
Stavros DimitrakoudisUniversity of Alberta | UAlberta · Department of Physics
Stavros Dimitrakoudis
PhD
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49
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Introduction
Stavros Dimitrakoudis currently works at the Department of Physics, University of Alberta. Stavros does research in Space Physics and Astrophysics. Their most recent publication is 'A Multimessenger Picture of the Flaring Blazar TXS 0506+056: implications for High-Energy Neutrino Emission and Cosmic Ray Acceleration'.
Additional affiliations
February 2014 - May 2015
Publications
Publications (49)
We perform the first dedicated comparison of five hadronic codes (AM$^3$, ATHE$\nu$A, B13, LeHa-Paris, and LeHaMoC) that have been extensively used in modeling of the spectral energy distribution (SED) of jetted active galactic nuclei. The purpose of this comparison is to identify the sources of systematic errors (e.g., implementation method of pro...
The relationship between auroral, ground, and plasma sheet signatures in the late growth phase is crucial for understanding the sequence of events during a substorm expansion phase onset. Here we show conjugate ground‐auroral‐satellite observations of a substorm that occurred on 18 September 2021, between 04:45 and 05:00 UT, where four auroral acti...
The sequence of events associated with the triggering of energy release during substorm expansion phase onset is still not well‐understood. Oberhagemann and Mann (2020b, https://doi.org/10.1029/2019gl085271) proposed a new substorm onset mechanism, where the transition toward parallel proton pressure anisotropy during tail stretching in the late gr...
Plain Language Summary
Geomagnetically induced currents (GICs) flowing along electrically conductive infrastructure, such as power transmission lines, are produced by a naturally induced geoelectric field during geomagnetic disturbances, such as magnetic storms. GIC can cause widespread blackouts across power grids, resulting in the loss of electri...
Geomagnetically induced currents (GICs) can be driven in terrestrial electrical power grids as a result of the induced electric fields arising from geomagnetic disturbances (GMD) resulting from the dynamics of the coupled magnetosphere‐ionosphere‐ground system. However, a key issue is to assess an optimum spacing for the magnetometer stations in or...
Using ground magnetometer measurements from the IMAGE array over the timespan of one solar cycle, we apply wavelets to statistically assess the power of ultra‐low frequency (ULF) waves from L = 3.34 to L = 13.6 as a function of Kp, solar wind speed (Vsw ${V}_{\text{sw}}$), solar wind dynamic pressure (Pdyn ${P}_{\text{dyn}}$), Dst, and Bz ${B}_{z}$...
Blazar hadronic models have been developed in the past decades as an alternative to leptonic ones. In hadronic models the gamma-ray emission is associated with synchrotron emission by protons, and/or secondary leptons produced in proton-photon interactions. Together with photons, hadronic emission models predict the emission of neutrinos that are t...
The IceCube report of a excess of 13 ± 5 neutrino events in the direction of the blazar TXS 0506+056 in 2014–2015 and the 2017 detection of a high-energy neutrino event, IceCube-170922A, during a gamma-ray flare from the same blazar, have revived the interest in scenarios for neutrino production in blazars. We perform comprehensive analyses on the...
Blazars have been proposed as efficient particle accelerators and promising neutrino sources long before the discovery of astrophysical high-energy neutrinos. The recent report by the IceCube Collaboration of a $\sim 3.5\sigma$ excess of $13\pm5$ neutrino events in the direction of the blazar TXS 0506+056 during a six month-long period in 2014-2015...
Active galactic nuclei (AGN) with relativistic jets, powered by gas accretion onto their central supermassive black hole (SMBH), are unique laboratories for studying the physics of matter and elementary particles in extreme conditions that cannot be realized on Earth. For a long time since the discovery of AGN, photons were the only way to probe th...
Detection of the IceCube-170922A neutrino coincident with the flaring blazar TXS 0506+056, the first and only ~3σ high-energy neutrino source association to date, offers a potential breakthrough in our understanding of high-energy cosmic particles and blazar physics. We present a comprehensive analysis of TXS 0506+056 during its flaring state, usin...
Detection of the IceCube-170922A neutrino coincident with the flaring blazar TXS 0506+056, the first and only 3-sigma high-energy neutrino source association to date, offers a potential breakthrough in our understanding of high-energy cosmic particles and blazar physics. We present a comprehensive analysis of TXS 0506+056 during its flaring state,...
