Astrofisica delle alte energie da Terra e dallo Spazio

High Energy Astrophysics from Ground and Space

Staff

Denis Bastieri​, Elisa Bernardini, ​Eugenio Bottacini​, Giovanni Busetto, Stefano Ciroi​, ​Alessandro De Angelis​, Michele Doro, Alberto Franceschini​, Mose’ Mariotti​, Piero Rafanelli, ​Riccardo Rando, ​Luca Zampieri (INAF OAPD)

PostDoc

Marco Berton, ​Aleksandr Burtovoi, ​Valentina Cracco, ​Giovanni La Mura​, Ruben Lopez-Coto, Simona Paiano​, Elisa Prandini​

PhD student

​Sina Chen, Enrico Congiu, ​Michele Fiori, Luca Foffano

Research activities

Our research activities are focused on the study of those mechanisms at the origin of those phenomena at the highest energies that populates the Universe and that are at the basis of the emission of ultra-relativistic particles (cosmic rays). Such emission is essentially connected with shock waves around compact objects of galactic nature (pulsar, micro quasars and supernova remnants) or of extragalactic nature (active galactic nuclei)
With the aim of discovering the sources of such energetic radiation, we have participated from the very initial phases to international experiments in the field of gamma-ray astronomy such as the Fermi satellite and the MAGIC telescopes, currently providing top-level results in the field. We are also involved in the study of X-ray catalog meant to discover new potentially interesting sources and in optical observation of various extragalactic targets, mainly focussed to the determination of the distance.
Our work has a strong internationally oriented collaboration component. For what deals future instruments, we are participating to the construction of the Cherenkov Telescope Array (CTA) as well as in the design of the new satellite MeV mission, called e-Astrogam.
Our specifici research lines are:


Technology

Our team takes part to the development of novel detectors for the observation of astrophysical sources.
 For land-based observations we need single-photon sensors (for visible and near-UV light). For the most part the detectors we develop and test in our laboratories are based on silicon photomultipliers. In an all-encompassing approach we design and test also light guides, mirrors and readout electronics.
Our detectors are brought to the existing observatories (e.g. in MAGIC, the Cherenkov telescope at the Canary islands) to be installed and tested in real-life conditions.
Detectors for space-based observations have a similar structure to those used in high-energy physics: silicon trackers, calorimeters, etc. We took part to the design, assembly and qualification of existing instruments (e.g. Fermi-LAT) and we are on the front line in defining the current proposals for the next-generation observatories (e-Astrogam, AMEGO).
Software activities include the design of new detector systems and their characterization by means of detailed simulation.
 Hardware activities focus on the assembly and test of new sensor prototypes, new data-acquisition electronics and data processing systems.

Contact: Mosè Mariotti, Riccardo Rando, Manuela Mallamaci


Black holes and relativistic jets in active galactic nuclei

Recent astronomical observations seem to confirm the idea that several galaxies host at their center a supermassive black hole with a mass thousands times larger than our sun. These galaxies, dubbed Active Galactic Nuclei (AGN), show very complex emission and absorption spectra, generated by the superposition of thermal and several components of non-thermal emission. About 10% of the active galaxies also show a highly collimated jet of relativistic particles  that extends over thousands of kpc. Depending on the line of sight from the Earth, these galaxies are dubbed radiogalaxies or blazars.

The focus of our research group is characterizing the physical conditions present in the AGN jet through the study of the electromagnetic emission of these objects, in particular those that reach the most extreme energies.

Contact: Elisa Prandini, Elisa Bernardini


Radiative mechanisms in galactic objects

Inside our Galaxy, there are several systems formed by a compact object, either a neutron star or a black hole, and a companion star that is been swallowed up by the compact object. Most of this acceleration is related to remnants of supernova explosions. In particular, there are systems formed by a compact object, either a neutron star or a black hole, and of a companion star that is disrupted and falls onto the compact object. These two sources rotate around the center of mass in an elliptical orbit. In some situations, these sources expel two jets of radiation and relativistic mass with a mechanism still unveiled, but very well studied. The nature of these jets is similar, but at a small scale, to the jets of active galactic nuclei. This is one of the reason why the study of these jets is of great interest. The gamma radiation –that images the highest energy phenomena occurring inside these binary systems – is an optimal way of investigating these phenomena.

