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Register a new userOrigin of Hydrogen Ionization in the 1 pc Galactic Central Region
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We study a possible connection between processes of gamma-ray emission and hydrogen ionization in a few pc of central region around Sgr A*. Previous investigations showed there is a discrepancy between interpretation of gamma-ray and ionization data if gamma-rays are generated by proton-proton collisions. Here we provided analysis of processes of ionization and emission basing on analytical and numerical calculations of kinetic equations which describe processes of particle propagation and their energy losses. The origin of gamma rays could be either due to collisions of relativistic protons with the dense gas of the surrounding circumnuclear disk (CND) or bremsstrahlung and inverse Compton scattering of relativistic electrons. The hydrogen ionization in this case is produced by a low energy component of the CR spectrum. We found that if ionization is produced by protons the expected ionization rate of hydrogen in the CND is of the same order as derived from IR observations. So we do not see any discrepancy between the gamma-ray and ionization data for the hadronic model. In the case of ionization by electrons we obtained the ionization rate one order of magnitude higher than follows from the IR data. In principle, a selection between the leptonic and hadronic interpretations can be performed basing on measurements of radio and X-ray fluxes from this region because the leptonic and hadronic models give different values of the fluxes from there. We do not exclude that gamma-ray production and hydrogen ionization in the CND are due to a past activity of Sgr A* which occurred about 100 year ago. Then we hypothesize that there may be connection between a past proton eruption and a flux of hard X-rays emitted by Sgr A* hundred years ago as follows from the observed time variability of the iron line seen in the direction of GC molecular clouds.
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We analyse the 6.4 keV iron line component produced in the Galactic Center (GC) region by cosmic rays in dense molecular clouds (MCs) and in the diffuse molecular gas. We showed that this component, in principle, can be seen in several years in the direction of the cloud Srg B2. If this emission is produced by low energy CRs which ionize the interstellar molecular gas the intensity of the line is quite small, < 1%. However, we cannot exclude that local sources of CRs or X-ray photons nearby the cloud may provide much higher intensity of the line from there. Production of the line emission from molecular clouds depends strongly on processes of CR penetration into them. We show that turbulent motions of neutral gas may generate strong magnetic fluctuations in the clouds which prevent free penetration of CRs into the clouds from outside. We provide a special analysis of the line production by high energy electrons. We concluded that these electrons hardly provide the diffuse 6.4 keV line emission from the GC because their density is depleted by ionization losses. We do not exclude that local sources of electrons may provide an excesses of the 6.4 keV line emission in some molecular clouds and even reproduce a relatively short time variations of the iron line emission. However, we doubt whether a single electron source provides the simultaneous short time variability of the iron line emission from clouds which are distant from each other on hundred pc as observed for the GC clouds. An alternative speculation is that local electron sources could also provide the necessary effect of the line variations in different clouds that are seen simultaneously by chance that seems, however, very unlikely.
We report a new 1-pc (30) resolution CS($J=2-1$) line map of the central 30 pc of the Galactic Center (GC), made with the Nobeyama 45m telescope. We revisit our previous study of the extraplanar feature called polar arc (PA), which is a molecular cloud located above SgrA* with a velocity gradient perpendicular to the Galactic plane. We find that the PA can be traced back to the Galactic disk. This provides clues of the launching point of the PA , roughly $6times10^{6}$ years ago. Implications of the dynamical time scale of the PA might be related to the Galactic Center Lobe (GCL) at parsec scale. Our results suggest that in the central 30 pc of the GC, the feedback from past explosions could alter the orbital path of the molecular gas down to the central tenth of parsec. In the follow-up work of our new CS($J=2-1$) map, we also find that near the systemic velocity, the molecular gas shows an extraplanar hourglass-shaped feature (HG-feature) with a size of $sim$13 pc. The latitude-velocity diagrams show that the eastern edge of the HG-feature is associated with an expanding bubble B1, $sim$7 pc away from SgrA*. The dynamical time scale of this bubble is $sim3times10^{5}$ years. This bubble is interacting with the 50 km s$^{-1}$ cloud. Part of the molecular gas from the 50 km s$^{-1}$ cloud was swept away by the bubble to $b=-0.2deg$. The western edge of the HG-feature seems to be the molecular gas entrained from the 20 km s$^{-1}$ cloud towards the north of the Galactic disk. Our results suggest a fossil explosion in the central 30 pc of the GC a few 10$^{5}$ years ago.
It has been recently proposed that the broad line region in active galactic nuclei originates from dusty clouds driven from the accretion disk by radiation pressure, at a distance from the black hole where the disk is cooler than the dust sublimation temperature. We test this scenario by checking the consistency of independent broad line region and accretion disk reverberation measurements, for a sample of 11 well studied active galactic nuclei. We show that independent disk and broad line region reverberation mapping measurements are compatible with a universal disk temperature at the H{beta} radius of T[R(H{beta})]=1670(231) K which is close to typical dust sublimation temperatures.
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The empirical relations in the black hole-accretion disk-relativistic jet system and physical processes behind these relations are still poorly understood, partly because they operate close to the black hole within the central light year. Very long baseline array (VLBA) provides unparalleled resolution at 15 GHz with which to observe the jet components at sub-milliarcsecond scales, corresponding to sub-pc-scales for local blazars. We discuss the jet inner structure of blazars, location and radiation mechanisms operating in the innermost parsec-scale region of blazars, and evidence for jet-excited broad-line region (BLR) ouflowing downstream the jet. Outflowing BLR can provide necessary conditions for production of high energy emission along the jet between the base of the jet and the BLR and far beyond the BLR as evidenced by recent observations. Flat spectrum quasars and low synchrotron peaked sources are the most likely objects to host the outfllowing BLR. From the $gamma$-ray absorption arguments, we propose that the jet-excited region of the outflowing BLR in quasars is small and/or gas filling factor is low, and that the orientation and opening angle of the outflowing BLR can lead to relevant $gamma$-ray absorption features observed in quasars.
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