We are pleased to address the comment on our paper from Shprits et al. since we believe it supports our conclusion that magnetopause shadowing and ultralow-frequency (ULF) wave outward transport can drive fast losses into the heart of the ultra-relativistic electron radiation belt and produce a remnant belt. As reported by Baker et al., the Septemb...
Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the...
Blazars, a subclass of active galactic nuclei, are prime candidate sources for the high energy neutrinos recently detected by IceCube. Being one of the brightest sources in the extragalactic X-ray and γ-ray sky as well as one of the nearest blazars to Earth, Mrk 421 is an excellent source for testing the scenario of the blazar-neutrino connection,...
Blazars are prime candidate sources for the high energy neutrinos recently detected by IceCube. Being one of the brightest sources in the extragalactic X-ray and $\gamma$-ray sky as well as one of the nearest blazars to Earth, Mrk 421 is an excellent source for testing the scenario of the blazar-neutrino connection. Here, we model the spectral ener...
We present two ways of modeling the spectral energy distribution of blazars in the hadronic context and discuss the predictions of each "hadronic variant" on the spectral shape, the multi-wavelength variability, the cosmic-ray flux, and the high-energy neutrino emission. Focusing on the latter, we then present an application of the hadronic model t...
We present electron phase space density (PSD) calculations as well as
concurrent Pc5 and chorus wave activity observations during two intense
geomagnetic storms caused by interplanetary coronal mass ejections (ICMEs)
resulting in contradicting net effect. We show that, during the 17 March
2013 storm, the coincident observation of chorus and relativ...
Ultra-low frequency (ULF) waves can contribute to the transport, acceleration and loss of electrons in the radiation belts through inward and outward diffusion. However, the most appropriate parameters to use to specify the ULF wave diffusion rates are unknown. Empirical representations of diffusion coefficients often use Kp; however, specification...
We present a method of constraining the properties of the γ-ray emitting region in flat spectrum radio quasars in the one-zone
proton synchrotron model, where the γ-rays are produced by synchrotron radiation of relativistic protons. We show that for
low enough values of the Doppler factor δ, the emission from the electromagnetic (EM) cascade which...
The recent IceCube discovery of 0.1-1 PeV neutrinos of astrophysical origin
opens up a new era for high-energy astrophysics. Although there are various
astrophysical candidate sources, a firm association of the detected neutrinos
with one (or more) of them is still lacking. A recent analysis of plausible
astrophysical counterparts within the error...
The recent discovery of extragalactic PeV neutrinos opens a new window to the exploration of cosmic ray accelerators. The
observed PeV neutrino flux is close to the Waxman–Bahcall upper bound implying that gamma-ray bursts (GRBs) may be the source
of ultrahigh energy cosmic rays (UHECRs). Starting with the assumption of the GRB–UHECR connection, we...
We present the neutrino and UHECR spectra obtained from a detailed fitting of the spectral energy distribution (SED) of Mrk 421 (March 2001) using two variations of the leptohadronic model. In particular, while the low-energy component (optical to X-rays) of the SED is fitted by synchrotron emission of primary electrons in both models, the high-ene...
We explore a one-zone hadronic model that may be able to reproduce γ-ray burst (GRB) prompt emission with a minimum of free
parameters. Assuming only that GRBs are efficient high-energy proton accelerators and without the presence of an ab initio
photon field, we investigate the conditions under which the system becomes supercritical, i.e. there is...
The recent discovery of extragalactic PeV neutrinos opens a new window to the
exploration of cosmic-ray accelerators. The observed PeV neutrino flux is close
to the Waxman-Bahcall upper bound implying that gamma-ray bursts (GRBs) may be
the source of ultra-high energy cosmic rays (UHECRs). Starting with the
assumption of the GRB-UHECR connection, w...
Aims: We investigate the role of the second synchrotron self-Compton (SSC) photon generation to the multiwavelength emission from the compact regions of sources that are characterized as misaligned blazars. For this, we focus on the nearest high-energy emitting radio galaxy Centaurus A and we revisit the one-zone SSC model for its core emission. Me...
We apply a recently developed time-dependent one-zone leptohadronic
model to study the emission of the blazar Mrk 421. Both processes
involving proton-photon interactions, i.e. photopair (Bethe-Heitler) and
photopion, have been modeled in great detail using the results of Monte
Carlo simulations, like the SOPHIA event generator, in a self-consisten...
Aims: We investigate the role of the second synchrotron self-Compton (SSC)
photon generation to the multiwavelength emission from the compact regions of
sources that are characterized as misaligned blazars. For this, we focus on the
nearest high-energy emitting radio galaxy Centaurus A and we revisit the
one-zone SSC model for its core emission. Me...
