Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........64s&link_type=abstract
PhD Dissertation, California Univ. Berkeley, CA United States
Astronomy and Astrophysics
Astronomy
X Rays, Gamma Rays, Galactic Structure, Accretion Disks, Interstellar Matter, Annihilation Reactions, Black Holes (Astronomy), Gamma Ray Spectrometers, Positron Annihilation, Stellar Mass, Supernovae
Scientific paper
We present an observation of the Galactic Center region by HEXAGONE, a high-resolution, balloon-borne gamma-ray spectrometer with an 18 deg full width at half maximum (FWHM) field of view. The spectrum shows a 511 keV line from positron annihilation with a flux of (10.0 +/- 2.4) x 10-4 photons/cm2/s and FWHM (2.9 +1.0, 1.1) keV. This line has been seen from the Galactic Center by many instruments and is thought to be mostly diffuse, originating in the interstellar medium along the Galactic Plane, but possibly with a variable component from a point source near the Galactic Center. Another feature at (163.7 +/- 3.4) keV was observed with flux (1.55 +/- 0.47) x 10-3 photons/cm2/s and FWHM (24.4 +/- 9.2) keV. It is modeled as Compton backscattering of annihilation radiation from positrons created in an accreting plasma near a stellar-mass black hole, possibly 1E1740.7-2942, which has previously emitted a flare of Doppler-broadened annihilation radiation. Regardless of geometry, a minimum annihilation line flux of 0.026 photons/cm2/s or 1044 annihilations/s would have been required to create this feature. This is twice the flux of the 1E1740.7-2942 flare, the brightest annihilation flux ever observed. The unscattered annihilation radiation may have been occulted or may have arrived before our observation, the backscatter delayed by light travel time. Accretion disk and spherical shell geometries illustrate these two possibilities. No continuum from three-photon annihilation of orthopositronium, which is expected to accompany the annihilation line, was detected. We set a 2sigma upper limit of 0.90 on the fraction of positrons annihilating via positronium. We searched for the 68, 78, and 1157 keV lines from the decay of (44)Ti, whose presence would indicate a Galactic supernova hidden by dust in visible light and less than approximately100 years old. The combined fluxes correspond to (1.78 +/- 1.00) solar masses of (44)Ti at the Galactic Center. Three additional short pointings within 40 deg of the Galactic Center showed excess emission above the Galactic Plane, which we fit either as diffuse or as a new point source. If diffuse, the extent in Galactic latitude from 35-120 keV is 33 +/- 8 deg FWHM. Finally, we describe the new, model-independent method used to remove the effect of the instrument response from the spectrum.
No associations
LandOfFree
A hard x-ray and gamma-ray observation of the Galactic Center region does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A hard x-ray and gamma-ray observation of the Galactic Center region, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A hard x-ray and gamma-ray observation of the Galactic Center region will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1264575