INTERACTING COSMIC RAYS WITH MOLECULAR CLOUDS: A BREMSSTRAHLUNG ORIGIN OF DIFFUSE HIGH-ENERGY EMISSION FROM THE INNER 2 Degree-Sign Multiplication-Sign 1 Degree-Sign OF THE GALACTIC CENTER

Journal Article · Tue Jan 01 00:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/762/1/33· OSTI ID:22167309

Yusef-Zadeh, F.; Roberts, D. A.; Royster, M. ^[1]; Hewitt, J. W. ^[2]; Wardle, M. ^[3]; Tatischeff, V. ^[4]; Cotton, W. ^[5]; Uchiyama, H.; Nobukawa, M.; Tsuru, T. G. ^[6]; Heinke, C. ^[7]

---

1. Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)
2. Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Department of Physics and Astronomy, and Research Center for Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, NSW 2109 (Australia)
4. Center de Spectrometrie Nucleaire et de Spectrometrie de Massse, IN2P3/CNRS and Univ. Paris-Sud, F-91405 Orsay Campus (France)
5. NRAO, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
6. Cosmic Ray Group, Physics, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo, Kyoto 606-8502 (Japan)
7. Department of Physics, Room 238 CEB, University of Alberta, Edmonton, AB T6G 2G7 (Canada)

The high-energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray, and {gamma}-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using the Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of {approx}GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas. The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of Fe I 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra, and the H.E.S.S. observatories. The inferred physical quantities from modeling multiwavelength emission in the context of bremsstrahlung emission from the inner {approx}300 Multiplication-Sign 120 pc of the Galactic center are constrained to have the cosmic-ray ionization rate {approx}1-10 Multiplication-Sign 10{sup -15} s{sup -1}, molecular gas heating rate elevating the gas temperature to 75-200 K, fractional ionization of molecular gas 10{sup -6}-10{sup -5}, large-scale magnetic field 10-20 {mu}G, the density of diffuse and dense molecular gas {approx}100 and {approx}10{sup 3} cm{sup -3} over 300 pc and 50 pc path lengths, and the variability of Fe I K{alpha} 6.4 keV line emission on yearly timescales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV {gamma}-rays detected by Fermi and that the cosmic-ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds.

• OSTI ID: 22167309
• Journal Information: Astrophysical Journal, Vol. 762, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
COSMIC ELECTRONS
COSMIC GASES
COSMIC PHOTONS
EMISSION SPECTRA
GAMMA ASTRONOMY
GAMMA DETECTION
GEV RANGE
HEATING RATE
INTERSTELLAR MAGNETIC FIELDS
IONIZATION
KEV RANGE
MILKY WAY
PHOTON EMISSION
SYNCHROTRON RADIATION
TELESCOPE COUNTERS
TEV RANGE
X RADIATION
X-RAY DETECTION