Gamma-Ray Burst Polarimetry: History and Future Prospects
25/11/2024
Gamma-Ray Bursts (GRB) are the brightest electromagnetic events in the Universe since the Big Bang. As such they have intrigued the astrophysical community since their accidental discovery in 1967. Despite almost 60 years of intense research, resulting in over 10000 GRB detections, very little remains known about these violent events. While we know that these events are related to the death of massive stars or the merger of compact objects, we still lack an understanding of how, and where, the gamma-rays which give these events their name, are produced. Attempts to understand this have thus far focussed primarily on measurements of the time of arrival, the direction and energy of the gamma-ray emission. Measurements of the 4th parameter, the polarization, are rare, despite their significant potential to resolve theoretical models. In this talk I will discuss this potential in detail, while in parallel addressing the reasons for the lack of polarization measurements. Finally, I will present an overview of past missions as well as the missions which aim to provide the first detailed measurements in the coming decade.
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Recent observations of the near-Earth radiation environment: a plethora of galactic, solar and magnetospheric particles
22/11/2024
The near-Earth radiation space is a unique environment where particle populations of different origins coexist and evolve dynamically over time and space, spanning a wide energy range. Galactic cosmic rays – entering the heliosphere – are continuously modulated by the change in the solar wind and the associated heliospheric magnetic field. Moreover, changes in galactic particle fluxes show a very clear time-dependence, which is directly related to the periodical activity of the Sun. However, the Sun acts as both a modulator and a source of space radiation – especially during maxima of solar activity – with powerful emissions of the so-called solar energetic particles (SEPs). Despite notable improvements in the latest decades, the complex mechanisms underlying their origin and transport still challenge the development of a comprehensive picture of SEP events. Many efforts have also been directed at modelling the Earth’s trapped charged particle environment, as in the case of the South Atlantic Anomaly (SAA). Observations of the SAA radiation environment are crucial to validate these models (e.g., the NASA AE9/AP9 models), as well as to investigate the temporal evolution of the geomagnetic field, to study perturbations generated by space weather events (such as geomagnetic storms), and, last but not least, to safeguard spacecraft systems and human crew health. After the foundational results of successful past (PAMELA) and present (AMS-02) spaceborne missions, the CSES (China Seismo-Electromagnetic Satellite) mission aims to continue the study of the near-Earth radiation environment, through a constellation of low-Earth orbit satellites. This presentation will review the main results achieved by the High-Energy Particle Detector (HEPD-01) on board the CSES-01 satellite, which will be followed by the launch of the improved HEPD-02 detector on the CSES-02 satellite in December 2024.
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Magnetic field amplification in neutron star mergers and the role of the MRI
21/11/2024
The first detection of a binary neutron star merger has made sharp reality the long-standing paradigm that these cosmic fireworks are exciting laboratories for extreme physics. To get the most out of present and future observations, however, we require accurate models of the merger dynamics, which can only be achieved through numerical relativity simulations. One of the key factors in these simulations is the magnetic field, which plays a crucial role in shaping the dynamics of the system. It is also instrumental in the launching of relativistic jets and the associated gamma-ray bursts. In this seminar I will discuss the main mechanisms responsible for the amplification of the magnetic field, with a particular focus on the magneto-rotational instability and its potential role in binary neutron star mergers."
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La materia oscura illuminata
20/11/2024
La materia oscura è la misteriosa componente che si pensa costituisca la grande maggioranza di tutta la materia dell’universo, e l' INFN le sta dando la caccia. Sotto il nome Dark Matter Day 2024, viene organizzata e presentata una serie di eventi, che in tutto il mondo festeggiano il lavoro di migliaia di scienziati, che cercano di accendere una luce sul lato più misterioso ed oscuro dell’Universo.
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Complex MgII broad line time evolution in a quasar: Clues for a subparsec binary supermassive black hole?
20/11/2024
Supermassive binary black hole (SMBBH) systems are believed to form during the mergers of galaxies. While their existence is strongly predicted, there are still no confirmed cases due to observational challenges, particularly at close separations. However, indirect evidence - such as periodic variability in quasar photometry and complexity in their spectral lines - supports their presence.
A search for long-period variability (100 < P [days] < 600) in the SDSS Stripe 82 region, potentially missed in previous studies, was conducted. We used precisely calibrated (1%-2%) photometry in the SDSS gri bands collected over roughly six years. Lomb-Scargle periodograms identified the most likely candidates for such periodic variability, which were then cross-matched with other surveys across the electromagnetic spectrum (both photometry and spectroscopy) to confirm their variability and classification. Additional time series data from Pan-STARRS and ZTF extended the observational baseline to over 20 years. All identified candidates were quasars, with the top-ranked one (P = 278 days) marked as a variable source in the Chandra X-ray catalog. Possible explanations for the quasars' periodic behavior include radio jet precession, tilted or warped accretion disks, tidal disruption events, and other accretion-related phenomena.
The to-ranked quasar was further analyzed using new MgII line observations and archived SDSS spectra, providing three epochs of MgII data. A key finding was that the MgII line displayed a double-peaked profile that evolved over time. By comparing synthetic magnitudes with photometric data and applying the PoSKI model, which examines emission lines and light curves of SMBBH candidates, a correlation was found that suggests the presence of a closely orbiting SMBBH. These sources are of significant scientific value, as their eventual merger would release a tremendous amount of energy as gravitational waves.
