The cosmic ray distribution in sagittarius B

Roland M. Crocker, David Jones, Raymond J. Protheroe, Jürgen Ott, Ron Ekers, Fulvio Melia, Todor Stanev, Anne Green

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


The H.E.S.S. instrument has observed a diffuse flux of ∼TeV γ-rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region, suggesting that the γ-rays originate in collisions between cosmic-ray hadrons (CRHs) and ambient matter. Of particular interest, H.E.S.S. has detected γ-rays from the Sagittarius (Sgr) B molecular cloud complex. Prompted by the suggestion of a hadronic origin for the γ-rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed γ-rays). Intriguingly, we have uncovered nonthermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic-ray ionization rate is 10 times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (1) a hard (∼E -2.2), high-energy (≳TeV) population of CRHs is unavoidably required by the H.E.S.S. γ-ray data, and (2) the remaining broadband, nonthermal phenomenology is explained either by a rather steep (∼E -2.9) spectrum of primary electrons or a (∼E-2.7) population of CRHs. Perhaps unsurprisingly, no single power-law population of either leptons or hadrons can explain the totality of broadband, nonthermal Sgr B phenomenology.

Original languageEnglish (US)
Pages (from-to)934-948
Number of pages15
JournalAstrophysical Journal
Issue number2 I
StatePublished - 2007


  • Acceleration of particles
  • Galaxy: center
  • Radiation mechanisms: nonthermal
  • Supernova remnants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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