Mathematics – Logic
Scientific paper
Feb 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.3501w&link_type=abstract
American Astronomical Society, HEAD meeting #11, #35.01; Bulletin of the American Astronomical Society, Vol. 41, p.714
Mathematics
Logic
Scientific paper
We describe a tomographic method of mapping the gamma-ray sky above 200 keV with earth-occultation data from BATSE, the Burst And Transient Source Experiment on the Compton Gamma-Ray Observatory (CGRO). The method combines good sensitivity with 0.5° angular resolution over the whole sky. Our previous occultation analysis of the BATSE data indicates the presence of a significant number of unmodeled cosmic sources. The Earth's horizon cuts the sky in a cycle that repeats with the 51 day precession of the CGRO orbit plane, which is reflected in periodic effects due to the uncatalogued sources. Such cycles are then a natural data unit for all-sky mapping by a tomographic method using the Radon transform. Because the airmass profile of the horizon is nearly independent of energy, we obtain 0.5° angular resolution over the entire low-energy gamma-ray region. To improve sensitivity, we subtract a phenomenological model for the non-cosmic gamma-ray background from the raw count data before performing the imaging analysis, which uses a simple planar approximation to the inverse Radon transform on a tiling of the sky.
We present images in four broad energy bands (23-98 keV, 98-230 keV, 230-595 keV and 595-1800 keV) centered on selected sources to illustrate the power of this approach. Our preliminary results tentatively show several sources in the 230-595 keV and 595-1800 keV bands, which will be presented. We easily image the Crab in the 595-1800 keV band in a single precession cycle. With 64 cycles in the 9 year CGRO data set, we expect a flux-complete survey of the entire sky, with multiple independent sky maps achieving a combined sensitivity typically less than 125 mCrab near 1 MeV. This work has been supported by grants from NASA, JPL, and LSU.
Case Gary L.
Cherry Michael L.
Ling James C.
Lo Martin W.
Roland J. M.
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