91̽��

Abstract:

Context. PKS 0346-27 is a low synchrotron peaked blazar at redshift 0.991. The very high energy (VHE; E > 100 GeV) spectra of blazars are always affected by γγ absorption by the extragalactic background light (EBL), and subsequently no blazars have been detected in VHE γ -rays at redshifts exceeding 1. Aims. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S.: to observe flaring high-redshift ( z ≳ 1) blazars. Importantly, extending the redshift range of VHE-detected blazars to z ≳ 1 will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. Methods. We report H.E.S.S. ToO and multi-wavelength observations of the blazar PKS 0346−27. We analysed and modelled the H.E.S.S. data together with simultaneous data from Fermi -LAT, Swift (XRT and UVOT), using single-zone leptonic and hadronic models. Results. PKS 0346-27 was detected by H.E.S.S. at a significance of 6.3 σ during one night on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux have been determined. No evidence for intra-night γ -ray variability has been found. A flare in high-energy ( E > 100 MeV) γ -rays detected by Fermi -LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source’s Eddington limit, although alternative (e.g. multi-zone) models cannot be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state spectral energy distribution. However, it requires implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of ≳80.

Abstract:

DIPLODOCUS (Distribution-In-PLateaux methODOlogy for the CompUtation of transport equationS) is a novel framework being developed for the mesoscopic modelling of astrophysical systems via the transport of particle distribution functions through the seven dimensions of phase space, including continuous forces and discrete interactions between particles. This first paper in a series provides an overview of the analytical framework behind the model, consisting of an integral formulation of the relativistic transport equations (Boltzmann equations) and a discretisation procedure for the particle distribution function (Distribution-In-Plateaux). The latter allows for the evaluation of anisotropic interactions, and generates a conservative numerical scheme for a distribution function’s transport through phase space.

Abstract:

Abstract Accreting systems can launch powerful outflows which interact with the surrounding medium. We combine new radio observations of the accreting neutron star X-ray binary (XRB) Circinus X-1 (Cir X-1) with archival radio observations going back 24 years. The ∼3 pc scale wide-angle radio and X-ray emitting caps found around Cir X-1 are identified as synchrotron emitting shocks with significant proper motion and morphological evolution on decade timescales. Proper motion measurements of the shocks reveal they are mildly relativistic and decelerating, with apparent velocity of 0.14c ± 0.03c at a propagation distance of 2 pc. We demonstrate that these shocks are likely powered by a hidden relativistic (≳ 0.3c) wide-angle conical outflow launched in 1972 ± 3, in stark contrast to known structures around other XRBs formed by collimated jets over 1000s of years. The minimum time-averaged power of the outflow required to produce the observed synchrotron emission is ∼0.1LEdd, while the time-averaged power required for the kinetic energy of the shocks is $\sim 40 \left(\frac{n}{10^{-2} \textrm{cm}^{-3}}\right)L_\textrm{Edd}$, where n is the average ambient medium number density. This reveals the outflow powering the shocks is likely significantly super-Eddington. We measure significant linear polarisation up to 52 ± 6% in the shocks demonstrating the presence of an ordered magnetic field of strength ∼200 μG. We show that the shocks are potential PeVatrons, capable of accelerating electrons to ∼0.7 PeV and protons to ∼20 PeV, and we estimate the injection and energetic efficiencies of electron acceleration in the shocks. Finally, we predict that next generation gamma-ray facilities may be able to detect hadronic signatures from the shocks.