Energy Spectra of a Number of Celestial X-Ray Sources in the Energy Range from 2 to 60 Kiloelectron Volts

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Science  25 Nov 1966:
Vol. 154, Issue 3752, pp. 1000-1002
DOI: 10.1126/science.154.3752.1000


The emission of 20 to 60 kev x-rays by an astronomical object in the constellation of Cygnus has been observed with a balloon-borne x-ray telescope flown from Hyderabad, India. The balloon data, used in conjunction with data pertaining to the flux in the wavelength range from 2 to 10 Å can be fitted by a power law in photon energy varying as (hv)-1.7. The Cygnus object is the brightest object in the sky in the hard x-ray wavelength range and has the hardest spectrum of all observed objects that emit x-rays. The astronomical object should be capable of accelerating protons up to energies of the order of 1018 electron volts. Upper limits to the hard x-ray fluxes from Sco XR-1, Cyg XR-2, Oph XR-1, and Ser XR-1 are established; it is shown that the Sco XR-1 spectrum is very soft.