EDP Sciences
Free access
Volume 422, Number 3, August II 2004
Page(s) L47 - L50
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040172

A&A 422, L47-L50 (2004)
DOI: 10.1051/0004-6361:20040172


The distribution of cosmic-ray sources in the Galaxy, $\mathsf{\gamma}$-rays and the gradient in the CO-to-H $\mathsf{_2}$ relation

A. W. Strong1, I. V. Moskalenko2, 3, O. Reimer4, S. Digel5 and R. Diehl1

1  Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
    e-mail: aws@mpe.mpg.de
2  NASA/Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA
3  Joint Center for Astrophysics, University of Maryland, Baltimore County, Baltimore, MD 21250, USA
4  Ruhr-Universität Bochum, 44780 Bochum, Germany
5  W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA

(Received 5 April 2004 / Accepted 12 May 2004 )

We present a solution to the apparent discrepancy between the radial gradient in the diffuse Galactic $\gamma$-ray emissivity and the distribution of supernova remnants, believed to be the sources of cosmic rays. Recent determinations of the pulsar distribution have made the discrepancy even more apparent. The problem is shown to be plausibly solved by a variation in the $W_{\rm CO}$-to- N(H 2) scaling factor. If this factor increases by a factor of 5-10 from the inner to the outer Galaxy, as expected from the Galactic metallicity gradient, we show that the source distribution required to match the radial gradient of $\gamma$-rays can be reconciled with the distribution of supernova remnants as traced by current studies of pulsars. The resulting model fits the EGRET $\gamma$-ray profiles extremely well in longitude, and reproduces the mid-latitude inner Galaxy intensities better than previous models.

Key words: gamma rays -- galactic structure -- interstellar medium -- cosmic rays -- supernova remnants -- pulsars

© ESO 2004

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.