Context. Indirect observations of the cosmic-ray electron (CRE) distribution via synchrotron emission is crucial for deepening the understanding of the CRE transport in the interstellar medium, and ...in investigating the role of galactic outflows. Aims. In this paper, we quantify the contribution of diffusion- and advection-dominated transport of CREs in the galaxy M51 considering relevant energy loss processes. Methods. We used recent measurement from M 51 that allow for the derivation of the diffusion coefficient, the star formation rate, and the magnetic field strength. With this input, we solved the 3D transport equation numerically including the spatial dependence as provided by the measurements, using the open-source transport framework CRPropa (v3.1). We included 3D transport (diffusion and advection), and the relevant loss processes. Results. We find that the data can be described well with the parameters from recent measurements. For the best fit, it is required that the wind velocity, following from the observed star formation rate, must be decreased by a factor of 5. We find a model in which the inner galaxy is dominated by advective escape and the outer galaxy is composed by both diffusion and advection. Conclusions. Three-dimensional modelling of cosmic-ray transport in the face-on galaxy M51 allows for conclusions about the strength of the outflow of such galaxies by quantifying the need for a wind in the description of the cosmic-ray signatures. This opens up the possibility of investigating galactic winds in face-on galaxies in general.
Over the past few years, signatures of supernova remnants have been detected in gamma rays, particularly those that are known to be associated with molecular clouds. The detection of hadronic ...ionization signatures in spatial coincidence with gamma-ray signatures can help to unambiguously identify supernova remnants as sources of cosmic-ray protons. Our central aim is to develop a method to investigate whether the gamma rays are formed by cosmic-ray protons. To achieve this goal, we derived the position-dependent cosmic-ray-induced and photoinduced ionization rates. This is the first derivation of position-dependent profiles for cosmic-ray-induced ionization with an analytic solution for arbitrary cosmic-ray source spectra. The cosmic-ray-induced ionization has to be compared with photoionization for strong X-ray sources. For this purpose, measurements of X-ray spectra from supernova remnant shocks in the sub-keV to keV domain are necessary for a proper comparison. With instruments such as ALMA for the line signatures and CTA for the gamma-ray detection, this correlation study will help to identify sources of hadronic cosmic rays.
The IceCube neutrino observatory detected two distinct flares of high-energy neutrinos from the direction of the blazar TXS 0506+056: a \(\sim 300\) TeV single neutrino on September 22, 2017 and a ...\(3.5\sigma\) signature of a dozen TeV neutrinos in 2014/2015. In a previous work, it was shown that these two episodes of neutrino emission could be due to an inspiral of a supermassive binary black hole (SMBBH) close to its merger at the core of TXS 0506+056. Such an inspiral can lead to quasi-periodic particle emission due to jet precession close to the final coalescence. This model made predictions on when the next neutrino emission episode must occur. On September 18, 2022, IceCube detected an additional, \(\sim 170\) TeV neutrino in directional coincidence with the blazar TXS 0506+056, being consistent with the model prediction. Additionally, in April 2021, the Baikal Collaboration reported the detection of a \(224\pm 75\) TeV neutrino, with TXS 0506+056 being in the uncertainty range of the event direction. We show that these four distinct flares of neutrino emission from TXS 0506+056 are consistent with a precessing jet scenario, driven by an inspiraling SMBBH. Using improved modeling, we are now able to constrain the total mass together with the mass ratio for the binary. We predict when the next neutrino flares from TXS 0506+056 should be happening. Finally, we estimate the detection potential of the Laser-interferometer Space Antenna (LISA) for the merger in the future.
The first high-energy neutrino source identified by IceCube was a blazar - an active galactic nucleus driving a relativistic jet towards Earth. Jets driven by accreting black holes are commonly ...assumed to be needed for high-energy neutrino production. Recently, IceCube discovered neutrinos from Seyfert galaxies, which appears unrelated to jet activity. Here, we show that the observed luminosity ratios of neutrinos and hard X-rays from blazars TXS 0506+056 and GB6 J1542+6129 are consistent with neutrino production in a \(\gamma\)-obscured region near a central supermassive black hole, with the X-ray flux corresponding to reprocessed \(\gamma\)-ray emission with flux comparable to that of neutrinos. Similar neutrino - hard X-ray flux ratios are found for four Seyfert galaxies, NGC 1068, NGC 4151, CGCG 420-015 and NGC 3079, raising the possibility of a common neutrino production mechanism that may not involve a strong jet.
The recent detections of binary stellar mass black hole mergers by the LIGO and Virgo Collaborations suggest that such mergers are common occurrences. Galaxy mergers further indicate that ...supermassive black holes in centers of galaxies also merge and are typically expected to have had at least one merger in their lifetime, possibly many. In the presence of a jet, these mergers are almost always accompanied by a change of the jet direction and a connected jet precession motion, leading to interactions of the jet with ambient matter and producing very high-energy particles, and consequently high-energy gamma-rays and neutrinos. In this work, we investigate the possibility under which conditions such mergers could be the sources of the diffuse astrophysical neutrino flux measured by the IceCube Neutrino Observatory. The main free parameters in the calculation concern the frequency of the mergers and the fraction of energy that is transferred from the gravitationally released energy to neutrinos. We show that the merger rate for SMBBHs must lie between \(\sim 10^{-7}\) and \(10^{-5}\) Gpc\(^{-3}\) yr\(^{-1}\). The ratio of energy going to neutrinos during such mergers lies then between \(\sim 10^{-6} - 3\cdot 10^{-4}\). For stellar mass BBH mergers, the rate needs to be \(\sim 10-100\) Gpc\(^{-3}\) yr\(^{-1}\) and the expected ratio of neutrino to gravitational wave energy lies in a comparable range as for SMBBHs, \(\sim 2 \cdot 10^{-5} - 10^{-3}\). These values lie in a reasonable parameter range, so that the production of neutrinos at the level of the detected neutrino flux is a realistic possibility.
