Pulsars, transients and relativistic astrophysics

Abstract:

With the coincident detection of a gamma-ray flare and a neutrino from the blazar TXS 0506+056, active galactic nuclei (AGNs) have been put into focus as possible sources of the diffuse neutrino flux. We present a space and time-resolved model of the high-energy particle emission of a plasmoid assumed to travel along the axis of an AGN jet at relativistic speed. This was achieved by modifying the publicly available CRPROPA (version 3.1+) propagation framework that in our work is capable of being applied to source physics on sub-kpc scales. The propagation of a population of primary protons is modelled in a purely turbulent magnetic field and we take into account interactions of these protons with photons scattered from the accretion disc, synchrotron radiation emitted by ambient relativistic electrons, as well with themselves and with other ambient matter. Our model produces a PeV-neutrino flare caused mainly by photohadronic interactions of primaries with the accretion disc field. Secondary high-energy gamma-rays partly attenuate with the ambient photon fields whose combined optical depths achieve their minimal opacity for photons of around 10 TeV. Thus, our model is well capable of producing neutrino flares with a significantly reduced emission of gamma-rays in jets with a hadronic jet component that in the future can be fit to specific AGN flare scenarios.

Abstract:

We model the light curves of the novel and extremely luminous transient ASASSN-15lh at nine different frequencies, from infrared to ultraviolet photon energies, as an evolving relativistic disc produced in the aftermath of a tidal disruption event (TDE). Good fits to all nine light curves are simultaneously obtained when Macc ≃ 0.07 M⊙ is accreted on to a black hole of mass M ≃ 109 M⊙ and near-maximal rotation a/rg = 0.99. The best-fitting black hole mass is consistent with a number of existing estimates from galactic scaling relationships. If confirmed, our results represent the detection of one of the most massive rapidly spinning black holes to date, and are strong evidence for a TDE origin for ASASSN-15lh. This would be the first TDE to be observed in the disc-dominated state at optical and infrared frequencies.