scholarly journals The cosmic ray ionization rate in the central parsec of the Galaxy

2013 ◽  
Vol 9 (S303) ◽  
pp. 429-433
Author(s):  
Miwa Goto
Keyword(s):  
Galactic Center ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
High Energy ◽  
High Energy Astrophysics ◽  
The Galaxy ◽  
Γ Ray ◽  
Sgr A ◽  
Central Parsec ◽  
Crossing Point

AbstractCosmic rays represent a unique crossing point of high-energy astrophysics and astrochemistry. The cosmic ray ionization rate of molecular hydrogen (ζ2) measured by H3+ spectroscopy in the central parsec of the Galaxy is 2 orders of magnitude higher than that in the dense clouds outside the Galactic center. However, it is still too short, by the factor of 10,000, to agree with an extremely high ζ2 that accommodates the new γ-ray observations of Sgr A* and its environment.

scholarly journals Composition and Galactic Confinement of Cosmic Rays

1971 ◽  
Vol 2 ◽  
pp. 740-756
Author(s):  
Maurice M. Shapiro
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
High Energy Astrophysics ◽  
Transit Times ◽  
The Galaxy ◽  
Path Lengths

The ‘Galactic’ cosmic rays impinging on the Earth come from afar over tortuous paths, traveling for millions of years. These particles are the only known samples of matter that reach us from regions of space beyond the solar system. Their chemical and isotopic composition and their energy spectra provide clues to the nature of cosmic-ray sources, the properties of interstellar space, and the dynamics of the Galaxy. Various processes in high-energy astrophysics could be illuminated by a more complete understanding of the arriving cosmic rays, including the electrons and gamma rays.En route, some of theprimordialcosmic-ray nuclei have been transformed by collision with interstellar matter, and the composition is substantially modified by these collisions. A dramatic consequence of the transformations is the presence in the arriving ‘beam’ of considerable fluxes of purely secondary elements (Li, Be, B), i.e., species that are, in all probability, essentially absent at the sources. We shall here discuss mainly the composition of the arriving ‘heavy’ nuclei -those heavier than helium - and what they teach us about thesourcecomposition, the galactic confinement of the particles, their path lengths, and their transit times.

scholarly journals SiO and H2O Masers in the Central Parsec of the Galaxy

1998 ◽  
Vol 164 ◽  
pp. 229-230 ◽  
Author(s):  
Karl M. Menten ◽  
Mark J. Reid
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Images ◽  
Evolved Stars ◽  
The Galaxy ◽  
Sgr A ◽  
Central Parsec ◽  
Infrared Sources

AbstractWe have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.

scholarly journals Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI

2021 ◽  
Vol 923 (1) ◽  
pp. 24
Author(s):  
Nanase Harada ◽  
Sergio Martín ◽  
Jeffrey G. Mangum ◽  
Kazushi Sakamoto ◽  
Sebastien Muller ◽  
...  
Keyword(s):  
Galactic Center ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
High Energy ◽  
Photon Flux ◽  
Starburst Galaxy ◽  
Energy Feedback ◽  
The Difference ◽  
Uv Photons ◽  
Molecular Abundances

Abstract Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1−0) integrated intensity shows its association with “superbubbles,” cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10–150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10−11–6 × 10−10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ≳ 103 if the maximum visual extinction is ≳5, or a cosmic-ray ionization rate of ζ ≳ 10−14 s−1 (3–4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.

scholarly journals High-energy Galactic phenomena and the interstellar medium

1985 ◽  
Vol 106 ◽  
pp. 225-233
Author(s):  
Catherine J. Cesarsky
Keyword(s):  
Magnetic Fields ◽  
Interstellar Medium ◽  
Molecular Hydrogen ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Small Scale ◽  
The Galaxy ◽  
Γ Rays ◽  
Γ Ray

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).

scholarly journals THE GALACTIC CENTER

1981 ◽  
Vol 96 ◽  
pp. 281-295
Author(s):  
Ian Gatley ◽  
E. E. Becklin
Keyword(s):  
Angular Resolution ◽  
Galactic Center ◽  
Mass Density ◽  
High Angular Resolution ◽  
Density Structure ◽  
Unique Region ◽  
Ultimate Source ◽  
The Galaxy ◽  
Sgr A ◽  
Central Parsec

Recent infrared and radio observations of the Galactic Center are reviewed. For the region between 1 and 100 pc most of the observed phenomena can be explained by a large density of late-type stars, a ring of molecular material, and a number of regions of active star formation. The central parsec (Sgr A) appears to be a unique region of activity in the Galaxy; this result is based on recent high angular resolution data at 30 to 100 μm and high resolution spectral line observations at 12.8 μm. The observations are discussed in terms of the mass, density structure, and luminosity of the region; the ultimate source of the activity is discussed.

scholarly journals Diffuse gamma-ray emission from the Galactic center and implications of its past activities

2016 ◽  
Vol 11 (S322) ◽  
pp. 214-217
Author(s):  
Yutaka Fujita ◽  
Shigeo S. Kimura ◽  
Kohta Murase
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
High Energy ◽  
Accretion Flows ◽  
The Past ◽  
Sagittarius A ◽  
Sgr A

AbstractIt has been indicated that low-luminosity active galactic nuclei (LLAGNs) are accelerating high-energy cosmic-ray (CR) protons in their radiatively inefficient accretion flows (RIAFs). If this is the case, Sagittarius A* (Sgr A*) should also be generating CR protons, because Sgr A* is a LLAGN. Based on this scenario, we calculate a production rate of CR protons in Sgr A* and their diffusion in the central molecular zone (CMZ) around Sgr A*. The CR protons diffusing in the CMZ create gamma-rays through pp interaction. We show that the gamma-ray luminosity and spectrum are consistent with observations if Sgr A* was active in the past.

