EGRET observations of the extragalactic gamma-ray emission

Authors

P. Sreekumar, NASA Goddard Space Flight Center
D. L. Bertsch, NASA Goddard Space Flight Center
B. L. Dingus, The University of Utah
J. A. Esposito, NASA Goddard Space Flight Center
C. E. Fichtel, NASA Goddard Space Flight Center
R. C. Hartman, NASA Goddard Space Flight Center
S. D. Hunter, NASA Goddard Space Flight Center
G. Kanbach, Max Planck Institute for Extraterrestrial Physics
D. A. Kniffen, Hampden-Sydney College
Y. C. Lin, Stanford University
H. A. Mayer-Hasselwander, Max Planck Institute for Extraterrestrial Physics
P. F. Michelson, Stanford University
C. Von Montigny, Landessternwarte Heidelberg
A. Mücke, Max Planck Institute for Extraterrestrial Physics
R. Mukherjee, Barnard College
P. L. Nolan, Stanford University
M. Pohl, Technical University of Denmark
O. Reimer, Max Planck Institute for Extraterrestrial Physics
E. Schneid, Northrop Grumman corporation
J. G. Stacy, University of New Hampshire Durham
F. W. Stecker, NASA Goddard Space Flight Center
D. J. Thompson, NASA Goddard Space Flight Center
T. D. Willis, Stanford University

Document Type

Article

Publication Date

1-1-1998

Abstract

The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by EGRET aboard the Compton Gamma Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component that is generally believed to originate outside the Galaxy. Through a careful study and removal of the Galactic diffuse emission, the flux, spectrum, and uniformity of the extragalactic emission are deduced. The analysis indicates that the extragalactic emission is well described by a power-law photon spectrum with an index of -(2.10 ± 0.03) in the 30 MeV to 100 GeV energy range. No large-scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic high-energy gamma-ray emission is that it arises primarily from unresolved gamma-ray-emitting blazars. © 1998. The American Astronomical Society. All rights reserved.

Publication Source (Journal or Book title)

Astrophysical Journal

First Page

523

Last Page

534

Recommended Citation

Sreekumar, P., Bertsch, D., Dingus, B., Esposito, J., Fichtel, C., Hartman, R., Hunter, S., Kanbach, G., Kniffen, D., Lin, Y., Mayer-Hasselwander, H., Michelson, P., Von Montigny, C., Mücke, A., Mukherjee, R., Nolan, P., Pohl, M., Reimer, O., Schneid, E., Stacy, J., Stecker, F., Thompson, D., & Willis, T. (1998). EGRET observations of the extragalactic gamma-ray emission. Astrophysical Journal, 494 (2 PART I), 523-534. https://doi.org/10.1086/305222