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A probable 1970 hard X-ray outburst by 4U0041 + 32

Abstract

During a balloon test flight on 4 February 1970, an engineering model of the UCSD Cosmic X-ray Experiment, later flown on the OSO 7 satellite, observed what was apparently an unknown high-latitude X-ray source at α=0 h 45 min±5 min, δ = 33°±3°. The source had a 25–300 ke V flux of about 6×10−2 photons cm−2 s−1 and a very hard spectrum over that energy range. By the time of a subsequent balloon flight on 25 September 1970, the intensity had faded to below 10−2 photons cm−2 s−1 (99% confidence). Recent observations by several experimenters have led us to associate the balloon observation with the highly variable source 4U0041 + 32. Certain characteristics of this source, such as its high galactic latitude and hard spectrum extending to 300 keV, set it apart from other known transients.

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