Rubén López Coto

The Topo-Trigger: A New Stereo Trigger for Lowering the Energy Threshold of IACTs

The purpose of the hardware presented in this chapter is to decrease the energy threshold of the MAGIC telescopes without significantly increasing the data acquisition rate. To achieve this purpose, we developed an additional level of trigger that relies on the location in both MAGIC cameras where the trigger is issued to rule out accidental events. This allows to decrease the discriminator threshold, which results in a reduction of the energy threshold of the instrument. We simulated the Topo-trigger concept using the standard MAGIC MonteCarlo and tested it with real telescope data. In this chapter I show the concept and results of these tests.

Single Telescope Trigger for CTA

The goal of the LSTs for CTA, is to achieve the lowest possible energy threshold. To push the threshold down in energy, one of the most important systems is the camera trigger, that selects the events that are recorded. Since most of the problems when lowering the energy threshold of the system is that the accidental triggers increase, the trigger system needs to powerfully distinguish between the events containing cosmic showers and the ones containing only noise. Arrays of Cherenkov telescopes typically use multi-level trigger schemes to keep the rate of accidental triggers produced by direct NSB and PMT After Pulses low. At a first stage, individual telescopes produce a trigger signal from the pixel signals in the telescope camera. The final event trigger is then formed by combining trigger signals from several telescopes. I present in this chapter the work performed to develop, test and characterize an analog trigger system for the analog cameras of LSTs and MSTs.

The Crab Nebula: A Gamma-Ray Factory in Our Backyard

The Crab Nebula is the most studied astronomical source in the sky. At VHE gamma rays, it is the strongest steady source in the sky and the first one discovered, back in 1989. The source is very well studied at these energies, but there are still some open questions. In this chapter we shed light on two of them: the transition to the Klein-Nishina regime at multi-TeV energies and the study of enhancement emission during the flares at MeV energies detected by Fermi. For the first question, I performed a set of dedicated high zenith angle observations that allows to increase the collection area of the telescopes at the highest energies. I found that the best description of the spectrum at these energies is given by a log-parabola function. The study of the variability of the spectrum coincident with gamma-ray flares at MeV energies resulted in a non-detection of significant enhancement of the emission at VHE gamma rays.

Nova and Dwarf Nova Observations with MAGIC

Starting in fall 2012, the MAGIC collaboration conducted a nova follow-up program in order to detect a possible VHE gamma-ray component. The program responded to Fermi-LAT detections of different types of novae at GeV energies: it initially focussed on symbiotic novae and later extended to bright Classical Novae and additional outbursts from other Cataclysmic Variables. I will report on the observations performed with the MAGIC telescopes of the symbiotic nova YY Her, the DN ASASSN-13ax, and the Classical Nova V339 Del and present the contemporaneous updated analysis of Fermi-LAT data.

Introduction to Pulsar Wind Nebulae

Pulsar Wind Nebulae are nebulae of electrons and positrons powered by a central pulsar. In this chapter I give a detailed description of star evolution, centered on the description of supernova remnants, pulsars and pulsar wind nebulae. The basic properties of pulsars are explained, together with the emission mechanisms responsible for the production of gamma rays by these sources. I explain the physics of pulsar wind nebulae, with a description of their broadband emission and an explanation of their two main components: the synchrotron and inverse Compton emission. I also expose the state of the art models predicting gamma-ray emission from these sources.

Short Introduction to Cosmic Ray and \gamma -Ray Astronomy

In this chapter I give a brief introduction to the cosmic ray astronomy, the production mechanisms for cosmic rays and the galactic and extragalactic sources producing them. I also give an introduction to gamma-ray astronomy, the detection techniques and the mechanisms producing gamma rays. I finally describe all the sources known to date where gamma rays are produced.

The Imaging Atmospheric Cherenkov Technique and the IACTs MAGIC and CTA

In this chapter I describe the concept behind the detection of gamma rays through the imaging atmospheric Cherenkov technique. I also describe the IACT arrays on which this thesis focuses: the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes and the Cherenkov Telescope Array (CTA). The hardware and techniques used to analyze the data of MAGIC will be described in detail. I give an overview of the CTA project, together with a brief description of the telescope types involved in the project.

Introduction to Cataclysmic Variable Stars

Cataclysmic Variables are semi-detached binaries consisting of a White Dwarf that accretes material from a companion star (usually a Red Dwarf) that transfers matter to the White Dwarf. In this chapter I give a description of cataclysmic variable stars, their composition, classification and spectral characteristics.

Multiwavelength Campaign on AE Aquarii

AE Aquarii is a bright nova-like Cataclysmic Variable and one of the most studied objects of this type. Its broadband emission extends from radio up to X-rays. There were claims of variable VHE gamma-ray emission in the past by different experiments. The study presented in this chapter endeavoured to find this emission and characterize it. I searched for steady emission, steady emission coincident with high states at different wavelengths, pulsed emission at the spin frequency of the White Dwarf and pulsed emission at different frequencies and did not find any evidence of VHE gamma-ray emission. I established the most constraining upper limits for the steady and pulsed emission for this source and discussed the implication on the state of the art models predicting VHE gamma-ray emission.

The Puzzling PWN 3C 58

3C 58 is a peculiar source, likely the remnant of the Supernova in 1181 AD. It hosts one of the most powerful spin-down power pulsars in the galaxy and it was always consider a good candidate for VHE gamma-ray emission. It had, however, eluded the detection by all the VHE gamma-ray experiments in the past. To discover it, we needed a very deep exposure that turn into the detection of the least luminous VHE gamma-ray Pulsar Wind Nebula to date. With its detection, we shed light on the controversial matter of its distance and age, favoring a distance to the source of 2 kpc and an age of 2.5 kyr. We put 3C 58 in context with other Pulsar Wind Nebulae detected at VHE gamma rays and studied the characteristics of their X-ray and gamma-ray emission compared to the properties of the central pulsar, deriving general relations that can be applied to any source of this type.