A new method of reconstructing very-high-energy gamma-ray spectra: the Template Background Spectrum

Abstract

Very-high-energy (VHE, E>0.1 TeV) gamma-ray emission regions with angular extents comparable to the field-of-view of current imaging air-Cherenkov telescopes (IACT) require additional observations of source-free regions to estimate the background contribution to the energy spectrum. This reduces the effective observation time and deteriorates the sensitivity. A new method of reconstructing spectra from IACT data without the need of additional observations of source-free regions is developed. Its application is not restricted to any specific IACT or data format. On the basis of the template background method, which defines the background in air-shower parameter space, a new spectral reconstruction method from IACT data is developed and studied, the Template Background Spectrum (TBS); TBS is tested on published H.E.S.S. data and H.E.S.S. results. Good agreement is found between VHE gamma-ray spectra reported by the H.E.S.S. collaboration and those re-analysed with TBS. This includes analyses of point-like sources, sources in crowded regions, and of very extended sources down to sources with fluxes of a few percent of the Crab Nebula flux and excess-to-background ratios around 0.1. However, the TBS background normalisation introduces new statistical and systematic errors which are accounted for, but may constitute a limiting case for very faint extended sources. The TBS method enables the spectral reconstruction of data when other methods are hampered or even fail. It does not need dedicated observations of VHE gamma-ray-free regions (e.g. as the On/Off background does) and circumvents known geometrical limitations to which other methods (e.g. the reflected-region background) for reconstructing spectral information of VHE gamma-ray emission regions are prone to; TBS would be, in specific cases, the only feasible way to reconstruct energy spectra.

arXiv comment18 pages, accepted for publication (Astronomy and Astrophysics)

References in corpus (16)

• Observations of the Crab Nebula with H.E.S.S
• The energy spectrum of cosmic-ray electrons at TeV energies
• Background Modelling in Very-High-Energy gamma-ray Astronomy
• A high performance likelihood reconstruction of gamma-rays for Imaging Atmospheric Cherenkov Telescopes
• Implementation of the Random Forest Method for the Imaging Atmospheric Cherenkov Telescope MAGIC
• Discovery of very high energy gamma-ray emission from Centaurus A with H.E.S.S
• Detection of TeV gamma-ray Emission from the Shell-Type Supernova Remnant RX J0852.0-4622 with H.E.S.S
• Gamma-Hadron Separation in Very-High-Energy gamma-ray astronomy using a multivariate analysis method
• Temporal and spectral gamma-ray properties of Mkn421 above 250 GeV from CAT observations between 1996 and 2000
• Spectrum and variability of the Galactic Center VHE gamma-ray source HESS J1745-290
• Probing the extent of the non-thermal emission from the Vela X region at TeV energies with H.E.S.S
• Surveys with the Cherenkov Telescope Array
• A new analysis strategy for detection of faint gamma-ray sources with Imaging Atmospheric Cherenkov Telescopes
• A new template background estimate for source searching in TeV gamma-ray astronomy
• Discovery and follow-up studies of the extended, off-plane, VHE gamma-ray source HESS J1507-622
• Optimization of multivariate analysis for IACT stereoscopic systems

Cited by in corpus (3)

• Validation of open-source science tools and background model construction in $\gamma$-ray astronomy
• Statistical Tools for Imaging Atmospheric Cherenkov Telescopes
• The Making of Catalogues of Very-High-Energy γ-ray Sources