Abstracts of Interest
Selected by:
Gavin Rowell
Abstract: 2203.06142
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Full Text: [ PostScript, PDF]
Title:Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies
Download PDFAbstract: In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $\sigma_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the $5.0\,\sigma$ tension between the {\it Planck} CMB estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the {\it Planck} CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density $\Omega_m$, and the amplitude or rate of the growth of structure ($\sigma_8,f\sigma_8$). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the $H_0$--$S_8$ tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals.[Abridged]
Abstract: 2203.05839
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Full Text: [ PostScript, PDF]
Title:Inter-Calibration of Atmospheric Cherenkov Telescopes with UAV-based Airborne Calibration System
Download PDFAbstract: The recent advances in the flight capability of remotely piloted aerial vehicles (here after referred to as UAVs) have afforded the astronomical community the possibility of a new telescope calibration technique: UAV-based calibration. Building upon a feasibility study which characterised the potential that a UAV-based calibration system has for the future Cherenkov Telescope Array, we created a first-generation UAV-calibration prototype and undertook a field-campaign of inter-calibrating the sensitivity of the H.E.S.S. telescope array with two successful calibration flights. In this paper we report the key results of our first test campaign: firstly, by comparing the intensity of the UAV-calibration events, as recorded by the individual HESS-I cameras, we find that a UAV-based inter-calibration is consistent with the standard muon inter-calibration technique at the level of \SI{5.4}{\%} and \SI{5.8}{\%} for the two individual UAV-calibration runs. Secondly, by comparing the position of the UAV-calibration signal on the camera focal plane, for a variety of telescope pointing models, we were able to constrain the pointing accuracy of the HESS-I telescopes at the tens of arc-second accuracy level. This is consistent with the pointing accuracy derived from other pointing calibration methods. Importantly both the inter-calibration and pointing accuracy results were achieved with a first-generation UAV-calibration prototype, which eludes to the potential of the technique and highlights that a UAV-based system is a viable calibration technique for current and future ground-based $\gamma$-ray telescope arrays.
Abstract: 2203.05537
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Full Text: [ PostScript, PDF]
Title:Supernova remnant G46.8-0.3, a new case of interaction with molecular material
Download PDFAbstract: We present the first detailed study on the Galactic supernova remnant (SNR) G46.8-0.3 and its environment since its discovery more than 50 years ago. With new flux measurements from radio surveys plus a compilation from the literature we created an improved integrated radio spectrum of G46.8-0.3, which is well fitted by a simple power-law with an index alpha = -0.535 +/- 0.012, then excluding the presence of absorption by abundant ionised gas in the line of sight, or in the SNR's proximity. The analysis of local changes in the radio spectral index across G46.8-0.3 suggests a slight steepening at about 1 GHz, which does not impact on the integrated spectrum of the source. From atomic hydrogen (HI) spectra we placed the remnant at 8.7 +/- 1.0 kpc, and revisited the distance to the nearby HII region G046.495-00.241 to 7.3 +/- 1.2 kpc. From evolutionary models and our distance estimate, we conclude G46.8-0.3 is a middle-aged ($\sim$1 x 10^4 yr) SNR. We recognised several 12CO and 13CO molecular structures in the proximity of the remnant and used combined CO-HI profiles to derive the kinematic distances to these features and characterise their physical properties. We also provided compelling evidences for environmental molecular clouds physically linked to G46.8-0.3 at its centre, on its eastern edge, and towards the northern and southwestern rims on the far side of the SNR shell. Our study does not confirm that the remnant is embedded in a molecular cavity as previously suggested. G46.8-0.3 shows a line-of-sight coincidence with the gamma-ray source 4FGL J1918.1+1215c, detected at GeV energies by the space telescope Fermi. A rough analysis based on the properties of the interstellar matter close G46.8-0.3 indicates that the GeV gamma-rays photons detected in direction to the SNR can be plausibly attributed to hadronic collisions and/or bremsstrahlung radiation.
