Correlation between emission-line luminosity and gamma-ray dominance in the blazar 3C 279

Despite numerous studies, the origin of the gamma-ray emission from blazars is still debated, in particular whether it is produced by leptonic or hadronic processes. In this study, we are testing the leptonic scenario for the Flat Spectrum Radio Quasar (FSRQ) 3C 279, assuming that the gamma-ray emission is generated by inverse Compton scattering of external target photons from Broad Line Region (IC-BLR scenario). For this purpose we use a 10-year data set of the source consisting of the optical spectroscopy data from the Steward Observatory blazar monitoring program and Fermi-LAT gamma-ray data. We search for a possible correlation between the Compton dominance and the emission line luminosity using the discrete correlation function (DCF) analysis. As a result, we find no significant correlation between these two quantities at any time lag value, while the emission line luminosity displays a moderate correlation with the gamma-ray flux at a zero time lag. We also reveal that the optical synchrotron continuum flux shows a pronounced correlation with the gamma-ray flux, and therefore we interpret these results within the leptonic IC-BLR scenario where the Compton dominance variations are primarily induced by changes in the magnetic field, rather than in the emission line luminosity.Comment: 16 pages, 5 figures. Accepted for publication in Ap

Contribución al conocimiento de Porosagrotis gypaetina (Guen.) (Lep.:Noctuidae)

p.15-22Este trabajo tiene por finalidad brindar una descripcion detallada de los diferentes estados de desarrollo, asi como de los estadios larvales, de Porosagrotis gypaetina (Guen.) y estimar sus principales parametros biologicos. Se trata de una oruga conocida vulgarmente como gusano pardo que frecuenta cultivos de alfalfa, trebol bianco, maiz y girasol y determinadas malezas. Los caracteres considerados para su identificacion fueron, en el huevo: numero y distribucion de costas; en la larva: pigmentacion, distribucion de manchas y cerdas corporales; en la pupa: tamaño, forma y color y caracteristicas del cremaster; y en el adulto: ubicacion y coloracion de maculas y nervaduras alares. La emergencia de imagos alcanzo su maximo en abril y mayo. El periodo embrionario se completo en 22 a 26 dias. Aproximadamente la mitad de las larvas cumplieron su ciclo en 6 estadios y las restantes en 7; la duracion total del periodo larval fue de 134 a 141 dias, sin considerar la forma prepupal e independientemente del numero de estadios. Las orugas permanecieron como prepupas durante la temporada estival (aproximadamente 161 dias). El estado pupal duro 40 a 57 dias. Las observaciones realizadas permiten expresar que, inediante los caracteres descriptos, es factible reconocer la especie a traves no solo de los adultos, sino de sus estados inmaduros. Posee una sola generacion anual; transcurre el inviemo como larva; el daño tipico de corte lo produce a partir del cuarto estadio larval

Long-term monitoring of bright blazars in the multi-GeV to TeV range with FACT

Blazars like Markarian 421 or Markarian 501 are active galactic nuclei (AGN), with their jets orientated towards the observer. They are among the brightest objects in the very high energy (VHE) gamma ray regime (>100 GeV). Their emitted gamma-ray fluxes are extremely variable, with changing activity levels on timescales between minutes, months, and even years. Several questions are part of the current research, such as the question of the emission regions or the engine of the AGN and the particle acceleration. A dedicated longterm monitoring program is necessary to investigate the properties of blazars in detail. A densely sampled and unbiased light curve allows for observation of both high and low states of the sources, and the combination with multi-wavelength observation could contribute to the answer of several questions mentioned above. FACT (First G-APD Cherenkov Telescope) is the first operational telescope using silicon photomultiplier (SiPM, also known as Geigermode—Avalanche Photo Diode, G-APD) as photon detectors. SiPM have a very homogenous and stable longterm performance, and allow operation even during full moon without any filter, leading to a maximal duty cycle for an Imaging Air Cherenkov Telescope (IACT). Hence, FACT is an ideal device for such a longterm monitoring of bright blazars. A small set of sources (e.g., Markarian 421, Markarian 501, 1ES 1959+650, and 1ES 2344+51.4) is currently being monitored. In this contribution, the FACT telescope and the concept of longterm monitoring of bright blazars will be introduced. The results of the monitoring program will be shown, and the advantages of densely sampled and unbiased light curves will be discussed

Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded

Exploration des noyaux actifs de galaxies aux énergies extrêmes : analyse et modélisation des sursauts multi-longueurs d’onde et préparation du CTA

Many questions related to the physics of jets of Active Galactic Nuclei remain open. A particular subclass of AGN, blazars, have a jet pointing towards the Earth. Such suitable orientation of the jet allows us to probe a rich variety of poorly understood physical phenomena related to relativistic outflows. Blazars show non-thermal emission, originating from the jet, which is highly variable across the entire electromagnetic spectrum, from radio frequencies to TeV gamma-rays. The energy flux can enhance by an order of magnitude on time-scales as short as minutes, a phenomenon referred to as a “flare”, and as long as months or even years. Despite the growing amount of available multi-wavelength (MWL) data, the origin and the physical mechanisms behind the frequently observed flaring events in blazars are still not well understood. Many attempts have been made to describe the flares with different emission models, but detailed properties of flux variation patterns (light curves) in different wavebands remain difficult to reproduce. In order to identify physical processes that are involved during blazar outbursts, I have developed a versatile radiative code, based on a time-dependent treatment of particle acceleration, escape and radiative cooling. The code computes time evolution of the distribution function of electrons in the blazar emitting zone and the spectrum of the Synchrotron Self-Compton (SSC) emission by these electrons. I applied the code to a giant MWL flare of the blazar Mrk 421, a representative of the BL Lacertae class, which is the brightest VHE flare ever detected from this source. In our approach, we consider the flare as a moderate perturbation of the quiescent state and search for interpretations with a minimum number of free parameters. As a result, I developed a novel physical scenario of the flaring activity that describes the data set, comprising spectra in the high state of the source in different energy ranges, and MWL light curves from the optical domain to the VHE gamma-ray band. In this scenario, the process initiating the outburst is the second-order Fermi acceleration of particles due to turbulence arising in the vicinity of the blazar stationary emission region. In this thesis, I also performed analysis of High Energy Stereoscopic System (H.E.S.S.) data of two giant flares of the blazar 3C 279, a representative of the Flat Spectrum Radio Quasars (FSRQ) class. Finally, I contributed to preparation of Cherenkov Telescope Array (CTA), which is a new-generation ground-based gamma-ray observatory, expected to start operations in 2022. The instrument, which is presently under development, will have greatly improved performance compared to currently operating Imaging Atmospheric Cherenkov Telescopes (IACTs), including unprecedented spectral coverage from a few tens of GeV to ~300 TeV. In the context of CTA, I performed simulations of the optical performance of the Gamma-Ray Cherenkov Telescope (GCT), one of the three proposed designs of Small-Size Telescopes (SST) for CTA. Also, using the observations of bright stars done by the telescope prototype installed on the site of Paris Observatory in Meudon, I studied the effect of micro-roughness of the telescope mirrors on the point spread function (PSF) and calculated the level of the mirror polishing quality required to optimize the performancesDe nombreuses questions liées à la physique des jets des Noyaux Actifs de Galaxies restent ouvertes. Une classe particulière