Contacts: Luca Zampieri, Ruben Lopez-Coto, Aleksandr Burtovoi


Fundamental Physics

There are various topics in fundamental physics that can be probed with the observation of cosmic gamma-ray radiation. The reason is related to the high energies in play. The reasons are that these high energies are not reachable at Earth, and the cosmic distances can amplify phenomena, or connected to the presence of rare exotic objects that can interact with the Earth atmosphere. The principal topic of searches is surely the dark matter: most of the models in fact foresees that dark matter can annihilate or decay emitting radiation in the final products, at gamma energies. However, possible dependency of energy of the speed of light (Lorenz Invariance Violation) can be seen through the different in time of flight of photons at different energies. Other theories predict photons that can oscillate into axions like particles, and that can happen in astrophysical environment. The list does not finish here, and includes primordial black holes, magnetic monopoles, quark agglomerates, etc.

Contacts: Michele Doro, Alessandro de Angelis​


High-Energy Surveys

Sky surveys are a fundamental data basis for astronomy. They are used to systematically map the universe and its constituents and to discover new type of objects or new phenomena. Especially at energies above 15 keV, surveys reveal the non-thermal processes in astrophysical objects, which allow for a deep insight in the emission processes at work in the detected sources. Yet, detecting new sources is still challenging because of technological limitations of current space missions. To overcome such limitations, we take advantage of the combined use of the INTEGRAL mission (ESA) and of the Swift mission (NASA) to reveal new extragalactic and galactic sources. We use them to study the cosmological evolution of active galactic nuclei (AGNs), the formation of supermassive black holes in the early universe, and to discover new phenomena.

Contatto: Eugenio Bottacini


Multiple frequency investigation of active galactic nuclei

Active galactic nuclei (AGNs) are among the few cosmic sources that can emit photons at all frequencies, from radio waves to gamma rays, and are the brightest non-transient objects in the Universe, to such an extent that they are still visible at very large distances. The origin of this immense luminosity is primarily a material disc that is accreted by a supermassive black hole. The great amount of radiation that we can observe is emitted by converting the gravitational binding energy of accreted material into luminosity. Though these objects may look very different from each other and be classified into different categories (Seyfert galaxies, Quasars, Radiogalaxies, blazars), thanks to the unification models today we know that these sources are all related to the same object type and to the presence or absence of a plasma jet, magnetically accelerated at relativistic speeds close to the black hole. Though in the course of years many properties of these objects and the extreme physical phenomena that characterize them have been understood, several aspects remain unclear. The origin and dynamics of the ionized gas that is observed at large distances from the black hole in many AGNs, for example, are still uncertain. Likewise, we still need to clarify how AGNs evolve over time, how material jets originate from the vicinity of the black hole, what physical phenomena apply at such high energies, and how the AGN interacts with the galaxy that hosts it. Our research group deals with all these aspects, mainly through optical spectroscopy, but also by observing AGNs at other frequencies such as radio, X-rays and gamma rays. In addition to acquiring new data with numerous telescopes, including the Asiago observatories, we are focusing on the analysis of large online data archives, such as the Sloan Digital Sky Survey or the 6 Degree Field Survey, which allow to retrieve extensive information on this type of objects.

Contact: Stefano Ciroi


Observational Cosmology

High energy astrophysics has deep ties with the Cosmology. A particular interest is the photon-photon interaction, amongst those of high energy produced by cosmic sources and of extragalactic and cosmic radiation (Cosmic Microwave Background CMB, EBL), with the subsequent production of pairs of electrons and positrons. This phenomenon causes a cosmic opacity effect for the high energy photons, with a massive cross section if the product of the photon energies is larger than the squared mass of an electron. Therefore, photons with energies higher than 100 TeV are observable only inside our galaxy, photons with energies between 10-50 TeV interact with the far IR, and those around TeV energies with optical and UV photons. The spectral observations of blazar, in particular at several redshifts, and the identification of the absorption in the spectrum provide a tool of extraordinary interest to link the intensity and the energy of the background light at different cosmic epochs.  This radiation, that represent the integral of all the processes of energy production of cosmic sources between now and the Big Bang, is hardly ever directly observable because it is blurred by local sources (Zodiacal light, interplanetary dust emission, emission from the Galaxy), therefore the indirect observation of the effects of photon-photon interactions is crucial.
One of this radiative components of particular interest are the sources responsible of the cosmic re-ionization at z=10 with residual background in the near IR. TeV blazar observations at z>1 will provide interesting limits, or even detections. In addition, the study of the blazar sample in a wide redshift interval will allow to put decisive limits on the evolution history of the main cosmic sources, far away galaxies and AGN, dominant of the energy production by thermonuclear burning in stars and by gravitational accretion in AGN. Another interesting topic for the subgroup will be the statistical studies of the source population at high and very high energies, for example based on the all-sky Fermi catalogue, out of which a high fraction (>30%) are non-identified sources. Lastly, other topics regarding the extragalactic gamma background and the origin of the high energy background neutrinos observed by IceCube

Contacts: Alberto Franceschini, Giulia Rodighiero, Simona Paiano


Parallel Computation (htc) e a low power (lpc)