Active galactic nuclei are firm favourites to be revealed as the source of cosmic rays, but solid evidence has proven elusive. A model taking both local and global nuclei propagation into account may ...help to close the deal.
The luminosity ratio of electrons to protons as it is produced in stochastic acceleration processes in cosmic ray sources is an important quantity relevant for several aspects of the modeling of the ...sources themselves. It is usually assumed to be around 1: 100 in the case of Galactic sources, while a value of 1: 10 is typically assumed when describing extragalactic sources. It is supported by observations that the average ratios should be close to these values. At this point, however, there is no possibility to investigate how each individual source behaves. When looking at the physics aspects, a 1: 100 ratio is well supported in theory when making the following assumptions: (1) the total number of electrons and protons that is accelerated are the same; (2) the spectral index of both populations after acceleration is αe=αp≈2.2. In this paper, we reinvestigate these assumptions. In particular, assumption (2) is not supported by observational data of the sources and PIC simulation yield different spectral indices as well. We present the detailed calculation of the electron-to-proton ratio, dropping the assumption of equal spectral indices. We distinguish between the ratio of luminosities and the ratio of the differential spectral behavior, which becomes necessary for cases where the spectral indices of the two particle populations are not the same. We discuss the possible range of values when allowing for different spectral indices concerning the spectral behavior of electrons and protons. Additionally, it is shown that the minimum energy of the accelerated population can have a large influence on the results. We find, in the case of the classical minimum energy of T0,e=T0,p=10 keV, that when allowing for a difference in the spectral indices of up to 0.1 with absolute spectral indices varying between 2.0 < α < 2.3, the luminosity ratio varies between 0.008 < Kep < 0.12. The differential particle number ratio is in the range 0.008<K˜ep<0.25 and depends on the energy.
The origin of cosmic rays is one of the long-standing mysteries in physics and astrophysics. Simple arguments suggest that a scenario of supernova remnants (SNRs) in the Milky Way as the dominant ...sources for the cosmic ray population below the knee could work: a generic calculation indicates that these objects can provide the energy budget necessary to explain the observed flux of cosmic rays. However, this argument is based on the assumption that all sources behave in the same way, i.e. they all have the same energy budget, spectral behavior and maximum energy. In this paper, we investigate if a realistic population of SNRs is capable of producing the cosmic ray flux as it is observed below the knee. We use 21 SNRs that are well-studied from radio wavelengths up to gamma-ray energies and derive cosmic ray spectra under the assumption of hadronic emission. The cosmic ray spectra show a large variety in their energy budget, spectral behavior and maximum energy. These sources are assumed to be representative for the total class of SNRs, where we assume that about 100–200 cosmic ray emitting SNRs should be present today. Finally, we use these source spectra to simulate the cosmic ray transport from individual SNRs in the Galaxy with the GALPROP code for cosmic ray propagation. We find that the cosmic ray budget can be matched well for these sources. We conclude that gamma-ray emitting SNRs can be a representative sample of cosmic ray emitting sources. In the future, experiments like CTA and HAWC will help to distinguish hadronic from leptonic sources and to further constrain the maximum energy of the sources and contribute to producing a fully representative sample in order to further investigate the possibility of SNRs being the dominant sources of cosmic rays up to the knee.
Although several theories exist for the origin of cosmic rays (CRs) in the region between the spectral "knee" and "ankle," this problem is still unsolved. A variety of observations suggest that the ...transition from Galactic to extragalactic sources occurs in this energy range. In this work, we examine whether a Galactic wind that eventually forms a termination shock far outside the Galactic plane can contribute as a possible source to the observed flux in the region of interest. Previous work by Bustard et al. estimated that particles can be accelerated to energies above the "knee" up to Rmax = 1016 eV for parameters drawn from a model of a Milky Way wind. A remaining question is whether the accelerated CRs can propagate back into the Galaxy. To answer this crucial question, we simulate the propagation of the CRs using the low-energy extension of the CRPropa framework, based on the solution of the transport equation via stochastic differential equations. The setup includes all relevant processes, including three-dimensional anisotropic spatial diffusion, advection, and corresponding adiabatic cooling. We find that, assuming realistic parameters for the shock evolution, a possible Galactic termination shock can contribute significantly to the energy budget in the "knee" region and above. We estimate the resulting produced neutrino fluxes and find them to be below measurements from IceCube and limits by KM3NeT.