d’AGN, les blazars, a un jet pointant vers la Terre. Une telle orientation du jet nous permet de sonder une riche variété de phénomènes physiques mal compris sur les écoulements relativistes. Les blazars montrent une émission non thermique, provenant du jet, qui est très variable sur tout le spectre électromagnétique, des radiofréquences aux rayons gamma du TeV. Le flux d’énergie peut augmenter d’un ordre de grandeur sur des échelles de temps aussi courtes que quelques minutes, un phénomène appelé “sursaut” (flare), et aussi longues que des mois ou même des années. Malgré la quantité croissante de données disponibles sur plusieurs longueurs d’onde (multi-wavelength, MWL), l’origine et les mécanismes physiques derrière les sursauts fréquemment observés dans les blazars ne sont toujours pas bien compris. De nombreuses tentatives ont été faites pour décrire les flares avec différents modèles d’émission, mais les propriétés détaillées de l’évolution temporelle des flux dans différentes bandes spectrales restent difficiles à reproduire. Afin d’identifier les processus physiques impliqués lors des sursauts de blazars, j’ai développé un code radiatif polyvalent, basé sur un traitement dépendant du temps de l’accélération des particules, de l’échappement et du refroidissement radiatif. Le code calcule l’évolution dans le temps de la fonction de distribution des électrons dans la zone d’émission du blazar et le spectre de l’émission Synchrotron Self-Compton (SSC) par ces électrons. J’ai appliqué le code à un sursaut multi-lambda géant du blazar Mrk 421, représentant de la classe des BL Lacertae, qui est le sursaut le plus brillant détecté jusqu’ici en provenance de cette source. Dans notre approche, nous considérons le sursaut comme une perturbation modérée de l’état de flux stationnaire et recherchons des interprétations avec un nombre minimum de paramètres libres. En conséquence, j’ai développé un nouveau scénario physique de l’activité observé pendant le sursaut, qui décrit l’ensemble des données, comprenant des spectres à l’état haut de la source dans différentes gammes d’énergie, et des courbes de lumière multi-lambda du domaine optique aux rayons gamma VHE. Dans ce scénario, le processus déclenchant le sursaut est l’accélération des particules par un processus de type Fermi du second ordre, dû à la turbulence qui emerge au voisinage de la région d’émission stationnaire du blazar. Dans cette thèse, j’ai également effectué une analyse des données du High Energy Stereoscopic System (H.E.S.S.) de deux sursauts géants du blazar 3C 279, représentant de la classe des Flat Spectrum Radio Quasars (FSRQ). Enfin, j’ai contribué à la préparation du Cherenkov Telescope Array (CTA), qui est un observatoire de rayons gamma au sol de nouvelle génération, dont l’entrée en service est prévue à partir de 2022. L’instrument, qui est actuellement en cours de développement, aura des performances considérablement améliorées par rapport aux Imaging Atmospheric Cherenkov Telescopes (IACTs) qui sont actuellement en fonctionnement, y compris une couverture spectrale sans précédent de quelques dizaines de GeV à ~300 TeV. Dans le cadre du CTA, j’ai effectué des simulations de performances optiques du Gamma-Ray Cherenkov Telescope (GCT), l’un des trois modèles proposés de télescopes de petite taille (SST) pour CTA. De plus, en utilisant les observations d’étoiles brillantes effectuées par le prototype de télescope installé sur le site de l’Observatoire de Paris à Meudon, j’ai étudié l’effet de la micro-rugosité des miroirs du télescope sur la fonction d’étalement du point (PSF) et calculé le niveau de qualité de polissage des miroirs requis pour optimiser les performances

