Scenarios for Ultrafast Gamma-Ray Variability in AGN

Abstract

We analyze three scenarios to address the challenge of ultrafast gamma-ray variability reported from active galactic nuclei. We focus on the energy requirements imposed by these scenarios: (i) external cloud in the jet, (ii) relativistic blob propagating through the jet material, and (iii) production of high-energy gamma-rays in the magnetosphere gaps. We show that while the first two scenarios are not constrained by the flare luminosity, there is a robust upper limit on the luminosity of flares generated in the black hole magnetosphere. This limit depends weakly on the mass of the central black hole and is determined by the accretion disk magnetization, viewing angle, and the pair multiplicity. For the most favorable values of these parameters, the luminosity for 5-minuteflares is limited by´-2 10 erg s 43 1, which excludes ablack hole magnetosphere origin of the flare detected from IC310. In the scopes of scenarios (i) and (ii), the jet power, which is required to explain the IC310 flare, exceeds the jet power estimated based on the radio data. To resolve this discrepancy in the framework of scenario (ii), it is sufficient to assume that the relativistic blobs are not distributed isotropically in the jet reference frame. A realization ofscenario (i) demands thatthe jet power during the flare exceedsby a factor 10 2 the power of the radio jet relevant to a timescale of 10 8 years.

Physics of Pair Producing Gaps in Black Hole Magnetospheres

“…The magnetospheric gap has been considered as possible candidate site for producing the rapid γ-ray variability seen from certain AGN, especially radio galaxies (e.g., Levinson & Rieger 2011;Aleksić et al 2014;Aharonian et al 2017;Katsoulakos & Rieger 2018). The most promising source seems to be M87 (Katsoulakos & Rieger 2018).…”

GRB 170817A Associated with GW170817: Multi-frequency Observations and Modeling of Prompt Gamma-Ray Emission

“…In the case of small angles (|1−cos θ| 1, but θ can be 1/Γ jet ), we can write Γ jet /δ = (α 2 + 1)/2 (Giannios et al 2010;Aharonian et al 2017), here α = θΓ jet and Equation (33) take the form…”

Electron transport with re-acceleration and radiation in the jets of X-ray binaries

“…Furthermore, the maximum amplitude of the magnetic fluctuation is to be ∼ 10 3 G within the acceleration zone, provided that we assume the ratio of the turbulent magnetic energy density to the ordered one as ζ = 1 and the inner boundary of acceleration zone as 10 4 R g . Besides, the characteristic temperature of background thermal electrons is considered as a low value of 0.001 in units of m e c 2 for the sake of simplicity (see also Aharonian, Barkov & Khangulyan 2017 for the physics in active galactic nuclei jets). On the contrary, one should treat more complex physical processes involved in a thermal plasma, such as thermal Comptonization, thermal synchrotron radiation, pair creation and annihilation (e.g.…”