Tensions between the diffuse gamma-ray sky observed by the Fermi Large Area Telescope (LAT) and the diffuse high-energy neutrino sky detected by the IceCube South Pole Neutrino Observatory question ...our knowledge about 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 for 10-30% of the neutrino flux measured by IceCube. Our recent results highlighted that the associated IceCube neutrinos arrived in a local gamma-ray minimum (dip) of three strong neutrino point-source candidates. We increase the sample of neutrino-source candidates to study their gamma-ray light curves. We generate the one-year Fermi-LAT light curve for 8 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 apply the Bayesian block algorithm on the light curves to characterize their variability. Our results indicate that GB6 J1040+0617 was in the phase of high gamma-ray activity, while none of the other 7 neutrino source candidates were statistically bright during the detection of the corresponding neutrinos and that indeed even most of the times neutrinos arrived in a faint gamma-ray phase of the light curves. This suggests that the 8 source-candidate blazars (associated with 7 neutrino events) in our reduced sample are either not the sources of the corresponding IceCube neutrinos, or that an in-source effect (e.g. suppression of gamma rays due to high gamma-gamma opacity) complicates the multimessenger scenario of neutrino emission for these blazars.
We present a new energy transport code that models the time dependent and non-linear evolution of spectra of cosmic-ray nuclei, their secondaries, and photon target fields. The software can inject an ...arbitrary chemical composition including heavy elements up to iron nuclei. Energy losses and secondary production due to interactions of cosmic ray nuclei, secondary mesons, leptons, or gamma-rays with a target photon field are available for all relevant processes, e.g., photo-meson production, photo disintegration, synchrotron radiation, Inverse Compton scattering, and more. The resulting x-ray fluxes can be fed back into the simulation chain to correct the initial photon targets, resulting in a non-linear treatment of the energy transport. The modular structure of the code facilitates simple extension of interaction or target field models. We will show how the software can be used to improve predictions of observables in various astrophysical sources such as jetted active galactic nuclei (AGN). Since the software can model the propagation of heavy ultrahigh-energy cosmic rays inside the source it can precisely predict the chemical composition at the source. This will also refine predictions of neutrino emissions - they strongly depend on the chemical composition. This helps in the future to optimize the selection and analyses of data from the IceCube neutrino observatory with the aim to enhance the sensitivity of IceCube and reduce the number of trial factors.
Analyzing single-dish and VLBI radio, as well as \textit{Fermi}-LAT \(\gamma\)-ray observations, we explained the three major flares in the \(\gamma\)-ray light curve of FSRQ J1048+7143 with the ...spin--orbit precession of the dominant mass black hole in a supermassive black hole binary system. Here, we report on the detection of a fourth \(\gamma\)-ray flare from J1048+7143, appearing in the time interval which was predicted in our previous work. Including this new flare, we constrained the mass ratio into a narrow range of \(0.062<q<0.088\), and consequently we were able to further constrain the parameters of the hypothetical supermassive binary black hole at the heart of J1048+7143. We predict the occurrence of the fifth major \(\gamma\)-ray flare that would appear only if the jet will still lay close to our line sight. The fourth major \(\gamma\)-ray flare also shows the two-subflare structure, further strengthening our scenario in which the occurrence of the subflares is the signature of the precession of a spine--sheath jet structure that quasi-periodically interacts with a proton target, e.g. clouds in the broad-line region.
In cosmic ray physics extensive progress has been made in recent years, both concerning theory and observation. The vast details in direct, indirect and secondary detections on the one hand provide ...the basis for a detailed modeling of the signatures via cosmic-ray transport and interaction, paving the way for the identification of Galactic cosmic-ray sources. On the other hand, the large number of constraints from different channels of cosmic-ray observables challenges these models frequently. In this review, we will summarize the state-of-the art of the detection of cosmic rays and their secondaries, followed by a discussion what we can learn from coupling our knowledge of the cosmic-ray observables to the theory of cosmic-ray transport in the Galactic magnetic field. Finally, information from neutral secondaries will be added to draw a multimessenger-picture of the non-thermal sky, in which the hypothesis of supernova remnants as the dominant sources survives best. While this has been known since the 1930s, evidence for this scenario is steadily growing, with the first detection of hadronic signatures at GeV energies detected for three SNRs with Fermi. The existence of SNRs as PeVatrons, however, is not validated yet. The discussion of this and other open questions concerning the level of anisotropy, composition and spectral shape of the cosmic-ray energy spectrum is reviewed. Future perspectives of how to find the smoking cosmic-ray source gun concludes this review.
Multi-wavelength observations indicate that some starburst galaxies show a dominant non-thermal 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 gamma-ray and neutrino emission. In this work, a homogeneous, steady-state two-zone multi-messenger model of the non-thermal 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 multi-messenger data - from radio to gamma-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.
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