Extragalactic sources of high-energy cosmic gamma-rays, like blazars and quasars, are usually highly variable and the temporal characteristics of their light curves are key to the understanding of their physics. In order to deal with blazar flares in different parts of electromagnetic spectrum – from gamma-rays and X-rays to visible light - we developed a new approach to correlation study based on Monte Carlo simulations and the Fourier convolution.

http://inspirehep.net/record/1395730/files/DHrupec.pdf

Extragalactic sources of rapidly variable high energy gamma radiation

The imaging atmospheric Cherenkov technique for high-energy gamma-ray astronomy is emerging as an important new technique for studying the high energy universe. Current experiments have data rates of ≈ 20 TB / year and duty cycles of about 10%. In the future, more sensitive experiments may produce up to 1000 TB/year. The data analysis task for these experiments requires keeping up with this data rate in close to real-time. Such data analysis is a classic example of a streaming application with very high performance requirements. This class of application often benefits greatly from the use of non-traditional approaches for computation including using special purpose hardware (FPGAs and ASICs), or sophisticated parallel processing techniques. However, designing, debugging, and deploying to these architectures is difficult and thus they are not widely used by the astrophysics community. This paper presents the Auto-Pipe design toolset that has been developed to address many of the difficulties in taking advantage of complex streaming computer architectures for such applications. Auto-Pipe incorporates a high-level coordination language, functional and performance simulation tools, and the ability to deploy applications to sophisticated architectures. Using the Auto-Pipe toolset, we have implemented the front-end portion of an imaging Cherenkov data analysis application, suitable for real-time or offline analysis. The application operates on data from the VERITAS experiment, and shows how Auto-Pipe can greatly ease performance optimization and application deployment of a wide variety of platforms. We demonstrate a performance improvement over a traditional software approach of 32 x using an FPGA solution and 3.6 x using a multiprocessor based solution.

Acceleration of atmospheric Cherenkov telescope signal processing to real-time speed with the Auto-Pipe design system

It has been more than 60 years since astronomers turned their attention towards the 7֊ray window (> 100 TeV). Nowadays, 7֊ray astronomy has won its place as a separate branch of astronomy in its own right. The present thesis introduces the reader to 7-ray observations in the 〜 100 GeV-100 TeV energy window, but focuses, in particular, on the efforts to describe and detect the pulsed, Very High-Energy (VHE) 7-ray emission from pulsars. Pulsars are highly magnetised {B 〜 101շ G) ， rapidly rotating (P ~ 10—2 s) neutron stars. Periodic radio emission from pulsars has been detected in more than 1,500 cases, in contrast to their 7-ray signature which has been confirmed for only six of them and only up to a few GeV. There are many models in existence which attempt to reproduce the observed pulsed profiles and energy spectra in high energies (optical, X and ๆ rays). Nevertheless, two classes of models are the most popular: the Polar Cap and the Outer Gap models. Both predict spectral cut-offs at tens of GeV, which are consistent with previous upper limits in the VHE range. The six most energetic pulsars have been detected with the EGRET (Energetic Gamma Ray Experiment Telescope) instrument on-board the с GRO (Compton Gamma Ray Observatory) satellite. Probing the universe at higher energies requires a different detection technique. The Imaging Atmospheric Technique (lACT) exploits the Earth's atmosphere with the use of large, ground-based reflectors that are very sensitive to Cherenkov light (300-600 nm). The latter is produced during electromagnetic particle cascades, triggered by the interaction of VHE 7 rays with the top atmospheric layers. So far there has not been a confirmed pulsar detection using Cherenkov astronomy. The High Energy Stereoscopic System (H.E.S.S.) in Namibia is an array of four telescopes, which is sensitive above 100 GeV. H.E.S.S. uses the lACT to reject the lO3 times more abundant cosmic-ray events that suppress the 7-ray signal. The system is capable of stereoscopic observations of the same source with all four telescopes, which further eliminates background events. Despite the fact that imaging with H.E.S.S. is not effective below 100 GeV, lower energy events can still be recorded, along with a large portion of the background. The present thesis deals with the least energetic events ( 1 eV). The data were optimised for the lowest energies, and the lowest energy threshold achieved was 75 GeV (in the case of PSR B1706-44). In all cases studied, the author coded and applied a number of periodicity tests that check for significant deviations from random noise. The resulting probabilities were not significantly low to support signal presence. Based on the background levels in the data sets, the author derived upper limits on the integral and differential flux. These upper limits were consistent with the Polar Cap and Outer Gap scenarios, within statistical errors, but constrain the alternative model of a spectrum with a simple exponential cut-off in the case of PSR B1706—44. Despite the lack of detection, these results represent the lowest energies explored with H.E.S.S.， yet.

