FERMI LARGE AREA TELESCOPE STUDY OF COSMIC RAYS AND THE INTERSTELLAR MEDIUM IN NEARBY MOLECULAR CLOUDS

Journal Article · Fri Aug 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/755/1/22· OSTI ID:22039174

Ackermann, M ^[1]; Ajello, M; Allafort, A; Bechtol, K; Berenji, B; Blandford, R D; Bloom, E D; Borgland, A W; Bottacini, E; Buehler, R ^[2]; Baldini, L; Bellazzini, R; Bregeon, J ^[3]; Ballet, J ^[4]; Barbiellini, G ^[5]; Bastieri, D ^[6]; Bonamente, E ^[7]; Brandt, T J ^[8]; Brigida, M ^[9]; Bruel, P ^[10] ; others, and

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1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
2. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
3. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
4. Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d'Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France)
5. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
6. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
7. Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
8. CNRS, IRAP, F-31028 Toulouse cedex 4 (France)
9. Dipartimento di Fisica 'M. Merlin' dell'Universita e del Politecnico di Bari, I-70126 Bari (Italy)
10. Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Palaiseau (France)

We report an analysis of the interstellar {gamma}-ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within {approx}300 pc from the solar system. The {gamma}-ray emission produced by interactions of cosmic rays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained {gamma}-ray emissivities above 250 MeV are (5.9 {+-} 0.1{sub stat}{sup +0.9}{sub -1.0sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1}, (10.2 {+-} 0.4{sub stat}{sup +1.2}{sub -1.7sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1}, and (9.1 {+-} 0.3{sub stat}{sup +1.5}{sub -0.6sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1} for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by {approx}20% in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, X{sub CO} = N(H{sub 2})/W{sub CO}, is found to be (0.96 {+-} 0.06{sub stat}{sup +0.15}{sub -0.12sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1}, (0.99 {+-} 0.08{sub stat}{sup +0.18}{sub -0.10sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1}, and (0.63 {+-} 0.02{sub stat}{sup +0.09}{sub -0.07sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1} for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of X{sub CO} in the vicinity of the solar system. From the obtained values of X{sub CO}, the masses of molecular gas traced by W{sub CO} in the Chamaeleon, R CrA, and Cepheus and Polaris flare regions are estimated to be {approx}5 Multiplication-Sign 10{sup 3} M{sub Sun }, {approx}10{sup 3} M{sub Sun }, and {approx}3.3 Multiplication-Sign 10{sup 4} M{sub Sun }, respectively. A comparable amount of gas not traced well by standard H I and CO surveys is found in the regions investigated.

• OSTI ID: 22039174
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 755; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
CARBON MONOXIDE
COSMIC RADIATION
EMISSIVITY
ENERGY DEPENDENCE
GAMMA RADIATION
GEV RANGE
HYDROGEN
MASS
MEV RANGE
MOLECULES
PHOTON EMISSION
PHOTONS
SOLAR SYSTEM
TELESCOPES
VARIATIONS