MUON ACCELERATION IN COSMIC-RAY SOURCES Klein, Spencer R; Mikkelsen, Rune E; Tjus, Julia Becker
The Astrophysical journal,
12/2013, Volume:
779, Issue:
2
Journal Article
Peer reviewed
Open access
Many models of ultra-high energy cosmic-ray production involve acceleration in linear accelerators located in gamma-ray bursts, magnetars, or other sources. These transient sources have short ...lifetimes, which necessitate very high accelerating gradients, up to 10 super(13) keV cm super(-1). At gradients above 1.6 keV cm super(-1), muons produced by hadronic interactions undergo significant acceleration before they decay. This muon acceleration hardens the neutrino energy spectrum and greatly increases the high-energy neutrino flux. Using the IceCube high-energy diffuse neutrino flux limits, we set two-dimensional limits on the source opacity and matter density, as a function of accelerating gradient. These limits put strong constraints on different models of particle acceleration, particularly those based on plasma wake-field acceleration, and limit models for sources like gamma-ray bursts and magnetars.
The popular JF12 analytic model by Jansson & Farrar provides a quantitative description of the Galaxy's large-scale magnetic field, which is widely used in various astrophysical applications. ...However, both the poloidal X-type component and the spiral disk component of JF12 exhibit regions in which the magnetic divergence constraint is violated. We first propose a cure for this problem, resulting in a truly solenoidal large-scale spiral field. Second, the otherwise straight field lines of the X-type component exhibit kinks in the Galactic plane that, in addition to implying the presence of a singular current sheet, may pose difficulties for e.g., numerical tracing of cosmic-ray particles. We propose and discuss two possible strategies to mitigate this problem. Although all corrections are kept as minimal as possible, the extended set of model parameters will have to be carefully readjusted in order to fully restore the agreement to observational data that the unmodified JF12 field is based on. Furthermore, the performance of our improved version of the field model is quantitatively assessed by test simulations using the CRPropa Galactic cosmic-ray propagation code.
Abstract
Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and ...neutrino production are still uncertain. Recent studies found that when transparent to
γ
-rays,
γ
-flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which
γ
-ray emission is suppressed during efficient neutrino production. A large proton and target photon density helps produce neutrinos while temporarily suppressing the observable
γ
-emission due to a large
γ
γ
opacity. We show that the Fermi-LAT
γ
-flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40 m Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and
γ
fluxes are correlated for both low and high states. This points to an active outflow that is
γ
-suppressed at the time of neutrino production. We find similar local
γ
-suppression in other blazars, including in MAGIC’s TeV flux of TXS 0506+056 and Fermi-LAT’s flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary
γ
-suppression, neutrino–blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube’s diffuse neutrino flux possibly with already existing data.
Abstract
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from their central region. These active galactic nuclei (AGN)-starburst composites ...are of special interest, as both phenomena on their own are potential sources of highly energetic cosmic rays and associated
γ
-ray and neutrino emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we show that the entire spectrum of multimessenger data—from radio to
γ
-rays including the neutrino constraint—can be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission region is not sufficient.
Abstract
On 2022 September 18, an alert by the IceCube Collaboration indicated that a ∼170 TeV neutrino arrived in directional coincidence with the blazar TXS 0506+056. This event adds to two ...previous pieces of evidence that TXS 0506+056 is a neutrino emitter, i.e., a neutrino alert from its direction on 2017 September 22, and a 3
σ
signature of a dozen neutrinos in 2014/2015. De Bruijn el al. showed that two previous neutrino emission episodes from this blazar could be due to a supermassive binary black hole (SMBBH) central engine where jet precession close to the final coalescence of the binary results in periodic emission. This model predicted a new emission episode consistent with the 2022 September 18 neutrino observation by IceCube. Here, we show that the neutrino cadence of TXS 0506+056 is consistent with an SMBBH origin. We find that the emission episodes are consistent with an SMBBH with mass ratios
q
≲ 0.3 for a total black hole mass of
M
tot
≳ 3 · 10
8
M
⊙
. For the first time, we calculate the characteristic strain of the gravitational wave emission of the binary, and show that the merger could be detectable by LISA for black hole masses <5 · 10
8
M
⊙
if the mass ratios are in the range 0.1 ≲
q
≲ 0.3. We predict that there can be a neutrino flare existing in the still-to-be-analyzed IceCube data peaking some time between 2019 August and 2021 January if a precessing jet is responsible for all three detected emission episodes. The next flare is expected to peak in the period 2023 January to 2026 August. Further observation will make it possible to constrain the mass ratio as a function of the total mass of the black hole more precisely and would open the window toward the preparation of the detection of SMBBH mergers.
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