Conveners
Extragalactic Sources: I - Stirling Auditorium
- Alberto Berti
Extragalactic Sources: II - Humphrey Auditorium
- Cecilia Lunardini
Extragalactic Sources: III - Chernoff Auditorium
- Matteo Cerruti (Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 8 E08028 Barcelona, Spain)
Extragalactic Sources: IV - BioSci 1102
- Jeremy Perkins (NASA/GSFC)
Blazars are key-elements in the understanding of the extragalactic Universe from the astroparticle physics point of view. These sources are jetted radio-loud active galactic nuclei dominated by non-thermal emission that extends across the electromagnetic spectrum. Their emission is a proof of cosmic particle acceleration and the production of ultra-relativistic particles within their physical...
Absorption and emission lines in the optical spectrum are typically used to investigate the presence of large-scale environments in active galactic nuclei. In BL Lac objects, this approach is hampered by the dominant non-thermal continuum of their relativistic jet, which prevents us from identifying the thermal emission of the photon fields produced by such large-scale structures.
However,...
As highly energetic physics laboratories, blazars are prime candidates to reveal the mysteries of the most energetic parts of our universe. For many of them, the very-high-energy (>0.2 TeV, VHE) γ-ray band as well as the X-ray bands are especially interesting since they host the most variable part of their emission.
We present a multiwavelength (MWL) data set of Mrk 501 obtained from 2017...
H 1426+428 is a, so called, extreme high-frequency-peaked BL Lac object (extreme HBL) located at a redshift of z = 0.129 that was detected on a number of occasions by the previous generation of ground-based gamma-ray telescopes (Whipple, CAT and HEGRA), with its VHE flux ranging up to 80% of the Crab Nebula (Crab Units, CU) above a few hundred GeV. Current-generation TeV observatories...
The origins of the GeV gamma-rays from nearby radio galaxies are unknown. Hadronic emission from magnetically arrested disks (MADs) around central black holes (BHs) is proposed as a possible scenario. Particles are accelerated in the MAD by magnetic reconnection and stochastic turbulence acceleration. We investigate the feature of the radio galaxies that can be explained by the MAD model. We...
Particle pre-acceleration remains an important unresolved problem in the diffusive shock acceleration (DSA) theory. This mechanism acting at merger shocks in galaxy clusters is thought to produce relativistic electrons that form the so-called radio relics detected in radio and X-ray. DSA at merger shocks may also generate high- and ultra-high-energy cosmic rays and associated gamma-ray...
Experimental observations have demonstrated a strong correlation between star-forming processes and gamma-ray luminosities. However, the very nature of these emissions is still under debate. Certainly, star-forming and starfurst galaxies (SFGs and SBGs) are well-motivated astrophysical emitters of gamma-rays and neutrinos through hadronic collisions. In this talk, I will present several...
The origins of cosmic MeV gamma-ray and high-energy neutrino backgrounds have been veiled in mystery since their discoveries. In this talk, I will propose raidiatively inefficient accretion flows in low-luminosity active galactic nuclei (AGN) as the common source of these backgrounds. Thermal electrons in low-luminosity AGN emit MeV gamma-rays by the Comptonization process, while non-thermal...
Gamma-ray observations of extreme astrophysical transient phenomena continue to play an important role in understanding both the physical emission mechanisms in these sources and their contribution to the cosmic-ray population. One transient class that continues to expand, but remains difficult to understand, are Fast Radio Bursts (FRBs). Due to their sporadic and short-lived emission (~ms),...
Secondary gamma-ray emission from distant TeV sources induced by the effects of propagation of gamma rays through the intergalactic medium could be used to probe the intergalactic magnetic field (IGMF). A proper realization of this opportunity requires a knowledge on the evolution of the source luminosity from GeV to TeV energies over the relevant period of time. Here we use a sample of MAGIC,...
The origin of the large-scale magnetic fields in the Universe is one of the long-standing problem in cosmology. To discriminate among the different explanations it is crucial to measure the intergalactic magnetic field (IGMF) in the voids among the galaxies. Gamma-rays coming from extragalactic sources can be used to constrain the IGMF due to their interaction with the intergalactic medium....
The paths of cosmic rays are deflected upon passing through the Galactic magnetic field structure. The strength of the deflections that these cosmic rays undergo is dependent on the strength and structure of the Galactic magnetic field. Unfortunately, our knowledge of the Galactic magnetic field is very limited, especially when considering the fields present in the Galactic halo region. In...
Axion-like particles (ALPs) are a broad class of pseudo-scalar bosons that generically arise from broken symmetries in extensions of the standard model. In many scenarios, ALPs can mix with photons in regions with high magnetic fields. Photons from distant sources can mix with ALPs, which then travel unattenuated through the Universe, before they mix back to photons in the Milky Way galactic...
After almost two decades of searches, in January 2019, MAGIC unambiguously detected TeV emission from the gamma-ray burst GRB 190114C. This long-awaited detection marked the beginning of the very high energy (VHE, $E>100$ GeV) era for GRB studies. After this historical achievement, the MAGIC collaboration continued its effort in the follow-up of GRBs. In December 2020, MAGIC detected GRB...
The multiwavelength observation of GRB 190114C, an extremely bright gamma-ray burst (GRB), opens a new window for studying the emission mechanism of GRBs. The Very-High-Energy (VHE; >100 GeV) detection by MAGIC suggested the inverse Compton process as the emission mechanism for the VHE gamma rays during the early afterglow phase of the burst. However, other VHE GRB detections have casted doubt...
Gamma-ray burst (GRB) emission in the very high energy (VHE, E>100GeV) band has been discussed and theorized for many years, but has eluded for a long time the observations. Only in the last years the Cherenkov telescopes MAGIC and H.E.S.S. have unequivocally proven that VHE GRB afterglow radiation is produced up to a few TeV for at least a (sub-)class of GRBs. This newly opened TeV spectral...
The Compton Spectrometer and Imager (COSI) is a Small Explorer (SMEX) satellite mission selected by NASA for development. COSI is a wide-field telescope designed to survey the entire gamma-ray sky at 0.2-5 MeV. It provides imaging, spectroscopy, and polarimetry of astrophysical sources, and its germanium detectors provide excellent energy resolution for emission line studies. The science...
