A new method of reconstructing VHE<i>γ</i>-ray spectra: the Template Background Spectrum

Fernandes, M. V.; Horns, D.; Kosack, K.; Rowell, G.

doi:10.1051/0004-6361/201323156

Cited by 4 publications

(2 citation statements)

References 23 publications

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“…A method was proposed in [21], in which the template background normalisation is done in reconstructed energy bands, and various lookup corrections are made to correct for the different shape of the acceptance for γ-like and hadron-like events. Although it provides consistent results with classical methods and can be applied in crowded regions where there are no γ-ray free regions (which will be a clear advantage in the context of the upcoming CTA), its complexity might introduce new systematics which are not easy to assess.…”

Section: Template Backgroundmentioning

confidence: 99%

The Making of Catalogues of Very-High-Energy γ-ray Sources

Naurois

2021

Universe

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Thirty years after the discovery of the first very-high-energy γ-ray source by the Whipple telescope, the field experienced a revolution mainly driven by the third generation of imaging atmospheric Cherenkov telescopes (IACTs). The combined use of large mirrors and the invention of the imaging technique at the Whipple telescope, stereoscopic observations, developed by the HEGRA array and the fine-grained camera, pioneered by the CAT telescope, led to a jump by a factor of more than ten in sensitivity. The advent of advanced analysis techniques led to a vast improvement in background rejection, as well as in angular and energy resolutions. Recent instruments already have to deal with a very large amount of data (petabytes), containing a large number of sources often very extended (at least within the Galactic plane) and overlapping each other, and the situation will become even more dramatic with future instruments. The first large catalogues of sources have emerged during the last decade, which required numerous, dedicated observations and developments, but also made the first population studies possible. This paper is an attempt to summarize the evolution of the field towards the building up of the source catalogues, to describe the first population studies already made possible, and to give some perspectives in the context of the upcoming, new generation of instruments.

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Section: Template Backgroundmentioning

confidence: 99%

The Making of Catalogues of Very-High-Energy γ-ray Sources

Naurois

2021

Universe

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“…Template background: the OFF counts are given by those events that have been discarded in the signal extraction selection based on a discriminating variable. In this method, first developed for the HEGRA experiment [44] and more recently refined for HESS [45], the discarded events are used to template the background.…”

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confidence: 99%

Statistical Tools for Imaging Atmospheric Cherenkov Telescopes

D’Amico

2022

Universe

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The development of Imaging Atmospheric Cherenkov Telescopes (IACTs) unveiled the sky in the teraelectronvolt regime, initiating the so-called “TeV revolution”, at the beginning of the new millennium. This revolution was also facilitated by the implementation and adaptation of statistical tools for analyzing the shower images collected by these telescopes and inferring the properties of the astrophysical sources that produce such events. Image reconstruction techniques, background discrimination, and signal-detection analyses are just a few of the pioneering studies applied in recent decades in the analysis of IACTs data. This (succinct) review has the intent of summarizing the most common statistical tools that are used for analyzing data collected with IACTs, focusing on their application in the full analysis chain, including references to existing literature for a deeper examination.

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Validation of open-source science tools and background model construction in γ-ray astronomy

Mohrmann

Specovius

Tiziani

et al. 2019

A&A

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In classical analyses of γ-ray data from imaging atmospheric Cherenkov telescopes (IACTs), such as the High Energy Stereoscopic System (H.E.S.S.), aperture photometry, or photon counting, is applied in a (typically circular) region of interest (RoI) encompassing the source. A key element in the analysis is to estimate the amount of background in the RoI due to residual cosmic ray-induced air showers in the data. Various standard background estimation techniques have been developed in the last decades, most of them rely on a measurement of the background from source-free regions within the observed field of view. However, in particular in the Galactic plane, source analysis and background estimation are hampered by the large number of, sometimes overlapping, γ-ray sources and large-scale diffuse γ-ray emission. For complicated fields of view, a three-dimensional (3D) likelihood analysis shows the potential to be superior to classical analysis. In this analysis technique, a spectromorphological model, consisting of one or multiple source components and a background component, is fitted to the data, resulting in a complete spectral and spatial description of the field of view. For the application to IACT data, the major challenge of such an approach is the construction of a robust background model. In this work, we apply the 3D likelihood analysis to various test data recently made public by the H.E.S.S. collaboration, using the open analysis frameworks ctools and Gammapy. First, we show that, when using these tools in a classical analysis approach and comparing to the proprietary H.E.S.S. analysis framework, virtually identical high-level analysis results, such as field-of-view maps and spectra, are obtained. We then describe the construction of a generic background model from data of H.E.S.S. observations, and demonstrate that a 3D likelihood analysis using this background model yields high-level analysis results that are highly compatible with those obtained from the classical analyses. This validation of the 3D likelihood analysis approach on experimental data is an important step towards using this method for IACT data analysis, and in particular for the analysis of data from the upcoming Cherenkov Telescope Array (CTA).

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A new method of reconstructing VHEγ-ray spectra: the Template Background Spectrum

Cited by 4 publications

References 23 publications

The Making of Catalogues of Very-High-Energy γ-ray Sources

The Making of Catalogues of Very-High-Energy γ-ray Sources

Statistical Tools for Imaging Atmospheric Cherenkov Telescopes

Validation of open-source science tools and background model construction in γ-ray astronomy

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