Astronomy and Astrophysics – Astronomy
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsa22a..03d&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SA22A-03
Astronomy and Astrophysics
Astronomy
7554 X Rays, Gamma Rays, And Neutrinos, 7594 Instruments And Techniques, 0300 Atmospheric Composition And Structure, 0355 Thermosphere: Composition And Chemistry
Scientific paper
The X-ray Astronomy Branch of the Naval Research Laboratory launched the Unconventional Stellar Aspect (USA) experiment aboard the Advanced Research and Global Observation Satellite (ARGOS) in 1999. USA is an X-ray timing experiment with a large collecting area and microsecond time resolution capable of conducting a broad program of studies of galactic X-ray binaries. USA consists of a collimated proportional counter X-ray telescope and two detectors with ~1000 cm2 effective area each, sensitive to photons in the 1-15 keV energy range. The Rossi X-ray Timing Explorer (RXTE) was launched on December 30, 1995 from NASA's Kennedy Space Center. The mission is managed and controlled by NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. RXTE features unprecedented time resolution in combination with moderate spectral resolution to explore the variability of X-ray sources. Time scales from microseconds to months are covered in an instantaneous spectral range from 2 to 250 keV. We have developed a new technique to measure the composition and structure of the upper atmosphere using atmospheric occultation of celestial x-ray sources. Both USA and RXTE provide energy-resolved photon extinction curves, and the combined energy ranges of USA and RXTE permit direct probing of the mesosphere and lower thermosphere (80-160 km). Roughly speaking, differential absorption among energy bands can provide composition information, and the shape of the light curves total density versus altitude. Two complementary algorithms have been employed in the data analysis. The first method employs basis functions derived from NRLMSIS-00 (Picone et al 2000) in a Discrete Inverse Theory maximum likelihood retrieval of densities and temperature by fitting the light curve. The second method is a direct inversion of the light curve to determine optical depths and optical depth scale height, from which temperature and density may be iteratively derived in a self-consistent manner from NRLMSIS-00 composition information. The results from both methods are compared to each other, standard atmospheric models, and data from the High Resolution Airglow and Aurora Spectrograph (HIRAAS), mounted alongside USA on the ARGOS satellite. This research is the first to study the neutral atmosphere in this energy range, and complements UV airglow remote sensing techniques used aboard ARGOS that are less sensitive to nighttime neutral density. Enhanced Empirical Models of the Thermosphere, J. M. Picone, A. E.Hedin, D. P. Drob, R. R. Meier, J. Lean, A. C. Nicholas, and S. E. Thonnard, Physics and Chemistry of the Earth, Part C: Solar-Terrestrial and Planetary Science, 25(5-6), 537-42 (2000). Keywords: upper atmosphere, X-rays, horizon crossing, occultations
Budzein S. A.
Determan Jon R.
Titarchuk Lev
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