Found 62 talks archived in Particle astrophysics, physical data and processes
Axion detection would be one of the most exciting moments in the entire history of science. This hypothetical particle can simultaneously explain two fundamental problems in Modern Physics: the mystery of dark matter and the CP problem of the strong interaction. In this talk, I will provide an overview of the status for the search for axions and I will explain how the DALI experiment can go beyond these frontiers.
The improvement on the Imaging Air Cherenkov Technique led to the discovery of a new class of compact binaries: the gamma-ray binaries. This small class consist of only five members, all of them composed by a massive star and a compact object. The nature of the compact object is unknown for all of them but PSR B1259-63, which contains a pulsar. It is crucial to study and monitor these systems not only to understand their behavior, the scenario accounting for the gamma-ray emission and their nature but also to comprehend why we have not detected more sources of this exclusive family. In this presentation, I will review the state-of-the-art of this field and I will present the observations performed with the MAGIC telescopes in order to unveil the nature of gamma-ray binaries.
Gamma Ray Bursts (GRBs) are among the most energetic transient phenomena frequently followed up by different observatories and yet several fundamental questions are still open. Fermi and MAGIC are continuing their observations of GRBs since several years, giving highest priorities to the most interesting events. This effort led to remarkable discoveries in the High Energy regime, showing potential for even more meaningful achievements in the Very High Energy (VHE) regime. Enhanced follow up strategies of MAGIC and soon to come CTA Large Size Telescopes (LST) observations create unique opportunities for the detection of GRBs at VHE. In this talk I will give an overview of the high energy GRB properties as seen by Fermi and show the potential for the first VHE detection with MAGIC and CTA LSTs.
The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes reported the discovery of the most distant gamma-ray source ever observed at very high energies, thanks to the “replay” of an enormous flare by a galactic gravitational lens as foreseen by Einstein’s General Relativity. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components separated by a 10–12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma-ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.
Work published in A&A 595, A98 (2016) ( http://www.aanda.org/articles/aa/abs/2016/11/aa29461-16/aa29461-16.html)
The small source class of gamma-ray binaries consists at present of six known objects with different orbital periods ranging from days up to several years. One of the best studied gamma-ray binary across all frequencies, LS I +61 303, is highly variable at any given orbital phase and was lately discovered to show on top of orbital also superorbital variability at high energies. In contrary, the other famous binary, LS 5039, shows no variations apart from those related to the orbital period. The other unresolved mystery in most of these sources is the nature of their compact object. Both neutron star (e.g. PSR B1259-63) and probable black hole (microquasar, e.g., Cyg X-3) binary systems have been detected at GeV energies, hence both types of compact object are viable in the undetermined systems. In this talk I will present the recent findings on the known gamma-ray binaries up to now and discuss their behavior at high and very high energies.
Using ~320h of good-quality Crab data from Feb 2007 to Apr 2014 the MAGIC telescopes measured the most energetic pulsed photons from a pulsar to date. The new results obtained probe the Crab Pulsar as the most compact TeV accelerator known to date. The remarkable detection of pulsed emission up to 1.5 TeV revealed by MAGIC imposes severe constraints on where and how the underlying electron population produces gamma-rays at these energies. Such TeV pulsed photons require a parent population of electrons with a Lorentz factor of at least 5E6. These results strongly suggest IC scattering off low-energy photons as the emission mechanism and a gamma-ray production region in the vicinity of the light cylinder, requiring a revision of the state-of-the-art models proposed to explain how and where gamma-ray pulsed emission from 100 MeV to 1.5 TeV are produced. Investigating the extension of the very high-energy spectral tail of the Crab Pulsar at energies above 400 GeV, the pulse profile was found to show two narrow peaks synchronized with those measured in the GeV energy range. The spectra of the two peaks follow two different power-law functions from 70 GeV up to 1.5 TeV and connect smoothly with the spectra measured above 10 GeV by the Large Area Telescope (LAT) on board the Fermi satellite.
The search for detection of gamma-rays in the very-high-energy range (VHE, >100GeV) from distant AGNs by Imaging Atmospheric Cherenkov Telescopes (IACTs) gets very complicated at high redshifts, not only because of the lower flux due to the distance of the source, but also due to the consequent absorption of gamma-rays by the extragalactic background light (EBL), affecting VHE sources at z~0.1 and beyond. The farthest source ever detected in the VHE domain was the blazar PKS1424+240, at redshift z>0.6. In the last months MAGIC, a system of two 17 m of diameter IACTs located in the Canary island of La Palma, has been able to go beyond that limit and to push the boundaries for VHE detection to redshifts z~1. The two sources detected and analyzed, blazar S30218+35 (Atel discovery #6349) and FSRQ PKS1441+25 (Atel discovery #7416) are located at redshift z=0.944 and z=0.939 respectively. S30218+35 is also the first gravitational lensed blazar ever detected in VHE. The multiwavelength dataset collected allowed us to test for the first time the present generation of EBL models at such distances. I will show results on MAGIC analysis on S30218+35 and PKS1441-25, including spectral energy distributions and EBL absorption studies, in a multi-wavelength context.
I will describe the roles of jets in several quite different astrophysical systems. These include exploding core collapse supernovae, expelling common envelopes, and heating gas in clusters of galaxies. Hot bubbles inflated by jets seem to be a key ingredient in the interaction of jets with the ambient gas. The understanding that jets can efficiently interact with the ambient gas leads to new notions, such as the jittering jets model to explode massive stars, and the grazing envelope evolution(GEE) that can replace the common envelope evolution in some cases.
Things should be made simple, but not simpler.
What we want to show is that General Relativity, as it stands today, can be considered as a gravitational theory of low velocity spinless matter, and therefore a restricted theory of gravitation.
Gravity is understood as a geometrization of spacetime. But spacetime is also the manifold of the boundary values of the spinless point particle in a variational approach. Since all known elementary matter, baryons, leptons and gauge bosons are spinning objects, it means that the manifold, which we call the kinematical space, where we play the game of the variational formalism of a classical elementary particle must be greater than spacetime.
Mathematics shows that this manifold for any arbitrary mechanical system is always a Finsler metric space, such that the variational formalism can be interpreted as a geodesic problem on this metric space.
This manifold is just the flat Minkowski space for the free spinless particle. Any interaction modifies its flat Finsler metric as gravitation does.
The same thing happens for the spinning objects, but now the Finsler metric space has more dimensions and its metric is modified by any interaction, so that to reduce gravity to the modification only of the metric of the spacetime submanifold is to make a simpler theory, the gravitational theory of spinless matter.
Even the usual assumption that the modification of the metric only produces a Riemannian metric of the spacetime is also a restriction because in general the coefficients for a Finsler metric, are also dependent on the velocities. Removal of the velocity dependence of metric coefficients is equivalent to consider the restriction to low velocity matter.
In the spirit of unification of all forces, gravity cannot produce, in principle, a different and simpler geometrization than any other interaction.
References: arXiv: 1203.4076
- TBDThursday March 7, 2024 - 10:30 GMT (Aula)
- TBDProf. Kentaro NagamineThursday March 21, 2024 - 10:30 GMT (Aula)