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The European Solar Telescope. Europe's bid for leadership in solar science
18/11/2024
This talk will introduce the project of the European Solar Telescope (EST),
considered a key European research infrastructure, and its role in advancing solar physics.
We'll discuss the relevant solar phenomena — like magnetic field interactions and solar
eruptions — that create space weather and solar storms on Earth. Their study requires
high-resolution, multi-layer observation. The EST, with its 4.2-meter Gregorian design and
adaptive optics system will provide unprecedented data in magnetic field measurements
and observations across a broad spectral range. These capabilities are set to transform our
understanding of solar activity by enabling detailed studies of solar magnetic fields and
plasma dynamics.
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Fiber networks in Orion: star formation and width variations
13/11/2024
The Herschel observations unveiled the complex organisation of the interstellar medium in networks of parsec-scale filaments over the past decade. Despite their variety of scales throughout the interstellar medium, the analysis of these same observations revealed filaments in nearby low-mass clouds to have a characteristic width of ~0.1 pc. The origin of this characteristic width and its impact on star formation, however, has been a matter of intense discussions in the past years. Even more with the identification of small-scale filamentary structures harboured inside the Herschel filaments. These networks of fibers have been recognised describing the gas structures in star-forming regions at sub-parsec scales, thus critically challenging the existence of a typical width for filaments. I am going to present our study of the dense gas organisation prior to the formation of stars in a sample of 7 star-forming regions within Orion. This EMERGE Early ALMA Survey includes OMC-1/-2/-3/-4 South, LDN 1641N, NGC 2023, and the Flame Nebula, all surveyed at high spatial resolution (4.5'' or ~2000 au) in N2H+ (1−0) using ALMA+IRAM-30m observations. I will present the star-forming gas spatial distribution, its column density variations, its thermal structure, and its internal motions across the152 fibers identified in our survey.
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From clouds to fragments: on the multi-scale interplay between gravity and turbulence
08/11/2024
The star formation mechanism occurs in well defined structures that can be identified and studied in great details in our own Galaxy: the process starts in giant molecular clouds, objects extended up to several tens of parsecs, within which elongated sub-structures, called filaments, may form. Inside filaments, round-like condensations extended up to ~1pc in radius, the so-called clumps, are the natural birth site of the pre- and proto- stellar fragments, inside which will origin the future stars.
There are still many open questions in this hierarchical view of the star formation process: are these structures relatively confined from each other, or is the large-scale environment affecting the dynamics of the formation down to clumps and fragments? Is there a continuous interplay of the various forces involved in the process, namely turbulence, gravity (and magnetic fields), at all scales? Or is there a relevant scale at which gravity will start to dominate the collapse, with critical implications on the star-formation mechanism?
After a general overview of the problem, I will present in details some recent results focused on the interplay between gravity and turbulence at the filament, clump and fragment scales. To investigate this interplay at the larger scales, we have combined the dynamics of so-called 70 micron quiet clumps, i.e. very pristine regions not yet strongly affected by feedbacks, with the dynamics of the parent filaments in which they are embedded. At smaller scales, I will discuss the different scenarios of fragments formation in light of the most recent results from the SQUALO (Star formation in QUiescent And Luminous Objects) project. This ALMA survey has been designed to investigate the formation properties in a sample of massive clumps selected to be at various evolutionary stages and with the common feature that they are all accreting at the clump scales.
Our results show that a large scales we observe a continuous interplay between turbulence and gravity, where the former creates structures at all scales and the latter takes the lead above a critical value of the surface density is reached, ~ 0.1 g cm^-2. At the same time, the fragmentation properties show several indications that the fragment are "clump-fed", i.e. the process is dynamical and the gravity dominates the collapse inside our massive clumps.
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The EVN, JIVE and SKA through the decades – history, people and politics
24.10.2024
I will give an overview of the historical development of these three pillars of global radio astronomy from their origins in the 1970s, 1980s and 1990s respectively to the current day. All three have travelled along different routes to maturity, the EVN as a global “grass roots” collaboration, JIVE as a European Research Infrastructure Consortium (ERIC), and SKA as an Inter-Governmental (Treaty) Organisation. I will also touch on key issues in these collaborations including the interactions between the radio astronomy community and their funding agency and government counterparts as well as the political environments at national, regional and global level that created the opportunities for new infrastructures.
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Unleashing the Fury: The Power and Impact of Supermassive Black Hole Winds
23/10/2024
Supermassive black hole (SMBH) winds are powerful outflows, capable of reaching velocities up to half the speed of light, driven by the immense energy near these massive objects. These ultra-fast outflows (UFOs) carry significant mass and energy, playing a potential role in shaping galaxy evolution over cosmic time. In this talk, we will present the latest insights into SMBH winds, leveraging X-ray and multi-wavelength observations along with advanced modeling techniques. We’ll also explore their connection to other high-energy phenomena such as variable AGN, SMBH binaries, and tidal disruption events. In particular, we'll highlight new findings on quasi-periodic outflows (QPOuts) in close binary black hole systems, which may serve as electromagnetic precursors to LISA gravitational wave sources. Finally, we’ll offer a sneak peek at groundbreaking results from XRISM/Resolve’s spectroscopic observations of the powerful UFO in quasar PDS 456.
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