95 research outputs found
Study of hadron and gamma-ray acceptance of the MAGIC telescopes: Towards an improved background estimation
No full textCosmic Rays origin studies in the W 44 region with Fermi-LAT and MAGIC observations
No full textW44 is a well-known Supernova Remnant (SNR) observed in high-energy gamma-rays, widely studied to investigate cosmic ray (CR) acceleration. Several analyses of the W44 surroundings showed the presence of a gamma-ray emission offset from the radio SNR shell. This emission is thought to originate from escaped high-energy CRs. We present a detailed analysis of the W44 region as seen by Fermi-LAT, focusing on the spatial and spectral characteristics of both W44 SNR and its surroundings. The spatial analysis was limited to energies above 1 GeV in order to exploit the improved angular resolution of the instrument, deriving a detailed description of the region morphology. The spectral analysis was extended down to 100 MeV, favouring the hadronic origin of gamma-rays. Observations of the North-Western region of W44 were conducted with the MAGIC telescopes in the very-high-energy gamma-ray band. We analysed MAGIC data above 130 GeV exploiting the spatial information derived from the Fermi-LAT analysis above 1 GeV. Here we show the results of both analyses and the combined Fermi-LAT and MAGIC spectra. An interpretation model was developed, assuming that the gamma-ray emission from the surroundings is due to clouds located near W44 and illuminated by CRs escaping along the SNR’s magnetic field lines, thus obtaining constraining information on the diffusion coefficient of the escaped CRs
Deciphering the gamma-ray sky
No full textThis thesis presents a novel spatial likelihood analysis for Imaging Atmospheric Cherenkov Telescopes (IACTs) and its use to analyse observations of the gamma-Cygni supernova remnant (SNR) with the MAGIC telescopes, a system of two IACTs. SNRs are the prime candidate source for the origin of the galactic component of cosmic rays (CRs).
These objects are sufficiently extended to be resolved with gamma-ray telescopes. This allows the determination of different acceleration regions of a source, but poses issues for the current analysis approach for IACT data. IACTs detect the Cherenkov light generated in air showers, which are cascades of energetic particle that result from the interaction of gamma-rays with the molecules in the atmosphere. Currently, the emission from a source is determined using the aperture photometry approach, in which the number of gamma-ray events from the source region is compared against a source-free background control region. In the case of superimposed emission regions, an event count cannot be attributed to one emission region. Furthermore, extended objects or objects of complex morphology make the definition of the source region a difficult task.
These issues can be overcome by a spatial likelihood analysis of the skymaps of IACTs. In this approach, a user-defined source template is convolved with the instrument response functions (IRFs) and the "realistic" model fitted to the event count maps via a Poissonian likelihood fit. The data analyses of space-based gamma-ray telescopes, such as the Fermi Large Area Telescope (LAT), are based on this technique. For IACTs the determination of the IRFs, however, is a challenging task: because the atmosphere is part of the detector, the IRFs cannot be measured in the laboratory but need to be computed from Monte-Carlo events for each observation individually. This thesis presents SkyPrism, a software package performing such an analysis on MAGIC data including the accurate determination of the IRFs.
Using SkyPrism it was possible to analyse observations of the ~7000 year old gamma-Cygni SNR taken with MAGIC between 2015 and 2017. CRs are accelerated and confined in the shock region by magnetic turbulences ahead and behind the shock, making the level of turbulence an important ingredient of the acceleration process. Only a small high energetic fraction of CRs may escape the fast shocks of young SNRs (10000 years) almost all CRs have already escaped. I studied the escape of CRs from the shock into the interstellar medium using 85 hours of MAGIC data and 9 years Fermi-LAT data covering the energy range from 5 GeV to 5TeV. Using the theoretical model of the diffusive shock acceleration, I determined that the maximum energy of the CRs confined in the shock region decreases faster with the lifetime of the SNR than expected and that the level of turbulence is not constant over the lifetime of the SNR.Diese Dissertation befasst sich mit der Entwicklung einer Likelihood basierten Analyse für Daten von abbildenden Luft Cherenkov Teleskopen (IACTs) und deren Anwendung auf Beobachtungen des gamma-Cygni Supernova Überrestes mit den MAGIC Teleskopen, einem System von zwei IACTs. Nach heutigem Wissensstand wird der galaktische Anteil der kosmischen Strahlung (CR), relativistischer Teilchen, welche hochenergetische Gammastrahlung erzeugen, hauptsächlich in den Schockwellen der Überreste von Supernovae (SNR) beschleunigt.
