Gamma-ray astronomy

Abstract:

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). At TeV energies and above gamma rays can induce electromagnetic cascades, whose charged component is sensitive to intervening intergalactic magnetic fields (IGMFs). When interpreting gamma-ray measurements in the energy range between a few GeV and hundreds of TeV, one has to carefully account for effects due to IGMFs, which depend on their strength and power spectrum. Therefore, gamma-ray-induced electromagnetic cascades can be used as probes of cosmic magnetism, since their arrival distribution as well as spectral and temporal properties can provide unique information about IGMFs, whose origin and properties are currently poorly understood. In this contribution we present an efficient three-dimensional Monte Carlo code for simulations of gamma-ray propagation. We focus on the effects of different configurations of IGMFs, in particular magnetic helicity and the power spectrum of stochastic fields, on the morphology of the arrival directions of gamma rays, and discuss the prospects for detecting pair haloes around distant blazars.

Abstract:

The connection between accretion and jet production in accreting white dwarf binary systems, especially dwarf novae, is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. Here we present densely-sampled radio coverage, obtained with the Arcminute MicroKelvin Imager Large Array, of the dwarf nova SS Cyg during its February 2016 anomalous outburst. The outburst displayed a slower rise (3 days mag^-1) in the optical than typical ones, and lasted for more than 3 weeks. Rapid radio flaring on timescales <1 hour was seen throughout the outburst. The most intriguing behavior in the radio was towards the end of the outburst where a fast, luminous (“giant”), flare peaking at ~20 mJy and lasting for 15 minutes was observed. This is the first time that such a flare has been observed in SS Cyg, and insufficient coverage could explain its non-detection in previous outbursts. These data, together with past radio observations, are consistent with synchrotron emission from plasma ejection events as being the origin of the radio flares. However, the production of the giant flare during the declining accretion rate phase remains unexplained within the standard accretion-jet framework and appears to be markedly different to similar patterns of behavior in X-ray binaries.

Abstract:

The measurement of γ-rays originating from active galactic nuclei offers the unique opportunity to study the propagation of very-high-energy photons over cosmological distances. Most prominently, γ-rays interact with the extragalactic background light (EBL) to produce e+e- pairs, imprinting an attenuation signature on γ-ray spectra. The e+e- pairs can also induce electromagnetic cascades whose detectability in γ-rays depends on the intergalactic magnetic field (IGMF). Furthermore, physics beyond the Standard Model such as Lorentz invariance violation (LIV) or oscillations between photons and weakly interacting sub-eV particles (WISPs) could affect the propagation of γ-rays. The future Cherenkov Telescope Array (CTA), with its unprecedented γ-ray source sensitivity, as well as enhanced energy and spatial resolution at very high energies, is perfectly suited to study cosmological effects on γ-ray propagation. Here, we present first results of a study designed to realistically assess the capabilities of CTA to probe the EBL, IGMF, LIV, and WISPs.

Abstract:

The Giant Radio Array for Neutrino Detection (GRAND) aims at detecting ultra-high energy extraterrestrial neutrinos via the extensive air showers induced by the decay of tau leptons created in the interaction of neutrinos under the Earth's surface. Consisting of an array of ∼105 radio antennas deployed over ∼2 × 105km2, GRAND plans to reach, for the first time, an all-flavor sensitivity of ∼1.5 × 10-10GeVcm-2 s-1 sr-1 above 5 × 1017 eV and a sub-degree angular resolution, beyond the reach of other planned detectors. We describe here preliminary designs and simulation results, plans for the ongoing, staged approach to the construction of GRAND, and the rich research program made possible by GRAND's design sensitivity and angular resolution.

Abstract:

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). The Giant Radio Array for Neutrino Detection (GRAND) aims at detecting ultra-high energy extraterrestrial neutrinos via the extensive air showers induced by the decay of tau leptons created in the interaction of neutrinos under the Earth's surface. Consisting of an array of ∼10 5 radio antennas deployed over ∼2 × 10 5 km 2 , GRAND plans to reach, for the first time, an all-flavor sensitivity of ∼1.5 × 10 -10 GeVcm -2 s -1 sr -1 above 5 × 10 17 eV and a sub-degree angular resolution, beyond the reach of other planned detectors. We describe here preliminary designs and simulation results, plans for the ongoing, staged approach to the construction of GRAND, and the rich research program made possible by GRAND's design sensitivity and angular resolution.