Abstract: 2203.05458
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Full Text: [ PostScript, PDF]
Title:The H.E.S.S. transients follow-up system
Download PDFAbstract: Observations of astrophysical transients have brought many novel discoveries and provided new insights into physical processes at work under extreme conditions in the Universe. Multi-wavelength and multi-messenger observations of variable objects require dedicated procedures and follow-up systems capable of digesting and reacting to external alerts to execute coordinated follow-ups. The main functions of such follow-up systems are the processing, filtering, and ranking of incoming alerts, the fully automated rapid execution of the observations according to an observation strategy tailored to the instrument, and real-time data analysis with feedback to the operators and other instruments. H.E.S.S. has been searching for transient phenomena since its inauguration in 2003. In this paper, we describe the transients follow-up system of H.E.S.S, which became operational in 2016. The transients follow-up system allows H.E.S.S. to conduct a more versatile, optimised, and largely autonomous transient follow-up program, combining all major functionalities in one systematic approach. We describe the design, central functionalities, and interfaces of the transients follow-up system in general and its three main components in detail: the Target of Opportunity (ToO) alert system, the data acquisition and central control system, and the real-time analysis. We highlight architectural decisions and detailed features that enable fully automatic ToO follow-up and indicate key performance metrics of the sub-systems. We discuss the system's capabilities and highlight the need for a fine-tuned interplay of the different sub-systems to react quickly and reliably. Lessons learnt from the development, integration, and operation of the H.E.S.S. transients follow-up system are reviewed in light of new and large science infrastructures and associated challenges in this exciting new era of interoperable astronomy.
Abstract: 2203.04106
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Full Text: [ PostScript, PDF]
Title:Basics of Fourier Analysis for High-Energy Astronomy
Download PDFAbstract: The analysis of time variability, whether fast variations on time scales well below the second or slow changes over years, is becoming more and more important in high-energy astronomy. Many sophisticated tools are available for data analysis and complex practical aspects are described in technical papers. Here, we present the basic concepts upon which all these techniques are based. It is intended as a condensed primer of Fourier analysis, dealing with fundamental aspects that can be examined in detailed elsewhere. It is not intended to be a presentation of detailed Fourier tools for data analysis, but the reader will find the theoretical basis to understand available analysis techniques.
Abstract: 2202.07681
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Full Text: [ PostScript, PDF]
Title:Gamma rays reveal proton acceleration in thermonuclear novae explosions
Download PDFAbstract: Classical novae are cataclysmic binary star systems in which the matter of a companion star is accreted on a white dwarf (WD). Accumulation of the matter in a layer eventually causes a thermonuclear explosion on the surface of the WD, brightening the WD to ~ 10 5 solar luminosities and triggering ejection of the accumulated matter. They provide extreme conditions required to accelerate particles, electrons or protons, to high energies. Here we present the detection of gamma rays by the MAGIC telescopes from the 2021 outburst of RS Ophiuchi (RS Oph), a recurrent symbiotic nova, that allowed us, for the first time, to accurately characterize the emission from a nova in the 60 GeV to 250 GeV energy range. The theoretical interpretation of the combined Fermi -LAT and MAGIC data suggests that protons are accelerated to hundreds of GeV in the nova shock. Such protons should create bubbles of enhanced Cosmic Ray density up to about 13 pc from the recurrent novae.
Abstract: 2202.08201
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Full Text: [ PostScript, PDF]
Title:Revealing time-resolved particle acceleration in the recurrent Nova RS Ophiuchi
Download PDFAbstract: Recurrent Novae result from thermonuclear explosions in the outer layers of White Dwarfs, as they accrete from their Red Giant companions. Ejected material drives an expanding shock into the companion star's wind, accelerating particles to relativistic energies. We report the H.E.S.S. detection of very-high-energy gamma rays from the recurrent Nova RS Ophiuchi up to a month after the 2021 outburst. A common origin of the H.E.S.S. emission and the high-energy emission detected with Fermi-LAT is favoured, due to their similar decay profiles, $\propto t^{-1.7}$. The peak flux in very-high-energies is delayed by two days with respect to Fermi-LAT. These observations reveal time-dependent particle energization, and provide a real-time window on an efficient cosmic accelerator. With this measurement, we establish recurrent Novae as multi-TeV Galactic transient sources.
This page created: Tue Mar 15 10:06:55 ACDT 2022 by Gavin Rowell
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