Diese Objekte sind ausgedehnt genug, sodass sie sich auch mit Gammastrahlen Teleskopen auflösen lassen. Dies ermöglicht einerseits eine genauere Untersuchung der verschiedenen Beschleunigungsregionen innerhalb des Objekts, stellt andererseits jedoch eine Herausforderung für die aktuellen Analysemethoden von IACTs dar. IACTs detektieren das Cherenkov Licht von Luftschauern, Teilchenkaskaden, die aus der Wechselwirkung von Gammastrahlung mit Luftmolekülen resultieren. Aktuell wird die Intensität einer Quelle aus den Daten von IACTs mittels der Apertur-Photometrie ermittelt. Dazu wird die Anzahl der detektierten Gammastrahlen-Ereignisse aus einem Gebiet um die Quelle mit der Anzahl an Ereignissen aus einem gleichgroßen Kontrollbereich ohne Quelle ermittelt. Überlagern sich jedoch Emissionsregionen, so lässt sich nicht bestimmen, zu welcher Region ein Ereignis zählt. Sehr ausgedehnte Quellen oder Objekte mit komplexer Morphologie stellen zudem ein Problem hinsichtlich der Wahl der Quellregion dar.
Durch eine räumliche Likelihood Analyse auf der Basis von Himmelskarten von IACTs lassen sich die Schwierigkeiten vermeiden. Dabei wird eine benutzerdefinierte Morphologie mit der Instrumentenantwort (IRF) gefaltet und dieses "realistische" Quellmodel mittels eines Poisson-Likelihood Fits an die Messdaten angepasst. Bei satellitengestützten Gamma-Teleskopen wie dem Fermi Large Area Telescope (LAT), wird diese Methode bereits angewandt. Die Schwierigkeit für IACTs ist die Bestimmung der IRF. Da die Atmosphäre ein Bestandteil des IACTs ist, kann die IRF nicht vorab im Labor ermittelt werden, sondern muss mit Hilfe von Monte-Carlo Simulationen für jede Beobachtung individuell bestimmt werden. Diese Arbeit präsentiert das Software Paket SkyPrism, das eine solche Analyse inklusive der Bestimmung der IRFs, für die MAGIC Teleskope durchführt.
Mit Hilfe von SkyPrism konnten MAGIC Beobachtungsdaten von dem ca. 7000 Jahren alten gamma-Cygni SNR analysiert werden. Während des Beschleunigungsvorgangs in SNR Schockwellen streut die CR an magnetischen Turbulenzen vor und hinter dem Schock, wodurch der Grad der Turbulenzen ein wichtiger Bestandteil des Beschleunigungsvorgangs wird. Aus den schnellen Schockwellen von jüngeren SNR (10000 Jahre) bereits nahezu die gesamte CR der Schockwelle entkommen ist und keine Beschleunigung mehr stattfindet. Die Beobachtungen mit den MAGIC Teleskopen (85 Stunden Beobachtungszeit) und dem Fermi-LAT (9 Jahre Daten) über einen Energiebereich von 5 GeV bis 5 TeV ermöglichten zum ersten Mal eine Untersuchung, wie die CR der Schockwelle eines SNR ins interstellare Medium entkommt. Mittels eines theoretischen Models für die Schockbeschleunigung konnte ermittelt werden, dass die maximale Energie, zu der die CR beschleunigt und im Schockbereich gehalten werden kann, schneller mit der Lebensdauer des SNR abnimmt als erwartet und der Grad an Turbulenzen über die Lebensdauer des SNR nicht konstant sein kann
MAGIC observations of the diffuse γ-ray emission in the vicinity of the Galactic center
No full textAims. In the presence of a sufficient amount of target material, γ-rays can be used as a tracer in the search for sources of Galactic cosmic rays (CRs). Here we present deep observations of the Galactic center (GC) region with the MAGIC telescopes and use them to infer the underlying CR distribution and to study the alleged PeV proton accelerator at the center of our Galaxy.Methods. We used data from ≈100 h observations of the GC region conducted with the MAGIC telescopes over five years (from 2012 to 2017). Those were collected at high zenith angles (58−70 deg), leading to a larger energy threshold, but also an increased effective collection area compared to low zenith observations. Using recently developed software tools, we derived the instrument response and background models required for extracting the diffuse emission in the region. We used existing measurements of the gas distribution in the GC region to derive the underlying distribution of CRs. We