Nuclear γ\gamma-ray emission from very hot accretion flows

Optically thin accretion plasmas can reach ion temperatures $T_{\rm i} \geq 10^{10}$K and thus trigger nuclear reactions. Using a large nuclear interactions network, we studied the radial evolution of the chemical composition of the accretion flow toward the black hole and computed the emissivity in nuclear $\gamma$-ray lines. In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit. The overall luminosity in the de-excitation lines for a solar composition of plasma can be as high as few times $10^{-5}$ the accretion luminosity ($\dot{M}c^2$) and can be increased for heavier compositions up to $10^{-3}$. The efficiency of transformation of the kinetic energy of the outflow into high energy ($\geq 100$~MeV) $\gamma$-rays through the production and decay of $\pi^0$-mesons can be higher, up to $10^{-2}$ of the accretion luminosity. We show that in the ADAF model up to 15 percent of the mass of accretion matter can `evaporate' in the form of neutrons.Comment: 7 pages, 7 figure

Nuclear reactions in hot astrophysical plasmas with T>1010T>10^{10} K

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperatures $T \geq 10^{10}$ K has been recognized for more than thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power have not previously allowed detailed theoretical studies. Recent developments in these areas make it timely to conduct comprehensive studies on the nuclear properties of very hot plasmas formed around compact relativistic objects such as black holes and neutron stars. Such studies are of great interest in the context of scientific programs of future low-energy cosmic $\gamma$-ray spectrometry. In this work, using the publicly available code TALYS, we have built a large nuclear network relevant for temperatures exceeding $10^{10}$ K. We have studied the evolution of the chemical composition and accompanying prompt gamma-ray emission of such high temperature plasmas. We present the results on the abundances of light elements D, T, $^3$He, $^4$He, $^{6}$Li, $^{7}$Li $^{9}$Be, $^{10}$B, $^{11}$B, and briefly discuss their implications on the astrophysical abundances of these elements.Comment: 39 pages, 26 figure

On the shape of the gamma-ray spectrum around the "π0\pi^0-bump"

The "pion-decay" bump is a distinct signature of the differential energy spectrum of $\gamma$-rays between 100 MeV and 1 GeV produced in hadronic interactions of accelerated particles (cosmic rays) with the ambient gas. We use the recent parametrisations of relevant cross-sections to study the formation of the "pion-decay" bump. The $\gamma$-ray spectrum below the maximum of this spectral feature can be distorted because of contributions of additional radiation components, in particular, due to the bremsstrahlung of secondary electrons and positrons, the products of decays of $\pi^\pm$-mesons, accompanying the $\pi^0$-production. At energies below 100 MeV, a non-negligible fraction of $\gamma$-ray flux could originate from interactions of sub-relativistic heavy ions. We study the impact of these radiation channels on the formation of the overall $\gamma$-ray spectrum based on a time-dependent treatment of evolution of energy distributions of the primary and secondary particles in the $\gamma$-ray production region.Comment: submitted to A&

Detection of persistent gamma-ray emission toward SS433/W50

The microquasar SS433 features the most energetic jets known in our Galaxy. A large fraction of the jet kinetic power is delivered to the surrounding W50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. Here we report on the detection of a persistent gamma-ray signal from the direction of SS433/W50 with the Fermi Large Area Telescope. The steady flux and a narrow spectral energy distribution with a maximum around 250 MeV suggest that gamma-rays are rendered by the bulk jet kinetic power through proton-proton collisions at the SS433/W50 interaction regions. If the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution may represent a significant fraction of the total galactic cosmic-ray flux at GeV energies.Comment: Accepted for publication in ApJ

Gamma-ray emission of hot astrophysical plasmas

Very hot plasmas with ion temperature exceeding $10^{10}$ K can be formed in certain astrophysical environments. The distinct radiation signature of such plasmas is the $\gamma$-ray emission dominated by the prompt de-excitation nuclear lines and $\pi^0$-decay $\gamma$-rays. Using a large nuclear reaction network, we compute the time evolution of the chemical composition of such hot plasmas and their $\gamma$-ray line emissivity. At higher energies, we provide simple but accurate analytical presentations for the $\pi^0$-meson production rate and the corresponding $\pi^0\to2\gamma$ emissivity derived for the Maxwellian distribution of protons. We discuss the impact of the possible deviation of the high energy tail of the particle distribution function from the "nominal" Maxwellian distribution on the plasma $\gamma$-ray emissivity.Comment: 11 pages, 10 figure