We examine the neutrino and cosmic ray spectra resulting from two models of
fitting the spectral energy distribution (SED) of the blazar Mrk~421 using a
self-consistent leptohadronic code. The $\gamma$-ray emission is attributed to
either synchrotron radiation of ultra-high energy protons (LHs model) or to
synchrotron radiation from electrons that...
Τhe mechanisms behind gamma-ray bursts (GRBs) are not yet well
understood. Here we investigate a model where a spectral energy
distribution (SED) that looks surprisingly like a typical GRB prompt
emission is generated starting with merely high energy protons and a
magnetic field. Using a selfconsistent, time-dependent code we show that
when the den...
We investigate the origin of high-energy emission in blazars within the
context of the leptohadronic one-zone model. We find that $\gamma$-ray
emission can be attributed to synchrotron radiation either from protons
or from secondary leptons produced via photohadronic processes. These
possibilities imply differences not only in the spectral energy
d...
We present results on the radiative and neutrino signatures of the one-zone hadronic model. Assuming that protons are injected at a certain rate in a homogeneous spherical volume containing a magnetic field, the evolution of the system can be described by five coupled kinetic equations, for protons,
electrons,
photons,
neutrons and neutrinos, respe...
We present a time-dependent approach to the one-zone hadronic model in the
case where the photon spectrum is produced by ultrarelativistic protons
interacting with soft photons that are produced from protons and low magnetic
fields. Assuming that protons are injected at a certain rate in a homogeneous
spherical volume containing a magnetic field, t...
We present some results on the radiative signatures of the one zone hadronic
model. For this we have solved five spatially averaged, time-dependent coupled
kinetic equations which describe the evolution of relativistic protons,
electrons, photons, neutrons and neutrinos in a spherical volume containing a
magnetic field. Protons are injected and los...
In this work we study the energy distribution of protons and produced secondary particles which result from photomeson and Bethe-Heitler processes in interactions of soft photons with protons accelerated in a shock wave by the first order Fermi process. For this purpose we have developed a code which simulates the diffusive shock acceleration mecha...
Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be γ-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3D hydrogen cloud map from the available data and assuming a diffusion coefficient o...
Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be gamma-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3-D hydrogen cloud map from the available data and assuming a diffusion coeffici...
Energy is among the characteristics of Ultra High Energy Cosmic Rays (E > 5 ×10¹⁹eV) which could be estimated experimentally based on simulations. This paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, are simulated to derive the lateral dist...
Diffuse VHE γ radiation from the Galactic Centre ridge observed by the H.E.S.S. telescope has been convincingly linked with the propagation of recently accelerated cosmic rays that interact with molecular hydrogen clouds during their diffusion. Through a series of time-dependent simula- tions of that diffusion for different propagation parameters w...
The non-linear back reaction of accelerated cosmic rays at the shock fronts, leads to the formation of a smooth precursor with a length scale corresponding to the diffusive scale of the energetic particles. Past works claimed that shocklets could be created in the precursor region of a specific shock width, which might energize few thermal particle...
This The energy is among the characteristics of Ultra High Energy Cosmic Rays (E<5 x 1019 eV) which could be estimated experimentally. The following paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of vertical extensive air showers is simulated to derive the Lateral Distribution Functions...
We present several ancient celestial spheres from the 8th century B.C. found throughout Greece, mainly in Thessaly, at the temple of Itonia Athena, but also in Olympia and other places. These celestial spheres have an axis, equator and several meridians and they have several markings with the symbol of stars (today's symbol for the Sun) $\odot$. Su...
We present several bronze artifacts from the Archaic Age in Greece
(750-480 BC) that resemble celestial spheres or forms of other
astronomical significance. They are studied in the context of the Dark
Age transition from Mycenaean Age astronomical themes to the
philosophical and practical revival of astronomy in the Classical Age
with its plethora...
We provide a fresh analysis of the constellations in Aratos Phenomena by
using the astronomical program Cybersky (by Stephen Schimpf) to check
each reference of constellations within the poem for validity in 2800
BCE and 300 BCE (the later accounting for the broader period of time
covering Eudoxus of Cnidus and Aratus of Soli). In each case, the
la...
High energy cosmic rays are most probably accelerated in astrophysical environments such as SNR and AGN jets and hotspots. In that case it is expected that the relativistic particles will interact in their acceleration sites with ambient photon fields and produce high energy electrons, gamma-rays as well as neutrinos. We present calculations from a...