Hard X-ray observations of the quasar 3C 273.

Abstract

The quasar 3C 273 was observed with a balloon-borne phoswich scintillator detector system launched on December 12, 1983 from Hyderabad, India. 3C 273 was tracked for 130 minutes and the background was measured in the same ranges of elevation and azimuth when the source was not in the field of view, for approximately the same duration. The fluxes in the 18-25, 25-40, 40-60 and 60-120 keV energy intervals, in units of 10^-4 photons cm^-2 s^-1 keV^-1 are 11.73±4.20, 2.18±0.64, 1.40±0.29 and 0.30±0.19 respectively. The fluxes above 25 keV are consistent with the balloon observations of 3C 273 by Bezler et al., on September 28, 1981 and about trice as high as the 1978/1979 HEAO-1 measurements. However, the observations taken in conjunction with the lower energy (1-20 keV) data of December 17, 1983 from EXOSAT satellite, indicate possible spectral variations between 1981 and 1983.