Radiation signatures of nuclear reactions in very hot astrophysical plasmas

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperatures kT>1 MeV has been recognized for more than thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power did not allow detailed theoretical studies. In this thesis, using the publicly available code TALYS, I have built a large nuclear reaction network relevant for temperatures exceeding 1MeV. It contains about 270 nuclear species and include the calculation of gamma-ray emissivity due to different nuclear reactions. The pi0-mesons production are also included. An approach to calculate the gamma-ray spectra through p + p to pi0 channel for an arbitrary proton distribution is also proposed. The nuclear network is applied to two-temperature accretion disk models the so-called Advection Dominated Accretion Flows (ADAF) and Shapiro-Lightman-Eardly (SLE). The gamma-rays emissivity are calculated for a wide parameter space including initial chemical composition. For a 10 solar mass black hole, both models can produce nuclear gamma-ray lines luminosities as large as L_N ~ 10^{34} erg/s. SLE is not an effective source of pi0 photons, whereas ADAF luminosity can be as large as L_pi ~ 10^{35} erg/s. ADAF regime is hot enough to evaporate neutrons. They can reach the companion star atmosphere and initiate secondary nuclear reactions

Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies

Using publicly available Monte Carlo codes as well as compilation of published data on p--p interactions for proton kinetic energy below 2 GeV, we parametrize the energy spectra and production rates of $\gamma$-rays by simple but quite accurate ($\leq 20 \%$) analytical expressions in a broad range from the kinematic threshold to PeV energies.Comment: 19 pages, 15 figures, v2 version fixes the cross reference

Excitation and destruction of nuclei in hot astrophysical plasma around black holes

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperaturesT >10^10 K has been recognized for thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power have not previously allowed detailed theoretical studies. Recent developments in these areas make it timely to conduct comprehensive studies of the nuclear properties of very hot plasmas formed around compact relativistic objects such as black holes and neutron stars. Such studies are of great interest in the context of scientific programs of future low-energy cosmic gamma-ray spectrometry. In this work, using the publicly available code TALYS, we have built a large nuclear network relevant for temperatures exceeding 10^10 K. We then study the evolution of hot accretion plasmas for such high temperatures due to the destruction of nuclei at inelastic collisions, calculate the resulting gamma-ray spectra due to the superposition of prompt excitation gamma-ray lines, and present the results on the abundances of D, T, 3He.Fil: Kafexhiu, Ervin. Max-planck-institut Für Kernphysik; AlemaniaFil: Vila, Gabriela Soledad. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Aharonian, Felix A.. Dublin Instute For Advanced Studies; Irlanda11th Symposium on Nuclei in the CosmosHeidelbergAlemaniaUniversity of HeidelbergMax-Planck-Institut für Kernphysi

Energetic gamma-ray emission from solar flares

Recent advances in the $\gamma$-ray observations of solar flares by the \textit{Fermi} satellite, demand revisions in the hadronic $\gamma$-ray flux computation below 1 GeV. In this work we utilize recently updated pion production cross sections, along with an accurate description of low energy nuclear interactions. Applying these new interaction descriptions to model the \textit{Fermi} Large Area Telescope (LAT) solar flare data, we infer the primary particle spectral parameters. Application of this new cross section description leads to significantly different spectral parameters compared to those obtained previously. Furthermore, the inclusion of nuclei in these calculations leads to a primary spectrum that is generally harder than that required from proton only considerations. Lastly, the flare data at lower MeV energies, detected by the \textit{Fermi} Gamma-ray Burst Monitor (GBM), is demonstrated to provide additional low-energy spectral information.Comment: 11 pages, 9 figures, Ap