Conveners
Extragalactic sources
- Emma Storm (GRAPPA, University of Amsterdam)
Extragalactic sources
- John Gallagher
We have discovered a rare new form of long-term radio variability in the light-curves of active galaxies (AG) (arXiv:1702.06582, arXiv:1702.05519) --- Symmetric Achromatic Variability (SAV) --- a pair of opposed and strongly skewed peaks in the radio flux density observed over a broad frequency range. We propose that SAV arises through gravitational milli-lensing when relativistically moving...
The jets of active galactic nuclei (AGN) are among the most powerful systems in the Universe. Their emission spans over an extremely wide energy range, from radio to gamma-rays or even TeV energies, and often shows pronounced variability with timescales anywhere between a few years and several minutes. Therefore, high-cadence, multi-band monitoring programs are essential in the investigation...
We present a search for hour-scale very high energy (VHE) flares from 187 blazars monitored by the HAWC observatory. With a wide field of view of ~2 sr and sensitivity to energies above a few hundred GeV, HAWC functions as a survey instrument and facilitates searches for rapid variability in the VHE band. The currently operational HAWC real-time flare monitor takes advantage of this capability...
Extensive observations by Fermi, AGILE, and TeV telescopes have opened a new window into the high-energy physical processes of AGNs and raised questions about the physics of their jets, their formation and cosmological evolution, and their impact on their environments and the growth of structure in the Universe. Multiwavelength observations in X-rays and at GeV and TeV energies point to a...
Robust connections exist between various energy regions in the spectra of nearby galaxies. The flux ratios from widely separated spectral regions are often remarkably constant while originating via very different processes with varying efficiencies. Although the radio-far infrared (FIR) correlation is best known, consistent flux ratio relationships also are found between gamma-rays and the...
Despite intensive research, some fundamental properties of the most luminous particle accelerators and transients like AGNs, GRBs, etc. are unknown. Location and mechanisms of particle acceleration, connection to flaring and quiescent states, leptonic vs hadronic emission are open questions. Complexity of environments and processes make it hard to disentangle different scenarios. This suggests...
The recent observations of powerful, minute-timescale TeV flares from
several blazars pose serious challenges to theoretical models for the
blazar emission. In this talk, I will discuss the magnetic
reconnection model for the blazar flaring. I argue that radiation
emitted from the reconnection layers can account for the observed
“envelope” of ~day-long blazar activity as well as the fastest
...
Very high energy gamma-rays produced by extragalactic sources are absorbed in the intergalactic medium. High energy photons interact with low energy photons from the extragalactic background light (UV to IR) producing pairs of electron - positrons. Newly created leptons scatter CMB photons to gamma-ray energies. Spectral properties, halo extension and time delay due to the cascade strongly...
A Type Ia supernova (SNIa) could go entirely unnoticed in the Milky Way and nearby starburst galaxies, due to the large optical and near-IR extinction in the dusty environment, low radio and X-ray luminosities, and a weak neutrino signal. But the recent SN2014J confirms that Type Ia supernovae emit γ-ray lines from $^{56}$Ni→$^{56}$Co→$^{56}$Fe radioactive decay, spanning 158 keV to 2.6 MeV....
It is widely accepted that supernova (SN) shocks can accelerate particles to very high energies, although the maximum energies are still unclear. These accelerated particles can interact with other particles to produce gamma-ray emission. Details of the process are not well characterized, including the dynamics and kinematics of the SN shock wave, the nature and magnitude of the magnetic...
Using a simplified model for the hadronic emission from young supernova remnants (SNRs), we derive an expression to calculate the hadronic luminosity with time, depending on the supernova (SN) ejecta density profile and the density structure of the surrounding medium. We then use this to estimate the gamma-ray emission from SN 1987A, the nearest visible supernova to us in over 300 years. The...
