γ-Ray line emission from SS433

Abstract

We report here preliminary evidence for γ-ray line emission from the region of SS433. The observations were accomplished with the high-resolution γ-ray spectrometer aboard the HEAO 3 satellite¹. One of the line features reported here, located at an energy of 1.5 MeV, has a statistical significance of ∼6 σ during a particular 18-day interval. Another feature appears near 1.2 MeV. Both features exhibit fractional linewidths, ΔE/E, of ∼1%. The intensity of the 1.5-MeV feature is variable by a factor of ∼3 on a time scale of days with a 46-day time average value of 1.5±0.3×10⁻³ photons cm⁻² s⁻¹. The 1.2-MeV feature is similarly variable with a time average intensity of 1.1±0.2×10⁻³ photons cm⁻² s⁻¹. The combined power in the lines is ∼2 × 10³⁷ erg s⁻¹, assuming isotropic emission from SS433. Phenomena previously observed^2,3 from SS433 have been interpreted in terms of a kinematic model^4,5 in which two oppositely directed jets of relativistic material (ν = 0.26c) are ejected from a central source. Our observed energies may be explained in terms of this kinematic model as blue- and red-shifted components of the 1.369-MeV line from a nuclear transition of ²⁴Mg from its first excited state to its ground state. Both components appear to vary in energy over the duration of the observation in a manner roughly consistent with the pattern seen in the optical regime², in which ‘movement’ of optical features is accounted for by a precession of the axis of the jets with a 163.51-day period⁶. However, this identification implies an anomolously high magnesium abundance relative to carbon and oxygen.