The complex broadband X-ray spectrum of the starburst galaxy M82
- Institute of Geophysics and Planetary Physics, L-413, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
The broadband X-ray spectrum of the prototypical starburst galaxy M82 is very complex. At least three spectral components are required to fit the combined {ital ROSAT} and {ital ASCA} spectrum in the 0.1{endash}10 keV range. The observed X-ray flux in this band is dominated by a hard {Gamma}=1.7, heavily absorbed power-law component which originates in the nucleus and near-nuclear disk of the galaxy. Among the candidates for the origin of this hard X-ray emission, the most plausible appears to be inverse-Compton scattered emission from the interaction of the copious infrared photon flux of M82 with supernova-generated relativistic electrons. The measured intrinsic luminosity of the power-law component agrees closely with calculations of the expected inverse-Compton luminosity. Moreover, the radio and X-ray emission in the nucleus of M82 have the same spectral slope, which should be the case if both types of emission are nonthermal and are associated with a common population of electrons. The other two spectral components, thermal plasmas with characteristic temperatures kT{approx}0.6 and 0.3 keV, are associated with the star formation and starburst-driven wind in M82. The warmer thermal component is heavily absorbed as well and must also originate in the central region of the galaxy. The softer thermal component, however, is not absorbed, and is likely to represent the X-ray emission that extends along the minor axis of M82. The amount of absorption required in the three-component model suggests that the intrinsic luminosity of M82 in the 0.1{endash}10 keV band is about four times greater than its observed luminosity of 4{times}10{sup 40}ergss{sup {minus}1}. {copyright} {ital 1997} {ital The American Astronomical Society}
- Research Organization:
- Lawrence Livermore National Laboratory
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 530003
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 478; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
X-Rays from NGC 3256: High-Energy Emission in Starburst Galaxies and Their Contribution to the Cosmic X-Ray Background
No X-ray-luminous starbursts in the {ital Einstein} medium sensitivity survey, either