Spatial likelihood analysis for MAGIC telescope data

Abstract

Context. The increase in sensitivity of Imaging Atmospheric Cherenkov Telescopes (IACTs) has lead to numerous detections of extended γ-ray sources at TeV energies, sometimes of sizes comparable to the instrument's field of view. This creates a demand for advanced and flexible data analysis methods that are able to extract source information using the photon counts in the entire field of view.Aims. We present a new software package, "SkyPrism", aimed at performing 2D (3D if energy is considered) fits of IACT data that possibly contain multiple and extended sources. The fits are based on sky images binned in energy. Although the development of this package was focused on the analysis of data collected with the MAGIC telescopes, it can further be adapted to other instruments, such as the future Cherenkov Telescope Array. Methods. We have developed a set of tools that in addition to sky images (count maps) compute the instrument response functions of MAGIC (effective exposure throughout the field of view, point spread function, energy resolution, and background shape) based on the input data, Monte Carlo simulations, and the pointing track of the telescopes. With this information, the package can perform a simultaneous maximum likelihood fit of source models of arbitrary morphology to the sky images providing energy spectra, detection significances, and upper limits. Results. We demonstrate that the SkyPrism tool accurately reconstructs the MAGIC point spread function, on-and off-axis performance as well as the underlying background. We further show that for a point source analysis with the MAGIC default observational settings, SkyPrism gives results compatible with those of the standard tools while being more flexible and widely applicable.

Gamma-ray Spectral and Morphological study of HESS J1912+101 observed by MAGIC and Fermi-LAT

“…The MAGIC data processed with the MAGIC Analysis and Reconstruction Software (MARS) with the standard MARS analysis chain [4]. Additionally, we use SkyPrism, a three dimensional (2× spatial and energy) likelihood software for MAGIC data, specifically developed to perform morphological and spectral studies of extended sources [5]. SkyPrism allows for the independent modeling of multiple sources ideal of complex sources, hence it is ideal for regions such as the HESS J1912+101.…”

MAGIC observations of the diffuse γ-ray emission in the vicinity of the Galactic center

“…A high-level analysis of the acquired data was performed with the set of utilities available in the MAGIC SkyPrism package (Vovk et al 2018). SkyPrism provides a set of routines, aimed at 2D spatial likelihood analysis of MAGIC data, which allows us to self-consistently account for sources of complex morphology within the field of view.…”

“…Such contamination of the background map with excess γray signal can be avoided if contributions from locations close to known γ-ray sources are excluded during map construction (Vovk et al 2018). We thus mask out camera regions that correspond to the Galactic plane and use the rest of the camera (free from known or expected sources) to estimate the corresponding background.…”

“…Collaboration 2018). We continued observing the GC during 2015−2017, adding up to a total exposure time of ≈100 h. In addition, we employ the recently developed 2D likelihood analysis package SkyPrism (Vovk et al 2018), which provides a more sensitive analysis of extended sources for MAGIC.…”

Analysis Methods for Neutrino Follow-up Observations with MAGIC

“…With a maximum likelihood test the values for those parameters that describe the real data best are calculated. [9] 2.1 The Point Source Search In the context of point source search with SkyPrism, the neutrino uncertainty region is scanned by testing a point source model on each position of a predefined grid. The resulting test statistic (TS) value gives information about the probability of the existence of a gamma-ray source at each specific position.…”