Temporal analysis of the least energetic events in pulsar data from observations with the high energy stereoscopic system

Hybrid computing systems consisting of multiple platform types (e.g., general purpose processors, FPGAs etc.) are increasingly being used to achieve higher performance and lower costs than can be obtained with homogeneous systems (e.g., processor clusters). Different platforms have different languages and simulators associated with them. Auto-pipe has been developed as a toolset to reduce the complexity inherent in deploying an application to a diverse resource set. In Auto-Pipe, applications are expressed using the data flow coordination language X, which describes the application in terms of interactions between functional blocks. As part of the Auto-Pipe system, X-sim has been developed as a federated distributed simulator that can be used to conveniently and efficiently simulate applications. After a short introduction to Auto-Pipe and the X language, this paper considers issues involved with total system simulation of an application mapped to a hybrid resource set. The paper then demonstrates the use of X-sim with a realtime signal processing application employed in the VERITAS gamma-ray astronomy project.

https://www.cse.wustl.edu/~roger/papers/gtfc07.pdf

A Federated Simulation Environment for Hybrid Systems

Single photon counting plays an essential role for a wide variety of applications, ranging from biomedical research to astronomy. In gamma-ray astronomy, the Cherenkov telescope MAGIC is used to detect Cherenkov photons generated in atmospheric air showers. Since the flux of Cherenkov photons from air showers is low, the development of new single photon detectors with high quantum efficiency is necessary. The concept of the Back Illuminated Drift Silicon Photomultiplier (BID SiPM) is a novel detector design for single photon counting. It combines the principles of a silicon photomultiplier (SiPM) and a drift diode. The back illuminated drift silicon photomultiplier is operated as back illuminated detector thus providing a fill factor of 100%. A high quantum efficiency of about 80% in a wavelength region of 300 - 1000 nm can be achieved. The drift region is used to focus electrons from the back through the depleted bulk to the small point-like avalanche region. The time jitter of the electrons limits the time resolution of the detector to about 1 ns as simulation results show. A prototype of an avalanche region which can be combined with a drift structure was produced at the MPI Semiconductor Laboratory as proof of principle. The detector concept and results of measurements of dark rate and leakage current are presented.

Back Illuminated Drift Silicon Photomultiplier as Novel Detector for Single Photon Counting

The MAGIC telescope, presently at its commissioning phase, will become fully operative by the end of 2003. Placed at the Roque de los Muchachos Observatory (ORM) on the island of La Palma, MAGIC is the largest among new generation ground-based gamma ray telescopes, and will reach an energy threshold as low as 30 GeV. The range of the electromagnetic spectrum between 10 and 250 GeV remains to date mostly unexplored. Observations in this energy region are expected to provide key data for the understanding of a wide variety of astrophysical phenomena belonging to the so-called ``non thermal Universe'', like the processes in the nuclei of active galaxies, the radiation mechanisms of pulsars and supernova remnants, and the enigmatic gamma-ray bursts. An overview of the telescope and its physics goals is presented.

/pdf/the-magic-telescope-for-gamma-ray-astronomy-above-30-gev-3jhansgg13.pdf

C. Domingo

Papers

The MAGIC Telescope for Gamma-Ray Astronomy above 30 GeV