ABSTRACT We report on the radio brightening of the blazar TXS 0506+056 (at z = 0.3365), and we support its identification by the IceCube Neutrino Observatory as a source of the high-energy (HE) ...neutrino IC-170922A. Data from the Monitoring Of Jets in AGN with VLBA Experiments (MOJAVE)/Very Long Baseline Array (VLBA) survey indicate that its radio brightness has abruptly increased since 2016 January. When decomposing the total radio flux density curve (in the period 2008 January to 2018 July), provided by the Owens Valley Radio Observatory, into eight Gaussian flares, the peak time of the largest flare overlaps with the HE neutrino detection, while the total flux density has exhibited a threefold increase since 2016 January. We reveal the radio structure of TXS 0506+056 by analysing very long baseline interferometry (VLBI) data from the MOJAVE/VLBA survey. The jet components maintain quasi-stationary core separations. The structure of the ridge line is indicative of a jet curve in the region 0.5–2 mas (2.5–9.9 pc projected) from the VLBI core. The brightness temperature of the core and the pc-scale radio morphology support a helical jet structure at small inclination angle (<8${^{\circ}_{.}}$2). The jet pointing towards the Earth is a key property facilitating multimessenger observations (HE neutrinos, γ-rays and radio flares). The radio brightening preceding the detection of a HE neutrino is similar to the one reported for the blazar PKS 0723–008 and IceCube event ID5.
Abstract
A steady-state, semi-analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity obtained by Webb et al. is generalized to take into account more ...general cosmic-ray boundary spectra. This involves solving a mixed Dirichlet–Von Neumann boundary value problem at the edge of the jet. The energetic particle distribution function
f
0
(
r
,
p
) at cylindrical radius
r
from the jet axis (assumed to lie along the
z
-axis) is given by convolving the particle momentum spectrum
f
0
(
∞
,
p
′
)
with the Green’s function
G
(
r
,
p
;
p
′
)
, which describes the monoenergetic spectrum solution in which
f
0
→
δ
(
p
−
p
′
)
as
r
→ ∞ . Previous work by Webb et al. studied only the Green’s function solution for
G
(
r
,
p
;
p
′
)
. In this paper, we explore for the first time, solutions for more general and realistic forms for
f
0
(
∞
,
p
′
)
. The flow velocity
u
=
u
(
r
)
e
z
is along the axis of the jet (the
z
-axis).
u
is independent of
z
, and
u
(
r
) is a monotonic decreasing function of
r
. The scattering time
τ
(
r
,
p
)
=
τ
0
(
p
/
p
0
)
α
in the shear flow region 0 <
r
<
r
2
, and
τ
(
r
,
p
)
=
τ
0
(
p
/
p
0
)
α
(
r
/
r
2
)
s
, where
s
> 0 in the region
r
>
r
2
is outside the jet. Other original aspects of the analysis are (i) the use of cosmic ray flow lines in (
r
,
p
) space to clarify the particle spatial transport and momentum changes and (ii) the determination of the probability distribution
ψ
p
(
r
,
p
;
p
′
)
that particles observed at (
r
,
p
) originated from
r
→ ∞ with momentum
p
′
. The acceleration of ultrahigh-energy cosmic rays in active galactic nuclei jet sources is discussed. Leaky box models for electron acceleration are described.
LOPES, the LOFAR prototype station, was an antenna array for cosmic-ray air showers operating from 2003 to 2013 within the KASCADE-Grande experiment. Meanwhile, the analysis is finished and the data ...of air-shower events measured by LOPES are available with open access in the KASCADE Cosmic Ray Data Center (KCDC). This article intends to provide a summary of the achievements, results, and lessons learned from LOPES. By digital, interferometric beamforming the detection of air showers became possible in the radio-loud environment of the Karlsruhe Institute of Technology (KIT). As a prototype experiment, LOPES tested several antenna types, array configurations and calibration techniques, and pioneered analysis methods for the reconstruction of the most important shower parameters, i.e., the arrival direction, the energy, and mass-dependent observables such as the position of the shower maximum. In addition to a review and update of previously published results, we also present new results based on end-to-end simulations including all known instrumental properties. For this, we applied the detector response to radio signals simulated with the CoREAS extension of CORSIKA, and analyzed them in the same way as measured data. Thus, we were able to study the detector performance more accurately than before, including some previously inaccessible features such as the impact of noise on the interferometric cross-correlation beam. These results led to several improvements, which are documented in this paper and can provide useful input for the design of future cosmic-ray experiments based on the digital radio-detection technique.
