Spectral Energy Distribution Modeling of Markarian 501 through a non-linear least square minimization

So far the Spectral Energy Distribution (SED) of Active Galactic Nuclei (AGN), in particular blazars, have been obtained in a heuristics way. This is mainly due to both the many free parameters of the emission model and the severe lack of simultaneous multi-frequency data. This leads to non-rigorous and possibly biased analyses, and makes it difficult to compare results coming from different analyses. However, recent simultaneous multi-frequency campaigns are providing long-term broad-band coverages of source activity, and large multi-frequency data sets are becoming available. So emission model fitting may be attempted with better profit now. The main aim of this thesis is to develop a statistical approach that fits AGN SEDs in a rigorous way. Such an approach consists in a Chi squared -minimization, based on the Levenberg-Marquardt algorithm, that returns the most likely values of the SED parameters, plus a method devised to obtain the related uncertaintes. The whole minimization process is implemented in a C++ code. However, this approach may reveal unexpected features of the Chi squared-manifold that might affect convergence, due to spurious correlations between model parameters and/or inadequacy of the currently available datasets. For these reasons, a statistical analysis will be carried out on the solutions obtained from several minimizations, each starting from different points of the parameter space. This approach is applied to different activity states of the blazar Markarian 501, in a Synchrotron Self Compton (SSC) framework. In particular, starting from available observations of this source taken with the ground-based Major Atmospheric Gamma-ray Imaging Cherenkov telescopes (MAGIC) in 2011, 7 multi-frequency datasets were obtained. Based on multi-frequency and simultaneity requirements, all datasets include also data provided by the Swift UVOT, Swift XRT, and Fermi LAT orbiting telescopes. The SED modelling of each dataset will be performed through a non-linear Chi squared-minimization in order to obtain the most likely values of the parameters describing the SSC model. Finally, it is worth remarking that this approach is not only a rigorous statistical method to find the most likely source parameters for different scenarios, but it also represents a powerful tool to efficiently discriminate between different emission models

Characterization of Microbulk Micromegas detectors through digital image processing

International audienceMicrobulk Micromegas (MICRO-MEsh GAseous Structure) detectors are gaseous parallel plate detectors for the tracking of charged particles, used mainly in rare-event searches thanks to their intrinsic high radiopurity. The core of such detectors (mesh, pillars, and readout) can be produced through standard photolithography techniques starting from a single foil of copper-coated kapton. In particular, the quality of the mesh resulting from this process plays a crucial role in particle detection, and also in the energy resolution. The aim of this paper is to provide for the first time a method that allows to probe the quality of the mesh through image processing techniques. This method has been applied to nine detectors

A single photoelectron calibration system for the NectarCAM camera of the Cherenkov Telescope Array Medium-Sized Telescopes

International audienceThis contribution aims to introduce the single photo-electron system designed to calibrate the camera of the Medium-Sized Telescopes of the Cherenkov Telescope Array (CTA). This system will allow us to measure accurately the gain of the camera’s photodetection chain and to constrain the systematic uncertainties on the energy reconstruction of gamma rays detected by CTA. The system consists of a white painted screen, a fishtail light guide, a flasher and an XY motorization to allow movement. The flashes guided by the fishtail mimic the Cherenkov radiation and illuminate the focal plane under the screen homogeneously. Then, through the XY motorisation, the screen is moved across the entire focal plane of the NectarCAM camera, which consists of 1855 photo-multiplier tubes. In this contribution, we present the calibration system and the study on its optimum scan positions required to cover the full camera effectively. Finally, we illustrate the results of the calibration data analysis and discuss the performance of the system

REST-for-Physics, a ROOT-based framework for event oriented data analysis and combined Monte Carlo response

International audienceThe REST-for-Physics (Rare Event Searches Toolkit for Physics) framework is a ROOT-based solution providing the means to process and analyze experimental or Monte Carlo event data. Special care has been taken to the traceability of the code and the validation of the results produced within the framework, together with the connectivity between code and stored data, registered through specific version metadata members. The framework development was originally motivated to cover the needs of Rare Event Searches experiments (experiments looking for phenomena having extremely low occurrence probability, like dark matter or neutrino interactions or rare nuclear decays). The framework components naturally implement tools to address the challenges in these kinds of experiments. The integration of a detector physics response, the implementation of signal processing routines, or topological algorithms for physical event identification are some examples. Despite this specialization, the framework was conceived thinking in scalability. Other event-oriented applications could benefit from the data processing routines and/or metadata description implemented in REST, being the generic framework tools completely decoupled from dedicated libraries. REST-for-Physics is a consolidated piece of software already serving the needs of different physics experiments - using gaseous Time Projection Chambers (TPCs) as detection technology - for detector data analysis and characterization, as well as generic R&D. Even though REST has been exploited mainly with gaseous TPCs, the code could be easily applied or adapted to other detector technologies. We present in this work an overview of REST-for-Physics, providing a broad perspective to the infrastructure and organization of the project as a whole. The framework and its different components will be described in the text

MAGIC observations of the microquasar V404 Cygni during the 2015 outburst

The microquasar V404 Cygni underwent a series of outbursts in 2015, June 15–31, during which its flux in hard X-rays (20–40 keV) reached about 40 times the Crab nebula flux. Because of the exceptional interest of the flaring activity from this source, observations at several wavelengths were conducted. The MAGIC telescopes, triggered by the INTEGRAL alerts, followed-up the flaring source for several nights during the period June 18–27, for more than 10 h. One hour of observation was simultaneously conducted on a giant 22 GHz radio flare and a hint of signal at GeV energies seen by Fermi-LAT. The MAGIC observations did not show significant emission in any of the analysed time intervals. The derived flux upper limit, in the energy range 200–1250 GeV, is 4.8 × 10−12 photons cm−2 s−1. We estimate the gamma-ray opacity during the flaring period, which along with our non-detection points to an inefficient acceleration in the V404 Cyg jets if a very high energy emitter is located further than 1 × 1010 cm from the compact object.ISSN:0035-8711ISSN:1365-2966ISSN:1365-871

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances