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A new method to perform data-model comparison in Fermi-LAT analysis
- Source :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, EDP Sciences, 2021, 656, pp.A81. ⟨10.1051/0004-6361/202141553⟩
- Publication Year :
- 2021
- Publisher :
- EDP Sciences, 2021.
-
Abstract
- The analysis of Fermi Large Area Telescope (LAT) gamma-ray data in a given Region Of Interest (RoI) usually consists of performing a binned log-likelihood fit in order to determine the sky model that, after convolution with the instrument response, best accounts for the distribution of observed counts. While tools are available to perform such a fit, it is not easy to check the goodness-of-fit. The difficulty of the assessment of the data/model agreement is twofold. First of all, the observed and predicted counts are binned in three dimensions (two spatial dimensions and one energy dimension) and comparing two 3D maps is not straightforward. Secondly, gamma-ray source spectra generally decrease with energy as the inverse of the energy square. As a consequence the number of counts above several GeV generally falls into the Poisson regime, which precludes performing a simple $\chi^2$ test. We propose a method that overcomes these two obstacles by producing and comparing spatially integrated count spectra for data and model at each pixel of the analysed RoI. The comparison is performed following a log-likelihood approach that extends the $\chi^2$ test to histograms with low statistics. This method can take into account likelihood weights that are used to account for systematic uncertainties. We optimize the new method so that it provides a fast and reliable tool to assess the goodness-of-fit of Fermi-LAT data and we use it to check the latest gamma-ray source catalog on 10~years of data.<br />Comment: Accepted in Astronomy & Astrophysics
- Subjects :
- 010504 meteorology & atmospheric sciences
Astrophysics::High Energy Astrophysical Phenomena
FOS: Physical sciences
Astrophysics
Poisson distribution
01 natural sciences
Square (algebra)
Convolution
symbols.namesake
Region of interest
Histogram
0103 physical sciences
[PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det]
Data model (GIS)
Instrumentation and Methods for Astrophysics (astro-ph.IM)
010303 astronomy & astrophysics
0105 earth and related environmental sciences
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics
methods: statistical
Astronomy and Astrophysics
gamma rays: general
methods: data analysis
Space and Planetary Science
symbols
Astrophysics - High Energy Astrophysical Phenomena
Astrophysics - Instrumentation and Methods for Astrophysics
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Algorithm
Energy (signal processing)
Fermi Gamma-ray Space Telescope
Subjects
Details
- ISSN :
- 14320746 and 00046361
- Volume :
- 656
- Database :
- OpenAIRE
- Journal :
- Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....df9312c6697cb7aa028e2d92ce8e262d