Diffuse Continuum Gamma Rays from the Galaxy

نویسندگان

  • ANDREW W. STRONG
  • IGOR V. MOSKALENKO
  • OLAF REIMER
چکیده

We have carried out a new study of the diffuse Galactic γ-ray continuum radiation using a cosmic-ray propagation model which includes nucleons, antiprotons, electrons, positrons, and synchrotron radiation. We show that models based on locally measured electron and nucleon spectra and synchrotron constraints are consistent with γ-ray measurements in the 30 MeV – 500 MeV range, but outside this range excesses are apparent. A harder nucleon spectrum is considered but fitting to γ-rays causes it to violate limits from positrons and antiprotons. A harder interstellar electron spectrum allows the γ-ray spectrum to be fitted above 1 GeV as well, and this can be further improved when combined with a modified nucleon spectrum which still respects the limits imposed by antiprotons and positrons. A large electron/inverse Compton (IC) halo is proposed which reproduces well the high-latitude variation of γ-ray emission; this is taken as support for the halo size for nucleons deduced from studies of cosmic-ray composition. Halo sizes in the range zh = 4–10 kpc are favoured by both analyses. The halo contribution of Galactic emission to the high-latitude γ-ray intensity is large, with implications for the study of the diffuse extragalactic component and signatures of dark matter. The constraints provided by the radio synchrotron spectral index do not allow all of the <30 MeV γ-ray emission to be explained in terms of a steep electron spectrum unless this takes the form of a sharp upturn below 200 MeV. This leads us to prefer a source population as the origin of the excess low-energy γ-rays, which can then be seen as a continuation of the hard X-ray continuum measured by OSSE, GINGA and RXTE. Subject headings: cosmic rays — diffusion — Galaxy: general — ISM: general — gamma rays: observations — gamma rays: theory

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Osse Observations of the Soft Gamma Ray Continuum from the Galactic Plane at Longitude 95

We present the results of OSSE observations of the soft gamma ray continuum emission from the Galactic plane at longitude 95 •. Emission is detected between 50 and 600 keV where the spectrum is fit well by a power law with photon index −2.6 ± 0.3 and flux (4.0 ± 0.5) × 10 −2 photons s −1 cm −2 rad −1 MeV −1 at 100 keV. This spectral shape in this range is similar to that found for the continuum...

متن کامل

Diffuse Emission from the Galactic Plane and Unidentified EGRET Sources

Diffuse Galactic gamma-ray emission is produced in interactions of cosmic rays with gas and ambient photon fields and thus provides us with an indirect measurement of cosmic rays in various locations in the Galaxy. The diffuse gamma-ray continuum is more intense than expected both at energies below 200 keV and above 1 GeV. The existing models for the high-energy excess are reviewed in the light...

متن کامل

Positron Annihilations at the Galactic Center: Generating More Questions Than Answers

The bulge of our Galaxy is illuminated by the 0.511 MeV gamma-ray line flux from annihilations of nonrelativistic positrons. The emission is strongly concentrated at the Galactic Center (GC), in contrast to gamma-ray maps tracing nucleosynthesis (e.g., the 1.809 MeV line from decaying Al) or cosmic ray processes (e.g., the 1–30 MeV continuum), which reveal a bright disk with a much less promine...

متن کامل

ar X iv : a st ro - p h / 01 01 06 8 v 1 4 J an 2 00 1 MODELS FOR GALACTIC COSMIC - RAY PROPAGATION

A new numerical model of particle propagation in the Galaxy has been developed, which allows the study of cosmic-ray and gamma-ray production and propagation in 2D or 3D, including a full reaction network. This is a further development of the code which has been used for studies of cosmic ray reacceleration, Galactic halo size, antiprotons and positrons in cosmic rays, the interpretation of dif...

متن کامل

Diffuse Galactic Continuum Gamma Rays. a Model Compatible with Egret Data and Cosmic-ray Measurements

We present a study of the compatibility of some current models of the diffuse Galactic continuum γrays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the “conventional mo...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 1998