Gamma-ray astronomy

Abstract:

The blazar PKS 0903 - 57 has recently been classified as a flat spectrum radio quasar at a redshift of z = 0.2621 . In March and April 2020, Fermi-LAT and AGILE reported tremendous activity in high-energy γ rays with the flux increasing by  ∼ 2 orders of magnitude compared to quiescence. The flare was observed with H.E.S.S. in very-high-energy γ rays for six nights with a total observation time of 13.1 h, resulting in the discovery of PKS 0903 - 57 in this energy band with an average flux of 1.5 × 10 − 10 ph cm − 2 s − 1 above an energy threshold of  ∼ 180 GeV corresponding to 60% of the Crab Nebula flux above the same threshold. The very-high-energy γ-ray flux was strongly variable. X-ray and optical data were collected with Swift and ATOM, and also indicate significant variability. The observed multiwavelength flux and spectral variability during the H.E.S.S. observation window suggest variability time scales on the order of a few hours and reveal complex correlation patterns. The lack of absorption beyond that of the extragalactic background light in the γ-ray domain suggests that the emission region was located outside of the broad-line region. A leptonic one-zone modeling of the six H.E.S.S. observation nights using the dusty torus as seed photons for the inverse-Compton scattering, results in a low magnetization of the emission region. This implies that shock acceleration is likely the main driver during the event.

Abstract:

DIPLODOCUS (Distribution-In-PLateaux methODOlogy for the CompUtation of transport equationS) is a framework being developed for the general transport of particle distribution functions through the seven dimensions of phase space, including forcing terms and interactions between particles. Following Paper I, which details the mathematical background, this second paper provides an overview of the numerical implementation in the form of the code package Diplodocus $.$ jl, written in Julia, including the description of a novel Monte-Carlo sampling technique for the pre-computation of anisotropic collision integrals. In addition to the discussion of numerical implementation, a selection of test cases are presented to examine the package’s capabilities. These test cases focus on micro-scale physical effects: binary collisions, emissive interactions and external forces that are relevant to the modelling of jetted astrophysical sources, such as Active Galactic Nuclei and X-Ray Binaries.

Abstract:

We present the discovery of radio emission from the Be/X-ray binary A0538−66 with the Australian Square Kilometre Array Pathfinder, and results from a subsequent weekly monitoring campaign with the MeerKAT radio telescope. A0538−66, located in the Large Magellanic Cloud, hosts a neutron star with a short spin period ( ms) in a highly eccentric -d orbit . Its rare episodes of super-Eddington accretion, rapid optical and X-ray flares, and other peculiar properties make it an interesting system among high-mass X-ray binaries. Our MeerKAT data reveal that it is also one of the most radio-luminous neutron star X-ray binaries observed to date, reaching (at 1.28 GHz), with radio emission that appears to be orbitally modulated. We consider several possible mechanisms for the radio emission, and place A0538−66 in context by comparing it to similar systems.