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We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free-free absorption along the line of sight. We focus on one cloud, G0.13--0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (alpha^{74MHz}_{327MHz}=1.3pm0.3) nonthermal emission from the Galactic center region. This cloud lies adjacent to the nonthermal radio filaments of the Arc near l~0.2^0 and is a strong source of 74 MHz continuum, SiO (2-1) and FeI Kalpha 6.4 keV line emission. This three-way correlation provides the most compelling evidence yet that relativistic electrons, here traced by 74 MHz emission, are physically associated with the G0.13--0.13 molecular cloud and that low energy cosmic ray electrons are responsible for the FeI Kalpha line emission. The high cosmic ray ionization rate ~10-13 s-1 H-1 is responsible for heating the molecular gas to high temperatures and allows the disturbed gas to maintain a high velocity dispersion. LVG modeling of multi-transition SiO observations of this cloud implies H2 densities ~104-5 cm-3 and high temperatures. The lower limit to the temperature of G0.13-0.13 is ~100K, whereas the upper limit is as high as 1000K. Lastly, we used a time-dependent chemical model in which cosmic rays drive the chemistry of the gas to investigate for molecular line diagnostics of cosmic ray heating. When the cloud reaches chemical equilibrium, the abundance ratios of HCN/HNC and N2H+/HCO+ are consistent with measured values. In addition, significant abundance of SiO is predicted in the cosmic ray dominated region of the Galactic center. We discuss different possibilities to account for the origin of widespread SiO emission detected from Galactic center molecular clouds.
Synchrotron-emitting, nonthermal filaments (NTFs) have been observed near the Galactic center for nearly four decades, yet their physical origin remains unclear. Here we investigate the possibility that NTFs are produced by the destruction of molecul
This letter presents a Nyquist-sampled, high-resolution [CI] 3P1-3P0 map of the -0.2 deg < l < 1.2 deg x -0.1 deg < b < 0 deg region in the Central Molecular Zone (CMZ) taken with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope.
We report the analysis of the Fermi-Large Area Telescope data from six nearby giant molecular clouds (MCs) belonging to the Gould Belt and the Aquila Rift regions. The high statistical {gamma}-ray spectra above 3 GeV well described by power laws make
The recently observed data by AMS-02 clearly confirms that the positron flux rises with energy and shows a peak near a few hundred GeV. This rising positron flux cannot be explained by interactions of cosmic rays with interstellar hydrogen gas. In th
Cosmic-rays constitute the main ionising and heating agent in dense, starless, molecular cloud cores. We reexamine the physical quantities necessary to determine the cosmic-ray ionisation rate (especially the cosmic ray spectrum at E < 1 GeV and the