrotron and inverse-Compton (IC) radiative cooling becomes important. In this paper, we investigate the general thermodynamic and radiative properties (and hence the observational appearance) of an optically thin relativistically hot plasma stirred by driven magnetohydrodynamic (MHD) turbulence and cooled by radiation. We find that if the system reaches a statistical equilibrium where turbulent heating is balanced by radiative cooling, the effective electron temperature tends to attain a universal value θ=kT_e/m_ec²~ 1/√τ_T, where τT = n_eσT^L « 1 is the system's Thomson optical depth, essentially independent of the strength of turbulent driving and hence of the magnetic field. This is because both MHD turbulent dissipation and synchrotron cooling are proportional to the magnetic energy density. We also find that synchrotron self-Compton (SSC) cooling and perhaps a few higher order IC components are automatically comparable to synchrotron in this regime. The overall broad-band radiation spectrum then consists of several distinct components (synchrotron, SSC, etc.), well separated in photon energy (by a factor ~τ_T^-1) and roughly equal in power. The number of IC peaks is checked by Klein–Nishina effects and depends logarithmically on τT and the magnetic field. We also examine the limitations due to synchrotron self-absorption, explore applications to Crab PWN and blazar jets, and discuss links to radiative magnetic reconnection.

• Research Organization: Univ. of Colorado, Boulder, CO (United States); Univ. of New Hampshire, Durham, NH (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0008409; SC0008655
• OSTI ID: 1540627
• Journal Information: Monthly Notices of the Royal Astronomical Society, Vol. 477, Issue 3; ISSN 0035-8711
• Publisher: Royal Astronomical SocietyCopyright Statement
• Country of Publication: United States
• Language: English