scholarly journals 7.8. Particle cascades in Sgr A∗: the possibility of observing their γ-ray signature

1998 ◽  
Vol 184 ◽  
pp. 307-308
Author(s):  
Sera Markoff ◽  
Fulvio Melia ◽  
Ina Sarcevic
Keyword(s):  
Black Hole ◽  
Particle Physics ◽  
Galactic Center ◽  
Theoretical Models ◽  
High Energy ◽  
Massive Black Hole ◽  
Inverse Compton Scattering ◽  
Black Hole Candidate ◽  
Γ Ray ◽  
Sgr A

The recent detection of a γ-ray flux from the direction of the Galactic center by EGRET on the Compton GRO raises the question of whether this is a point source (possibly coincident with the massive black hole candidate Sgr A∗) or a diffuse emitter. Using the latest experimental particle physics data and theoretical models, we have examined in detail the γ-ray spectrum produced by synchrotron, inverse Compton scattering and mesonic decay resulting from the interaction of relativistic protons with hydrogen accreting onto a point-like object. Such a distribution of high-energy baryons may be expected to form within an accretion shock as the inflowing gas becomes supersonic. This scenario is motivated by hydrodynamic studies of Bondi-Hoyle accretion onto Sgr A∗, which indicate that many of its radiative characteristics may ultimately be associated with energy liberated as this plasma descends down into the deep potential well. Earlier attempts at analyzing this process concluded that the EGRET data are inconsistent with a massive point-like object (Mastichiadis & Ozernoy, 1994). Our results demonstrate that a more careful treatment of the physics of p-p scattering suggests that a ~ 106M⊙ black hole may be contributing to this high-energy emission.

scholarly journals SAS-2 gamma ray observations related to a galactic halo

1979 ◽  
Vol 84 ◽  
pp. 483-484
Author(s):  
C. E. Fichtel ◽  
G. A. Simpson ◽  
D. J. Thompson
Keyword(s):  
Energy Spectrum ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Average Intensity ◽  
General Direction ◽  
Γ Radiation ◽  
The Galaxy ◽  
Γ Ray

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse γ radiation observed by SAS 2 away from the galactic plane in the energy range above 35 MeV has revealed no evidence supporting a cosmic ray halo surrounding the galaxy in the general shape of a sphere. The diffuse γ radiation does consist of two components. One component is related to the galactic disk on the basis of its correlation with the 21-cm measurements, the continuum radio emission, and galactic coordinates. Further its energy spectrum is similar to that in the plane, and its intensity distribution joins smoothly to the intense radiation from the plane. The other component appears isotropic, at least on a coarse scale, and has a steep energy spectrum. The degree of isotropy which has been established for the “isotropic” radiation and the steep energy spectrum, which distinguishes it from the galactic disk radiation, place strong constraints on galactic halo models for the origin of this component. Theoretical models involving a galactic halo have generally postulated a halo with dimensions of the order of the Galaxy and hence a radius, at least in the plane, of about 15 kpcs. Since the Sun is about 10 kpc from the galactic center, if such a halo exists and is responsible for the γ rays (through, for example, black body Compton radiation), a very marked anisotropy would be seen, with the γ ray intensity from the general direction of the galactic center being much larger than that from the same latitudes in the anticenter direction. In fact, no such anisotropy is seen; specifically the ratio of the average intensity in the (300° < ℓ < 60°, 20° < |b| < 40°) region to that in the (100° < ℓ < 250°, 20° < |b| < 40°) region was found to be 1.10±0.19 compared to a calculated value for a model with a uniform cosmic ray sphere with a 15 kpc radius of 2.85. The ratio between the average γ-ray intensity from regions with |b| < 60° to that from 20° < |b| < 40° is found to be 0.87±0.09. If the region is assumed to be spherical, but with a larger radius and a uniform cosmic ray density, the upper limit (2σ) set for the anisotropy demands that the radius be at least 45 kpc. An extragalactic origin for the isotropic component currently appears to be a more plausible explanation.

scholarly journals UVscope and its application aboard the ASTRI-Horn telescope

2021 ◽  
Author(s):  
Maria Concetta Maccarone ◽  
Giovanni La Rosa ◽  
Osvaldo Catalano ◽  
Salvo Giarrusso ◽  
Alberto Segreto ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Single Photon ◽  
Photon Counting ◽  
Light Flux ◽  
Cosmic Ray ◽  
High Energy ◽  
Wide Field ◽  
High Energy Astrophysics ◽  
Single Photon Counting ◽  
Photon Counting Mode

AbstractUVscope is an instrument, based on a multi-pixel photon detector, developed to support experimental activities for high-energy astrophysics and cosmic ray research. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300-650 nm. The instrument can be used in a wide field of applications where the knowledge of the nocturnal environmental luminosity is required. Currently, one UVscope instrument is allocated onto the external structure of the ASTRI-Horn Cherenkov telescope devoted to the gamma-ray astronomy at very high energies. Being co-aligned with the ASTRI-Horn camera axis, UVscope can measure the diffuse emission of the night sky background simultaneously with the ASTRI-Horn camera, without any interference with the main telescope data taking procedures. UVscope is properly calibrated and it is used as an independent reference instrument for test and diagnostic of the novel ASTRI-Horn telescope.

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