Understanding Blazar emission through multifrequency observations.

The heart of this thesis is the study of the multifrequency behaviour of a very special family of active galactic nuclei (AGNs) called blazars. The emission of these sources is generally dominated by non-thermal radiation from a plasma jet, making them the best candidates to investigate the properties of jets in AGNs. We present an analysis of the flux and broad-band spectral variability of these objects from radio to the gamma-rays. The radio, optical and near-infrared data were mostly obtained thanks to the Whole Earth Blazar Telescope (WEBT) Collaboration and Steward Observatory blazar spectropolarimetric monitoring, while high-energy data come from space observatories. In particular, ultraviolet and X-ray data were taken from Swift and gamma-ray data from Fermi. We produce multifrequency light curves that allow us to investigate the variability properties of these objects on different time scales, the correlation between flux changes in the different bands and possible time delays. From these results we infer which are the most plausible physical mechanisms for blazar emission and the jet structure, in particular where the emission is located and the jet possible curvature. From this collection of multifrequency data we can determine the energy spectral distribution (SED). Observing simultaneously at different frequencies and in different brightness states, we can detect whether there are emission contributions that are not coming from the jet, but from the AGN nucleus. In some cases we are able to observe activity states in which emission might flow from the accretion disk, while in other ones it comes from the disk after reprocessing by fast-moving gas clouds around the accretion disk, known as broad line region (BLR). The detection of the accretion disk and/or BLR emission is very important because it helps us to understand the relation between the blazars and the other types of AGNs. This is a challenging topic since very high-quality data are needed, especially at ultraviolet frequencies, i.e. in a spectral region strongly affected by Galactic absorption. Once we have built light curves and SEDs we use them to test different jet models proposed to describe blazar emission. We know that the blazar emission at low energies is synchrothron radiation produced by relativistic electrons moving in a magnetic field. The radiation at high energies is likely produced by an inverse Compton process, where soft photons are scattered by the same relativistic electrons. However, the origin of these photons is still under discussion. As for the variability mechanisms, particle injection, acceleration and cooling are likely at work, together with shocks propagating along the jet and orientation effects in curved and dynamic jets. Recently, a lot of observing effort has been devoted in providing polarimetric data in order to obtain information on the behaviour of the magnetic field. We analyze a wide dataset of polarimetric data on several blazars to identify characteristic properties. We found a variety of behaviours, some of them ordered but the majority of them resulting in a chaotic trend, so that a simple and all-inclusive explanation is not possible. Indeed, it is very likely that turbulence affects the magnetic field most of the time. All the above issues are still matter of debate and are expected to provide a wide research field to explore for many years

Fotometria e calibrazione infrarossi. User Manual

Manuale dove si descrivono le procedure di calibrazione e fotometria infraross

Software di riduzione dati della Camera Infrarossa CAINDR. User Manual

User Manual- Software per la riduzioni dei dati infrarossi della camera CAINDR, situata nel Telescopio Carlos Sanchez (TCS) all'Osservatorio del Teide (Tenerife, Spagna

A New Statistical Approach to the Optical Spectral Variability in Blazars

We present a spectral variability study of a sample of about 25 bright blazars, based on optical spectroscopy. Observations cover the period from the end of 2008 to mid 2015, with an approximately monthly cadence. Emission lines have been identified and measured in the spectra, which permits us to classify the sources into BL Lac-type or FSRQs, according to the commonly used EW limit. We have obtained synthetic photometry and produced colour-magnitude diagrams which show different trends associated with the object classes: generally, BL Lacs tend to become bluer when brighter and FSRQs become redder when brighter, although several objects exhibit both trends, depending on brightness. We have also applied a pattern recognition algorithm to obtain the minimum number of physical components which can explain the variability of the optical spectrum. We have used NMF (Non-Negative Matrix Factorization) instead of PCA (Principal Component Analysis) to avoid un-realistic negative components. For most targets we found that 2 or 3 meta-components are enough to explain the observed spectral variability