We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is ...observed, confirming the presence of the so-called
second-knee
feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
Context. Shocks in jets and hot spots of active galactic nuclei (AGN) are one prominent class of possible sources of very high-energy cosmic-ray particles (above 1018 eV). Extrapolating their ...spectrum to their plausible injection energy from some shock implies an enormous hidden energy for a spectrum of index ~−2. Some analyses suggest the particles’ injection spectrum at source to be as steep as −2.4 to −2.7, which exacerbates the problem, by a factor of 106. Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy goes into the required flux of energetic particles, thus one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Aims. Sequences of consecutive oblique shock features, or conical shocks, have been theoretically predicted and eventually observed in many AGN jets. Based on that, we use by analogy the Comptonization effect and propose a scenario of a single injection of particles consecutively accelerated by several oblique shocks along the axis of an AGN jet. Methods. We developed a test-particle approximation Monte Carlo simulations to calculate particle spectra by acceleration at such a shock pattern while monitoring the efficiency of acceleration by calculating differential spectra. Results. We find that the first shock of a sequence of oblique shocks establishes a low-energy power-law spectrum with ~E-2.7. The following consecutive shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs, and characteristic depletion at low energies, which could explain the puzzling apparent extra source power. Conclusions. Our numerical calculations show a variation of spectral indices, a general spectral flattening, and starved spectra, which connect to the relativistic nature of the shocks, the multiple shock acceleration conditions, and the steepness of the magnetic field to the shock normal. This helps in understanding the jet-magnetic field geometry and the irregular or flat spectra observed in many AGN jets (e.g., CenA, 3C 279, PKS 1510-089). Furthermore, the E-2.4 − E-2.7 ultra-high-energy cosmic-ray injected source spectra claimed by many authors might be explained by the superposition of several, perhaps many, emission sources, all of which end their particle shock-acceleration sequence with flatter, starved spectra produced by two or more consecutive oblique shocks along their jets. It might also imply a mixed component of the accelerated particles above 1019 eV. Moreover, the present acceleration model can explain the variability of inverted gamma-ray spectra observed in high redshifted flaring extragalactic sources.
Context.
Tensions between the diffuse gamma-ray sky observed by the
Fermi
Large Area Telescope (
Fermi
-LAT) and the diffuse, high-energy neutrino sky detected by the IceCube South Pole Neutrino ...Observatory raise questions about our knowledge of high-energy neutrino sources in the gamma-ray regime. While blazars are among the most energetic persistent particle accelerators in the Universe, studies suggest that they could account for up to 10–30% of the neutrino flux measured by IceCube.
Aims.
Our recent results highlight that the associated IceCube neutrinos arrived in a local gamma-ray minimum (dip) of three strong neutrino point-source candidates. Here, we increase the sample of neutrino-source candidates in order to study their gamma-ray light curves.
Methods.
We generated the one-year
Fermi
-LAT light curve for eight neutrino-source candidate blazars (RBS 0958, GB6 J1040+0617, PKS 1313-333, TXS 0506+056, PKS 1454-354, NVSS J042025-374443, PKS 0426-380, and PKS 1502+106), centered on the detection time of the associated IceCube neutrinos. We applied the Bayesian block algorithm to the light curves to characterize their variability.
Results.
Our results indicate that GB6 J1040+0617 was in a phase of high gamma-ray activity, while none of the other seven neutrino-source candidates were statistically bright during the detection of the corresponding neutrinos; indeed, most of the time neutrinos arrived in a faint gamma-ray phase of the light curves. This suggests either that the eight source candidate blazars (associated with seven neutrino events) in our reduced sample are not the sources of the corresponding IceCube neutrinos, or that an in-source effect (e.g., the suppression of gamma rays due to high gamma-gamma opacity) complicates the multimessenger scenario of neutrino emission for these blazars.
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins 4, 8 EeV and E ≥ 8 EeV, the most ...significant signal is a dipolar modulation in R.A. at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index β = 0.79 0.19. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Additionally, we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.
Context. The mass function of supermassive black holes in our cosmic neighborhood is required to understand the statistics of their activity and consequently the origin of ultra high energy ...particles. Aims. We determine a mass function of supermassive black hole candidates from the entire sky except for the Galactic plane. Methods. Using the 2MASS catalogue as a starting point, and the well-established correlation between black hole mass and the bulge of old population of stars, we derive a list of nearby black hole candidates within the redshift range z < 0.025, then perform an additional selection based on the Hubble type. We present our resulting catalogue elsewhere. The final list of black hole candidates above a mass of MBH > 3 × 106 $M_{\odot}$ has 5829 entries. We perform a Hubble-type correction to account for selection effects, which reduces this number to 2919 black hole candidates. Here we use this catalogue to derive the black-hole mass function. We also correct for volume, so that this mass function is a volume-limited distribution to redshift 0.025. Results. The differential mass function of nearby black hole candidates is a curved function, with a straight simple power-law of index -3 above 108 $M_{\odot}$ that becomes progressively flatter towards lower masses, turns off towards a gap below 3 × 106 $M_{\odot}$, and then extends into the range where nuclear star clusters replace black holes. The shape of this mass function can be explained in a simple merger picture. Integrating this mass function over the redshift range for which it has been derived, infers a total number of black holes with z < 0.025, and MBH > 107 $M_{\odot}$ of about 2.4 × 104, or, if we average uniformly, 0.6 for every square degree on the sky.
Abstract
In interactions of ultra-high-energy cosmic ray (UHECR) protons with cosmic microwave background photons, we focus in this work on photopion production reactions and the effects of the ...measured, broad, energy-loss distributions in these reactions on the evolution of the protons’ density functions in energy space. We rely on a Fokker–Planck transport equation in energy space whose transport coefficients are calculated using laboratory measurements. We also derive a Fokker–Planck potential that accounts for both systematic (drift) and stochastic (dispersive) energy losses due to photopion production reactions. Our results show that dispersive energy losses have significant effects on estimating the protons’ horizon distance and their energy spectrum, as well as to elucidate a broadness in the GZK cutoff. We use the derived Fokker–Planck potential to assign a characteristic probability for a proton to clear the potential barrier as a function of energy. This estimate of probability can be used to assist observations in distinguishing between protons and heavy ions as charged particles. Our model is able to account for the so-called super GZK particles as a classic diffusion-over-a-barrier manifestation of the transport of UHECR protons in energy space in quantifying the extent and broadness of the GZK cutoff.
PDF
