Hard X-Ray Spectral Feature Detected in the Region of MCG 8-11-11
Abstract
During a balloon flight of the High Energy Astronomical Telescope on 1995 July 29, a region of the sky of 2.5d width around the Seyfert galaxy MCG 8-11-11 was studied over the photon energy range 20-300 keV. An excess at the 9 σ level--well described by a power-law photon spectrum with a slope of α = 2.1 +/- 1.2, plus a Gaussian line centered at 112 +/- 6 keV having a flux of (9.0 +/- 3.4) × 10-4 photons cm-2 s-1 and a FWHM of 32 +/- 6 keV--was detected in the energy range 20-160 keV. A contemporary detection of a strong γ-ray flux in the veto system of the telescope suggests that the observed spectral feature may be the result of double-Compton backscattering of a 511 keV line source incident on an external cloud. If associated with the Seyfert galaxy MCG 8-11-11, the present measurement would provide the first evidence for electron-positron pair annihilation flux emission from an active galactic nucleus. An observation of the Crab Nebula as an in-flight calibration source of the telescope is also decribed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1997
- DOI:
- 10.1086/310479
- Bibcode:
- 1997ApJ...475L..89P
- Keywords:
-
- GALAXIES: INDIVIDUAL ALPHANUMERIC: MCG 8-11-11;
- GALAXIES: SEYFERT;
- RADIATION MECHANISMS: NONTHERMAL;
- X-RAYS: GALAXIES;
- X-RAYS: GENERAL;
- Galaxies: Individual: Alphanumeric: MCG 8-11-11;
- Galaxies: Seyfert;
- Radiation Mechanisms: Nonthermal;
- X-Rays: Galaxies;
- X-Rays: General