Synthetic gamma-ray lightcurves of Kerr black-hole magnetospheric activity from particle-in-cell simulations

Abstract

Context. The origin of ultra-rapid flares of very high-energy radiation from active galactic nuclei remains elusive. Magnetospheric processes, occurring in the close vicinity of the central black hole, could account for these flares. Aims. We aim to bridge the gap between simulations and observations by synthesizing gamma-ray lightcurves in order to characterize the activity of a black-hole magnetosphere, using kinetic simulations. Methods. We perform global axisymmetric two-dimensional general-relativistic particle-in-cell simulations of a Kerr black-hole magnetosphere. We include a self-consistent treatment of radiative processes and plasma supply, as well as a realistic magnetic configuration, with a large-scale equatorial current sheet. We couple our particle-in-cell code with a ray-tracing algorithm, in order to produce synthetic lightcurves. Results. These simulations show a highly dynamic magnetosphere, as well as very efficient dissipation of the magnetic energy. An external supply of magnetic flux is found to maintain the magnetosphere in a dynamic state, otherwise the magnetosphere settles in a quasi-steady Wald-like configuration. The dissipated energy is mostly converted to gamma-ray photons. The lightcurves at low viewing angle (face-on) mainly trace the spark gap activity and exhibit high variability. On the other hand, no significant variability is found at high viewing angle (edge-on), where the main contribution comes from the reconnecting current sheet. Conclusions. We observe that black-hole magnetospheres with a current sheet are characterized by a very high radiative efficiency. The typical amplitude of the flares in our simulations is lower than what is detected in active galactic nuclei. Such flares could result from the variation of parameters external to the black hole.

Gamma-radiation sky maps from compact binaries

“…Such phenomena are likely to cause additional high-energy emission (see e.g. [169]). A method which attempts to determine the CS based solely on tracing field lines from large distances will likely fail to capture this additional emission region.…”

Pair-Regulated Klein-Nishina Relativistic Magnetic Reconnection with Applications to Blazars and Accreting Black Holes

“…Due to high magnetic and radiation energy densities, reconnection in relativistic compact object environments is likely to be highly radiative, and much recent work on radiative reconnection is related to these systems, including studies of: pulsar winds (Pétri 2012;Cerutti & Philippov 2017;Cerutti et al 2020), pulsar wind nebulae Cerutti et al 2012aCerutti et al , 2013Cerutti et al , 2014aYuan et al 2016), pulsar magnetospheres (Lyubarskii 1996;Uzdensky & Spitkovsky 2014;Philippov et al 2015;Cerutti et al 2016;Philippov & Spitkovsky 2018;Hakobyan et al 2019), magnetar magnetospheres (Schoeffler et al 2019), gamma-ray bursts (McKinney & Uzdensky 2012), accreting black holes (Beloborodov 2017;Werner et al 2019;Sironi & Beloborodov 2020), blazars (Nalewajko et al 2011(Nalewajko et al , 2012(Nalewajko et al , 2018Ortuño-Macías & Nalewajko 2020;Mehlhaff et al 2020), and black hole magnetospheres (Parfrey et al 2019;Crinquand et al 2020a). Some studies have not focused on a single object class, but have still been motivated by some combination of the above (e.g.…”

Magnetic Hair and Reconnection in Black Hole Magnetospheres

“…The evolution of Φ is estimated analytically using Faraday's law, and assuming a constant reconnection rate on the equator at the stagnation surface (see supplement) [23]. In this toy model Φ decays exponentially on a timescale τ ≈ 3r g / v θ , with v θ the θ component of the plasma 3-velocity in the orthonormal tetrad basis (Fig.…”