Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987aj.....93.1484m&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 93, June 1987, p. 1484-1501.
Astronomy and Astrophysics
Astronomy
25
Spaceborne Astronomy, X Ray Sources, Brightness, Error Analysis, Heao 2, Poisson Density Functions, Signal To Noise Ratios
Scientific paper
A method which uses the correct measurement error distribution (Poisson) and which naturally takes into account detections as well as upper limits has been developed to search for flux variability in X-ray sources. The method is applied to 256 sources observed at least twice with the Einstein Observatory Imaging Proportional Counter. These sources have, in the very large majority of cases, an X-ray flux in the range 1×10-13 to 6×10-12erg cm-2s-1 (0.2 - 3.5 keV). Thirty-one sources show flux variations with amplitude ranging from about 20% to a factor of 6. Flux variations of small amplitude seem to be fairly common, but can be detected only in bright sources or in sources observed with very long exposures. Variations of a factor of 2 or more are seen in about 15% of the sources for which variations of such an amplitude are detectable.
Garilli Bianca
Maccacaro Tommaso
Mereghetti Sandro
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