Swift multi-wavelength observations of the high-redshift Blazar S5 0836+710 (4C 71.07)

We present the preliminary results of a year-long Swift monitoring campaign of the high-redshift (z=2.172) flat-spectrum radio quasar (FSRQ) S5 0836+710 (4C 71.07). The campaign, based on one observation per month, 5 ks each observation, for 12 months, allowed us to investigate the synchrotron and nuclear emission contributions to the optical-UV frequency range of its spectral energy distribution and the X-ray spectral variations along a baseline of a year. We obtained a high-accuracy determination of UVOT magnitudes, an X-ray photon index with an uncertainty of the order of 5%, and well-sampled light curves both in the optical-UV and X-ray energy bands to study their possible modulations and correlations. Our study allowed us to exploit the unique Swift capabilities in terms of both simultaneous energy coverage and schedule flexibility. The Swift monitoring campaign was supported by observations by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) Collaboration, which provided radio, near-infrared, and optical photometric data as well as optical polarimetry. Moreover, a spectroscopic monitoring was obtained at the William Herschel Telescope (WHT) and the Nordic Optical Telescope (NOT). All these observations will allow us to obtain a comprehensive picture of the jet as well as of the nuclear source emission. <P /

Multiwavelength behaviour of the blazar OJ 248 from radio to γ-rays

We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006-2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the Gamma-Ray Large Area Space Telescope (GLAST)-AGILE Support Program of the Whole Earth Blazar Telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (γ-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman α intervening system at z = 0.525. Two major outbursts were observed in 2006-2007 and in 2012-2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio-optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the γ-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches ∼19 per cent during the early stage of the 2012-2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarization angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour/structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg II broad emission line with an essentially stable flux of 6.2 × 10- 15 erg cm- 2 s- 1 and a full width at half-maximum of 2053 km s- 1

Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds

We compare the Gaia DR2 and Gaia EDR3 performances in the study of the Magellanic Clouds and show the clear improvements in precision and accuracy in the new release. We also show that the systematics still present in the data make the determination of the 3D geometry of the LMC a difficult endeavour; this is at the very limit of the usefulness of the Gaia EDR3 astrometry, but it may become feasible with the use of additional external data. We derive radial and tangential velocity maps and global profiles for the LMC for the several subsamples we defined. To our knowledge, this is the first time that the two planar components of the ordered and random motions are derived for multiple stellar evolutionary phases in a galactic disc outside the Milky Way, showing the differences between younger and older phases. We also analyse the spatial structure and motions in the central region, the bar, and the disc, providing new insights into features and kinematics. Finally, we show that the Gaia EDR3 data allows clearly resolving the Magellanic Bridge, and we trace the density and velocity flow of the stars from the SMC towards the LMC not only globally, but also separately for young and evolved populations. This allows us to confirm an evolved population in the Bridge that is slightly shift from the younger population. Additionally, we were able to study the outskirts of both Magellanic Clouds, in which we detected some well-known features and indications of new ones

Investigating the puzzling synchrotron behaviour of Mkn 421

<p>We present the preliminary results of a huge observing effort spent on the BL Lac object Mkn 421 by the Whole Earth Blazar Telescope (WEBT; http://www.oato.inaf.it/blazars/webt/). The multiwavelength analysis covers the period 2007-2015, including the 2012-2013 outburst detected at optical and X-ray frequencies. The WEBT continuous monitoring was performed with 35 optical and near-infrared telescopes, collecting more than 6000 data points, while UV and X-ray data were acquired by the Swift satellite during 709 pointings at the source. Optical polarimetry was provided by the Calar Alto, Liverpool, Steward, and St. Petersburg observatories. We investigate the synchrotron emission from the Mkn 421 jet with the main goal of understanding the different behaviour of the optical and X-ray radiations, which are expected to come from the same emission mechanism. Moreover, we study the relationship between the flux and polarization variability, focussing on episodes characterized by wide rotations of the electric vector polarization angle.</p