The Blazar Hadronic Code Comparison Project

International audienceBlazar hadronic models have been developed in the past decades as an alternative to leptonic ones. In hadronic models the gamma-ray emission is associated with synchrotron emission by protons, and/or secondary leptons produced in proton-photon interactions. Together with photons, hadronic emission models predict the emission of neutrinos that are therefore the smoking gun for acceleration of relativistic hadrons in blazar jets. The simulation of proton-photon interactions and all associated radiative processes is a complex numerical task, and different approaches to the problem have been adopted in the literature. So far, no systematic comparison between the different codes has been performed, preventing a clear understanding of the underlying uncertainties in the numerical simulations. To fill this gap, we have undertaken the first comprehensive comparison of blazar hadronic codes, and the results from this effort will be presented in this contribution

FACT - Searching for periodicity in five-year light-curves of Active Galactic Nuclei

The First G-APD Cherenkov Telescope (FACT) has been monitoring Active Galactic Nuclei (AGN) for the past five years. The use of robust silicon photomultipliers (SiPMs) allows for a continuous, unbiased sampling even during bright-light conditions. This dataset promises insights into the core regions of AGN by investigating the periodicity of the sources. Periodic changes in the flux could indicate a binary nature of the supermassive black holes. A study using the Lomb-Scargle periodogram to find periodicity in monitored AGN is presented. Repeating patterns in the observation times, like moon periods and seasonal effects, affect the analysis by introducing spurious peaks into the periodogram. The zenith-dependence of the observed γ-ray rates further complicate the interpretation. Showing no variability at TeV energies, the γ-ray flux of the Crab Nebula is used to characterize this latter effect, before applying the Lomb-Scargle algorithm.ISSN:1824-803

Higher Order Temperature Dependence of SiPM used in FACT

Solid state photosensors, usually called SiPM or G-APD, seem ideal devices to be used in Imaging Atmospheric Cherenkov Telescopes (IACT). Nevertheless, their temperature dependence poses questions about their suitability in the harsh environment intrinsic to the operation of IACTs. While detailed measurements in the laboratory are possible with some sample sensors, limited data about the performance and uniformity of large samples exist. The First G-APD Cherenkov Telescope (FACT) is pioneering the usage of SiPMs for IACTs. Its camera consists of 1440 SiPMs and it is operated since October 2011 each night when observation conditions permit. Using no temperature stabilization system for the sensors, their temperature is closely coupled to the outside temperature that can change by more than 20 ∘C. While the strong temperature dependence of the gain of the sensors was shown to be easily compensated by adapting the applied voltage, there could also be higher order temperature dependencies of parameters like optical cross-talk, after-pulsing and wavelength dependent photon-detection efficiency. While external calibration devices could be used, one would have to proof that these devices do not have their own temperature dependencies. Instead, we use the constant flux of high energetic cosmic ray particles as calibration device. Their measured flux can depend on variable absorption and scattering of Cherenkov light e.g. due to dust and clouds, as well as on seasonal variations of the atmosphere. Nevertheless, using data sets where the temperature drastically changed within short time periods, we show that temperature dependencies of FACT, including the SiPMs, are well under control.ISSN:1824-803

Single Photon Extraction for FACT’s SiPMs allows for Novel IACT Event Representation

Imaging Atmospheric Cherenkov Telescopes provide large gamma-ray collection areas > 10^4 m^2 and successfully probe the high energetic gamma-ray sky by observing extensive air showers during the night. The First G-APD Cherenkov Telescope (FACT) explores silicon based photoelectric converters (called G-APDs or SiPMs) which provide more observation time with strong moonlight, a more stable photon gain over years of observations, and mechanically simpler imaging cameras. So far, the signal extraction methods used for FACT originate from sensors with no intrinsic quantized responses like photomultiplier tubes. This standard signal extraction is successfully used for the long time monitoring of the gamma-ray flux of bright blazars. However, we now challenge our classic signal extraction and explore single photon extraction methods to take advantage of the highly stable and quantized single photon responses of FACT's SiPM sensors. Instead of having one main pulse with one arrival time and one photon equivalent extracted for each pixel, we extract the arrival times of all individual photons in a pixel’s time line which opens up a new dimension in time for representing extensive air showers with an IACT. In this contribution, we will introduce our novel IACT event representation which is a list of single photon arrival times for each pixel (Photon-Stream). We will discuss our single photon extractor, its performance and its limitations. We will present example events where we identify individual, single air shower Cherenkov photons in the pool of individual, single night sky background photons.ISSN:1824-803