The rate of ionization by cosmic rays in interstellar gas directly associated with γray emitting supernova remnants is for the first time calculated to be several orders of magnitude larger than the Galactic average. Analysis of ionization-induced chemistry yields the first quantitative prediction of the astrophysical H + 2 emission line spectrum, which should be detectable together with H + 3 lines. The predicted coincident observation of those emission lines and γ-rays will help prove that supernova remnants are sources of cosmic rays.

Context. Energetic gamma rays (GeV to TeV photon energy) have been detected toward several supernova remnants (SNRs) that are associated with molecular clouds. If the gamma rays are produced mainly by hadronic processes rather than leptonic processes like bremsstrahlung, then the flux of energetic cosmic ray nuclei (>1 GeV) required to produce the gamma rays can be inferred at the site where the particles are accelerated in SNR shocks. It is of great interest to understand the acceleration of the cosmic rays of lower energy (<1 GeV) that accompany the energetic component. These particles of lower energy are most effective in ionizing interstellar gas, which leaves an observable imprint on the interstellar ion chemistry. A correlation of energetic gamma radiation with enhanced interstellar ionization can thus be used to support the hadronic origin of the gamma rays and to constrain the acceleration of ionizing cosmic rays in SNR. Aims. We propose a method to test the hadronic origin of GeV gamma rays from SNRs associated with a molecular cloud. Methods. We use observational gamma ray data for each SNR known to be associated with a molecular cloud, modeling the observations to obtain the underlying proton spectrum under the assumption that the gamma rays are produced by pion decay. Assuming that the acceleration mechanism does not only produce high energy protons, but also low energy protons, this proton spectrum at the source is then used to calculate the ionization rate of the molecular cloud. Ionized molecular hydrogen triggers a chemical network forming molecular ions. The relaxation of these ions results in characteristic line emission, which can be predicted. Results. We show that the predicted ionization rate for at least two objects is more than an order of magnitude above Galactic average for molecular clouds, hinting at an enhanced formation rate of molecular ions. There will be interesting opportunities to measure crucial molecular ions in the infrared and submillimeter-wave parts of the spectrum.

Context. 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. Whether these gamma rays are generated by cosmic-ray electrons emitting bremsstrahlung or experiencing inverse Compton scattering, or by cosmic-ray protons interacting with ambient hydrogen is usually not known. 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. Aims. 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. Methods. To calculate hadronic signatures from cosmic-ray-induced ionization to examine the origin of the observed gamma rays from molecular clouds associated with supernova remnants, we solved analytically the transport equation for cosmic-ray protons propagating in a molecular cloud, including the relevant momentum-loss processes, and determined the proton flux at any penetration depth into the cloud. Results. Because the solution of the transport equation is obtained for arbitrary source functions, it can be used for a variety of supernova remnants. We derived the corresponding theoretical ionization rate as a function of the penetration depth from the positiondependent proton flux, and compared it with photoinduced ionization profiles for available X-ray data in a case study with four supernova remnants associated with molecular clouds. Three of the remnants show a clear dominance of the hadronically induced ionization rate, while for one remnant, X-ray emission seems to dominate by a factor of 10. Conclusions. 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. For sources dominated by cosmic-ray-induced ionization (e.g., W49B), the ionization profiles can be used in the future to map the spatial structure of hadronic gamma rays and rotation-vibrational lines induced by cosmic-ray protons. 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.

It is widely believed that supernova remnants are the best candidate sources for the observed cosmic ray flux up to the knee, i.e. up to ∼PeV energies. Indeed, the gamma-ray spectra of some supernova remnants can be well explained by assuming the decay of neutral pions which are created in hadronic interactions. Therefore, fitting the corresponding gamma spectra allows us to derive the spectra of cosmic rays at the source which are locally injected into our Galaxy. Using these spectra as a starting point, we propagate the cosmic rays through the Galaxy using the publicly available GALPROP code. Here, we will present first results on the contribution of those SNRs to the total cosmic ray flux and discuss implications.

We present a fully analytical, time-dependent leptonic one-zone model that describes a simplified radiation process of multiple interacting ultrarelativistic electron populations, accounting for the flaring of GeV blazars. In this model, several mono-energetic, ultrarelativistic electron populations are successively and instantaneously injected into the emission region, i.e., a magnetized plasmoid propagating along the blazar jet, and subjected to linear, time-independent synchrotron radiative losses, which are caused by a constant magnetic field, and nonlinear, timedependent synchrotron self-Compton radiative losses in the Thomson limit. Considering a general (time-dependent) multiple-injection scenario is, from a physical point of view, more realistic than the usual (time-independent) single-injection scenario invoked in common blazar models, as blazar jets may extend over tens of kiloparsecs and, thus, most likely pick up several particle populations from intermediate clouds. We analytically compute the electron number density by solving a kinetic equation using Laplace transformations and the method of matched asymptotic expansions. Moreover, we explicitly calculate the optically thin synchrotron intensity, the synchrotron self-Compton intensity in the Thomson limit, as well as the associated total fluences. In order to mimic injections of finite duration times and radiative transport, we model flares by sequences of these instantaneous injections, suitably distributed over the entire emission region. Finally, we present a parameter study for the total synchrotron and synchrotron self-Compton fluence spectral energy distributions for a generic three-injection scenario, varying the magnetic field strength, the Doppler factor, and the initial electron energy of the first injection in realistic parameter domains, demonstrating that our model can reproduce the typical broad-band behavior seen in observational data. Contents