present a discussion of the associated biases and limitations of such an approach.Results. We obtain a significant detection for all four model components used to fit our data (Sgr A*, “Arc”, G0.9+0.1, and an extended component for the Galactic Ridge). We observe no significant difference between the γ-ray spectra of the immediate GC surroundings, which we model as a point source (Sgr A*) and the Galactic Ridge. The latter can be described as a power-law with index 2 and an exponential cut-off at around 20 TeV with the significance of the cut-off being only 2σ. The derived cosmic-ray profile hints to a peak at the GC position and with a measured profile index of 1.2 ± 0.3 is consistent with the 1/r radial distance scaling law, which supports the hypothesis of a CR accelerator at the GC. We argue that the measurements of this profile are presently limited by our knowledge of the gas distribution in the GC vicinity.Key words: gamma rays: general / gamma rays: ISM / Galaxy: center / cosmic rays⋆ Tables and sky maps are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A190⋆⋆ Corresponding authors: Christian Fruck, Ievgen Vovk, Yuki Iwamura and Marcel Strzys (e-mail: [email protected])
The Galactic Center region imaged with MAGIC and variability searches during the G2 pericenter passage
No full textResolving the origin of very-high-energy gamma-ray emission from the PeVatron candidate SNR G106.3+2.7 using MAGIC telescopes
No full textISSN:1824-803
Galactic Center Observations with CTAO LST-1
No full textVery-high-energy gamma-ray observations of the central part of the Milky Way Galaxy allow for morphological study of cosmic-ray propagation around the supermassive black hole Sgr A*. An interpretation of the diffuse gamma-ray component, which spans a few hundred parsecs in longitude, is the PeVatron scenario: the spectral energy distribution follows a power law up to a few tens of TeV, with a spatial distribution that is aligned with the central molecular zone and accelerated cosmic rays that propagate in the vicinity of Sgr A*. Nevertheless, differences in the findings of earlier studies persist among current-generation telescopes, each offering different interpretations based on different analytical approaches. The MAGIC telescopes for example presented a hint of a presence of a spectral turnover at around 20 TeV, possibly in tension with the PeVatron scenario. We analyzed Galactic Center data taken by the Large-Sized Telescope prototype (LST-1) for the Cherenkov Telescope Array Observatory (CTAO), the next-generation project of a ground-based gammaray observatory currently under commissioning. Despite the limited sensitivity due to the current monoscopic observation, the relatively wide field of view and the large-zenith-angle observation technique allow LST-1 to study the diffuse emission in the TeV range. In this contribution, we will report the current status of studies of the Galactic Center diffuse emission by including our results from LST-1 observations
Excess estimation in On/Off measurements including single-event variables
No full textSignal estimation in the presence of background noise is a common problem in many scientific disciplines. An “On/Off” measurement is when the background itself is imprecisely measured, which is the case for instance of observations performed in astronomy. We propose a new method for estimating the signal rate based on the Bayesian formalism. It uses information on single-event variables and their distribution for the signal and background population. Events are thereby weighted according to their likelihood of being a signal or a background event and background suppression can be achieved without performing data selection cuts. Simulating “On/Off” measurements from imaging atmospheric Cherenkov observations, we conclude that this new method is capable of increasing the resolution of the signal estimation, in particular for background dominated observations
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