Backscatter, anisotropy, and polarization of solar hard X-rays

Journal Article · Sun Jan 15 04:00:00 EST 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155830· OSTI ID:5188068

Bai, T; Ramaty, R

Hard X-rays incident upon the photosphere with energies > or approx. =15 keV have high probabilities of backscatter due to Compton collisions with electrons. This effect has a strong influence on the spectrum, intensity, and polarization of solar hard X-rays - especially for anisotropic models in which the primary X-rays are emitted predominantly toward the photosphere. We have carried out a detailed study of X-ray backscatter, and we have investigated the interrelated problems of anisotropy, polarization, center-to-limb variation of the X-ray spectrum, and Compton backscatter in a coherent fashion. The results of this study are compared with observational data. Because of the large contribution from backscatter, for an anisotropic primary X-ray source which is due to bremsstrahlung of accelerated electrons moving predominantly down toward the photosphere, the observed X-ray flux around 30 keV does not depend significantly on the position of flare on the Sun. For such an anisotropic source, the X-ray spectrum observed in the 15-50 keV range becomes steeper with the increasing heliocentric angle of the flare. These results are compatible with the data. The degree of polarization of the sum of the primary and reflected X-rays with energies between about 15 and 30 keV can be very large for anisotropic primary X-ray sources, but it is less than about 4% for isotropic sources. We also discuss the characteristics of the brightness distribution of the X-ray albedo patch created by the Compton backscatter. The height and anisotropy of the primary hard X-ray source might be inferred from the study of the albedo patch.

• Research Organization: Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center
• OSTI ID: 5188068
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 219:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
ATMOSPHERES
BACKSCATTERING
BASIC INTERACTIONS
BREMSSTRAHLUNG
COMPTON EFFECT
ELASTIC SCATTERING
ELECTROMAGNETIC INTERACTIONS
ELECTROMAGNETIC RADIATION
ENERGY RANGE
HARD X RADIATION
INTERACTIONS
IONIZING RADIATIONS
KEV RANGE
KEV RANGE 10-100
MONTE CARLO METHOD
PHOTOSPHERE
POLARIZATION
RADIATIONS
SCATTERING
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR FLARES
SOLAR RADIATION
SPECTRA
STARS
STOKES PARAMETERS
SUN
X RADIATION
X-RAY SPECTRA